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NASA’s Discovery programme

Low-cost exploration of the solar system

NASA’s Discovery programme: low-cost missions to explore the solar system (© NASA).NASA’s Discovery programme: low-cost missions to explore the solar system (© NASA).The InSight mission comes under the umbrella of the US space agency’s Discovery programme. Initiated in the early 1990s, Discovery is an alternative to other more costly, more imposing US programmes such as New Frontiers (with a budget of 750 million to 1 billion dollars) or Flagship (with a budget of 1.5 to 2 billion dollars).

To explore the solar system with automated spacecraft, NASA was in the habit of designing complex probes bristling with numerous instruments to meet a wide variety of scientific objectives. During the development phase, scientists’ expectations sometimes led to new instruments being added, thus increasing the size and complexity of the spacecraft. This increase in complexity was matched by an increase in costs. Budget overruns could sometimes mushroom uncontrollably, while development deadlines were repeatedly postponed. The huge effort made could doubtless lead to major discoveries, but on the down side, the consequences of a loss were catastrophic. Unfortunately, and despite all the attention paid to risk management, losses did occasionally occur.

Discovery and the "faster, better, cheaper" approach

In 1992, the sudden loss of Mars Observer just before it was to orbit Mars led NASA to support an initiative designed to revolutionize the way space exploration was carried out. Coined FBC for “faster, better, cheaper”, this approach was intended to reduce costs and development times while obtaining better results. For the cost of a single large mission, the idea was to have several small missions to maximize scientific feedback while spreading out the risk.

The Discovery programme was directly derived from the FBC approach. It funds low-cost missions with a pre-set, fixed budget of up to 450 million dollars excluding launch costs. Each mission focuses on a specific scientific theme. The postponement of the InSight mission from 2016 to 2018, along with its consequences, is a very rare exception to this rule.

The mission has a short three-year development cycle. The Principal Investigator (PI) is responsible for selecting the instruments and ensuring that the mission complies with budgetary constraints. Missions under the Discovery programme have to meet three main criteria: expand our knowledge of the solar system, develop new technologies to push back the frontiers of space exploration, and attract young people and the general public into the space science and technology sector.

NASA initially planned to launch one Discovery mission every two years, but budgetary constraints obliged the agency to be more flexible in its schedule.

Mars Pathfinder paving the way for the Discovery programme

Artist’s view of Sojourner, the Pathfinder mission’s small rover, exploring Ares Vallis (© Manchu/Ciel & Espace).Artist’s view of Sojourner, the Pathfinder mission’s small rover, exploring Ares Vallis (© Manchu/Ciel & Espace).

In 1996—almost 40 years after the Viking probes—the second mission of the Discovery programme, Mars Pathfinder, lifted off towards Mars.

Mainly of a technological nature, this mission was designed to test a low-cost method of placing instruments and a mini-rover on the Martian soil.

A huge success in terms of both its popularity (with the very first images of the landing site being relayed almost immediately over the Internet) and its technical prowess, this mission appeared to validate NASA’s choice of approach.
Unfortunately, two years later the successive loss of Mars Climate Orbiter and Mars Polar Lander under the Mars Surveyor programme raised important questions about NASA’s low-cost approach and led to a complete reorganization of the Mars exploration programme.

Following these incidents, several enquiry boards were formed. Their verdict was that by wishing to rush the spacecraft development cycle and reduce costs to a minimum, deficiencies had occurred in certain critical areas, particularly in documentation and testing, absolutely vital to a mission’s success. However, the FBC approach symbolized by the Discovery programme was still relevant enough to gather support.

InSight, 12th mission of the Discovery programme

InSight is the twelfth mission of the Discovery programme to be launched. It was shortlisted in May 2011 along with two other finalists—Titan Mare Explorer (TIME) and Comet Hopper—obtaining sufficient funds to kick off project phase A, preliminary design.

A selection board finally chose InSight in August 2012 as part of the Discovery programme. At the time, the mission was known as the Geophysical Monitoring Station, shortened to GEMS. However, the name was changed to avoid confusion with an X-ray observatory developed by NASA. Thus InSight was born.

While the fervour triggered by the Curiosity rover’s spectacular landing on Mars in August 2012 no doubt helped tip the balance in favour of InSight, it should be remembered that the mission’s science goals are particularly important, and that we currently know very little of the inner workings of the Red Planet because no seismic measurements have ever been taken in situ. Although geophysicists would like to have deployed a network of seismometers over the Martian surface, such a mission is clearly out of the question in the framework of a programme such as Discovery, which explains why InSight will only be operating a single seismic measurement unit.

A second factor that perhaps weighed in to tip the balance is that InSight’s two competitors, Time Mare Explorer and Comet Hopper, required the advanced Stirling radioisotope generator (ASRG) as a power source.

Time Mare Explorer was designed to splash down and float on a hydrocarbon sea on Titan, one of Saturn’s moons already visited by Europe’s Huygens probe in January 2005. The Comet Hopper mission was intended to land on the Wirtanen comet several times to take scientific measurements and study the comet’s interaction with the Sun. In both cases, solar arrays alone would not have provided enough power, making it vital to carry a radioisotope thermoelectric generator (RTG), a system that converts the heat released by the decay of radioactive material into electricity.

NASA had already kicked off the ASRG development programme to replace the RTG used at that time (known as the MRTG for “multi-mission radioisotope thermoelectric generator”), by a lighter, more efficient RTG able to generate more power with a smaller quantity of plutonium 238. The ASRG project was shelved for financial reasons when the InSight mission was selected.

The InSight probe needs only solar arrays to fulfil its power supply needs, unlike other Martian probes that required an RTG, such as Viking in 1976 and the huge Curiosity rover in 2012.

Last updated : 31 july 2017

SEIS, an international project

Partners & partnerships

The InSight mission, part of NASA’s Discovery programme, is flying a truly international array of scientific instruments.

The Very Broad Band pendulums central to the SEIS instrument and the evacuated container have been developed in France by the technical and scientific teams of the French space agency (CNES), the Institut de Physique du Globe de Paris (CNRS/Paris Diderot University), the Paris Diderot University space campus, and manufacturer SODERN. The VBB proximity electronic units have been developed by the Institut de Recherche en Astrophysique et Planétologie (IRAP space astrophysics laboratory) in Toulouse in cooperation with the Institut Supérieur de l'Aéronautique et de l'Espace (ISAE), the latter having developed the instrument’s noise model.

The InSight mission is the result of an international collaboration between NASA and several European laboratories (© CNES/IPGP/David Ducros).The InSight mission is the result of an international collaboration between NASA and several European laboratories (© CNES/IPGP/David Ducros).

The pendulums and evacuated sphere were manufactured and assembled on the premises of SODERN. The instrument was funded by CNES, which also carried out numerous tests within its Toulouse facilities. Other tests were carried out by the Institut de Physique du Globe de Paris, particularly on its Paris site at St-Maur. Numerous CNES laboratories also contributed to various studies. The Institut de Minéralogie et de Physique des Matériaux et de Cosmochimie carried out contamination studies, the Laboratoire de Météorologie Dynamique (LMD) helped model winds, and the CERMES laboratory affiliated with the Ecole Nationale des Ponts et Chaussées carried out analyses concerning the instrument’s legs.

Members of the CNES technical team with the flight model of the SEIS seismometer (© CNES/MARTIN Emmanuelle)..Members of the CNES technical team with the flight model of the SEIS seismometer (© CNES/MARTIN Emmanuelle).

Several European and American laboratories have also helped in the technological development of SEIS. Imperial College London provided the short-period sensors which round out the frequency range to which the VBB pendulums are sensitive, while the Max Planck Institute for Solar System Research (MPS) in Lindau designed the levelling system used to align the seismometer horizontally once on Mars. Federal university ETH Zurich was responsible for developing the electronics unit containing the various acquisition and control boards that manage SEIS.

NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, already actively involved in developing the InSight probe alongside US manufacturer Lockheed Martin, also brought its expertise to bear in the case of SEIS by providing both the cable connecting the instrument to the lander and all the seismometer’s thermal protective systems: the Remote Warm Enclosure Box, the dome-shaped Wind and Thermal Shield, and finally the titanium evacuated sphere containing the VBB pendulums, which raised in itself numerous technological challenges.

French university and CNRS laboratories will be analysing the data received from Mars. They include the Laboratory of Planetology and Geodynamics (LPG) in Nantes, the IRAP space astrophysics laboratory in Toulouse, the Paris-based LMD for weather and climatology research, and the GeoAzur mixed research unit in Nice.

The latter will also support the “seismo at school” network to help disseminate seismological and meteorological mission data among primary and secondary schools.

The InSight Team at NASA's Jet Propulsion Laboratory, JPL, in January 2018 (© NASA).The InSight Team at NASA's Jet Propulsion Laboratory, JPL, in January 2018 (© NASA).

Last updated : 28 october 2016

Mission development schedule

A short, intense development schedule tough on all the participants

All space missions are divided up into various phases designated by letters. A project begins with phase A and finishes with phase F, when the spacecraft is decommissioned.

InSight’s preliminary design phase A was kicked off in May 2011 when the mission (at that time known as GEMS) was shortlisted, along with two other projects, as a finalist in the 12th iteration of the Discovery programme. Phase A examines and documents the project’s feasibility. In August 2012, InSight was definitively chosen as the Discovery programme’s 12th mission.

In September 2012, the project moved into phase B, which entails the team in charge of the mission proving that the proposed concept is valid. Next comes phase C, initiated in InSight’s case in June 2013. This is when the definitive version of the probe was designed. Once this final version had been given the green light, manufacturing as such could begin, signalling the start of phase D. This development phase included construction and thorough testing of the various subsystems, and finally their integration to form the final spacecraft.

Once assembled, the probe has to be fully tested once again before being taken to the launch pad for its journey to Mars. Once there, after the routine checks have been carried out and the scientific instruments (SEIS and HP3) have been deployed, the operating phase can begin. Phase E, as this is known, is when the first scientific data is acquired. For InSight, this phase will last at least two Earth years (equivalent to one Martian year). If the systems are still working well at the end of this period, NASA may decide to extend the mission.

A short development cycle

In all, just five years separate the start of phase A in May 2011 and the launch, initially scheduled for March 2016. The InSight mission’s development cycle has obviously been very short, in keeping with all NASA’s Discovery missions.

Keeping to such a tight schedule has been a major challenge for all the teams involved in the mission. Theoretically, the technical risks appeared minimal and the design process looked as if it was going to be seamless. One of the reasons for this is that the InSight lander is almost a carbon copy of the Phoenix probe that successfully landed on Mars in May 2008.

Following in the footsteps of a predecessor having already undergone its baptism of fire and having been able to implement the lessons learned from that mission, it was logical to consider that (almost) everything would go smoothly. This impression was no doubt consolidated by the fact that several components for InSight could be reused from previous missions. This was the case, for example, of the IDA, a robotic arm first used for Mars Surveyor 2001, and the two technical cameras, a colour version of the danger avoidance and navigation cameras used on US rovers Spirit, Opportunity and—more recently—Curiosity.
Yet, as often occurs in the space sector, things did not work out exactly as planned. Even if a mission looks at the outset very similar to a previous attempt, it rapidly becomes unique in its own right.

Indeed, the InSight probe certainly is unique in terms of its payload, i.e. the instruments it is designed to land on Mars. Mission managers had clearly stated from the start that the SEIS seismometer and the HP3 heat flow sensor were going to be the project’s major unknown, the part where risks ran the highest. The future would show that these risks were actually greater than imagined in the case of the seismometer.

The SEIS instrument was not designed specifically for the InSight mission. Its legacy goes back to Mars 96, a mission launched on November 1996 that included two landing capsules containing the Optimism broad band seismometer. Despite the probe’s tragic destiny, crashing into the Pacific Ocean after being unable to break free from Earth’s gravity, development work on the seismometer continued thanks to funding from the French space agency, CNES.

Over the years, the prototypes developed have offered increasingly better performance. An enhanced version was considered for the Netlander mission, unfortunately abandoned in detailed design phase B. A new, even more enhanced model was offered to the European Space Agency for ExoMars, but it was finally rejected, leaving the InSight probe the difficult task of depositing on Mars an instrument that has benefitted from almost 20 years of constant development, and which has crystallized so many of its designers’ hopes and efforts.

Unfortunately, adversity lies in the details, and while the delicate pendulums central to the seismometer were already mature from a technical viewpoint, the difficulties encountered were linked to a part that nobody had really suspected as a possible source of problems: the evacuated sphere. The latter is designed to house the pendulums, offering them an ideal environment in which to work on Mars.

The sphere is crucial to the seismometer’s operation as it both isolates the instrument’s pendulums from the huge temperature differences on Mars and protects them from contamination by particles that could upset their fragile mechanisms. It must remain perfectly sealed at all times, the smallest leak being considered unacceptable.

When the sphere was delivered to CNES in July 2015, a leak was detected. Despite the considerable efforts made by the technical teams to understand and repair the problem, additional leaks occurred, leading NASA and CNES to issue a joint statement on 22 December 2015 announcing the suspension of the March 2016 launch and its possible postponement to May 2018.

Last updated : 28 january 2018

Launcher

InSight will lift off aboard the powerful Atlas V launch vehicle

US launcher Atlas V (© United Launch Alliance).US launcher Atlas V (© United Launch Alliance).

On 5 May 2018, the InSight probe will be blasted towards Mars by the extremely powerful US launcher Atlas V, one of Ariane 5’s direct rivals. Atlas V is a two-stage vehicle: the first stage burns a mixture of kerosene and liquid oxygen, while the second—the Centaur upper stage—is powered by liquid oxygen and liquid hydrogen.

Given InSight’s relatively light weight, no strap-on boosters will be necessary. The Atlas V launch vehicle is so powerful that, unusually for a mission to Mars, it is planned to lift off not from Cape Canaveral in Florida, but from the Vandenberg Air Force Base in California.

Interplanetary spacecraft are generally launched from the Cape Canaveral Air Force Station to benefit from the sling effect due to Earth’s rotation, which is maximal at the equator. InSight will not need this helping hand, which is why the launch is scheduled from Vandenberg, a first in the history of Mars exploration.

The Atlas V 401 launcher version chosen has a 4-metre-diameter fairing under which InSight will be stowed.

An unusual feature of the launch, due to the room available under the fairing, is that the solar arrays for the cruise stage are to be installed in their final configuration, i.e. fully deployed. As they are not designed to be stowed in a folded position during the launch then deployed following separation of the probe from the launcher in space, they do not include any hinged mechanisms.

The launcher also carry two additional MarCO telecom nanosatellites. They will accompany InSight on its journey to Mars and relay telemetry data to Earth during the critical landing phase.

The Atlas V 401 rocket will lift off from the Launch Complex n°3 from Vandenberg Air Force base (© NASA).The Atlas V 401 rocket will lift off from the Launch Complex n°3 from Vandenberg Air Force base. The InSight launch windows opens on May 5, 2018 at 4:00 am, before dawn (© NASA).

Last updated: 26 february 2018

Cruise stage

Cruise Stage 1
Cruise stage 6
Cruise Stage 2
Cruise Stage 4
Cruise Stage 3
Cruise Stage 5

InSight’s mother ship

The InSight probe’s cruise stage (© NASA).The InSight probe’s cruise stage (© NASA).

The InSight lander will travel to Mars as part of a spacecraft specially designed to journey through interplanetary space. This cruise stage, as it is known, is 2.64 metres in diameter and 1.76 metres tall. It has several features to increase its autonomy.

The cruise stage has its own rectangular solar arrays. Covering an area of 3.2 m², they provide the spacecraft’s power supply. They are small enough to be stowed as they are, without having to be unfurled after the launch, which removes the risk of problems on deployment.

Small thrusters are used to change the spacecraft’s orientation and trajectory, and stabilize the cruise stage in all three axes. Sun and star sensors enable the spacecraft to calculate its position, the stars playing the role of sextants. Several X-band telecom antennas are used to communicate with Earth.

The cruise stage is designed to transport InSight to Mars along a trajectory precisely calculated by interplanetary guidance systems. The cruise stage/InSight lander assembly will take six months to complete its journey.

The InSight probe’s cruise stage. Note the spacecraft’s cylindrical structure and fixed solar arrays (© NASA/JPL-Caltech/Lockheed Martin).The InSight probe’s cruise stage. Note the spacecraft’s cylindrical structure and fixed solar arrays (© NASA/JPL-Caltech/Lockheed Martin).

It is only once in the vicinity of Mars that the cruise stage, having fulfilled its mission, will separate from its passenger to plunge into the unfathomable depths of space, where it will constantly revolve around the Sun, a forthwith silent testimony to human ingenuity.

Last updated: 28 October 2016

The InSight lander

A platform hosting all that is needed to operate on Mars

The InSight lander comprises a bus (or “platform”) 1.5 m across and mounted on three legs each fitted with a suspension system designed to absorb shocks. The role of this structure, which is made of composite materials, is to host the various subsystems controlling critical aspects. These include the power supply, radio communications, propulsion and thermal control, all of which are coordinated by an onboard computer.

  • Solar array (© rights reserved).Solar array (© rights reserved).

    On Mars, InSight will depend on solar power

    To obtain the power crucial to its operation, InSight depends on a solar array connected to rechargeable batteries. The cruise stage is fitted with two rectangular solar arrays together providing a surface area of 3.2 m² and providing 957 watts when near the Terre, and 477 watts when in the vicinity of Mars.

    The InSight lander itself has its own ultra-flexible circular solar arrays covering 4.2 m². They are deployed approximately 20 minutes after landing, the time needed for the dust raised by the retrorockets to settle again. With a diameter of 2.15 meters, they are slightly larger than those of the Phoenix probe. This additional power supply will be most welcome, allowing InSight to be untroubled by dark periods with little solar illumination, whether due to dust storms or the rigours of the Martian winter.

    On Mars, dust is the solar arrays’ number one enemy. Dust storms on the Red Planet make the atmosphere cloudy and consequently lower the arrays’ performance. Slowly but surely, Martian dust also settles on the arrays themselves, blown off occasionally by swirling or gusting wind—a natural but random solution.

    Testing the unfurling of one of InSight’s solar arrays (© NASA/JPL-Caltech/Lockheed Martin)Testing the unfurling of one of InSight’s solar arrays (© NASA/JPL-Caltech/Lockheed Martin).

    The lander’s solar arrays can recharge the two 25 amp hour lithium batteries designed to power the spacecraft during darkness.

    The SEIS seismometer will consume around 5 watt (8,5 watt in peak), depending on the measurement mode activated. In winter, when the period of solar illumination is shorter and the solar arrays therefore provide less electrical power, SEIS will record fewer data. On the other hand, at other times it will be switched to campaign mode to maximize the number and quality of seismic measurements, a mode requiring more power.

    Last updated : 17 December 2018

  • Thruster nozzles (© rights reserved).Thruster nozzles (© rights reserved).

    Propulsion system

    Although propelled towards Mars by the vast quantities of energy released by the powerful Atlas V launcher, the InSight probe also has several of its own thrusters fulfilling different functions.

    Four small thrusters, each generating a thrust of roughly 4.5 N, are used by the attitude control system to adjust or alter the probe’s orientation in space. Four other slightly more powerful thrusters (roughly 22 N each) are used for trajectory correction manoeuvres during the journey to Mars. Finally, 12 pulsed retrorockets, each capable of developing a thrust of approximately 300 N, are ignited during the final landing phase for deceleration and orientation control.

    All of InSight’s thrusters run on hydrazine. This simple but toxic chemical compound, consisting of two nitrogen and four hydrogen atoms, passes through a catalytic bed where it decomposes violently into gases (ammonia, hydrogen and nitrogen) that are ejected through the nozzles, generating thrust. This technique is described as cold gas propulsion since there is no actual combustion per se, in contrast to rocket engines that either run on liquid mixtures of hydrogen/oxygen or kerosene/oxygen, or that burn solid propellants.

    InSight will carry hydrazine, stored in spherical tanks pressurized by helium.

    Last updated : 28 October 2016

  • The NASA satellite américain Mars Reconnaissance Orbiter (© NASA)The NASA satellite américain Mars Reconnaissance Orbiter (© NASA)

    A complete set of antennas for communicating with Earth

    The telecommunications subsystem is absolutely essential to the success of the InSight mission, whether during the cruise phase between Earth and Mars, the descent to the Martian surface, or of course the two years the lander will spend listening to Martian tremors.

    The cruise stage, responsible for getting the lander to its destination, has two low-gain antennas (LGA) for receiving and transmitting signals, plus two medium-gain horn antennas (MGA). Communications with the 34-metre antennas of NASA’s Deep Space Network (DSN) take place in X-band. The low-gain antennas are used for the first 35 days of the voyage to Mars before switching over to the more powerful medium-gain antennas for the rest of the interplanetary journey. Mission controllers can use these various antennas to send instructions to the probe and receive telemetry data. The radio signals will also be used to pinpoint InSight’s exact position in space by determining its speed and distance from Earth.

    Once the lander separates from the cruise stage, radio communications will be mainly via UHF using the helical antenna attached to InSight's deck. Data will thus be relayed back to the spacecraft orbiting Mars. During the landing, InSight will use UHF to transmit crucial information back to the American Mars Reconnaissance Orbiter (MRO), which has been orbiting Mars since 2006, as well as to its two "guardian angels," MarsCO-A and MarsCO-B, the suitcase-sized nanosatellites that will be accompanying the probe on its journey.

    During the scientific observation phase, the Mars Reconnaissance Orbiter will act as InSight's main communications radio relay. It will fly over the Elysium Planitia twice a day, at 3 in the morning and 3 in the afternoon. Should there be a problem, InSight has been designed to be able to exchange data with two other American orbiters, Mars Odyssey and MAVEN, which are thus backup relay stations. Finally, the lander module has two medium-gain antennas (MGA) that can transmit data directly to Earth. Put to good use for the RISE experiment, these horn antennas can also communicate with InSight (albeit at lower data rates) if the UHF transmissions should fail.

    Last updated : 28 October 2016

  • Multi-layer insulation material (© IPGP/Philippe Labrot).Multi-layer insulation material (© IPGP/Philippe Labrot).

    How to avoid under- or over-heating on Mars

    Space is an extreme environment, characterized especially by enormous variations in temperature, whether in interplanetary space or on the surface of celestial bodies that do not enjoy the benign conditions of our own planet: this may be because they are too close or too far from the Sun; they may have no air (as on the Moon) or, on the other hand, have a very dense atmosphere laden with greenhouse gases (as on Venus); or again they may lack climate-regulating systems such as oceans.

    Space is an environment of superlatives, with temperatures that can fall to several hundred degrees Celsius below zero but which can also rise to 100°C or 200°C if directly exposed to the Sun’s blinding rays when unfiltered or scattered by an atmosphere. Even though the components of space probes are by nature designed to cope with massive temperature ranges, they still need to be protected from both cold and heat. This is the role of the thermal control system.

    InSight is therefore fitted with passive and active thermal control systems. Passive systems include heat shields, layers or coatings of insulating materials, special paints and heat pipes; while active systems include radiators and thermostats. Designed for the equatorial Martian environment, these systems will maintain the interior of the probe at relatively benign temperatures, varying between -15°C and +40°C. Delicate electronic systems such as those controlling the SEIS seismometer are kept in an insulated enclosure known as the Warm Electronic Box (WEB).

    Last updated : 28 October 2016

  • RAD 750 processor (©  rights reserved).RAD 750 processor (© rights reserved).

    RAD 750 processor and VxWorks operating system

    InSight is controlled by two redundant computers, each using the RAD 750 processor. This chip, clocked at 115,5 MHz (compared with 20 megahertz speed of the RAD6000 processor used on Phoenix), is based on the IBM and Motorola PowerPC 750 processor available to the public in the 2000s. These days, when even the simplest telephone boasts considerable computing power, the technical features of InSight's computer might raise a few eyebrows. However, it has been designed to operate in space, an environment that would rapidly destroy our smartphones, tablets or computers.

    The RAD 750 processor and its motherboard have been hardened to withstand the hostile conditions of space, in particular radiation and extreme variations in temperature. Electrical power consumption is very low. For data storage, InSight has 16 Gb of flash memory. The operating system is VxWorks, with programs written in C and C++.

    Only one of the on-board computers is active at any given time, the second remaining dormant. If a fault appears on the active unit, InSight can automatically switch to the backup unit and continue where it left off.

    The RAD 750 system has already flown several times, including for Mars missions, so has been both tried and tested. It has been used in the Mars Reconnaissance Orbiter, the Curiosity rover and the MAVEN orbiter.

    Last updated : 29 january 2018

Entry, descent and landing (EDL) hardware

Landing system

  • Nested structure of the InSight probe (© NASA).Nested structure of the InSight probe (© NASA).

    A nested structure like a Russian doll

    Upon leaving the Earth, InSight resembles a Russian doll. It comprises first of all a landing capsule attached to a cruise stage (a cylinder flanked by solar arrays), designed to get the lander to its destination. Once near Mars, the landing capsule will separate from the cruise stage, which will then be of no further use.

    The landing capsule itself comprises several elements: the forward part is occupied by a broad heat shield, while the rear part is fitted with a shield enclosing a parachute. The InSight lander, with its legs and solar arrays folded, is sandwiched between the forward heat shield and the rear shield.

    Last updated: 28 October 2016

  • Manufacture of the InSight heat shield (© NASA).Manufacture of the InSight heat shield (© NASA).

    Tackling the hellish conditions of atmospheric entry

    During its descent to the Martian surface, the InSight lander will be protected by a huge 62 kg heat shield 2.65 m in diameter, covered in ablative tiles.

    Approaching the planet at a speed of 6.3 km/s, InSight will hit the upper part of the Martian atmosphere with great violence. At an altitude of 125 km, the layer of air surrounding Mars is very thin, but despite that, frictional forces will be considerable, causing the surface of the spacecraft to heat very rapidly to several thousand degrees.

    The heatshield protects the InSight probe from the heating caused by the friction with the atmosphere during the entry phase (© NASA).The heatshield protects the InSight probe from the heating caused by the friction with the atmosphere during the entry phase (© NASA).

    By slowly burning off, the heat shield's ablative tiles will absorb a large part of the thermal energy released on entering the atmosphere, thus protecting the lander.

    Last updated: 28 October 2016

  • Wind tunnel test of InSight's 12-metre-diameter parachute. The tunnel is 24 m high by 37 m long (© NASA)Wind tunnel test of InSight's 12-metre-diameter parachute. The tunnel is 24 m high by 37 m long (© NASA).

    A large-diameter parachute

    Despite the massive braking effect due to the friction of the heat shield in the upper layers of the Martian atmosphere, InSight's speed is too high for it to land softly on the Martian soil.

    At an altitude of roughly 9 km, the lander will deploy a parachute, a wide fabric corolla 12 m in diameter. InSight's parachute uses what is known as a disk-gap-band structure.

    It is opened by a pyrotechnic mortar, since a parachute extractor cannot be used on account of the Martian atmosphere’s low density and the high speed of the probe.

    Last updated: 28 October 2016

  • Final descent phase under power (© NASA/JPL).Final descent phase under power of the InSight probe (© David Ducros).

    Retrorockets for final braking

    The InSight lander’s final braking is down to three clusters of four retrorockets attached to the probe platform. Consuming hydrazine stored in a pressurized tank, each thruster develops approximately 300 Newtons.

    The retrorockets on InSight are pulsed, unlike, for example, the variable-thrust engines used on the Viking probes in 1976 and the Curiosity rover in 2012. The thrust for InSight is controlled by the onboard computer, which commands the incessant ignition and shut-down of the thrusters.

    The latter are only cut off completely when the probe legs are in contact with the ground. However, the exhaust from the motors is such that the landing site will be only slightly disturbed by the lander's arrival, and the quantity of dust stirred up by the gas jets will be minimal.

    Last updated: 28 October 2016

  • Descent radar altimeter of the InSight probe (© NASA/JPL-Caltech/Lockheed Martin). Descent radar altimeter of the InSight probe (© NASA/JPL-Caltech/Lockheed Martin).

    Descent radar altimeter

    Attached to the bottom of the InSight platform is a descent radar designed to measure the changes in speed and altitude during its descent towards the Martian surface.

    InSight's descent radar (© NASA/JPL-Caltech/Lockheed Martin) With four radio antennas (one pair for altitude and three pairs for horizontal speed), the radar will initialize at a height of roughly 6 km.

    The data provided by the radar will be essential for the onboard computer, since it has the heavy responsibility of controlling the incredible choreography that will allow the InSight lander to descend safe and sound onto the rust-coloured surface of the Red Planet.

    The InSight lander integrated in the cruise stage and viewed from below, showing the antennas of the descent radar (© NASA / JPL-Caltech).The InSight lander integrated in the cruise stage and viewed from below, showing the antennas of the descent radar (© NASA / JPL-Caltech).

    Last updated: 4 april 2018

The Instrument Deployment Arm (IDA)

A two-metre-long robotic arm

InSight has a sophisticated robotic arm designed for a single purpose: to deploy with the greatest precision and safety possible the mission's two main instruments, namely the SEIS seismometer and the HP3 heat flow sensor.

3D graphic representation of the IDA in the process of lifting the SEIS seismometer (© NASA).3D graphic representation of the IDA in the process of lifting the SEIS seismometer (© NASA).

Contrary to what you might think, even once firmly on its three legs, the landing phase is still not over for InSight.

Its two main instruments— SEIS and HP3 —are still about one metre from the Martian surface, with which they absolutely must make contact before they can begin to take any measurements.

With the aid of two cameras, project engineers need to choose a landing site for these two instruments before setting them down using the robotic arm.

InSight’s Instrument Deployment Arm (IDA) is exactly the same as the one built for the Mars Surveyor mission in 2001, subsequently cancelled after the unexplained disappearance of the Mars Polar Lander above Mars' South Pole in December 1999. This arm was itself derived from the one on the Mars Polar Lander. The robotic arm on the 2001 Mars Surveyor had been designed not to place an instrument on the surface of Mars, but the Marie Curie rover, an exact copy of the small Sojourner vehicle from the Pathfinder probe that had trundled over the Red Planet in 1997.

Stored in a container for over a decade awaiting eventual re-use, the 2001 Mars Surveyor robotic arm was finally awoken from its long slumber for the InSight mission.

Testing the IDA. An engineer is handling the protective cover of the instrument deployment camera (IDC) (© NASA/JPL-Caltech/Lockheed Martin).Testing the IDA. An engineer is handling the protective cover of the instrument deployment camera (IDC) (© NASA/JPL-Caltech/Lockheed Martin).

Since there have been many technical advances since it was first designed, refurbishing the IDA to as-new condition and re-certifying it for spaceflight provided Jet Propulsion Laboratory engineers with some interesting and unusual challenges. Once out of its container, the arm was scrupulously checked and tested by the engineers before being almost completely disassembled in order to replace certain parts before reassembly. The arm was judged to be in generally excellent condition despite its 13 years in storage.

Dimensions in metres of the IDA flown on the InSight probe (©NASA).Dimensions in metres of the IDA flown on the InSight probe (©NASA).

Attached to the lander’s deck, the IDA is structurally identical to a human arm: it comprises an upper limb linked to a forearm via a motorized elbow. The forearm ends in a mobile wrist to which an ingenious gripper is attached. The assembly has four degrees of freedom, each with a motor: two for the joint between the upper limb and the lander deck (the shoulder), one for the elbow, and one for the wrist.

The two tubular segments of the arm are made of a carbon fibre composite material combined with aluminium and titanium. The upper limb is 1 m long, as against 80 cm for the forearm. Extended to its limit, the arm can reach a zone 1.9 m from the lander.

The motors used have a long heritage in the history of Martian exploration, being used in particular for the Pathfinder mission on the little Sojourner rover (1997), then on the Spirit and Opportunity rovers (2004), and finally on the Phoenix polar probe (2008). A noteworthy feature of the motors is that they contain heater elements to withstand the rigours of the Martian climate.

The IDA on the InSight probe has no problem lifting the SEIS seismometer (29 kg), the wind and thermal shield (WTS, 9,5 kg) and the HP3 penetrator (3 kg). Each device to be placed on the ground is fitted with a "handle" consisting of a rigid rod terminating in a sphere. This is designed so that it can be grasped as easily as possible by the gripper attached to the IDA.

A five-claw gripper

Detail of the gripper on InSight's robotic arm (© NASA).Detail of the gripper on InSight's robotic arm (© NASA).

The gripper is attached to the end of the robotic arm's forearm via a 20-cm-long umbilical.

JPL engineers initially envisaged using a magnetic gripper. The magnetic force was provided by a rare earth permanent magnet (neodymium iron boron), and the loads to be grasped were fitted with a magnetic puck.

Once near the objects to be placed on the ground, the gripper would be aligned automatically with the metal pucks attached to the objects. To make the set-down process more secure, a backup electromagnetic system was on hand to counteract the magnetic field, thereby releasing the load being transported.

Separating the gripper from its load would necessarily require an electric current to be passed. Hence there was no chance that the arm would inadvertently release its precious cargo if there were a sudden electrical failure during this deployment process. However, for reasons of reliability, the magnetic gripper was later replaced by a more conventional device, a five-digit pincer.

This question of reliability is linked to one of the features of the Martian environment, i.e. the constant presence of dust on every surface. With much of it containing oxides of iron, this dust is by its very nature attracted to magnetic surfaces. Since it would be impossible to keep the gripper clean on Mars, the risks created by dust-related interference forced the engineers to abandon their initial solution in favour of a more conventional—and more reliable—gripper.

Untroubled by the Martian environment, the current mechanical gripper cannot actually release its load by itself. The command to separate can only come from the Mission Control Centre on Earth, thus offering protection against any unintended release of the instruments by the arm.

Besides the gripper, InSight's robotic arm also has a bucket with a capacity of roughly 500 g of soil. However, this bucket is not intended for massive excavation works; its main role is to prepare the ground as well as possible before setting the instruments down. It allows engineers to shift a stone that is in the way, flatten a little mound in an otherwise optimal deployment sector, or simply check the nature of the ground.

Last updated : 2 february 2018

Technical cameras

InSight has two technical cameras

  • Locations of the IDC and ICC technical cameras on InSight (© NASA).Locations of the IDC and ICC technical cameras on InSight (© NASA).

    A colour camera for imaging the probe and its surroundings in stereo

    InSight's robotic arm IDA is fitted with a stereo colour camera (IDC) similar to the navigation cameras (NavCam) on the American Spirit and Opportunity rovers. Mounted on the segment corresponding to the forearm and near the elbow joint, it has a resolution of 1024 x 1024 pixels, and a 45° field of view. It is inclined at 20° to the arm, an angle that allows it to easily image the deck of the lander as well as its surroundings.

    The IDC will be an essential aid during the various deployment stages, when InSight's main two instruments—the SEIS seismometer and the HP3 heat flow sensor—will be gently placed on the ground.

    After landing, it will also allow engineers to inspect the probe’s deck and check the state of critical systems such as the solar arrays. Geologists will also be able to put it to good use by taking panoramic pictures of the Elysium Planitia, the probe’s landing site, and studying its geomorphology.

    The IDC camera mounted on the IDA robotic arm of InSight (© NASA/JPL-Caltech/IPGP/Philippe Labrot).The IDC camera mounted on the IDA robotic arm of InSight (© NASA/JPL-Caltech/IPGP/Philippe Labrot).

    Last updated: 28 October 2016

  • The ICC technical camera on the InSight probe (© NASA).The ICC technical camera on the InSight probe (© NASA).

    Objective: imaging the instrument placement zone

    In contrast to the IDC, InSight's second camera is immobile. The Instrument Context Camera (ICC) is riveted underneath the lander platform, facing the scientific instrument placement area at 45° to the horizontal. It too is derived from the cameras on the Spirit and Opportunity rovers, or more accurately, their hazard avoidance cameras (HazCam). It is a black and white wide-angle camera with a 124° field of view.

    The ICC is designed to provide the best possible images of the area in front of the robotic arm, which will appear completely clear. Using the IDC’s stereo-pair images, engineers will be able to construct a 3D digital model of the Martian terrain. This model will then be used to accurately determine the most appropriate locations for setting down the instruments.

    The ICC camera located under the InSight deck (© NASA/JPL-Caltech/IPGP/Philippe Labrot).The ICC camera located under the InSight deck (© NASA/JPL-Caltech/IPGP/Philippe Labrot).

    Last updated: 28 October 2016

Other instruments

InSight: a comprehensive geophysical observatory

Besides the SEIS seismometer, InSight has a fully equipped weather station (APSS, for Auxiliary Payload Sensor System) with temperature and wind sensors, as well as three sensors to be installed on Mars for the first time: the HP3 heat flow sensor, a fluxgate magnetometer and an ultrasensitive barometer for detecting infrasound. To crown it all, the telecommunications system will be used to accurately monitor the planet’s rotation and disturbances caused by its liquid core.

  • A penetrator for measuring heat flow

    The Heat flow and Physical Properties Package—written HP3 and pronounced "HP cubed" — is designed to measure the flow of heat escaping from the interior of the Red Planet. Proposed by the Berlin Institute of Planetary Research (part of DLR, the German Aerospace Centre), HP3 will penetrate the Martian soil to a depth of 5 m using a self-propelled mechanical mole, measuring how temperature varies with depth. Like SEIS, HP3 will be set on the ground by InSight's robotic arm, IDA.

    HP<sup>3</sup> with, from left to right, the penetrator, the main deployable chamber and finally the technical cable (© DLR/HP<sup>3</sup> team).HP3 with, from left to right, the penetrator, the main deployable chamber and finally the technical cable (© DLR/HP3 team).

    A cooling planet

    The telluric planets of the solar system that have a solid surface are all warm spheres that are slowly but surely cooling down through contact with the space vacuum. In addition to the thermal energy they acquired when they were formed, most of the internal heat of small planets is produced by the decay of radioactive atoms, mainly thorium and uranium, but also potassium.

    As continental drift, volcanic eruptions and earthquakes all demonstrate, the geology of planet Earth is still vigorous despite its great age. Born at the same time, 4.5 billion years ago, Mars' fate has been quite different. On the Red Planet, the plate tectonic mechanism that cracks the rocky crust into shifting plates seems never to have occurred. Although the impressive volcanic cones visible on the Martian surface are evidence of a violent past, no volcanoes are active today: the last lava lakes in the caldera of the great volcanoes appear to be several hundreds of millions years old, with the most recent (and very rare) lava flows dating back less than 10 million years. To assist in the interpretation of HP <sup>3</sup> data, numerical 3-D simulations of Mars cooling are performed on Earth (© Ana Plesa / DLR).To assist in the interpretation of HP 3 data, numerical 3-D simulations of Mars cooling are performed on Earth (© Ana Plesa / DLR).

    Finally, the formerly ubiquitous magnetic field is a mere shadow of its former self. It must have disappeared at least 3 billion years ago, and only traces of it still exist in the oldest crust of the planet. In contrast to Earth, Mars seems to have lost much of its internal heat. Is the planet no more than just a cold sphere, or do its depths still contain reservoirs of near-molten rock, the final trace of a once powerful planetary engine now breathing its last? One of planetary researchers’ top priorities is to determine the energy budget of Mars, which is where HP3 comes in..

    Mars in a Minute video series : How Did Mars Get Such Enormous Mountains ? (© JPL-Caltech).

    HP3

    In order to measure the current heat flow from Mars, i.e. the quantity of heat that continues to escape from its surface before disappearing into cold space, InSight carries a novel instrument known as HP3 (pronounced HP cubed). The Heat Flow and Physical Properties Package is actually just a highly sophisticated thermometer. With a mass of approximately 3 kg, HP3 comprises several subsystems:

    • A metal support structure 36 cm long resting on four legs 10 cm in diameter that encloses the mole, as well as two cables (or “tethers”) coiled up in two compartments.

    • A mole capable of burrowing into the soil. This mole has:

      • An electromechanical hammer device that drills by impact.

      • A tilt meter (STATIL) that reports the mole's deviation from the vertical during drilling and is protected from the unavoidable mechanical shocks due to the percussive mechanism.

      • A heated sleeve (TEM-A) fitted with temperature sensors to determine the soil’s thermal conductivity.

    • A 3-metre-long technical cable that connects the instrument to the electronics unit, coiled comfortably in the lander’s remote warm enclosure box (RWEB).

    • A 5-metre-long scientific cable that connects the mole to the support structure, provides electrical power and carries data. Fourteen passive temperature sensors are also soldered at regular intervals along the cable. Finally, markers are positioned on either side of the cable to monitor the penetration depth using an optoelectronic system (Tether Length Monitor). At 35 mm, the scientific tether is slightly wider than the mole's borehole to allow the temperature sensors to make good contact with the walls and hence with the soil.

    • An electronics unit inside the lander’s RWEB, a compartment isolated from the rigours of the Martian climate.

    The mole for the HP<sup>3</sup> experiment (© Max Planck Institute/DLR)The mole for the HP3 experiment (© Max Planck Institute/DLR)

    Deployment

    Once InSight has landed on Elysium Planitia, the HP3 instrument—initially attached to the lander’s deck—will be lifted up by the robotic arm (IDA) and then set down on the surface at a location chosen specifically by the scientists as suitable for drilling. During deployment, the technical tether will unwind behind the instrument, which will therefore remain connected to the InSight lander. The process of placing HP3 on the surface of Mars should start on sol (Martian day) 44 after landing and extend to sol 58. The mole drilling operation per se will then be able to start. L'instrument HP<sup>3</sup> (© DLR/HP<sup>3</sup> Team)The HP3 instrument will be placed on the ground by InSight's robotic arm once the SEIS instrument has been correctly deployed. The mole, trailing a ribbon cable fitted with temperature sensors behind it, will bury down a maximum of 5 m (© DLR/HP3 Team).

    The maximum penetration depth for HP3 is five metres. Theoretically, it should be possible to reach this depth in a few hours, though in reality the engineers and scientists involved will be working step by step, advancing with great care so as to minimize as far as possible any risks during the crucial drilling phase, thereby maximizing the collection of scientific data.

    The mole will be programmed to penetrate the Martian soil to a depth of 50 cm before stopping. There will then be pause of 48 hours to allow the frictional heat between the mole and the ground to dissipate. Thermal conductivity measurements will then be made over the course of a day before restarting the drilling process. At this pace, under ideal conditions and provided all goes according to plan, the 5-metre depth limit should normally be reached by the end of a month of operation.

    Of course, there is nothing to guarantee that the mole will be able to penetrate that far below the surface of Mars. As anybody who has tried to erect a tent by hammering tent pegs into the ground will know, the soil may prove to be a real challenge in itself. The planetary scientists chose the landing site for the InSight probe on the vast Elysium Planitia with great care. High resolution imagery, together with measurements of thermal inertia (the ability of a surface to cool down faster or slower) and radar soundings led to the selection of a region where the surface is not too loose (to avoid the probe and its instruments sinking too deep) or too hard (which would prevent the HP3 from penetrating the ground). If however (for whatever reason), the progress of the mole should become very difficult, drilling will be stopped.

    Similar to the mole on Britain’s small Beagle 2 capsule, lost during Christmas 2003, the mole is undoubtedly the heart of the HP3 instrument. All the scientific results of this experiment depend on its ability to drill through the Martian subsoil. The greater the depth achieved by the mole, the shorter the measurement time required to fulfil NASA's scientific objectives. The HP<sup>3</sup> mole is approximately 16 cm long (© DLR/HP<sup>3</sup> Team).The HP3 mole is approximately 16 cm long (© DLR/HP3 Team).

    To drive itself into the ground, the HP3 mole (which resembles the pointed end of a ballpoint pen) will not be using a rotating auger but an ingenious hammering mechanism. A metal slug is propelled forward by the magnetic field generated by a coil, then restored to its striking position by a spring, ready to start the cycle over again. At each forward impulse the mole will force its tip a little further into the Martian regolith. The vibration associated with this drilling process will naturally be carefully measured by the SEIS seismometer, which will already be listening out.

    In addition to its hammer mechanism, the HP3 mole has a tilt meter (STATIL) that detects changes in direction relative to the horizontal. Combined with the Tether Length Monitor (TLM), a device that measures the length of the cable as it unwinds, the tilt meter can determine the absolute depth of the mole, a piece of information essential for establishing the soil temperature profiles. The TLM is an optoelectronic sensor that counts the passage of markers located on each side of the scientific cable. Finally, the mole is encased by a heated sleeve (TEM-A) that has its own temperature sensors.

    For the sake of completeness, it is worth mentioning that the HP3 experiment includes a radiometer mounted underneath the lander platform and facing towards a part of the surface unobstructed by the instruments on the ground or in the probe's shadow. Contrary to what its name might imply, the role of this sensor is not to measure the radiation striking the Martian crust but simply to measure the heat flow (infrared radiation) emanating from the surface and defining its temperature (specialists refer to the “brightness temperature”).

    The radiometer on the HP<sup>3</sup> experiment (© NASA).The radiometer on the HP3 experiment (© NASA).

    First measurements of heat flow since the Apollo lunar missions

    The HP3 experiment will take the first measurements of heat flow on a planet other than Earth. For the moment, the only extraterrestrial heat flow data we have were obtained on the Moon during the Apollo 15 and 17 missions (the American astronauts used manual augers to bore into the surface and place temperature probes in the subsoil).

    By studying the ease with which the wave of heat emanating from the heated sleeve propagates into the Martian surface, scientists will be able to determine the thermal conductivity of the regolith, i.e. the ability of the Martian soil to conduct heat. It should be possible to measure the heat flow accurately even if the soil conductivity turns out to be very low. The daily attenuation of the diurnal temperature wave will provide HP3 with another means of characterizing the ground’s thermal conductivity.

    The variation of temperature with depth, i.e. the thermal gradient, will be another important parameter for HP3 to determine. The scientific tether that the mole trails behind it as it makes its way down through the regolith will provide power and transmit data. As we have seen, this tether is fitted with a dozen or so temperature sensors located at regular 35 cm intervals. These sensors will be able to provide a changing profile of temperature versus depth.

    The depth of penetration therefore has to be measured accurately, given that the mole may well be unable to descend perfectly vertically, and it is highly probable that it starts to skew at some point in time. The tilt meter fitted to the mole will allow its orientation in the subsoil to be measured at all times, but this is just one step in determining the depth, which can only be known precisely by using the Tether Length Monitor (TLM). The purpose of this optoelectronic sensor will be to count the passage of markers attached on either side of the scientific tether as it gradually unwinds. Knowing the tilt, the depth reached by the mole can be calculated unambiguously from the length of cable behind it.

    The thermal measurements made by HP3 will establish the heat flow, i.e. the ease with which Mars' residual heat leaves the planet to be dissipated in the cold dark depths of space. Theoreticians estimate that the power dissipated into space by the Martian surface should be between 17 and 29 mW/m2 (compared to Earth’s mean heat flow of 87 mW/m2). Using this crucial piece of information, planetary scientists will be able to probe the depths of the Martian globe indirectly. Hence they will be able to estimate the temperature of the Martian mantle and place limits on the abundance of thermogenic radioactive elements that the Red Planet might still possess deep within.

    Although the proper execution of the experiment depends heavily on the mole's ability to make its way down through the Martian soil, the measurements made by HP3 will nevertheless always suffer interference from a number of unavoidable phenomena that will have to be measured and then removed from the data. One of the most obvious of these is the heating of the ground at daybreak, followed by its cooling overnight. Though they will affect the data collected by HP3, other temperature variations are harder to quantify, such as the annual temperature variations due to the climate or those related to variations in the inclination of the planet's axis of rotation (variations in obliquity, though these are less at the equator).

    If the HP3 mole reaches a depth of 5 m as expected, it will register the disturbance in the surface temperatures generated by the shadows from the lander and the SEIS instrument’s WTS only after one year.

    In addition to the thermal information, the soil’s greater or lesser resistance to the motion of the mole will provide important information on its physical properties. Many unknowns remain as to the characteristics of the Martian soil, whether on the surface or, more especially, in the depths yet to be explored.

    Planetary protection

    Given that the planet Mars is a priority target for traces of life, past or present, space agencies are obliged to take a great number of precautions to avoid any contamination with terrestrial microorganisms, whose astonishing ability to withstand the hellish rigours of spaceflight are well proven. This is the domain of planetary protection. Desiccated, exposed to harmful ultraviolet radiation from the sun and to cosmic rays, and loaded with toxic compounds such as perchlorates, the Martian surface is hostile to life by definition, or at least as far as we know. The depths of the planet might seem more benign in comparison, and it is precisely these depths that HP3 is intended to explore, albeit down to only a few metres.

    NASA has therefore listed a number of prerequisites that HP3 must satisfy in order to reduce the risk of contaminating the subsoil of the Red Planet as far as possible. Lying at the equator, the Elysium Planitia has a dry regolith completely free of ice. If such ice is indeed present in the form of beads or spindles, it is at depths inaccessible to the HP3 mole (though in other regions of the planet, such as at the higher latitudes, white ice may be found just a few centimetres below the surface).

    Through its very operation, the HP3 mole will create transient waves of heat whether during drilling or obtaining active conductivity measurements with the TEM-A heated sleeve. These temperature rises should vary between +10°C and +50°C, causing the ground (initially at roughly -55°C) to reach a temperature of around 0°C.

    Since there is no ice, HP3 will be unable to create microscopic pockets of liquid water to fill the pores of the soil. However, the Martian soil at the landing site could contain hydrated minerals, i.e. crystalline structures containing molecules of water. One of the rules of planetary protection stipulates that any water potentially liberated by HP3 during drilling or active measurement of thermal conductivity must displace no particle greater than or equal to 50 nm (a nanometre is 10-9 m). To meet this constraint, engineers determined the number of molecular layers liberated by heating the mole and how they varied with time. These short-lived aqueous films tend to spread out in all directions through capillary action, but their thickness would not be enough to displace soil particles as small as 50 nm. HP3 was therefore given the green light by planetary protection officials.

    The mole does not have its own source of energy, but is supplied with electrical power through the scientific cable. There is therefore no chance that it could break free to penetrate the depths of the soil all by itself. However, the planetary protection protocols to be applied during the HP3 experiment try to cover all cases, including that involving a partial or total breakage of the cable to which the mole is attached. So, if during the drilling process the scientific cable connecting the mole to its compartment should break, power to the mole will be automatically cut off and drilling would cease immediately.

    Last updated: 28 October 2016

  • The fluxgate magnetometer (© UCLA).The fluxgate magnetometer (© UCLA).

    The first magnetometer on the surface of Mars

    The InSight probe has a complete instrument package for characterizing the atmosphere as well as the environmental electromagnetic noise in which the ultrasensitive SEIS seismometer is expected to function. The Auxiliary Payload Sensor System (APSS) includes a magnetometer developed by the University of California, Los Angeles.

    Called the InSight FluxGate (IFG), this magnetometer will be the first to record magnetic data directly on the surface of Mars. It has a sensitivity of 0.1 nT (nanotesla).

    Last updated: 28 October 2016

  • A complete weather station

    The TWINS sensors from InSight's weather station (© NASA).The TWINS sensors from InSight's weather station (© NASA).

    Like all self-respecting geophysical stations, InSight comes with a complete weather station, or Auxiliary Payload Sensor System (APSS) whose primary purpose is to help characterize the influence of the landing site on the measurements made by the SEIS seismometer.

    Seismometers are very sensitive instruments, capable of recording with great precision all sorts of phenomena that may have nothing to do with ground tremors and the propagation of seismic waves. SEIS is no exception, and like the seismometer on the Viking Mars probes before it, the slightest gust of wind or variation in temperature will disturb it.

    The environment of the landing site will therefore be characterized in as much detail as possible by APSS, a sophisticated weather station bristling with temperature sensors, wind sensors and anemometers providing information about wind speed and direction, and finally, an ultrasensitive pressure sensor.

    TWINS

    The sensors used for TWINS (Temperature and Wind Sensors for InSight) are very similar to the REMS (Rover Environmental Monitoring Station) sensors used on the Curiosity rover, which has been trundling around the Gale impact crater since 2012. One of the sensors is mounted on the deck while the second is attached to the Instrument Deployment Arm (IDA) behind the Instrument Deployment Camera (IDC). These will record the air temperature, wind speed and direction twice per second throughout the mission, i.e. one Martian year (which is two Earth years).

    Pressure sensor

    The air inlet of the ultrasensitive pressure sensor of the APSS weather station (© NASA/JPL-Caltech/IPGP/Philippe Labrot).The air inlet of the ultrasensitive pressure sensor of the APSS weather station located on the deck of the InSight lander (© NASA/JPL-Caltech/IPGP/Philippe Labrot).

    An ultrasensitive pressure sensor capable of reacting to pressure variations in the order of a dozen µPa (i.e. 10-7 mbar) is mounted on the lander's deck underneath the WTS (the shield being lifted up by the robotic arm so as to be placed over the SEIS instrument once it is on the surface).

    Atmospheric disturbances

    The various subsystems of the APSS weather station (temperature sensors, wind vane, anemometer, barometer and magnetometer) will play a crucial part in interpreting the data provided by the SEIS seismometer. SEIS will certainly be influenced by interference from the incessant activity of the Martian atmosphere; the slightest gust of wind will transfer energy to the ground that will then be recorded by the seismometer. Similarly, the continuous and tiny changes in air pressure will translate as a very subtle drumming of the surface.

    At any given instant and at any given location, the effect of the constantly fluctuating pressure field is to press or release the ground (loading and unloading respectively), as if a multitude of invisible fingers were drumming on the Martian surface like a computer keyboard, deforming the ground. Using the ultrasensitive pressure sensor in the APSS, these pressure variations can be measured and then removed from the signal acquired by the SEIS seismometer. Similarly, the variations in temperature recorded by the temperature sensors will be subtracted (decorrelated) from the data provided by the seismometer.

    Besides its supporting role in acquiring seismic data, the APSS weather station will naturally also help to improve our understanding of Mars' current weather and climate. In addition to studying the wind, InSight will also investigate high-altitude clouds, fog on the surface, dust devils or atmospheric opacity due to suspended dust particles, for example. On the same subject, the camera on the robotic arm and the solar arrays (as a result of the drop in power due to the deposition of a layer of dust) will also make their contribution.

    Dernière mise à jour : 2 January 2019

  • RISE, InSight's geodesy experiment, exploits the spacecraft’s radio communications system with Earth (© NASA).RISE, InSight's geodesy experiment, exploits the spacecraft’s radio communications system with Earth (© NASA).

    Investigating the rotation of Mars to deduce its interior structure

    The RISE geodesic experiment does not require any specific instrument. It relies on the InSight lander's telecommunications system, which allows it to precisely measure variations in distance between the spacecraft and Earth due to the rotation of the planet Mars about its axis.

    Like all the planets in the solar system, Mars turns like a top around an axis of rotation passing through the north and south poles. The Red Planet makes a complete rotation every 24 hours and 37 minutes, with its axis inclined at roughly 25° to its orbital plane around the Sun. Its rotation and the inclination of its axis are therefore quite similar to those of Earth, which makes one rotation every 24 hours around an axis inclined at just over 23°. Other planets in the solar system depart from these values and show some astonishing features: Venus rotates very slowly (116 days) in the opposite direction, while Uranus has an axis of rotation that is practically parallel to the orbital plane whereby the poles are inclined towards the Sun, while the equator is at 90°!

    The rotation of planets is well known, and even though there may be a few special cases that are poorly explained (like Venus and Uranus), it might be tempting to assume that the phenomenon is rather banal. Nevertheless, the continuous accurate study of how Mars rotates about its axis has a major advantage, namely that of discovering more about the depths of this celestial body.

    Planets in the solar system, such as Mars and Earth, are not necessarily uniform rocky spheres like cosmic billiard balls. Their interiors are structured in the form of layers of different thicknesses and composition. Moving from the surface towards the centre, the three most important layers are the crust, the mantle and finally the metal core.

    If we take two spheres, one completely homogeneous, the other with a structure in the form of layers of differing densities, and we then make them spin like tops, we quickly observe that the rotational motions are not the same. The manner in which the material is distributed throughout the volume of the two spheres (what physicists call the moment of inertia) is different, and this has an effect on how objects rotate. An experiment can easily be carried out using a hard-boiled egg and a raw egg. Once set spinning, the two objects will not behave in the same way in space since the structure of the raw egg, which combines both liquid and solid, is different from that of the hard-boiled egg, which is entirely solid.

    Precession and nutation

    A detailed study of the rotational motion of a planet about its axis shows that over the course of time the position of the axis varies in space. The axis describes a circle about a fixed vertical position: this is precession. For planet Earth, the axis of rotation makes a complete turn in the heavens every 25,770 years on average. This terrestrial precession, known as precession of the equinoxes, is directly linked to significant climatic changes. The celestial drift of Mars' axis of rotation is much slower, only making a complete turn in 165,000 years.

    If we observe in fine detail the path traced by the axis of rotation of Earth or Mars, we see that neither axis describes a perfect circle, but oscillates regularly about a central position. These very slight oscillations define nutation: Earth requires 18.6 years to complete one of these small oscillations, as against less than one Martian year (two Earth years) for the Red Planet.

    Precession and nutation of the planet Mars (© IPGP/David Ducros).Turning on its axis like a top, Mars forces its axis of rotation to describe a circle about some arbitrary position. This is the phenomenon of precession. Superimposed on the circle itself are small oscillations, a phenomenon known as nutation (© IPGP/David Ducros).

    By very finely characterizing the rotational parameters of Mars about its axis (rotational period, values of precession and nutation), geophysicists will be able to obtain a more accurate idea of its interior structure. InSight has therefore been fitted with two medium-gain antennas attached to its deck that look a bit like splayed-out yoghurt pots. These antennas establish direct radio communication between Earth and Mars in X-band, bypassing the relay satellites in orbit around the Red Planet (the downside is that the data rate is lower).

    In addition to providing the capability of communicating directly with InSight, the radio signal emitted by the medium-gain antennas can be used to measure the distance between Earth and Mars remarkably accurately (to roughly 10 cm) through a Doppler technique. In terms of listening time, InSight needs simply to be monitored for at least 2 hours per week for one Earth year using the 34 m diameter antennas of NASA's deep space network (DSN).

    If the distance should change between a radio transmitter and receiver, the frequency of the radio signal will do the same. Sitting on the Martian equator and being moved around despite itself by the planet’s rotation, InSight’s distance from the Earth will be constantly changing. By following these changes in the distance between Earth and Mars, RISE will provide detailed information on the way in which the planet turns on its axis and on changes in direction of its rotational axis over the course of time (precession and nutation).

    In turn, geophysicists will be able to deduce what is hidden out of sight below the surface, i.e. the nature and distribution of mass within the planetary sphere (moment of inertia). It will thus be possible to estimate not only the size and density (and hence the mineralogical composition) of the core, but also the density of the mantle. Precession alone will provide information on the radius and density of the core, but these two parameters are linked, one changing with the other. By studying the nutation, the radius of the core can be separated from its density (the two measurements becoming independent of one another). In particular, RISE should be able to reduce the current uncertainty surrounding the size of the core by a factor of ten.

    InSight is not the first probe to have measured the rotation of the planet Mars. Similar experiments were carried out in 1976 by the Viking probes, and then 20 years later in 1997 by Pathfinder. A measurement campaign was also carried out in 2011 when the Opportunity rover was in hibernation. These first data were sufficient to place limits on the size of Mars' metal core. Twenty years after Pathfinder, InSight will take up the baton to refine our understanding of Mars' internal structure. The precession measurements will be ten times better than those made by the Viking probes, and the duration of the observations will be extended, hence improving accuracy.

    Last updated: 28 October 2016

Launch

The first Martian probe to lift off from Vandenberg

Unusually, the InSight probe will lift off from the Vandenberg Air Force Base in California. This military base is not normally used as a starting point for spacecraft heading for Mars, which instead lift off from the Cape Canaveral Air Force Station in Florida. The sling effect is greater there as launches are eastward, in the same direction as the Earth’s rotation.

It is forbidden to launch eastwards from Vandenberg because of urban areas, whereas Cape Canaveral is located along the East Coast of the United States. Launchers therefore head out over the Atlantic Ocean, the sling effect increasing the initial velocity of departing spacecraft. The Atlas V launcher is so powerful, that InSight does not actually need the extra speed offered by the Earth’s rotation, explaining the decision to lift off from Vandenberg.

Vandenberg, built in 1941, has been a military base from the outset, serving among other things as the firing site for ballistic missiles housed in numerous silos. The area south of the launch pads is free of any obstructions, so it can also launch military or civil satellites into polar orbits around the Earth. Vandenberg was also fully equipped to launch the US Space Shuttle, though the dedicated infrastructures were never used in the end.

Vandenberg and Cape Canaveral launch bases (© rights reserved).Vandenberg and Cape Canaveral launch bases (© rights reserved).

Last updated: 28 October 2016

Cruise & Orbit phases

A six-month journey to Mars

InSight’s trajectory from Earth to Mars (© NASA).InSight’s trajectory from Earth to Mars (© NASA).

Once launched, InSight will take six and a half months travelling through interplanetary space to reach its target, the Red Planet. Its trajectory is a circular arc with one end on the Earth and the other on Mars. This transfer orbit is known as a Type I orbit, because its journey around the Sun remains below 180°, explaining a relatively short transit time.

InSight in cruise configuration (© NASA).InSight in cruise configuration (© NASA).

Contrary to what you might think, the launch vehicle used for InSight is not directed towards Mars but along a different trajectory. The rules of planetary protection, which stipulate that every precaution must be taken to avoid contaminating Mars with germs from Earth, have a surprising consequence. Automated spacecraft heading for Mars are actually launched so that they will miss their target. This procedure is designed so that the upper stage of the launcher, which trails behind the probes, will not crash into the Red Planet.

As InSight is not launched directly towards Mars, corrective manoeuvres are scheduled throughout its journey to eliminate the drift that is deliberately introduced at the beginning, thus bringing the probe back on track.

There are six Trajectory Correction Manoeuvres (TCMs) in all. The first takes place quite soon after launch and eliminates most of the deviation while correcting any injection errors. The second is scheduled halfway through the journey; all the others then take place during the approach phase, which starts 60 days before landing. They aim to refine InSight’s trajectory so that the spacecraft enters the Martian atmosphere with the desired precision. The atmospheric entry path angle is only -12,5°. If the probe penetrates the atmosphere with a shallower angle, it will bounce off and be lost in space. If, on the other hand, the angle is steeper, there will be so much friction that the lander will be incinerated. Great precision is also necessary to be able to land exactly on or very near the equatorial landing site, Elysium Planitia.

Besides the TCMs required to get the spacecraft to its entry point into the Mars system, the cruise phase is quite a calm period of the mission.

The InSight probe’s cruise stage in flight (© NASA).The InSight probe’s cruise stage in flight (© NASA).

Engineers check the probe’s instruments and various subsystems on many occasions, while interplanetary navigators keep a close eye on the trajectory. During the cruise phase, only the seismometer’s horizontal SP sensor can work and therefore be tested. The VBB sensors and vertical SP sensor will be saturated due to the zero gravity.

On Earth, while InSight is travelling through the dark realms of space, the various mission teams continue to work hard to guarantee the mission’s success and prepare for both the landing and the scientific measurements to be initiated once the lander has arrived safe and sound on Mars.

Last updated: 26 february 2018

Interplanetary navigation

Travelling through deep, dark space

Antennas belonging to NASA’s Deep Space Network (© NASA/JPL).Antennas belonging to NASA’s Deep Space Network (© NASA/JPL).

To guide InSight through the interplanetary space separating Earth from Mars, navigators analyse radio signals transmitted by the probe and received on Earth.

On Earth, radio communication is through NASA’s Deep Space Network (DSN). In space, InSight has several different radio antennas.

Three terrestrial receiving stations have been set up at strategic points of the globe, in Goldstone (California, United States), Canberra (Australia) and Madrid (Spain). The distribution of these stations ensures that at least one is facing Mars at any time. Radio communication between Earth and the InSight probe takes place in X-band, a very high frequency range around 10 GHz suitable for long-distance communication through space.

Distance measurement

To check InSight’s trajectory, the navigators traditionally determine the distance between the probe and our planet by precisely measuring the time taken by the signals to reach the spacecraft then return to Earth. Given that the speed of light is 300,000 kilometres per second, the distance travelled can easily be calculated from the time taken for a return trip.

Measuring speed through the Doppler effect

A second useful technique is based on the Doppler effect, which can be used to determine the relative speed of the spacecraft with respect to Earth by calculating the frequency shift of radio signals transmitted by InSight.

A common example to describe the Doppler effect is that of a traveller sitting on a bench near the railway track at a train station. A train arrives from the left, whistling as it comes. Throughout the train’s approach, the frequency of the whistling noise rises, becoming more strident. Once the train has passed and is moving away from the traveller, the phenomenon is reversed: the frequency gradually lowers and the sound of the train is deeper. The same technique is used in space to measure the InSight probe’s speed in relation to Earth.

Delta Differential One-way Ranging (Delta DOR)

Large antenna at ESA’s Cebreros station in Spain (© ESA).Large antenna at ESA’s Cebreros station in Spain (© ESA).

A third, more recent, technique has been developed to obtain information on the position of the spacecraft in directions that are not parallel but perpendicular to the Earth-spacecraft line of sight.

Delta differential one-way ranging, more commonly known as Delta DOR, uses antennas far away from each other (ideally on two different continents) to simultaneously receive a spacecraft’s radio signals.

In this case, antennas on two sites belonging to NASA’s deep space network are pointed towards InSight. Once the receiving session is over, the same antennas are pointed at a celestial reference point with a precisely known position. Quasars—which are particularly powerful natural radio beacons—are the preferred targets.

Quasars are used to correct measurement imprecisions due, for example, to solar activity, ionospheric perturbations (the ionosphere being the layer of ionized air that surrounds Earth), or the tiny drift of clocks used on Earth. For a given measurement, the chosen quasar must be located in a region of the sky close to the area being crossed by the probe.

Currently, engineers have to receive signals first from the quasar and then from the probe or vice versa. It is not possible to receive the radio waves from the quasar and the spacecraft being tracked at the same time.

Guiding the probe to its point of entry

Using the three techniques mentioned above, interplanetary navigators can determine InSight’s position at any point in time with great accuracy and in three dimensions. They can also determine the direction it is moving in and the speed at which it is moving. If necessary, trajectory correction manoeuvres are carried out to refine the probe’s course and ensure it arrives at the Mars system with the right speed and at the correct angle.

Throughout the cruise phase, the mission’s interplanetary navigators regularly check the spacecraft’s position as it travels through space, immediately scrutinizing the slightest anomaly or deviation to determine the cause. The success of the critical landing phase, and therefore the success of the whole mission, depends on the exactitude of the trajectory.

Last updated: 7 august 2017

Landing

The landing phase is not only the most spectacular but the most critical mission phase

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InSight’s landing phase is the most critical of all the mission phases. It starts exactly three hours before contact with the highest layers of the Martian atmosphere, some 125 km from the surface.

Based on Phoenix, a polar lander that successfully landed on Mars’s glacial boreal plains on 26 May 2008, the InSight probe has benefitted from all the lessons learned from this mission. The only major difference concerns the landing site: InSight will land on the equator, whereas Phoenix was sent to Mars’s arctic regions.

Separation from the cruise stage

Seven minutes before hitting the layer of air around Mars, pyrotechnic devices will shear the bolts attaching InSight to its cruise stage, allowing separation from the stage designed to safely guide the probe all the way to Mars.

For one and a half minutes, the capsule containing InSight will slowly rotate until its heat shield is pointing forward, towards its target planet. At this point, it is travelling very quickly, hurtling towards the Martian ground at the hypersonic speed of about 5.5 km/s.

Like a bullet fired from a gun, it enters the atmosphere along a ballistic trajectory with an entry angle of 12.5°. Whether landing on Earth or on Mars, the angle of entry is critical, much more so than speed. If the angle is too shallow, the probe will bounce off the atmosphere and be lost in space. If it is too steep, the friction against the capsule would be too great, turning the spacecraft into a ball of fire.

Atmospheric entry

To survive the intense frictional forces that characterize entry into the atmosphere, InSight is protected by a large heat shield covered in ablative tiles. By slowly burning off, the tiles will absorb the huge amount of energy caused by the atmosphere’s resistance to InSight’s arrival.

At the highest peak of deceleration, the probe will be subject to over 9G, a load that no human could withstand. The mobile masses of the VBB pendulums will at that point press against their end stops with a load equivalent to 2 kg on Earth, and they must resist the slightest deformation.

The entry vehicle, made up of a heat shield and a rear shield, contains the stowed lander. During this naturally turbulent stage, it is stabilized by small retrorockets. The capsule was nonetheless made to be globally stable from an aerodynamic point of view.

There is no guidance as such during the entry phase, which explains why the size of the landing ellipse delimiting the area in which InSight is likely to land is much bigger (130 km x 27 km) than that of the Curiosity rover.

When InSight lands on Mars on 26 November 2018, it will be autumn in the northern hemisphere, and the season of dust devils will have begun. The wind will be blowing large quantities of very fine dust particles into the air, possibly changing atmospheric properties significantly. The Martian weather will be therefore be monitored very closely during the weeks prior to the landing. Numerous simulations have shown, however, that the probe should be able to cope with a wide range of situations, even difficult ones.

Parachute-braked descent

After atmospheric entry, the second step for the InSight lander is a parachute-braked descent. Twelve metres across, the parachute will unfurl at around 9 km above the surface. Located 2.7 km below the mean level of Mars (a kind of virtual sea level), the landing site enables efficient braking due to a sufficiently big air column.

Despite having been slowed down during the entry phase, the probe will still be travelling at a supersonic speed (around 1.5 Mach, which is a little over the speed of sound and corresponds to approximately 350 m/s) when the parachute opens, complicating its task. There will be a huge stress on the parachute fabric and suspension lines, but the parachute has been specifically designed to be able to open fully at high speed without tearing. Due to the low atmospheric pressure on Mars and a need for speed, a drogue parachute would be of no use in fully deploying the main parachute. This step requires the energy provided by a mortar.

Fifteen seconds after deployment of the parachute, at an altitude of around 7.2 km and travelling at 443 km/h (or 123 m/s, which is the equivalent of around Mach 0.5 on Mars), the heat shield—having fulfilled its role—is ejected and drops down onto the Martian ground. It is not ejected right after the parachute’s opening because the chute is at first subject to strong oscillations. The heat shield is jettisoned only once these have settled down.

Ten seconds after the heat shield has been ejected, the lander’s three telescopic legs are free to deploy with no fear of contact. They unfold in quick succession, with 0.5 s between them.

Five seconds later, at around 6 km above the surface, the descent radar starts operating and seeks the Martian surface. It is designed to supply the InSight probe with precise information on its altitude and speed relative to the ground. The radar will lock on to the ground at an altitude of around 2,400 m. The radar data will be used until the probe is within 30 m, when parasitic reflections from the surface will interfere with navigation data, making them unusable.

Artist’s view of the InSight probe during its final (powered) landing stage on Elysium Planitia. To brake its descent, the spacecraft is fitted with three groups of pulsed retrorockets, each developing a thrust of around 300 newtons. Although by definition it is very sensitive to the least vibration, the SEIS seismometer has been designed to withstand the very violent bangs and bumps associated with a Mars landing (© IPGP/Manchu/Bureau 21).Artist’s view of the InSight probe during its final (powered) landing stage on Elysium Planitia. To brake its descent, the spacecraft is fitted with three groups of pulsed retrorockets, each developing a thrust of around 300 newtons. Although by definition it is very sensitive to the least vibration, the SEIS seismometer has been designed to withstand the very violent bangs and bumps associated with a Mars landing (© IPGP/Manchu/Bureau 21).

Final powered phase

With 1.3 km to go before landing, while still travelling at 224 km/h, InSight separates from its parachute, which remains attached to the rear shield of the capsule. Now in free fall, it drops like a stone towards the Red Planet, leaving behind the rear shield.

Very quickly, half a second later, the lander fires its retrorockets—three clusters of four hydrazine-powered thrusters each supplying a thrust of 300 N—to brake and stabilize the spacecraft. The onboard computer which controls the thrusters will seek to reduce horizontal speed and keep vertical speed constant. Depending on the situation, the probe may need to perform a manoeuvre to avoid the rear shield so that the parachute fabric cannot, by a dreadful stroke of bad luck, cover up the lander once on the ground.

When just 50 m from the ground, when the lander’s vertical speed has been reduced to 30 km/h, the contact sensors on the legs are activated. The Martian surface is then very close. InSight’s mean vertical speed will be only 8 km/h or so (a little more than 2 m/s) when it finally comes into contact with the surface, and its horizontal speed nearly three times less. The touchdown is recorded by the contact sensors. By then, InSight will have travelled hundreds of millions of kilometres through space to arrive at the Elysium Planitia region around 2 o’clock in the afternoon of this beautiful but cold winter day on Mars.

Mars in a Minute video series : How Do You Land on Mars ? (© JPL-Caltech).

The retrorockets are cut off less than 0.25 s after contact with the Martian surface to minimize deterioration of the landing site by the powerful gas jets from the thrusters. Any damage will be limited to the area underneath the landing platform, which may be hollowed out a little by the jets (a phenomenon known as site alteration).

For safety reasons, the solar arrays will only be unfurled 16 minutes after InSight’s arrival so as to minimize the influence of dust settling after the probe’s noisy arrival on Mars. This delay also limits the amount of dust that will settle on the lander deck.

This marks the end of the InSight lander’s journey and the beginning of a whole series of checking operations. The same cannot be said for the SEIS seismometer, which is still one metre above the Martian surface. The mission’s objective is to carefully place it on the dusty, rust-coloured ground. It is only once its three conical legs are firmly planted in the dust, after a long instrument deployment phase, that the landing per se will really be over.

Last updated: 11 november 2018

Landing Site

Final destination, Elysium Planitia

The selection of a landing site on Mars has to comply with two main constraints. The first is technical, and of interest mainly to the engineers involved, whose principle concern is to land the probe for which they are responsible safe and sound on the Martian soil. The second is scientific, and of particular interest to the mission investigators. The ideal landing site for them is an area where scientific experiments may be carried out in good conditions, and where there is maximum potential for discovery.

Map of Mars showing the landing sites of the main Martian probes (© NASA).Map of Mars showing the landing sites of the main Martian probes (© NASA).

Engineering constraints

Mission engineers are particularly interested in factors able to reduce the level of risk during landing. As the atmosphere helps to brake the probe during its descent, a low-altitude site is preferred in order to benefit from the thickest layer of air possible. A plain or depression will thus be more attractive than the summit of a volcano, for example. The engineers will also try to avoid steep, slippery slopes, a surface littered with large rocks or uneven ground with crevices or impact craters.

The ideal landing site is a naturally flat and unobstructed surface resembling a parking spot. Once the probe has landed, it must survive the hostile, demanding environment of Mars. The quality of solar illumination, along with daytime and night-time temperatures, are thus essential from this point of view. InSight’s engineers are not concerned as to whether the area is monotonous and of little geological interest, or that the first promising rocky outcrops are out of reach. Their main concern is to land the probe safely, because if the landing fails, there will be no scientific activity anyway. The driving factor is safety, whether during or after the landing.

Scientific constraints

Obviously, if after travelling several hundred million kilometres through space the probe arrives safe and sound but in an area of Mars of little scientific interest, it is not worth all the effort.

Scientists therefore insist on engineers accepting a certain level of risk so as to have the chance of exploring the most remarkable areas of the Red Planet.

Selection process

In the light of the above, it is easy to see that the landing site selection process is long and complicated, with numerous discussions between engineers on one side and scientists on the other.

The choice of InSight’s landing site was broken down into several steps. In September 2010, the selection committee definitively chose the Elysium Planitia region. Unusually, all the target zones identified by ellipses remained within this area. At this early stage in the selection process, it is more common to have the ellipses scattered all over the surface of Mars. This was not the case for InSight, which shows the importance given to engineering constraints.

The selection of a landing site for InSight was relatively simple, unlike that for previous missions to Mars, from the Viking probes of 1976 to the Curiosity rover in 2012. The main reason for this is that the lander is a geophysical measuring station and therefore the scientific investigators are more interested in what is going on underneath the surface than what is happening on top.

View of the InSight landing site on Elysium Planitia by the HiRISE camera on Mars Reconnaissance Orbiter (central part of the landing ellipse) (© NASA/JPL-Caltech/Univ. of Arizona)

View of the InSight landing site on Elysium Planitia by the HiRISE camera on Mars Reconnaissance Orbiter (central part of the landing ellipse). This region is one of the flattest and safest areas of the Red Planet, but it is not totally flat. The photo shows a group of impact craters, some of which could be the secondary craters of the Corinto crater about 1,000 km north. (© NASA/JPL-Caltech/Univ. of Arizona).

Much to the delight of the engineers involved, any flat site—however mundane—was potentially acceptable. The rule applied when selecting the InSight landing site was quite simply “land safely.”

Ideally, if the geophysicists could choose freely, ignoring landing constraints, InSight would have been sent to that part of Mars that appears the most affected by quakes, i.e. Tharsis. This huge swelling in the Martian crust, home to many huge volcanoes, appears to have gone through periods of intense seismic activity. Unfortunately, it is too high to allow a safe parachute-braked descent.

By May 2012, there were still around 20 potential sites in the running. By July 2013, participants had managed to whittle down the shortlist to four sites, and in January 2015, the final ellipse was chosen, as was a backup area should the first choice turn out to be impracticable.

Elysium Planitia

The InSight probe’s landing ellipse, taking uncertainty into account (© NASA).The InSight probe’s landing ellipse, taking uncertainty into account (© NASA).

On 26 November 2018, InSight will land on Elysium Planitia, an equatorial region at 4° N.

Elysium is a Latin term also known as the Elysian Fields, an area in Greek mythology where humans were judged after their death and where the righteous could live and finally rest from their labours. Should you ever have the chance to stroll along the Champs-Elysées in Paris, spare a thought for Mars and InSight !

The site is quite ancient (dating back to the Hesperian era, some 4 to 3.5 billion years ago), and its surface is flat with few rocks. There is no relief or steep slope likely to fool the descent radar.

The probe should be able to land upright without finding itself in a precarious position with one leg on a rock. The petal-like solar arrays should be able to open without hindrance from any obstacles. There are no thick layers of dust into which the probe could sink, rather like quicksand. The layer of dust deposited in this region by the atmosphere is less than 1 mm thick.

The ground should be perfect for the mission. The top layer, or regolith, is made up of crumbly, crushed rock thick enough yet not too solid to allow the HP3 mole to burrow down without too much difficulty.

InSight’s landing site may give geologists the chance to study the wrinkle ridges there (© rights reserved).InSight’s landing site may give geologists the chance to study the wrinkle ridges there (© rights reserved).

 

The available sunshine will allow the solar arrays to operate efficiently and the probe to benefit from relatively mild temperatures, at least as far as Mars goes. Finally, the site’s altitude and wind strength will allow the parachute to brake the spacecraft properly during its descent without too much buffeting.

From a seismic viewpoint, Elysium Planitia is of less interest than Tharsis, but its proximity to the rugged area separating the highlands of the southern hemisphere from the flat lowlands of the northern hemisphere (the famous Martian dichotomy), nonetheless makes it of interest.

On the surface, geologists have identified formations that could be worth investigating. There are also wrinkle ridges and landforms shaped by water, the wind or sediments. Bear in mind, however, that InSight’s main objective is to study the inner depths of Mars, and not geological surface features.

Landing ellipse

Whatever progress has been made in the feat of landing an automated spacecraft on Mars, there remains some uncertainty as to where exactly the legs will touch down on the rust-coloured planet.

This uncertainty is translated in the case of InSight by a landing ellipse 130 km long and 27 km wide, which is a relatively big area. The ellipse represents the zone where the probe has a 99% likelihood of landing.

The centre of the ellipse is located at exactly 4° N and 136° E. InSight’s closest companion will be the Curiosity rover, which landed at a similar longitude, but on the other side of the equator, at 4.5° S. Further East, inside the Gusev Crater, is the Spirit rover, whose last transmission dates back to 22 March 2010.

Mars in a Minute video series : How Do You Choose a Landing Site ? (© JPL/Caltech).

Orbital reconnaissance

InSight’s landing zone has already been photographed by the spy camera on the US Mars Reconnaissance Orbiter. The high-resolution images obtained up to now remain reassuring.

The study of different terrains within the landing ellipse will nevertheless continue up to the last moment, and if there is the slightest hitch, the probe will be directed to a backup site. If all goes according to plan, InSight’s landing site will be definitively confirmed in November 2017.

Last updated: 2 february 2018

Deployment of the instruments

The SEIS seismometer and the HP3 penetrator must be placed on the ground

Once safe and sound on the dreary, dusty plain known as Elysium Planitia, the InSight probe will initiate a crucial stage in the mission: the placing of the two main instruments, SEIS and HP3, carefully on the Martian soil.

Placement zone

La zone de déploiement des instruments SEIS et HP<sup>3</sup> mesure environ 3m<sup>2</sup> (© NASA)A deployment zone for SEIS and HP3 of around 3m² (© NASA).The limited movement of the robotic Instrument Deployment Arm (IDA)  means that the seismometer and HP3 penetrator must be positioned in front of the lander, within a crescent-shaped area approximately 3 m long and 2 m wide. The area available for the HP3 instrument (3.4 m²) is bigger than that allocated to the SEIS instrument (3.1 m²).

The area where the instruments are to be placed will be photographed in great detail by the InSight lander’s technical cameras. Attached to the IDA, the Instrument Deployment Camera (IDC) moves so as to take stereo-pair images overlapping by about 80% and will cover the whole surface. The first set of eight images is taken with the IDA above the lander deck, to ensure that the second shot, taken one metre above the ground, is reliable. Following that, 24 stereo-pair images will be recorded for input into a Digital Elevation Model (DEM) with a resolution of around one centimetre.

All the phases of the instrument setting-down process will also be photographed: pre-positioning the gripper then engagement, raising then lowering the instrument onto the ground, freeing the load, etc.

Sandpit

The whole deployment process will be simulated on Earth in a giant sandpit within a huge hangar before being carried out on Mars. A working model of the lander fitted with cameras and a robotic arm similar in all respects to the real probe is to be set up in an enclosure. The mock-up will also include dummy instruments identical in mass and volume to those sent to Mars.

Using the images from the technical cameras and supported by a digital elevation model (a computerized 3D model of the landing site), a terrain modelling the Martian surface down to the least detail can be created. The sandpit will be filled with a reddish material simulating the crushed, powdery soil that specialists call the regolith. Rocks of various shapes and sizes will then be added for realism, because unlike a Japanese garden, the objective is not aesthetic, but rather to stick as closely as possible to the ground truth!

Instrument deployment

Deployment of the SEIS seismometer by the InSight probe’s IDA (© NASA).Deployment of the SEIS seismometer by the InSight probe’s IDA (© NASA).

Once the few square metres of the landing site on Elysium Planitia have been duplicated on Earth, mission engineers will begin a series of tests that will lead to the development of a set of commands for the first step of the deployment process.

Once validated, these commands will be sent to Mars for the InSight probe to execute. This process will be repeated step by step until both instruments are correctly deployed on the Martian soil.

The team in charge of instrument deployment will obviously take their time. A detailed schedule, partly dictated by the telecommunications bandwidth allocated, has already been established. After each step of the deployment process, checks crucial to the go-ahead for further operations will be made. The engineers involved will have a comfortable margin at each key point and at the end of the deployment process in order to respond to the unforeseen situations inevitable with this kind of activity.

The critical deployment phase is split into six parts and could take up to two months after landing (with a margin of 20 sols). During this time, the teams will be constantly on hand, unlike during the scientific measurement phase, when the probe will be operating practically on its own. The operations schedule is given below:

  • Sols 0 - 5: initialization of the lander and preparation for instrument deployment.

  • Sols 6 - 18 : characterization by the cameras of the room available for positioning the instruments and selection of the most advantageous potential sites for deployment.

  • Sol 7 (science) : initiation of RISE data acquisition (geodesy).

  • Sols 19 - 31 : deployment of the SEIS seismometer (see details below). Start of measurements in engineering mode.

  • Sols 32 - 43 : deployment of the seismometer’s Wind and Thermal Shield (WTS). Start of SEIS scientific measurements (monitoring) from sol 40.

  • Sols 44 - 58 : deployment of the HP3 suite. Its mission accomplished, the robotic IDA returns to a stowed position on the lander.

  • Sols 59 - 69 : start of drilling operations with the HP3 mole.

Deployment of SEIS

The InSight probe’s robotic arm carefully places the WTS over SEIS (© NASA).The InSight probe’s robotic arm carefully places the WTS over SEIS (© NASA).

The SEIS seismometer’s deployment is the top priority. The rigidity of the communications and power supply cable will prevent the instrument being set down in certain parts of the deployment area.

In the event of an incident, it should be possible to lift the seismometer again and set it down elsewhere, but certain movements (such as to the rear) are forbidden due to cable constraints.

Once the seismometer is resting firmly on its levelling system tripod on the Martian soil, it must be covered by the Wind and Thermal Shield (WTS), which amounts to a large protective cover. The deployment engineers have to ensure that they leave a gap of at least 6 cm between the outside of the seismometer and the inside of the WTS.

Next comes HP3, designed to measure heat flow. No doubt to thank it for waiting so long, the HP3 mole will be allowed to start burrowing down into the Martian soil just after being set down on the surface.

Commissioning the SEIS seismometer

The InSight probe’s robotic IDA setting down HP3 (© NASA).The InSight probe’s robotic IDA setting down HP3 (© NASA).

The SEIS instrument will be commissioned through a series of successive steps described below.

First, SEIS will be placed on the ground with the gripper still attached. Preliminary measurements will then be taken in this configuration. If the position is unsuitable, the seismometer may be easily moved without having to try to grab the instrument’s carrying handle again with the gripper on the robotic arm, always a tricky manoeuvre.

Deploying a seismometer on the surface of another planet is a real challenge. It is absolutely crucial for SEIS to be set down on a surface inclined at less than 15°. The surface must also be flat, without any rocks, and able to support the seismometer and its heavy protective shield (WTS). Finally, the seismic coupling—in other words, the quality of contact between the soil and the seismometer’s legs—must be no less than excellent.

Up to now, the only instruments set down directly on the surface of a celestial body other than Earth—the Moon—have been placed there with the invaluable help of humans. This is the first time ever that a robot will be used. Even the Martian rovers have never carried out such an operation, even though they have sometimes moved sensors on robotic arms closer to rocks or the ground.

Once the SEIS seismometer is on the ground, the levelling system is activated in order to align the instrument horizontally to within 0.3°. Inside the evacuated sphere, the VBB pendulums are then recentred using the balancing device. For the launch, the pendulum recentering motor is stowed away, and the mobile mass is kept up near the end stop. Once on Mars, the mass is moved to precisely centre the pendulums and find the right balance between Martian gravity and the force used by the spring to bring the pendulums back into their central position. Once centred, they can be calibrated.

InSight probe with the SEIS and HP3 instruments on the ground (© NASA).InSight probe with the SEIS and HP3 instruments on the ground (© NASA).To check the quality of seismic coupling and confirm the choice of site, measurements will be taken in engineering mode for one Martian day (i.e. a sol). Engineering mode is quite resistant to temperature fluctuations (which are not corrected at this stage), but it does not offer high enough performance for scientific measurements. In this mode, the seismometer cannot be saturated, i.e. be submerged by the amplitude of signals recorded, which is an advantage.

If the data gathered during this first day are not satisfactory, the seismometer (still attached to the gripper) will be moved. If all is well, the IDA releases the instrument and proceeds to cover it with its protective shield, the WTS.

In this configuration, the Thermal Compensation Device Mechanism (TCDM) on each pendulum can then be activated. In its launch configuration, the TCDM is aligned vertically, a position in which it cannot affect the pendulum. Now that the seismometer is on Mars, it has to be positioned in order to reduce as much as possible the effects of variations in temperature.

The variations in temperature throughout a day will be observed in engineering mode, with the TCDM vertical (0°). The resulting seismic signal graph is a sine wave.

The following day, the TCDM is turned by 90°, its most efficient position. The aim is to efficiently reduce the effects of temperature variations by a factor of 10, for example. Contrary to what one might think, the TCDM’s effectiveness does not depend on the amplitude of variations, but the mean temperature. It is nonetheless possible that the TCDM dampens the movement too much.

Over the next few days, the TCDM may be rotated to a given angle to optimize its operation with respect to the observations of the previous days.

The seismometer will remain in engineering mode until the TCDM has been finally adjusted.It will then be switched to science mode, which is not compatible with strong temperature variations (now compensated by the TCDM), and less robust than engineering mode as there is a risk of the sensors being saturated in certain conditions. However, its measurement performance in this mode matches that required by the international scientific community.

Last updated: 7 august 2017

The Data

 Les données

  • Moyens

    Moyens de télécommunication

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  • Circulation

    La circulation des données & commandes (grand schéma)

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  • Type

    Les types de donnée

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Data Exploitation

Exploitation des données

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Donec mollis posuere sollicitudin.

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The future of Martian seismology

Networked seismometers, penetrators and optical sensors

Networked science

Artist’s view of the NetLander capsules’ atmospheric entry (© CNES/David Ducros).Artist’s view of the NetLander capsules’ atmospheric entry (© CNES/David Ducros). The InSight mission’s objective is to place a seismometer on Mars. Although instrument deployment, a key factor in acquiring high-quality data, has been the object of much attention, from the IDA robotic arm first placing SEIS on the ground to its horizontal alignment via a motorized levelling system, then the positioning of its Wind and Thermal Shield (WTS), the fact is that SEIS is still going to have to operate alone, which is not the best situation for a seismometer.

Forty years ago, when scientists attempted through the Viking mission to probe the depths of the Red Planet, there were already two seismometers involved. Similarly, a couple of instruments were flown aboard the automated capsules of Russia’s Mars 96 mission, which unfortunately never managed to break free of its Earth orbit.

In seismology, two is always better than one, but the principal objective of geophysicists is clear when you look at the projects that they have dreamed of and worked on: the NetLander mission, for example, was to have deployed four seismic stations, while the ambitious MESUR project planned to jettison no fewer than 16 seismometers over the surface of the Red Planet, without counting the four additional stations that could have been brought by Europe.

The Deep Space 2 penetrator (© NASA/JPL).The Deep Space 2 penetrator (© NASA/JPL).

Geophysicists are obviously seeking to contain the Martian globe within a tightly-meshed network of seismic stations disseminated all over the planet in order to establish on Mars a far more modest version of the global seismic network on Earth, currently made up of several tens of thousands of stations.

Up to now, projects involving the deployment of a network of seismometers on other planets have all been shelved at different times, mainly for budgetary reasons, but also because, as far as Mars is concerned, geophysical investigations have not been given the priority that geophysicists would like. They have been crowded out by exobiology activities seeking traces of past or current life. The main motivation in exploring Mars is the persistent quest to shed light on the origins of life.

A huge challenge therefore awaits the InSight mission: not only will it take the first real seismic measurements on Mars, but it will also explore the planet’s inner depths, from crust to core. This is a crucial step to understanding the origin and evolution of rocky planets in our solar system, and for this reason merits as much respect as other areas of research.

Despite the numerous techniques that geophysicists are going to use to fully benefit from InSight’s only seismometer, SEIS will inevitably be faced with certain limitations. This is why scientists and engineers continue to study projects involving the deployment of not one but multiple seismometers on Mars. InSight is paving the way, and marks the beginning of renewed interest in the geophysical aspects of the Red Planet. In 2021, a second seismic station— this time flown on Russia’s ExoMARS 2020 lander—will accompany InSight’s SEIS instrument, even if its installation will not necessarily be so optimal. More than ever before, the future of Martian seismology lies in networking.

Advantages of penetrators

Artist’s impression of the Mars 96 mission penetrators (© CNES/David Ducros).Artist’s impression of the Mars 96 mission penetrators (© CNES/David Ducros).

In past network-based projects, the seismometers were generally designed to be deployed on the ground using small capsules, which could also include other geophysical instruments as well as the indispensable weather station. In fact, the airbag-cushioned tetrahedral platform that landed the small Sojourner rover on Mars in July 1997 was originally designed to disseminate seismometers as part of the MESUR mission. Although autonomous in terms of power supply and telecommunications, these ground stations are not the ideal way of positioning a seismometer on the Martian surface.

This is because the quality of signals acquired by a seismometer depends, among other factors, on the way the seismometer is deployed and specifically the quality of the instrument’s coupling with the ground. If the seismometer is tilted or the coupling insufficient, the seismometer may not be able to feel the ground’s seismic motions properly.

Therefore, geophysicists have started investigating another way of deploying seismometers, that is to say using penetrators. A penetrator is a kind of sophisticated dart, generally bristling with miniaturized instruments and jettisoned by a mother ship orbiting the planet. The aim is for these penetrators to pierce the rocky surface of a planet and become firmly stuck in the soil.

Cut-away view of the Mars 96 penetrator in the Martian soil (© David Ducros).Cut-away view of the Mars 96 penetrator in the Martian soil (© David Ducros).

Russia’s Mars 96 mission was flying not only the capsules already mentioned, but also two penetrators. In addition to the different instruments chosen to study the soil’s mechanical, magnetic and chemical properties, these penetrators each contained a short-period seismometer. Sad to say, these also never managed to escape from Earth orbit and ended up, like the rest of the mission, in the Pacific Ocean.

In 1998, NASA also launched two penetrators aiming for Mars. Called Deep Space 2, they were carried on board Mars Polar Lander, designed to reach Mars’s South Pole in order to conduct various investigations. The Deep Space 2 penetrators did not include any seismometers, but served mainly as technology demonstrators to validate this novel method of piercing the Martian surface at speed rather than gently floating down onto it.

Unfortunately, the two Deep Space 2 penetrators—along with their host, Mars Polar Lander—disappeared without a trace on 3 December 1999 during landing. No sign of any of them has ever been found on the surface of Mars, and we still do not know to this day what stopped them in their tracks.

Despite the failure of these first attempts, penetrators remain particularly promising for geophysical exploration of the Red Planet. These probes are generally designed in the same way: they contain two parts, joined by a flexible connecting cable.

Upon hitting the ground, the upper part (which is wider) remains upon the surface, while the lower part (which is narrower and pointed) splits apart to drive down into the subsoil, trailing behind it the connecting cable. The upper part has a radio antenna for communication purposes. The power is provided either by a battery or, even better, a radioisotope thermoelectric generator, which generates electricity from the heat released when a small amount of radioactive material decays.

It is very likely that the first geophysical network mission to Mars uses neither capsules nor mini-landers, but penetrators containing ultra-sensitive broad band miniature seismometers. Fitted securely in the lower part of the penetrator, they will benefit from excellent coupling with the ground and be relatively well protected against perturbing elements on Mars, especially the atmosphere. If the penetrator manages to drive down deep enough, they could also be sheltered from the huge temperature variations on the surface that greatly complicate the collection of long-period seismic signals.

Astonishing sensitivity

Another line of research for planetary geophysicists concerns improving the sensitivity of seismometers while miniaturizing them (i.e. reducing their size, mass and power consumption). The InSight probe’s seismometer, SEIS, is already incredibly sensitive: it can measure ground displacements smaller than a hydrogen atom !

Although it is the stuff of which dreams are made, this technological feat is just the first step on geophysicists’ roadmap. In their laboratories, they are already investigating instrument concepts and prototypes that will be even more sensitive. Unlike SEIS, which uses electrodes to measure the displacement of the moving part of the pendulum, these new-generation seismometers will use optical interferometry sensors similar to those developed for the Earth-based Virgo instrument or the eLISA space mission.

The three probes of the eLISA space mission (© ESA).The three probes of the eLISA space mission (© ESA).

eLISA

Scheduled for 2030-2040, the eLISA mission entails deploying in space a gigantic optical interferometer using a constellation of three satellites connected by a laser beam.

Located one million kilometres from each other, the satellites will each form the apex of a triangle whose sides will be symbolized by the laser beams, used to constantly check the distance between the three satellites with an incredible precision.

The goal of this huge assembly is to trap gravitational waves. When the wrinkles that deform the fabric of space reach eLISA, they will displace—albeit on an infinitesimal scale—the satellites. As the latter are constantly checking their position relative to each other, this change in distance induced by the rippling wave, however small, will nevertheless be detected and measured.

To test and validate the technologies needed for eLISA, the European Space Agency initiated the LISA Pathfinder mission.

This successful proof-of-concept mission, which took place from December 2015 to July 2017, contained two metal cubes (known as “test masses”) floating freely in a chamber with no contact with the rest of the satellite. The cubes’ relative positions were constantly measured by a laser interferometer. Like a buoy buffeted by tidal motion, the two cubes oscillated under the effect of gravitational waves. However, in order for such small displacements to be detected, all possible sources of perturbation had to be correctly cancelled out or counteracted.

Artist’s view of the LISA Pathfinder probe (© ESA/C. Carreau).Artist’s view of the LISA Pathfinder probe (© ESA/C. Carreau).

Successfully launched on 3 December 2015, LISA Pathfinder was sent to Lagrange Point L1, an area of space 1.5 million kilometres from Earth, where the gravitational influences of the Sun and the Earth cancel each other out. The tranquillity reigning there is a clear advantage for the measurements undertaken by LISA Pathfinder, but it is not sufficient in itself because other forces come into play.

One of these is solar pressure, which acts upon spacecraft, affecting their movement. To counteract the pushing force of solar photons, LISA Pathfinder was fitted with a micro-propulsion system of ion thrusters to keep the satellite’s position stable (within a matter of nanometres).

Finally, the satellite itself disturbs the cubes in magnetic, electrical or gravitational terms. Everything that could possibly be done was done to minimize or cancel out these internal forces so that the displacement of the test masses reflected only the passing of gravitational waves and nothing else. The laser interferometer monitoring the cubes thus had to be able to detect extremely small movements in the order of a picometre (i.e. one trillionth of a metre).

All the technologies needed for LISA Pathfinder’s optical interferometry sensors are of great interest to planetary geophysicists, because a seismometer capable of following the displacements of the moving part (i.e. the test mass) using interferometry would raise the performance above that of current instruments.

To follow ground motion, the SEIS seismometer aboard InSight uses an electronic sensor that measures the electrical capacitance between two pairs of electrodes, one on the fixed part and the other on the moving part. The sensitivity offered by such a device already enables us to measure long-period movements of around one angstrom, i.e. 0.1 nanometres.

Using an optical sensor, measurements would be one hundred times more precise, thus opening up entirely new prospects in the area of planetary geophysics.

On Mars, geophysicists would be able to measure the extremely small oscillations caused by resonance following a quake, a meteorite impact or even the circulation of the atmosphere. On the Moon, such seismometers would detect “unusual” seismic signals like those generated by the impact of massive atomic nuclei, or even the oscillations caused by gravitational waves.

In December 1972, the Apollo 17 mission had in fact attempted to detect such waves through a gravimeter, but the technology available then was not up to taking the desired measurements. Gravitational waves were finally detected 40 years later, in February 2016, by two Earth-based observatories.

Last updated : 7 august 2017

Mars Cube One

InSight’s two guardian angels

On its journey to Mars, InSight will be accompanied by a couple of very special "guardian angels", namely two fully-autonomous nanosatellites the size of a suitcase. Their role will be to relay back to Earth crucial information during the landing phase.

Autonomous satellites the size of a suitcase

The Mars Cube One nanosatellite. This CubeSat satellite will act as a communications relay during the landing phase (© NASA/JPL).The Mars Cube One nanosatellite. This CubeSat satellite will act as a communications relay during the landing phase (© NASA/JPL).

The Mars Cube One (or "MarCO") nanosatellites, as they are called, are technology demonstrators meeting CubeSat standards. Their goal is to validate various systems that could play an essential part in the future of planetary exploration. Although nanosatellites (some built by universities) are becoming increasingly common around Earth, none has yet ventured into deep space.

The CubeSat nanosatellites are miniature satellites consisting of a variable number of units, each unit (U) being in the shape of a 10 cm cube. Each Mars Cube nanosatellite is assembled with 6 units (6U).

The two Mars Cube One satellites take up a relatively small volume: they are 36.6 cm long, 24.3 cm wide and 11.8 cm high, which is roughly the size of a small carry-on bag. They contain all the subsystems normally encountered in bigger satellites and are therefore fully autonomous. To prove it, each Mars Cube has two solar arrays, a cold gas propulsion system for trajectory corrections and changes in orientation, and solar sensors to find its bearings in space.

Designed as radio relays, they are also fitted with X-band communication antennas to both receive and transmit. The biggest is a rectangular unfurlable high-gain antenna whose design makes it fully comparable with the parabolic antennas ordinarily used on satellites. Medium- or low-gain antennas support the high-gain antenna. Finally, each MarCO also has a UHF antenna (for reception only) to listen to the UHF signals that will be sent from InSight during its descent onto Mars. A data rate of 8 kbps will be used for communications, whether between InSight and MarCO, or between the two MarCOs and the 70-metre antennas of NASA's terrestrial Deep Space Network (DSN).

Artist's impression of the two Mars Cube nanosatellites in the process of relaying data during InSight's landing phase (© NASA/JPL).Artist's impression of the two Mars Cube nanosatellites in the process of relaying data during InSight's landing phase (© NASA/JPL).

Orbiting the planet since March 2006, the Mars Reconnaissance Orbiter (MRO) has been chosen to monitor InSight as it plunges towards the rusty-looking surface of the Red Planet in November 2018.

However, despite its power, the Mars Reconnaissance Orbiter was never designed to receive UHF data from InSight and simultaneously retransmit the same information back to Earth on another frequency (X-band).

Furthermore, the relative positions of Earth, Mars and the MRO mean that the orbiter can only relay recorded data back to the ground control centre several hours after InSight has landed. Finally, and unlike other probes, InSight lacks the ability to transmit information directly to Earth during its descent to Mars, hence the advantage inherent in the two MarCO nanosatellites which, being able to receive and transmit radio signals at the same time, offer controllers on Earth the chance of following InSight's spectacular arrival on the Elysium Planitia live.

Stowaways

The nanosatellites will be launched at the same time as InSight in May 2018. The launch vehicle used to inject InSight into its Mars trajectory is so powerful that it can easily fly an additional payload. During the launch, the two MarCOs are attached in special containers to the lower part of the Centaur upper stage, near the nozzle, while InSight is tucked under the fairing right at the top, at the opposite end of the Centaur stage.

Artist's impression of the two Mars Cube nanosatellites flying in formation behind InSight (© NASA/JPL).Artist's impression of the two Mars Cube nanosatellites flying in formation behind InSight (© NASA/JPL).

The MarCOs will be deployed after the start of the Contamination Collision Avoidance Manoeuvre (CCAM). This is to avoid the upper Centaur stage crashing into the planet with the concomitant risk of surface contamination. The first Mars Cube is deployed while the CCAM is still in progress. The Centaur stage then rotates 180° along its own axis, releases the second Mars Cube, and terminates the CCAM.

From then on, the two Mars Cube nanosatellites will fly autonomously in formation behind InSight. Fitted with their own propulsion systems, they can alter their course during their journey from Earth to Mars. Six months after the launch, they will have a front-row seat for InSight’s landing, enabling them to retransmit the probe’s progress in real time. Once the mission has been completed, the two Mars Cubes will fly past Mars to lose themselves in interplanetary space.

Last updated: 28 October 2016

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