Mars Express

Mars Express is a space exploration mission being conducted by the European Space Agency (ESA). The Mars Express mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally referred to the speed and efficiency with which the spacecraft was designed and built.^[1] However "Express" also describes the spacecraft's relatively short interplanetary voyage, a result of being launched when the orbits of Earth and Mars brought them closer than they had been in about 60,000 years.

Mars Express consists of two parts, the Mars Express Orbiter and the Beagle 2, a lander designed to perform exobiology and geochemistry research. Although the lander failed to land safely on the Martian surface, the Orbiter has been successfully performing scientific measurements since early 2004, namely, high-resolution imaging and mineralogical mapping of the surface, radar sounding of the subsurface structure down to the permafrost, precise determination of the atmospheric circulation and composition, and study of the interaction of the atmosphere with the interplanetary medium.

Due to the valuable science return and the highly flexible mission profile, Mars Express has been granted two consecutive mission extensions until (at least) May 2009.

Some of the instruments on the orbiter, including the camera systems and some spectrometers, reuse designs from the failed launch of the Russian Mars 96 mission in 1996 (European countries had provided much of the instrumentation and financing for that unsuccessful mission). The basic design of Mars Express is based on ESA's Rosetta mission, on which considerable sum was spent on development. The same design was also used for the Venus Express mission in order to increase reliability and reduce development cost and time.

Mission profile and timeline overview

Mission overview

The Mars Express mission is dedicated to the orbital (and originally in-situ) study of the interior, subsurface, surface and atmosphere, and environment of the planet Mars. The scientific objectives of the Mars Express mission represent an attempt to fulfil in part the lost scientific goals of the Russian Mars-96 mission, complemented by exobiology research with Beagle-2. Mars exploration is crucial for a better understanding of the Earth from the perspective of comparative planetology.

The spacecraft originally carried seven scientific instruments, a small lander, a lander relay and a Visual Monitoring Camera, all designed to contribute to solving the mystery of Mars' missing water. All of the instruments take measurements of the surface, atmosphere and interplanetary media, from the main spacecraft in polar orbit, which will allow it to gradually cover the whole planet. The overall Mars Express budget excluding the lander is €150 million (roughly US$185 million).

Spacecraft construction

The prime contractor for the construction of Mars Express Orbiter was EADS Astrium Satellites.

Mission preparation

In the years preceding the launch of a spacecraft numerous teams of experts distributed over the contributing companies and organisations prepared the space and ground segments. Each of these teams focussed on the area of its responsibility and interfacing as required. A major additional requirement raised for the Launch and Early Orbit Phase (LEOP) and all critical operational phases was that it was not enough merely to interface; the teams had to be integrated into one Mission Control Team. All the different experts had to work together in an operational environment and the interaction and interfaces between all elements of the system (software, hardware and human) had to run smoothly for this to happen:

• The flight operations procedures had to be written and validated down to the smallest detail;
• The control system had to be validated;
• System Validation Tests (SVTs) with the satellite had to be performed to demonstrate the correct interfacing of the ground and space segments.
• Mission Readiness Test with the Ground Stations had to be performed;
• A Simulations Campaign was run.

Launch

The spacecraft was launched on June 2, 2003 at 23:45 local time (17:45 UT, 1:45 p.m. EDT) from Baikonur Cosmodrome in Kazakhstan, using a Soyuz-Fregat rocket. The Mars Express and Fregat booster were initially put into a 200 km Earth parking orbit, then the Fregat was fired again at 19:14 UT to put the spacecraft into a Mars transfer orbit. The Fregat and Mars Express separated at approximately 19:17 UT. The solar panels were then deployed and a trajectory correction maneuver was performed on June 4 to aim Mars Express towards Mars and allow the Fregat booster to coast into interplanetary space.

Near earth commissioning phase

The Near Earth Commissioning phase extended from the separation of the spacecraft from the launcher upper stage until the completion of the initial check out of the orbiter and payload. It included the solar array deployment, the initial attitude acquisition, the declamping of the Beagle-2 spin-up mechanism, the injection error correction manoeuvre and the first commissioning of the spacecraft and payload (final commissioning of payload took place after Mars Orbit Insertion). The payload was checked out one instrument at a time. This phase lasted about one month.

The interplanetary cruise phase

This five month phase lasted from the end of the Near Earth Commissioning phase until one month prior to the Mars capture manoeuvre and included trajectory correction manoeuvres and payloads calibration. The payload was mostly switched off during the cruise phase, with the exception of some intermediate check-outs. Although it was originally meant to be a "quiet cruise" phase, It soon became obvious that this "cruise" would be indeed very busy. There were star Tracker problems, a power wiring problem, extra manoeuvres, and on the 28th of October, the spacecraft was hit by one of the largest solar flares ever recorded.

Lander jettison

The Beagle 2 lander was released on December 19 at 8:31 UTC (9:31 CET) on a ballistic cruise towards the surface. It entered Mars' atmosphere on the morning of December 25. Landing was expected to occur at about 02:45 UT on December 25 (9:45 p.m. EST December 24). However, after repeated attempts to contact the lander failed Mars Express and the NASA Mars Odyssey orbiter, it was declared lost on February 6, 2004, by the Beagle 2 Management Board. On February 11, ESA announced an inquiry would be held into the failure of Beagle 2.

Orbit insertion

Mars Express arrived at Mars after a 400 million km journey and course corrections in September and in December 2003.

On December 20 Mars Express fired a short thruster burst to put it into position to orbit the planet. The Mars Express Orbiter then fired its main engine and went into a highly elliptical initial-capture orbit of 250 km × 150,000 km with an inclination of 25 degrees on December 25 at 03:00 UT (10:00 p.m., December 24 EST).

First evaluation of the orbital insertion showed that the orbiter had reached its first milestone at Mars. The orbit was later adjusted by four more main engine firings to the desired 259 km × 11,560 km near-polar (86 degree inclination) orbit with a period of 7.5 hours. Near periapsis the top deck is pointed down towards the Martian surface and near apoapsis the high gain antenna will be pointed towards Earth for uplink and downlink.

After 100 days the apoapsis was lowered to 10,107 km and periapsis raised to 298 km to give an orbital period of 6.7 hours.

MARSIS deployment

On May 4, 2005, Mars Express deployed the first of its two 20-metre-long radar booms for its MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) experiment. At first the boom didn't lock fully into place; however, exposing it to sunlight for a few minutes on May 10 fixed the glitch. The second 20 m boom was successfully deployed on June 14. Both 20 m booms were needed to create a 40 m dipole antenna for MARSIS to work; a less crucial 7-meter-long monopole antenna was deployed on June 17. The radar booms were originally scheduled to be deployed in April 2004, but this was delayed out of fear that the deployment could damage the spacecraft through a whiplash effect. Due to the delay it was decided to split the four week commissioning phase in two parts, with two weeks running up to July 4 and another two weeks in December 2005.

The deployment of the booms was a critical and highly complex task requiring effective inter-agency cooperation ESA, NASA, Industry and public Universities.

Nominal science observations began during July 2005. (For more info, see^[2] ,^[3] , and ESA Portal - Mars Express radar ready to work ESA press release.)

Operations of the spacecraft

Operations for Mars Express are carried out by a multinational team of engineers from ESA’s Operation Centre (ESOC) in Darmstadt. The team began preparations for the mission about 3 to 4 years prior to the actual launch. This involved preparing the ground segment and the operational procedures for the whole mission.

The Mission Control Team is composed of the Flight Control Team, Flight Dynamics Team, Ground Operations Managers, Software Support and Ground Facilities Engineers. All of these are located at ESOC but there are additionally external teams, such as the Project and Industry Support teams, who designed and built the spacecraft. The Flight Control Team consists of:

• The Spacecraft Operations Manager
• Eight Operations Engineers
• Three Mission Planners
• One Spacecraft Analyst
• Five Spacecraft controllers

The team build-up, headed by the Spacecraft Operations Manager, started about 4 years before launch . He was required to recruit a suitable team of engineers that could handle the varying tasks involved in the mission. For Mars Express the engineers came from various other missions. Most of them had been involved with Earth orbiting satellites.

Routine phase: Science return

Since orbit insertion Mars Express has been progressively fulfilling its original scientific goals. Nominally the spacecraft points to Mars while acquiring science and then slews to earth-pointing to downlink the data, although some instruments like Marsis or Radio Science might be operated while spacecraft is earth-pointing.

Mars Express Spacecraft Orbiter and subsystems

Structure

The Mars Express Orbiter is a cube-shaped spacecraft with two solar panel wings extending from opposite sides. The launch mass of 1123 kg includes a main bus with 113 kg of payload, the 60 kg lander, and 457 kg of propellant. The main body is 1.5 m × 1.8 m × 1.4 m in size, with an aluminium honeycomb structure covered by an aluminum skin. The solar panels measure about 12 m tip-to-tip. Two 20 m long wire dipole antennas extend from opposite side faces perpendicular to the solar panels as part of the radar sounder^[4].

Propulsion

The Soyuz/Fregat launcher provided most of the thrust Mars Express needed to reach Mars. The final stage of the Fregat was jettisoned once the probe was safely on a course for Mars. The spacecraft's on-board means of propulsion was used to slow the probe for Mars orbit insertion and subsequently for orbit corrections.^[4]

The body is built around the main propulsion system, which consists of a bipropellant 400 N main engine. The two 267-liter propellant tanks have a total capacity of 595 kg. Approximately 370 kg are needed for the nominal mission. Pressurized helium from a 35 liter tank is used to force fuel into the engine. Trajectory corrections will be made using a set of eight 10 N thrusters, one attached to each corner of the spacecraft bus. The spacecraft configuration is optimized for a Soyuz/Fregat, and was fully compatible with a Delta II launch vehicle.

Power

Spacecraft power is provided by the solar panels which contain 11.42 square meters of silicon cells. The originally planned power was to be 660 W at 1.5 AU but a faulty connection has reduced the amount of power available by 30%, to about 460 W. This loss of power is not expected to significantly impact the science return of the mission. Power is stored in three lithium-ion batteries with a total capacity of 64.8 Ah for use during eclipses. The power is fully regulated at 28 V. During routine phase, the spacecraft's power consumption is in the interval 450 W - 550 W.

Avionics

Attitude control (3-axis stabilization) is achieved using two 3-axis inertial measurement units, a set of two star cameras and two Sun sensors, gyroscopes, accelerometers, and four 12 N·m·s reaction wheels. Pointing accuracy is 0.04 degree with respect to the inertial reference frame and 0.8 degree with respect to the Mars orbital frame. Three on-board systems help Mars Express maintain a very precise pointing accuracy, which is essential to allow the spacecraft to communicate with a 35-metre and 70-metre dish on Earth up to 400 million kilometres away.

Communications

The communications subsystem is composed of 3 antennas: A 1.7 m diameter parabolic dish high-gain antenna and two omnidirectional antennas. The first one provide links (Telecommands uplink and Telemetry downlink) in both X-band (7.1 GHz) and S-band (2.1 GHz) and is used during nominal science phase around Mars. The low gain antennas are used during Launch and early operations to Mars and for eventual contingencies once in orbit. Two Mars lander relay UHF antennas are mounted on the top face for communication with the Beagle 2.

Earth Stations

Although communications with Earth were originally scheduled to take place with the ESA 35-meter wide Ground Station in New Norcia (Australia) New Norcia Station, the mission profile of progressive enhancement and science return flexibility have triggered the use of the newest ESA ESTRACK Ground Station in Cebreros Station, Madrid, Spain.

In addition, further agreements with NASA Deep Space Network have made possible the use of American stations for nominal mission planning, thus increasing complexity but with a clear positive impact in scientific returns.

This inter-agency cooperation has proven effective, flexible and enriching for both sides. On the technical side, it has been made possible (among other reasons) thanks to the adoption of both Agencies of the Standards for Space Communications defined in CCSDS

Thermal

Thermal control is maintained through the use of radiators, multi-layer insulation, and actively controlled heaters. The spacecraft must provide a benign environment for the instruments and on-board equipment. Two instruments, PFS and OMEGA, have infrared detectors that need to be kept at very low temperatures (about -180 °C). The sensors on the camera (HRSC) also need to be kept cool. But the rest of the instruments and on-board equipment function best at room temperatures (10-20 °C).

The spacecraft is covered in gold-plated aluminium-tin alloy thermal blankets to maintain a temperature of 10-20 °C inside the spacecraft. The instruments that operate at low temperatures to be kept cold are thermally insulated from this relatively high internal temperature, and emit excess heat into space using attached radiators.^[4]

Control Unit and Data storage

The spacecraft is run by two Control and Data management Units with 12 gigabits^[4] of solid state mass memory for storage of data and housekeeping information for transmission. The on-board computers control all aspects of the spacecraft functioning including switching instruments on and off, assessing the spacecraft orientation in space and issuing commands to change it.

Lander

The Beagle 2 lander objectives were to characterize the landing site geology, mineralogy, and geochemistry, the physical properties of the atmosphere and surface layers, collect data on Martian meteorology and climatology, and search for possible signatures of life. However, the landing attempt was unsuccessful and the lander was declared lost. A Commission of Inquiry on Beagle 2 identified four possible causes, including insufficiently strong airbags and problems with parts of the landing system colliding, but was unable to reach any firm conclusions.

Mars Express instruments

The scientific objectives of the Mars Express Payload are to obtain global high-resolution photo-geology (10 m resolution), mineralogical mapping (100 m resolution) and mapping of the atmospheric composition, study the subsurface structure, the global atmospheric circulation, and the interaction between the atmosphere and the subsurface, and the atmosphere and the interplanetary medium. The total mass budgeted for the science payload is 116 kg.^[5]

• Visible and Infrared Mineralogical Mapping Spectrometer (OMEGA)(Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) - France - Determines mineral composition of the surface up to 100 m resolution. Is mounted inside pointing out the top face. ^[6] Instrument mass: 28.6 kg^[7]

• Ultraviolet and Infrared Atmospheric Spectrometer (SPICAM) - France - Assesses elemental composition of the atmosphere. Is mounted inside pointing out the top face. Instrument mass: 4.7 kg^[7]

• Sub-Surface Sounding Radar Altimeter (MARSIS) - Italy - A radar altimeter used to assess composition of sub-surface aimed at search for frozen water. Is mounted in the body and is nadir pointing, and also incorporates the two 20 m antennas. Instrument mass: 13.7 kg^[7]
• Planetary Fourier Spectrometer (PFS) - Italy - Makes observations of atmospheric temperature and pressure (observations suspended in September 2005). Is mounted inside pointing out the top face.^[8] , currently working). Instrument mass: 30.8 kg^[7]
• Analyzer of Space Plasmas and Energetic Atoms (ASPERA) - Sweden - Investigates interactions between upper atmosphere and solar wind. Is mounted on the top face. Instrument mass: 7.9 kg^[7]
• High Resolution Stereo Camera (HRSC)- Germany - Produces color images with up to 2 m resolution. Is mounted inside the spacecraft body, aimed through the top face of the spacecraft, which is nadir pointing during Mars operations. Instrument mass: 20.4 kg^[7]
• Mars Express Lander Communications (MELACOM) - UK - Allows Mars Express to act as a communication relay for landers on the Martian surface. (Has been tested with Mars Exploration Rovers, and was used to support the landing of NASA's Phoenix mission)
• Mars Radio Science Experiment (Mars) - Uses radio signals to investigate atmosphere, surface, subsurface, gravity and solar corona density during solar conjunctions. It uses the communications subsystem itself.
• A small camera to monitor the lander ejection, VMC.
• More on Payload^[9]

Scientific discoveries and important events

For more than 5000 orbits, Mars Express Payload instruments have been nominally and regularly operated. HRSC camera has been stubbornly mapping the Martian surface with unprecedented resolution and has taken dozens of breath-taking pictures.

2004

• January 23
  • ESA announced the discovery of water ice in the South Polar ice cap, using data taken on January 18 with the OMEGA instrument.
• January 28
  • Mars Express Orbiter reaches final science orbit around Mars.

• March 17
  • Orbiter detects polar ice caps that contain 85% highly carbon dioxide (CO₂) ice and 15% water ice.^[10]

• March 30
  • A press release announces that the orbiter has detected methane in the Martian atmosphere. Although the amount is small, about 10 parts in a thousand million, it has excited scientists ask about its source. Since methane is removed from the Martian "air" very fast, there needs to be a current source that releases fresh methane still today. Because one of the possible sources could be microbial life, it is planned to verify the reliability of this data and especially watch for difference in the concentration in various places on Mars. It is hoped that the source of this gas can be discovered by finding its location of release.^[11]

• April 28
  • ESA announced that the deployment of the boom carrying the radar based MARSIS antenna was delayed. It described concerns with the motion of the boom during deployment, which can cause the spacecraft to be struck by elements of it. Further investigations are planned to make sure that this will not happen.

• July 15
  • Scientists working with the PFS instrument announced that they tentatively discovered the spectral features of the compound ammonia in the Martian atmosphere. Just like methane discovered earlier (see above), ammonia breaks down rapidly in Mars' atmosphere and needs to be constantly replenished. This points towards the existence of active life or geological activity; two contending phenomena whose presence so far have remained undetected.^[12]

2005

• In 2005, ESA scientists reported that the OMEGA (Visible and Infrared Mineralogical Mapping Spectrometer)(Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) instrument data indicates the presence of hydrated sulphates, silicates and various rock-forming minerals.

• February 8
  • The delayed deployment of the MARSIS antenna has been given a green light by ESA^[13] . It is planned to take place in early May 2005.

• May 5
  • The first boom of the MARSIS antenna was successfully deployed^[14] . At first, there was no indication of any problems, but later it was discovered that one segment of the boom did not lock^[15] . The deployment of the second boom was delayed to allow for further analysis of the problem.
• May 11
  • Using the Sun's heat to expand the segments of the MARSIS antenna, the last segment locked in successfully^[16] .
• June 14
  • The second boom was deployed, and on June 16 ESA announced it was a success^[17] .
• June 22
  • ESA announces that MARSIS is fully operational and will soon begin acquiring data. This comes after the deployment of the third boom on June 17, and a successful transmission test on June 19.^[18]

• July 28

These image, taken by the High Resolution Stereo Camera (HRSC), show a patch of water ice sitting on the floor of an unnamed crater near the Martian north pole.^[19]

2006

• September 21

ESA's Mars Express High Resolution Stereo Camera (HRSC) has obtained images of the Cydonia region, the location of the famous "Face on Mars". The massif became famous in a photo taken in 1976 by the American Viking 1 Orbiter. The image recorded with a ground resolution of approximately 13.7 metres per pixel.^[20]

• September 26

The Mars Express spacecraft has emerged from an unusually demanding eclipse season introducing a special, ultra-low-power mode nicknamed 'Sumo' - an innovative configuration aimed at saving the power necessary to ensure spacecraft survival. This mode was developed through tight teamwork between ESOC mission controllers, principal investigators, industry and mission management.^[21]

• October

In October 2006 the Mars Express spacecraft has encountered a superior solar conjunction (alignment of Earth-Sun-Mars Express). The angle Sun-Earth-MEX reached a minimum on 23-Oct at 0.39 deg. at a distance of 2.66 AU. Operational measures were undertaken to minimize the impact of the link degradation, since the higher density of electrons in the solar plasma heavily impacts the radio frequency signal. More on^[22]

• December

Following the loss of NASA JPL Mars spacecraft Mars Global Surveyor (MGS), Mars Express team was requested to perform actions in the hopes of visually identifyng the American spacecraft. Based on last ephemeris of MGS provided by JPL, the on-board high definition HRSC camera swept a region of the MGS orbit. Two attempts were made to find the craft, both unsuccessful.

2007

• January

First agreements with NASA-SPL undertaken for the support of Mars Express on the landing of the American lander Phoenix in May 2008

• February

The small camera VMC (used only once to monitor the lander ejection) has been recommissioned and first steps had been taken to offer students the possibility to participate in a campaign "Command Mars Express Spacecraft and take your own picture of Mars". Details to come.

• February 23

As result of the important science return, the Science Program Committee (SPC) has granted a mission extension until May 2009 to Mars Express.^[23]

• June 28

The High Resolution Stereo Camera (HRSC) has produced dramatic images of key tectonic features in Aeolis Mensae. ^[24]

2008

The Mars Express Team was the winner of the Sir Arthur Clarke Award for Best Team Achievement.

See also

• European Space Agency
• ExoMars
• Exploration of Mars
• Space exploration
• Unmanned space missions
• Mars Express AI Tool

External links

• ESA Mars Express project (official site)
• ESA Mars Express project (scientific site)
• ESA Mars Express operations site
• Mars Express Mission Profile by NASA's Solar System Exploration
• First Mars Express Science Conference presentations (at MarsToday.com)

Payload Principal Investigators Links

• HRSC FU Berlin^[25]
• MARSIS Uni Roma "La Sapienza"^[26]
• PFS IFSI/INAF^[27]
• SPICAM
• OMEGA Institut Astrophysique Spatial^[28]
• MELACOM Qinetiq^[29]
• RSE Uni Köln^[30]
• ASPERA^[31]

References

Spacecraft missions to Mars Flybys Mariner 4 · 6 · 7 · Mars 4 · Rosetta · Dawn Orbiters Mariner 9 · Mars 2 · 3 · 5 · 6 · Viking 1 · 2 · Phobos 2 · Mars Global Surveyor · 2001 Mars Odyssey · Mars Express · Mars Reconnaissance Orbiter Landers / Rovers Mars 3 · Viking 1 · 2 · Mars Pathfinder · Spirit · Opportunity · Phoenix Future missions Phobos-Grunt and Yinghuo-1 (2009) · MetNet (2009-2019) · Mars Science Laboratory (2011) · 2013 Mars Science Orbiter  · MAVEN (2013) · Astrobiology Field Laboratory (2016) · ExoMars (2016)  · Mars Sample Return Mission (2018+) See also Mars · Exploration · Colonization · Failed Mars missions · Mars Scout Program Bold italics indicates active missions

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