Separate paths for ExoMars - The Schiaparelli probe will separate from its parent spacecraft on 16 October 2016
October 14, 2016
Separate paths for ExoMars - The Schiaparelli probe will separate from its parent spacecraft on 16 October 2016
Schiaparelli lander – approach to Mars
On 16 October 2016, the journey to the Martian surface begins for the Schiaparelli lander, while the Trace Gas Orbiter (TGO) will enter orbit around Mars. At 16:42 CEST (14:42 UTC), Schiaparelli will be pushed into space at a velocity of 30 centimetres per second relative to the TGO.
The capsule containing the ExoMars Lander Schiaparelli will descend to the Martian surface underneath a parachute. On the back cover of the lander capsule, the COMARS+ (COMbined Aerothermal and Radiometer Sensors instrument package) will measure pressure, temperature and heat flux during the flight through the dusty atmosphere.
COMARS+ sensors on the heat shield of Schiaparelli
Four measurement sensors from DLR are housed on Schiaparelli. Three COMARS+ (COMbined Aerothermal and Radiometer Sensors instrument package) sensors on the back heat shield (small, white, circular sensors in a row from top to bottom in the centre of the image) will continuously measure the heat flux, temperature and pressure at various points on the spacecraft during its entry into the Martian atmosphere. In addition, a fourth sensor (circular sensor in the centre beneath the silver-coloured foil) will measure the radiant thermal flux of the excited carbon and carbon dioxide behind the bow shock.
Since 14 March 2016, the Trace Gas Orbiter (TGO) and the Schiaparelli lander have been flying together towards Mars for the ESA ExoMars mission. On 16 October 2016, the journey to the Martian surface begins for the lander, while the TGO will enter orbit around Mars. At 16:42 CEST (14:42 UTC), Schiaparelli will be pushed into space at a velocity of 30 centimetres per second relative to the TGO. Then, three days later on 19 October 2016, the lander will enter the Martian atmosphere at a speed of 21,000 kilometres per hour. At that moment, for Ali Gülhan – Head of the Department of Supersonic and Hypersonic Technology at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Institute of Aerodynamics and Flow Technology – probably the most exciting five minutes of his scientific career will begin. On the back of the landing capsule, his COMARS+ (COMbined Aerothermal and Radiometer Sensors instrument package) experiment will measure the dusty atmosphere’s pressure, temperature and heat flux throughout the entry to the Martian atmosphere. The landing site in the Meridiani Planum region was selected using three-dimensional terrain models created by DLR planetary researchers. The DLR Space Administration is coordinating the German contributions to the mission.
Measurements during the flight through the atmosphere
The descent that awaits the lander will be hot and probably also rather rough. In just under six minutes, protected from the heat for as long as possible by a two-piece capsule, Schiaparelli will be slowed from 21,000 to about 10 kilometres per hour. It will descend under a parachute for 10 kilometres and then – after jettisoning the parachute and heat shield – decelerate for 29 seconds using thrusters, and then drop the last two metres onto the Martian surface. “How the heat develops on the back side of a landing capsule – nobody has ever measured that in detail in flight," explains Gülhan. Three combined sensors and a radiometer on the surface will measure the thermal loads that the heat shield has to withstand. “Since we do not have this data yet, the capsules are always constructed with thick and cost-intensive material for safety reasons. If the exact thermal loads are known, weight can be saved on heat protection and thus more scientific instruments can be incorporated in future missions."
The atmosphere around the landing capsule can be reconstructed with the measurement data acquired by DLR. "At the moment, there are strong winds and a lot of dust on Mars, and the heated dust particles will be impacting the thermal protection at high speed." It is certain that this will have an effect, but what effect exactly the wind and dust particles will have on entry into the atmosphere has not been sufficiently researched. For the measurements during the flight, the COMARS+ instruments have to withstand a lot: "The challenges were huge. The electronics box and the sensors have had to endure the cold during the journey to Mars, but will also be subjected to extreme heat during the landing," stresses Gülhan.
Arrival in sleep mode
Before the COMARS+ sensors can measure how the heated gas molecules flow around the 2.4-metre-diameter landing capsule, the separation of the lander from the orbiter must succeed. Should the previously uploaded command not be autonomously executed, a new attempt will be made automatically 32 hours later, on 17 October 2016. To save energy, Schiaparelli will not be switched on during the three-day trip to Mars – it will wake up 75 minutes before entering the Martian atmosphere.
The landing of Schiaparelli – the Entry, Descent and Landing Demonstrator Module (EDM) – at a distance of 175 million kilometres from Earth, is a rehearsal for future missions. On the lander itself, in addition to COMARS+, there are four more instruments that, amongst other things, include a weather station to measure the wind speed, humidity, pressure, radiation and temperature on Mars. The DECA camera will acquire 15 images at 1.5-second intervals during the descent. With the remaining energy after the landing, measurements will continue for several days and the data will be transmitted to Earth.
Landing site without obstacles
Schiaparelli will land in a region called Meridiani Planum. This was selected primarily for one reason – it is a large, flat area with no obstacles. The lander will not be able to avoid obstacles during its descent onto the surface of Mars. "There on Mars, we have a flat region of several square kilometres," says DLR planetary researcher Ralf Jaumann, whose colleague Ernst Hauber will also evaluate the data from the Colour and Stereo Surface Imaging System (CaSSIS) camera on the TGO. In addition, the landing site is located near an area where the NASA rover Opportunity discovered a particular type of haematite, an iron oxide. "This type of iron oxide only forms in standing water – there could have been large quantities of water in Meridiani Planum in the past."
Searching for life on Mars
The scientific work with the four instruments on the TGO will begin in December 2017, when the probe is slowed down carefully and progressively brought into an orbit 400 kilometres above Mars. Then, the spacecraft will determine which trace gases can be detected in the Martian atmosphere. In particular, methane will be searched for because this gas is primarily produced by volcanic activity as well as biological processes, and could provide evidence of the existence of organisms on Mars. If the orbiter detects methane, the corresponding region will be examined with the CaSSIS camera. "With the high resolution images, we can then analyse the source of the methane," explains Jaumann.
The mission
ExoMars is a joint mission of the European Space Agency (ESA) and the Russian Space Agency Roscosmos. It includes the TGO and the Schiaparelli EDM. The DLR Institute of Aerodynamics and Flow Technology carried out extensive experiments in various wind tunnels at the DLR sites in Cologne and Göttingen, and controls the COMARS+ instrument. The DLR Institute of Planetary Research generated the three-dimensional terrain model for the landing site and operates the CaSSIS stereo camera as part of the international team. The DLR Institute of Aerospace Medicine was responsible for the 'planetary protection' control measurements that are intended to prevent the mission taking microorganisms from Earth to Mars. The DLR Space Administration supports the ExoMars mission by coordinating the German contributions. Numerous German companies are involved in ExoMars.
