ExoMars Trace Gas Orbiter

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ExoMars Trace Gas Orbiter

ExoMars Trace Gas Orbiter with Schiaparelli Lander
NSSDC ID 2016-017A
Mission goal Mars orbit
Client European space agencyESA ESA
Launcher Proton-M / Bris-M
Takeoff mass 4332 kg (total take-off mass),
3732 kg (orbiter take-off
mass) , 600 kg (land take-off mass)


Course of the mission
Start date March 14, 2016, 09:31:42 UTC
launch pad Baikonur 200/39
End date 2022 (planned)
March 14, 2016 begin
October 16, 2016 Schiaparelli-TGO separation
19th October 2016 TGO: Entry into Mars orbit
19th October 2016 Schiaparelli: Entry into the Martian atmosphere and landing
19.-23. October 2016 Schiaparelli: Investigation of the surface of Mars
December 2016 Trace Gas Orbiter changes inclination to final orbit (74 °)
December 2016 Descent in orbit, from T = 4 to 1  sol
January – December 2017 Atmospheric braking down to 400 km orbit
July 11 - August 11, 2017 Solar conjunction (Sun stands between Earth and Mars)
April 2018 Start of the scientific mission; Relay for NASA landers
December 2022 End of the main Trace Gas Orbiter mission
2023 Start of relay function for the ExoMars rover

The ExoMars Trace Gas Orbiter (short- TGO , English for [ExoMars-] trace gas - Orbiter ) is a mission of the European Space Agency (ESA) as part of the ExoMars -Project in collaboration with the Russian space agency Roskosmos to explore the Martian atmosphere . The orbiter was launched on March 14, 2016 by a Russian Proton rocket and entered orbit around Mars on October 19, 2016.

The primary goal is to gain a better understanding of the processes in the Martian atmosphere and to examine gases such as methane and other trace gases for biological or geological causes. The orbiter is also intended to help find possible landing sites for the ExoMars rover, which is Template: future / in 2 yearsplanned for 2022 , and then serve as a relay station to Earth.

In addition, the lander Schiaparelli was carried, with which landing techniques should be tested on Mars. When attempting to land the lander, radio contact with Schiaparelli was lost and could not be re-established. According to ESA, there was “no soft landing”.


The originally purely European project has undergone many changes over the years. As the financial volume grew, it initially came to a collaboration with NASA . When this withdrew again in 2012, it finally came to cooperation with Roskosmos.

Trace gas orbiter

The TGO was developed by ESA. The scientific instruments were developed in both Europe and Russia. The most important task is the investigation of methane and its decay products, also with regard to possible biological causes. The scientific mission began in April 2018 and is expected to run for five years Template: future / in 3 years. When Template: future / in 3 yearsthe ExoMars rover lands in 2023 , the orbiter will also serve as a relay station to Earth.

The most important goal is to gain a better understanding of methane and other trace gases in the Martian atmosphere. With less than 1% constituent in the already thin Martian atmosphere, they can nevertheless provide important information about possible biological or geological activities. Methane has been previously detected and its concentration has also been shown to change over time and different locations. Since methane is very short-lived in geological time periods, it is believed that there are currently active sources for this gas. Causes can be biological, but also chemical processes. On earth, methane is produced by living things during digestion and in digested sludge; Chemical processes such as the oxidation of (carbon-containing) iron or the interaction of ultraviolet radiation with meteorite material are also a possible cause.

The instruments are designed to detect various trace gases (methane, water vapor, nitrogen dioxide , ethine (acetylene) ) and exceed previous investigations in terms of accuracy by three orders of magnitude. Furthermore, seasonal changes in the composition and temperature of the atmosphere are to be determined in order to refine the models of the atmosphere. In addition, hydrogen can be detected with greater accuracy down to a depth of one meter. This could be used to find water ice hidden under the surface or possible sources of trace gases that could have an impact on future landing sites.

However, despite the high sensitivity of the NOMAD spectrograph, initial evaluations of the measurements by the TGO could not confirm the presence of methane gas in the Martian atmosphere.

Structure of the orbiter

ExoMars TGO (left) with Schiaparelli compared to Mars Express ; ExoMars TGO is the largest and heaviest Mars probe to date.

The structure was derived from earlier ExoMars scenarios and is largely determined by the capacity of the Proton launcher.

  • Probe: 3.2 m × 2 m × 2 m with solar cells (17.5 m span) and 2000  W power
  • Takeoff weight: 4332 kg (including 112 kg scientific instruments and 600 kg Schiaparelli)
  • Propulsion: Bipropellant ( methylhydrazine (MMH) as fuel, Mixed Oxides of Nitrogen (MON-1) as oxidizer), with a 424  N main engine for entry into Mars orbit and other major course corrections
  • Power supply: in addition to the solar cells, two lithium-ion batteries with a total of 5100  Wh capacity
  • Communication: a 2.2 m parabolic high gain antenna (High Gain Antenna - HGA, 65 Watt, X-Band) and three omnidirectional antennas (Low Gain Antenna - LGA) for communication with the earth and an Electra UHF transceiver from the NASA to communicate with landers and rovers on the surface


The orbiter carries the following measuring devices:

  • NOMAD ( Nadir and Occultation for MArs Discovery), three highly sensitive spectrometers , two for the range of infrared radiation and one for ultraviolet radiation , with which trace elements and other components of the Martian atmosphere are to be searched for.
  • ACS (Atmospheric Chemistry Suite), three infrared instruments designed to study the chemistry of the Martian atmosphere.
  • CaSSIS ( Color and Stereo Surface Imaging System ), a high-resolution camera with a resolution of five meters per pixel (from a height of around 400 km) to make color and stereo images of the Martian surface, especially of areas where with the help of NOMAD and ACS the leakage of trace gases was detected.
The FREND-like LEND instrument of the Lunar Reconnaissance Orbiter
  • FREND ( Fine Resolution Epithermal Neutron Detector ), a neutron detector that is supposed to detect deposits of water ice on and one meter below the surface and thus create an accurate water ice map of Mars.

Course of the mission

Preparations and start

After testing and integrating the entire hardware at Thales Alenia Space in Cannes (France), it was transported together with further ground equipment by convoy to Turin in Italy on December 17, 2015 . From Turin-Casselle airport everything was flown in three flights (December 18, 20 and 22, 2015) with an Antonov An-124 to the Baikonur Cosmodrome and then housed in a clean room to avoid forward contamination of Mars.

To prepare for take-off, a makeshift tent was set up inside a hall in Baikonur to ensure that the TGO and Schiaparelli are not contaminated by microbes from the earth. This is intended to meet the strict requirements for planetary protection , as the halls alone do not meet the western standards for the protection of Mars.

In the course of further preparations, Schiaparelli was filled with the compressed gas helium and 45 kg of hydrazine fuel in January 2016 . The helium, which is under high pressure, is required in order to be able to convey the fuel into the engines without pumps. The total of three fuel tanks are to supply nine small engines, which should slow down the lander further after being slowed down by the parachute on the way to the surface of Mars. On February 12, 2016, the lander was connected to the orbiter with 27 screws. These connections consist of taut brackets that, without explosives, separated Schiaparelli from the orbiter shortly before reaching Mars. By February 23, 2016, the orbiter was also completely refueled with 1.5 tons of oxidizer and one ton of hydrazine. On March 8, 2016, the entire spaceship was placed on the Proton rocket , which was brought to the launch pad a few days later (on March 11, 2016) and erected there vertically for launch.

The TGO was launched together with Schiaparelli on March 14, 2016 at 09:31 UTC with a Russian Proton rocket as planned in Baikonur. After the start, the Bris-M upper stage had to perform a total of four burning maneuvers in order to send the spaceship towards Mars ten hours later. At 20:13 UTC, the Bris-M upper stage was successfully separated from the probe. The first contact from the probe to the control center in Darmstadt was made at 21:29 UTC. After a seven-month flight, the probe entered Mars orbit on October 19, 2016.

During the solar conjunction in July / August 2017, the radio connection to earth was interrupted.

Trace gas orbiter

Full-size model of the orbiter in the ESOC building in Darmstadt

Because of Earth's favorable position with respect to Mars, the probe reached Mars just seven months later, in October 2016. Three days before the target, Schiaparelli separated from the orbiter to begin its descent towards the surface of Mars. On October 19, 2016, the orbiter initially swiveled into a high elliptical orbit around Mars, and then came to a circular orbit about 400 km high through atmospheric braking. For an optimal braking effect and to stabilize the alignment of the satellite, its solar modules were used like a kind of wing. Regular corrective maneuvers kept the periapsis at an altitude of around 110 km, and the orbiter sometimes came within 103 km of the surface of Mars. Overall, aerobraking was able to reduce speeds of more than 1000 m / s and the apoapsis was reduced from an original 33,200 km to 1,050 km. On February 20, 2018, the atmospheric braking was completed and TGO with its engine first brought into an orbit of 1050 × 200 km , which was corrected to a circular orbit of 400 km altitude by April 9. Then the scientific mission began, which is monitored by the European Space Control Center in Darmstadt.


Full-size model of the lander in the control center (ESOC) in Darmstadt, as planned after the lower and upper protective shields were dropped
Before and after image of the surface of Mars by NASA's Mars Reconnaissance Orbiter: The spots detected on October 20, 2016 are the crash site of the lander (black, above) and parachute (white, below). On the right side an enlarged representation of the framed area.

The lander should hit the atmosphere at around 21,000 km / h and then reduce its speed first with a heat shield and then with a parachute. The speed was then to be further reduced with brake rockets so long that the lander could finally hover about two meters above the Martian floor. From this height it should fall to the ground - intercepted by a deformable substructure. After landing, communication with Earth should take place, among other things, through a NASA orbiter ( 2001 Mars Odyssey or Mars Reconnaissance Orbiter ).

Shortly after the expected time of landing was announced by ESA that radio contact the lander to the Indian Pune contained Giant Metrewave Radio Telescope was canceled (GMRT) during the landing phase. At the same time, Schiaparelli's radio contact with the Mars Express space probe was broken. According to ESA, the data recorded by both sources as well as the mother ship and sent to Earth showed “that the phases of entry and descent into the atmosphere went as expected, but the events after the rear heat shield and parachute were dropped on a non-scheduled one Indicate course. The launch seems to have occurred earlier than planned. ”At the same time, ESA announced in an initial analysis on October 20, 2016:“ As far as the engines are concerned, it can be said with certainty that they were ignited for a short time, it but it looks like they stopped operating earlier than expected. ”The misconduct resulted in“ no soft landing. ”The impact location of the lander and the dropped parachute was determined on October 20, 2016 using photographs of the surface of Mars MRO recordings proven; at the same time, the ESA reported on October 21, 2016: “It is estimated that Schiaparelli fell from a height of between two and four kilometers and therefore hit at a speed of more than 300 km / h.” It is possible “that that Lander exploded on impact because the fuel tanks were probably still full. "

See also

Web links

Commons : ExoMars Trace Gas Orbiter  - collection of images, videos and audio files

Individual evidence

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  3. a b c Analysis of Schiaparelli's relegation data is in progress. In: ESA.int. October 20, 2016. Retrieved October 28, 2016 .
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  8. ExoMars (Exobiology on Mars). In: directory.eoportal.org. Retrieved October 28, 2016 .
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  12. European Mars probe arrives at launch site. In: Spaceflightnow.com. December 27, 2015, accessed January 5, 2016 .
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