ExoMars Trace Gas Orbiter

ExoMars Trace Gas Orbiter

ExoMars Trace Gas Orbiter
ExoMars Trace Gas Orbiter with Europe’s entry, descent and landing demonstration vehicle
Operator ESA and Russian Federal Space Agency
Major contractors Thales Alenia Space
Mission type Orbiter/carrier
Launch date January 2016[1]
Launch vehicle Proton rocket
Mission duration 1 Mars year orbital science mission
Telecom asset until 2022[2]
Satellite of Mars
Orbital insertion date October 2016
Homepage [1]
Mass 3,130 kg (6,900 lb)
Power 20m2 photovoltaic array (2000 W)
Orbital elements
Inclination 74°
Apoapsis 400 km near-circular altitude[3]

The ExoMars Trace Gas Orbiter (TGO) is a collaborative project between the European Space Agency (ESA) and the Russian Federal Space Agency (Roscosmos) to send a robotic orbiter-carrier to Mars in 2016 as part of the European-led ExoMars mission.[1][4]

The TGO would deliver the ExoMars EDM Schiaparelli lander and then proceed to map the sources of methane on Mars and other gases, and in doing so, help select the landing site for the ExoMars rover to be launched on 2018.


  • History 1
    • Attempted collaboration with NASA 1.1
    • Collaboration with Russia 1.2
    • Current status 1.3
  • Specifications 2
  • Science 3
    • Payload 3.1
    • Relay telecommunications 3.2
  • See also 4
  • References 5
  • External links 6


Investigations with space and Earth-based observatories, have demonstrated the presence of small amounts of methane on the atmosphere of Mars that has been shown to vary with location and time.[5][6][7] This may indicate the presence of life on Mars, but may also be produced by a geochemical process, volcanic or hydrothermal activity.[8][9][10][11]

The challenge to discern the source of methane in the atmosphere of Mars, prompted the independent planning of two orbiters that would carry instruments in order to determine if its formation is of biological or geological origin,[12][13] as well as its decomposition products such as formaldehyde and methanol.

Attempted collaboration with NASA

NASA's Mars Science Orbiter (MSO) was originally envisioned in 2008 as an all NASA endeavor aiming for a late 2013 launch window.[14][15] NASA and ESA officials agreed to pool resources and technical expertise and collaborate to launch only one orbiter.[16] The agreement, called Mars Joint Exploration Initiative, was signed on July 2009 and proposed to utilize an Atlas rocket launcher instead of a Soyuz rocket, which significantly altered the technical and financial setting of the European ExoMars mission. Since the ExoMars rover was originally planned to be carried by the TGO, a prospective agreement would require that the rover lose enough weight to fit aboard the Atlas launch vehicle with NASA's orbiter.[17] Instead of reducing the rover's mass, it was nearly doubled when the mission was combined with other projects to a multi-spacecraft programme divided over two Atlas V-launches:[16][18][19] the ExoMars Trace Gas Orbiter (TGO) was merged into the project, carrying a static meteorological lander slated for launch in 2016. The European orbiter would carry several instruments originally meant for NASA's MSO, so NASA scaled down the objectives and focused on atmosphere trace gases detection instruments for their incorporation in ESA's ExoMars Trace Gas Orbiter.[4][15][20]

Under the FY2013 Budget President Obama released on February 13, 2012, NASA terminated its participation in ExoMars due to budgetary cuts in order to pay for the cost overruns of the James Webb Space Telescope.[21][22] With NASA's funding for this project completely cancelled, most of ExoMars' plans had to be restructured.[23]

Collaboration with Russia

On March 15, 2012, the ESA's ruling council announced it will press ahead with its ExoMars program in partnership with the Russian space agency (Roscosmos), which plans to contribute two heavy-lift Proton launch vehicles and an additional entry, descent and landing system to the 2018 mission.[24][25][26][27][28]

Current status

Under the collaboration proposal with Roscosmos, the ExoMars mission will be split into two parts: the orbiter/lander mission in 2016 that would include the TGO and a static lander build by ESA; this would be followed by the ExoMars rover mission in 2018 —also to be launched with a Russian Proton rocket.

One of the key issues is the ever shortening time window to get the 2016 orbiter ready for flight. Senior figures at ESA and Italian space manufacturer Thales Alenia Space (TAS) scheduled a meeting in late March 2012 to determine whether the preparation schedule is still feasible.[28] Assuming everyone agrees the goals can be achieved in the four years available, a full contract will be released to TAS in April to get the hardware built.[25][28] An ESA official stated that the mission is likely to be enhanced by the contribution of Russian science instruments that will fly on the TGO.[24]


The proposed specifications are:[29]

  • Central tube that is 1.194 metres (3.92 ft) in diameter
  • 424 N bi-propellant main engine to be used to enter Mars orbit and maneuver
  • 20m2 solar arrays entirely covered with cells and capable of rotating one degree, generating about 2000 W of power at Mars
Thermal control
  • Spacecraft yaw axis control to ensure the three faces containing the science payload remain cold
  • 3,130 kg (6,900 lb)
  • Up to 135.6 kg (299 lb) of scientific instruments


The TGO would separate from the ExoMars stationary lander and provide it with telecommunication relay for 8 sols after landing. Then the TGO would aerobrake for seven months into a more circular orbit for science observations and would provide communications relay for the ExoMars rover to be launched in 2018, and would continue serving as a relay satellite for future landed missions until 2022.[2]

The mission would require detection, characterization of spatial and temporal variation, and localization of sources for a broad suite of atmospheric trace gases:


Nature of the methane source requires measurements of a suite of trace gases in order to characterize potential biochemical and geochemical processes at work. The orbiter would require very high sensitivity to (at least) the following molecules and their isotopomers: water (H2O), hydroperoxyl (HO2), nitrogen dioxide (NO2), nitrous oxide (N2O), methane (CH4), acetylene (C2H2), ethylene (C2H4), ethane (C2H6), formaldehyde (H2CO), hydrogen cyanide (HCN), hydrogen sulfide (H2S), carbonyl sulfide (OCS), sulfur dioxide (SO2), hydrogen chloride (HCl), carbon monoxide (CO) and ozone (O3). Detection sensitivities would be of 1-10 parts per trillion.

  • Spatial and temporal variability: Latitude-longitude coverage multiple times in a Mars year to determine regional sources and seasonal variations (reported to be large, but still controversial with present understanding of Mars gas-phase photochemistry.)
  • Correlation of concentration observations with environmental parameters of temperature, dust and ice aerosols (potential sites for heterogeneous chemistry.)
  • Mapping of multiple tracers (e.g., aerosols, water vapor, CO, CH4) with different photochemical lifetimes and correlations helps constrain model simulations and points to source/sink regions.
  • To achieve the spatial resolution required to localize sources might require tracing molecules at the ~1 part per billion concentration.


Like Mars Reconnaissance Orbiter, the Trace Gas Orbiter is a hybrid science-telecom orbiter.[3] Development of the spacecraft's science instruments is well under way. Its maximum science payload mass is projected to be about 115 kg and consist of:[30]

NOMAD and ACS will provide the most extensive spectral coverage of Martian atmospheric processes so far.[3][33] Twice per orbit, at local sunrise and sunset, they will be able to observe the Sun as it shines through the atmosphere. Detection of atmospheric trace species at parts-per-billion (ppb) level will be possible.
  • CaSSIS is a high-resolution (4.5 m/pixel), colour stereo camera for building accurate digital elevation models of the Martian surface. It will also be an important tool for characterizing candidate landing site locations for future missions.
  • FREND is a neutron detector that can provide information on the presence of hydrogen, in the form of water or hydrated minerals, in the top metre layer of the Martian surface.[32]

Relay telecommunications

Due to the challenges of entry, descent, and landing, Mars landers are highly constrained in mass, volume, and power. For landed missions, this places severe constraints on antenna size and transmission power, which in turn greatly reduce direct-to-Earth communication capability in comparison to orbital spacecraft. As an example, the capability downlinks on Spirit and Opportunity have only 1/600th the capability of the Mars Reconnaissance Orbiter downlink. Relay communication addresses this problem by allowing Mars surface spacecraft to communicate using higher data rates over short-range links to nearby Mars orbiters, while the orbiter takes on the task of communicating over the long-distance link back to Earth. This relay strategy offers a variety of key benefits to Mars landers: increased data return volume, reduced energy requirements, reduced communications system mass, increased communications opportunities, robust critical event communications and in situ navigation aide.[34] NASA will provide an Electra telecommunications relay and navigation instrument to assure communications between probes and rovers on the surface of Mars and controllers on Earth.[35] The TGO would provide the EDM lander and ExoMars rover with telecommunication relay and would continue serving as a relay satellite for future landed missions until 2022.[2]

See also


  1. ^ a b "Planetary Science Decadal Survey", J. L. Vago (PDF) (Arizona State University, Tempe (USA):  
  2. ^ a b c Allen, Mark; Witasse, Olivier (June 16, 2011), "2016 ESA/NASA ExoMars Trace Gas Orbiter", MEPAG June 2011,   (PDF)
  3. ^ a b c J Vago et al., "ExoMars, ESA’s next step in Mars exploration", ESA Bulletin magazine, number 155, August 2013, pages 12-23
  4. ^ a b MEPAG Report to the Planetary Science Subcommittee Author: Jack Mustard, MEPAG Chair. July 9, 2009 (pp. 3)
  5. ^ Mars Trace Gas Mission (September 10, 2009)
  6. ^ Mumma, Michael J.; et al.; Novak, Robert E.; Hewagama, Tilak; Bonev, Boncho P.; Disanti, Michael A.; Mandell, Avi M.; Smith, Michael D. (February 20, 2009). "Strong Release of Methane on Mars in Northern Summer 2003". Science 323 (5917): pp. 1041–1045.  
  7. ^ Hand, Eric (October 21, 2008). "Plumes of methane identified on Mars". Nature News. Retrieved August 2, 2009. 
  8. ^ Making Sense of Mars Methane (June 2008)
  9. ^ Steigerwald, Bill (January 15, 2009). "Martian Methane Reveals the Red Planet is not a Dead Planet". NASA's Goddard Space Flight Center (NASA). Retrieved January 24, 2009. 
  10. ^ Howe,, K. L.; Gavin, P.; Goodhart, T. and Kral, T. A. "40th Lunar and Planetary Science Conference (2009)" (PDF). 
  11. ^ Levin, Gilbert V. Levin; Patricia Ann Straat (September 3, 2009). "Methane and life on Mars". Proc. SPIE. Proceedings of SPIE 7441 (74410D): 74410D.  
  12. ^ Rincon, Paul (July 9, 2009). "Agencies outline Mars initiative". BBC News. Retrieved July 26, 2009. 
  13. ^ "NASA orbiter to hunt for source of Martian methane in 2016". Thaindian News. March 6, 2009. Retrieved July 26, 2009. 
  14. ^ Mars Trace Gas Mission - Science Rationale & Concept (10 September 2009)
  15. ^ a b Report to MEPAG on the ESA-NASA Joint Instrument Definition Team (JIDT) for the Proposed 2016 Orbiter-Carrier (29 July 2009)
  16. ^ a b "ESA Proposes Two ExoMars Missions". Michael A. Taverna ( 
  17. ^ NASA Could Take Role in European ExoMars Mission June 19, 2009
  18. ^ Amos, Jonathan (12 October 2009). "Europe's Mars plans move forward". BBC News. Retrieved 2009-10-12. 
  19. ^ "ESA Proposes Two ExoMars Missions". Michael A. Taverna ( 
  20. ^ "ExoMars Trace Gas Orbiter (TGO)". European Space Agency. 6 January 2012. Retrieved 2012-03-19. 
  21. ^ [2] Aviation Week (February 14, 2012)
  22. ^ "Experts React to Obama Slash to NASA’s Mars and Planetary Science Exploration". Ken Kremr (Universe Today). February 1, 2012. Retrieved 2012-02-18. 
  23. ^ "Have Europe’s Martian exploration plans been derailed by America?". Megan Whewell (MSN News). 15 February 2012. Retrieved 2012-02-15. 
  24. ^ a b "Europe Joins Russia on Robotic ExoMars". Amy Svitak (Aviation Week). Mar 16, 2012. Retrieved 2012-03-16. 
  25. ^ a b "ESA Ruling Council OKs ExoMars Funding". Peter B. de Selding (Space News). 15 March 2012. Retrieved 2012-03-16. 
  26. ^ "NASA drops ExoMars missions in 2013 budget". Optics. 15 February 2012. Retrieved 2012-02-15. 
  27. ^ Spacewatch: Uncertainties for ExoMars
  28. ^ a b c "Europe still keen on Mars missions". Jonathan Amos (BBC News). 15 March 2012. Retrieved 2012-03-16. 
  29. ^ "ExoMars Trace Gas Orbiter (TGO)". European Space Agency (ESA). 12 July 2012. Retrieved 2014-03-08. 
  30. ^ "ExoMars Trace Gas Orbiter Instruments". ESA. 20 February 2014. Retrieved 2014-03-08. 
  31. ^ Europe to invest 12 bln euros in a new space Odyssey, by Olga Zakutnyaya. Space Daily, 25 November 2012.
  32. ^ a b "Russia to Construct Landing Pad for Russian-European “ExoMars-2018” Space Mission". RIA Novosti (Russia). 4 August 2014. Retrieved 2014-08-05. 
  33. ^ "Europe". Jonathan Amos (BBC News). 18 June 2013. Retrieved 2013-06-18. 
  34. ^ Relay Orbiters for Enhancing and Enabling Mars In Situ Exploration (September 15, 2009)
  35. ^ "U.S., Europe Won’t Go It Alone in Mars Exploration". Peter B. de Selding (Spacew News). 26 September 2012. Retrieved 2012-09-27. 

External links

  • ESA - EXOMARS Trace Gas Orbiter