ExoMars Trace Gas Orbiter

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ExoMars Trace Gas Orbiter
ExoMars Trace Gas Orbiter.jpg
ExoMars Trace Gas Orbiter with Schiaparelli lander
Mission type Mars orbiter & lander
Operator ESA / RKA
COSPAR ID 2016-017A
SATCAT № 41388
Website exploration.esa.int/mars
Mission duration 7 years (planned)[1][2]
Spacecraft properties
Manufacturer Thales Alenia Space
Launch mass TGO: 3,732 kg (8,228 lb)[3]
EDM: 600 kg (1,300 lb)
Dry mass TGO: 1,432 kg (3,157 lb)
Payload mass TGO: 116 kg (256 lb)
EDM: 5 kg (11 lb)
Power ~2000 W
Start of mission
Launch date 14 March 2016 (2016-03-14)
09:31 UTC[4]
Rocket Proton-M/Briz-M
Launch site Baikonur 200/39
Contractor Khrunichev
Orbital parameters
Reference system Areocentric
Regime Circular
Eccentricity 0
Periareion 400 km (250 mi)
Apoareion 400 km (250 mi)
Inclination 74 degrees
Period 120 minutes
Epoch planned
Mars orbiter
Spacecraft component TGO
Orbital insertion 19 October 2016 (2016-10-19) (planned)
Mars lander
Spacecraft component EDM
Landing date 19 October 2016 (2016-10-19) (planned)
Landing site Meridiani Planum
Main telescope
Type Three-mirror anastigmat
Diameter 13.5 cm (5.3 in)
Focal length 88 cm (35 in)
Wavelengths from 0.475 µm (blue)
to 0.95 µm (near-infrared)
NOMAD Nadir and Occultation for MArs Discovery
ACS Atmospheric Chemistry Suite
CaSSIS Colour and Stereo Surface Imaging System
FREND Fine Resolution Epithermal Neutron Detector

ExoMars rover

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 an atmosphere research orbiter and the Schiaparelli demonstration lander to Mars in 2016 as part of the European-led ExoMars Programme.[5][6]

The Trace Gas Orbiter will deliver the ExoMars Schiaparelli EDM lander and then proceed with atmospheric mapping. A key goal of this mission is to gain a better understanding of methane (CH4) and other atmospheric gases present in the Martian atmosphere that could be evidence for possible biological or geological activity. The programme will follow with the Surface Science Platform and the ExoMars rover in 2020,[7] which will search for biomolecules and biosignatures; the TGO will also operate as a communication link with Earth, and various landers and rovers.


Investigations with space and Earth-based observatories have demonstrated the presence of small amounts of methane on the atmosphere of Mars that seems to vary with location and time.[8][9][10] This may indicate the presence of microbial life on Mars, or a geochemical process such as volcanism or hydrothermal activity.[11][12][13][14]

The challenge to discern the source of methane in the atmosphere of Mars prompted the independent planning by ESA and NASA of one orbiter each that would carry instruments in order to determine if its formation is of biological or geological origin,[15][16] as well as its decomposition products such as formaldehyde and methanol.

Attempted collaboration with NASA[edit]

NASA's Mars Science Orbiter (MSO) was originally envisioned in 2008 as an all NASA endeavor aiming for a late 2013 launch.[17][18] NASA and ESA officials agreed to pool resources and technical expertise and collaborate to launch only one orbiter.[19] 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 launched along the TGO, a prospective agreement would require that the rover lose enough weight to fit aboard the Atlas launch vehicle with NASA's orbiter.[20] 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:[19][21][22] the ExoMars Trace Gas Orbiter (TGO) was merged into the project, carrying a 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 atmospheric trace gases detection instruments for their incorporation in ESA's ExoMars Trace Gas Orbiter.[6][18][23]

Under the FY2013 budget President Obama released on 13 February 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.[24] With NASA's funding for this project cancelled, most of ExoMars' plans had to be restructured.[25]

Collaboration with Russia[edit]

On 15 March 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 2020 rover mission.[26][27][28][29][30]

Under the collaboration proposal with Roscosmos, the ExoMars mission is split into two parts: the orbiter/lander mission in March 2016 that includes the TGO and a 2.4 m (7.9 ft) diameter stationary lander build by ESA named Schiaparelli;[31] this will be followed by the ExoMars rover mission in 2020[7] —also to be launched with a Russian Proton rocket.


The 600 kg descent module Schiaparelli and orbiter completed testing and were integrated to a Proton rocket at the Baikonur cosmodrome in Kazakhstan in mid-January 2016.[32] The launch occurred at 09.31 GMT on 14 March 2016.[33] Four rocket burns occurred in the following 10 hours before the descent module and orbiter were released.[34] A signal from the orbiter was received at 21:29 GMT that day, which confirmed that the launch was completely successful and the spacecraft is functioning properly.[35]

Shortly after separation from the probes, a Brazilian ground telescope recorded small objects in the vicinity of the Briz-M upper booster stage and ExoMars, suggesting that the Briz-M stage exploded a few kilometers away, without damaging the orbiter or lander.[36] Briefing reporters in Moscow, the head of Roscosmos denied any anomaly and made all launch data available for inspection.[37] The spacecraft, which houses the Trace Gas Orbiter and the Schiaparelli lander are underway to Mars and are in working order.[38]


The two spacecraft are still attached to each other and on course to Mars. The Schiaparelli lander will separate from the TGO orbiter on 16 October 2016, three days before it arrives at Mars, and enter the atmosphere at 21,000 kilometres per hour (13,000 mph).[39] After Mars orbit injection, the orbiter will undergo several months of aerobraking to adjust its speed and manoeuver into a 400 km-high circular orbit above the planet, with actual science activities beginning in late 2017.[39]


Size of the Trace Gas Orbiter compared to the Mars Express and an average human

The specifications are:[40]

  • Central bus is 3.5m × 2m × 2m [41]
  • 424 N bi-propellant main engine to be used to enter Mars orbit and maneuver
  • 20m2 solar arrays spanning 17.5 m tip-to-tip, and capable of rotating one degree; will generate about 2000 W of power at Mars
Thermal control
  • Spacecraft yaw axis control to ensure the three faces containing the science payload remain cold
  • 3,732 kg (8,228 lb) – mass of the TGO
  • 4,332 kg (9,550 lb) – launch mass including the Schiaparelli lander[34]
  • Up to 135.6 kg (299 lb) of scientific instruments


Scale model of ExoMars Trace Gas Orbiter displayed during Paris Air Show 2015

The TGO will separate from the ExoMars Schiaparelli demonstration lander and will provide it with telecommunication relay for 8 sols after landing. Then the TGO will gradually aerobrake for seven months into a more circular orbit for science observations and will provide communications relay for the ExoMars rover to be launched in 2020, and will continue serving as a relay satellite for future landed missions until 2022.[2]

The FREND instrument will map hydrogen levels to a maximum depth of 1 m (3 ft 3 in) beneath the Martian surface.[42][43] Locations where hydrogen is found may indicate water-ice deposits, which could be useful for future crewed missions.

Particularly, the mission will characterise spatial, temporal variation, and localization of sources for a broad list of atmospheric trace gases. If methane (CH
) is found in the presence of propane (C
) or ethane (C
), that will be a strong indication that biological processes are involved.[44] However, if methane is found in the presence of gases such as sulfur dioxide (SO
), that would be an indication that the methane is a by-product of geological processes.[45]


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 has very high sensitivity to (at least) the following molecules and their isotopomers: water (H
), hydroperoxyl (HO
), nitrogen dioxide (NO
), nitrous oxide (N
), methane (CH
), acetylene (C
), ethylene (C
), ethane (C
), propane (C
),[citation needed] formaldehyde (H
), hydrogen cyanide (HCN), hydrogen sulfide (H
), carbonyl sulfide (OCS), sulfur dioxide (SO
), hydrogen chloride (HCl), carbon monoxide (CO) and ozone (O
). Detection sensitivities are at levels of 100 parts per trillion, improved to 10 parts per trillion or better by averaging spectra which could be taken at several spectra per second.[46]

  • 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, CH
    ) 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 the Mars Reconnaissance Orbiter, the Trace Gas Orbiter is a hybrid science-telecom orbiter.[47] Its science payload mass is about 115 kg and consist of:[48][49]

  • Nadir and Occultation for Mars Discovery (NOMAD) has two infrared and one ultraviolet spectrometer channels. Developed by Belgium.
  • Atmospheric Chemistry Suite (ACS) has three infrared spectrometer channels [50][51] Developed by Russia.
NOMAD and ACS will provide the most extensive spectral coverage of Martian atmospheric processes so far.[47][52] 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.
  • Color and Stereo Surface Imaging System (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. Developed by Switzerland.
  • Fine Resolution Epithermal Neutron Detector (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.[51] Developed by Russia.

Relay telecommunications[edit]

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 rovers 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.[53] NASA provided an Electra telecommunications relay and navigation instrument to assure communications between probes and rovers on the surface of Mars and controllers on Earth.[54] The TGO will provide the Schiaparelli demonstration lander and ExoMars rover with telecommunication relay; it will also serve as a relay satellite for future landed missions until 2022.[2]

See also[edit]


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External links[edit]