ExoMars Trace Gas Orbiter with Europe’s entry, descent and landing demonstration vehicle |
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| Operator | ESA and NASA |
|---|---|
| Mission type | Orbiter/carrier |
| Satellite of | Mars |
| Orbital insertion date | October 2016 |
| Launch date | January 2016[1] |
| Launch vehicle | Atlas V 421 rocket |
| Mission duration | 1 Mars year orbital science mission Telecom asset until 2022[2] |
| Mass | 3130 kg |
| Power | Photovoltaic array (140 W) |
| Orbital elements | |
| Apoapsis | 400 km near-circular altitude |
The ExoMars Trace Gas Orbiter (TGO), sometimes referred to as Trace Gas Mission (TGM) by NASA, is a flexible collaborative proposal within NASA and the European Space Agency (ESA) to send a new orbiter-carrier to Mars in 2016 as part of the European-led ExoMars mission.[1][3]
This orbiter would deliver the ExoMars Entry, Descent and Landing Demonstrator Module (EDM) static 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.
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A 2016 Mars Science Orbiter (MSO) or Trace Gas Mission (TGM) was originally envisioned in 2008 as an all NASA endeavor aiming for a late 2013 launch window.[4][5] However, following the Mars Joint Exploration Initiative, it was agreed that the European-lead Trace Gas Orbiter (TGO) would carry several instruments originally meant for the 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,[3] to be launched in 2016.[5]
If launched, the Trace Gas Orbiter (TGO) would be the successor to the Mars Reconnaissance Orbiter, which may still be operational at that time. The TGO would be launched as part of the ExoMars program in 2016 together with a static lander built by the European Space Agency.[6][7]
Under the collaboration proposal, the European ExoMars mission would be split into two parts: an 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 an Atlas V rocket.[7][8] This joint ESA-NASA mission could help settle whether the methane source in that planet is of biological or geological origin,[7][9] and would apparently reconcile technological and science goals with available budgets.[7]
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.
The two space agencies issued on January 18, 2010 an Announcement of Opportunity inviting scientists to propose instruments to be carried on the mission. Once the proposals have been evaluated, the winning teams will build the actual hardware.[10] Like Mars Reconnaisance Orbiter, the Trace Gas Orbiter would be a hybrid science-telecom orbiter. Development of the spacecraft’s five science instruments is well under way. NASA is responsible for four sensors and ESA is contributing the fifth.[11] Its maximum science payload mass is projected to be about 115 kg. The proposed payload instruments are:[2]
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 Reconnaisance 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.[12] The orbital science mission, 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]
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