Two years after its launch, ExoMars Trace Gas Orbiter (TGO) finally settles in its final orbit around Mars. The satellite, which carries the instrument NOMAD of the Royal Belgian Institute for Space Aeronomy (BIRA-IASB) on board, has just completed one year of atmospheric deceleration and is now circling around Mars every 2 hours, some 400 km above the Martian surface.
The Belgian instrument NOMAD, which will search for methane and other important gases in the Martian atmosphere, appears to have passed this period very well and is ready to start its scientific phase within a few weeks.
The last time NOMAD was awakened and put to work, dates back to March 2017, just before the aerobraking period started. During the aerobraking period, the orbit of TGO was corrected by taking a dive in the atmosphere of Mars during each orbit and gradually slowing the spacecraft until it reached a circular path.
During this phase, the instruments on board TGO underwent a lot of temperature changes from each pass through the top of the Martian atmosphere. It remained uncertain what effect this had on the instruments and whether they could survive such a long period of inactivity.
Instrument in excellent shape
Now that the instrument has been switched on after one year of inactivity, NOMAD fortunately appears to be in excellent health. Functional tests of the 3 NOMAD channels confirm that they are still fully operational.
The two most critical parts - the coolers that have to bring the detectors of the infrared channels to very low temperatures - functioned perfectly.
Additionally, the engineers and scientists also took the opportunity to update NOMAD’s onboard software, meaning that it is now ready to begin scientific measurements.
Extensive test phase
Until April 21, 2018, the TGO satellite and all instruments on board will be extensively tested. This is called the "commissioning" phase, during which time many tests and some scientific measurements will be made. The satellite will not be placed into the optimal viewing direction, and so the team must wait a while longer before the most scientifically-important measurements are made.
The center responsible for the operations of the satellite (the Mission Operation Center in Darmstadt) will, in the first instance, become familiar with the way the satellite behaves in its orbit around Mars.
For this purpose, the satellite will remain in its nominal orientation throughout, i.e. with NOMAD directed towards the planet (nadir). Solar occultation measurements with the NOMAD instrument directed towards the Sun, which are scientifically the most interesting, will not yet be possible. BIRA-IASB will use this time to further calibrate the instrument and to get acquainted with the thermal environment.
Ready for more complex maneuvers
At the end of the "commissioning" phase, the orbit will be perfectly known and the satellite will also be able to carry out more complex maneuvers, such as looking at the Sun for solar occultation measurements. Our scientists can then finally start analysing the measurements as the data is returned to Earth bit by bit.
Science in full
The Mission Operation Center will remain in control of the satellite for a few more months. After four months, the scientists will gain more control over which maneuvers TGO will carry out, as the Science Operations Center in Madrid takes over.
The center is responsible for the planning of the scientific measurements of the various instruments on board TGO, which means that, from then onwards, the observations will be planned to prioritise scientific objectives. We are already looking forward to the discoveries that NOMAD has in store for us!