Slowed by skimming through the very top of the upper atmosphere, ESA’s ExoMars Trace Gas Orbiter has lowered itself into a planet-hugging orbit and is about ready to begin testing the Red Planet for methane.
The ExoMars Trace Gas Orbiter arrived at Mars in October 2016 to investigate the potentially biological or geological origin of trace gases in the atmosphere. It will also serve as a relay, connecting rovers on the surface with their controllers on Earth.
European Space Agency (ESA) flight director Michel Denis said: “Since March 2017, we’ve been conducting a terrifically delicate ‘aerobraking’ campaign, during which we commanded it to dip into the wispy, upper-most tendrils of the atmosphere once per revolution, slowing the craft and lowering its orbit,
“This took advantage of the faint drag on the solar wings, steadily transforming the orbit. It’s been a major challenge for the mission teams supported by European industry, but they’ve done an excellent job and we’ve reached our initial goal.
“During some orbits, we were just 103 km above Mars, which is incredibly close.”
Although ESA had acquired experience with aerobraking on a test basis at the end of the Venus Express mission, this is the first time they have used the technique to achieve a routine orbit around another planet, however, this is what the ExoMars Trace Gas Orbiter was built for.
Aerobraking around an alien planet that is, typically, 225 million km away is an incredibly delicate undertaking. The thin upper atmosphere provides only gentle deceleration – at most some 17 mm/s each second.
If you braked your car at this rate from an initial speed of 50 km/h to stop at a junction, you’d have to start 6km in advance.
Denis added: “Aerobraking works only because we spent significant time in the atmosphere during each orbit, and then repeated this over 950 times,
“Over a year, we’ve reduced the speed of the spacecraft by an enormous 3600 km/h, lowering its orbit by the necessary amount.”