The ExoMars Trace Gas Orbiter, spacecraft launched by Roscosmos and ESA which arrived Mars orbit in October 2016, is going to change its orbit. It will reduce altitude and will start lasting another 12 months process of aerobraking to reduce speed and reach orbit with altitude of 400 km using for this minimal amount of propellant.
To show better why this maneuver will take one year we have to present some orbit data. Current apogee is 30000 km over surface of the Mars. After one year of reducing speed of altitude using only aerodynamic forces this value will be reduced to 400 km. Orbit will be changed from highly elliptical to more circular; perigee will be changed only slightly: from 200 km to 113 km.
Series of seven burns of 424 N main bipropellant thruster started on last Wednesday. Second burn was performed on Saturday. Until Monday perigee of TGO orbit was reduced to 140 km. Next five burns will be performed in March and April: on March 24, march 27, April 1 and April 6.
Planned maneuver is not necessary the easiest and less risky. During penetrating atmosphere orbiter will be exposed to friction between its surfaces like solar arrays and particles of atmosphere. Temperature on the solar panels will increase even to 70 degrees Celsius. If it will still increase orbiter will be forced by its algorithm to ignite thruster and reduce speed to avoid overheating.
Reaching correct orbit to perform series of scientific experiments and starting collecting data is planned for early 2018.