In 8 hours – if everything goes as planned – the MOM would have been inserted into Mars orbit of 423 km at periareion and 80,000 Kilometers at apoareion at an inclination of 150 degrees and with an orbital period of a little more than three days. Though a number of experiments are planned, the most important objectives of the mission – to demonstrate technology and capability – will largely have been accomplished on getting into orbit.
But the next few hours will be tense and nervous not only for ISRO mission staff but for the many millions of Indians who will be following the live webcast at http://webcast.isro.gov.in/. The critical operations will take place while the MOM spacecraft is occluded on the far side of Mars and when signals will be taking over 12 minutes to reach earth.
The critical Mars Orbit Insertion Burn Sequence will begin three hours ahead of the planned maneuver time when the spacecraft automatically switches over to its Medium Gain Antenna for communications since the High Gain Antenna will be pointing away from Earth during the retrograde burn.
21 minutes ahead of ignition, the spacecraft will begin the re-orientation to the proper attitude for the burn, pointing LAM to the direction of travel. The re-orientation is accomplished using the vehicle’s Reaction Wheels. Five minutes and 13 seconds ahead of the burn, the spacecraft passes into darkness – for the first time since leaving Earth last year. In advance, MOM will fully charge its battery to be in a safe configuration for the eclipse.
Three minutes ahead of the burn, the vehicle’s eight 22-Newton thrusters are enabled to start providing attitude control which they will continue to do throughout the main engine burn, keeping MOM pointing forward. Ignition of the Liquid Apogee Motor is planned at 1:47:32 UTC on Wednesday, September 24, 7:17 Indian Standard Time. The Mars Orbit Insertion burn has a planned duration of 24 minutes and 14 seconds, slowing the spacecraft down by 1,098.7 meters per second to be captured in an elliptical orbit around Mars. During the burn, the engines will consume 249.5 Kilograms of propellant leaving only about 40 Kilograms of propellant for the rest of the mission.Should something go wrong during the burn, MOM is programmed to react appropriately in order to achieve a stable orbit around Mars – even if that means to spend all the vehicle’s propellant to do so. In the event the Liquid Apogee Motor is not ignited or its burn is cut short, MOM would automatically switch to the 22-Newton thrusters to supply as much delta-v as possible. Due to their lower thrust, the 22N thrusters would need to fire much longer than LAM along a greater stretch around the periapsis pass which will increase propellant consumption and leave MOM in a higher orbit.