Payload Operations in Quiet Cruise: An Interplanetary Mission's Dilemma

Abstract

The International Rosetta Mission involves a 10 years long interplanetary cruise to rendezvous with the nucleus of a comet. In order to reduce the operations cost, the mission baseline excluded payload operations during cruise, with the exception of a few selected scientific phases (asteroids fly-bys) and of periodic instrument checkout slots. However, soon after launch, it was realised that many reasons can arise to operate the scientific instruments in phases when they were planned to be inactive, from anomaly investigation and troubleshooting to the detection of an unplanned scientific opportunity. In the first two years of flight the Rosetta mission control team had to trade-off the needs and advantages of unplanned payload operations requests with the increase in resources consumption on-board the spacecraft and on the ground. Based on the Rosetta experience, recommendations were derived for future interplanetary missions with a long cruise phase. First, it is easier to keep the level of instrument operations low if the level of spacecraft resources is low, whilst the workload and cost argument on the ground segment side is more difficult to defend. Also, payload operations in cruise can be of significant advantage to a mission, as they allow detection of critical anomalies well ahead of the main scientific mission. This can be achieved without jeopardizing the concept of quiet cruise by carefully inserting windows for payload operations around active mission phases, as part of the mission long-term planning. Finally, scientific operations during cruise are more justifiable if they relate to one of the mission science objectives. Their added value to the mission needs to be carefully assessed against the available resources. These rules are now being applied for the upcoming Rosetta mission phases.