Science operations planning of the Rosetta encounter with comet 67P/Churyumov-Gerasimenko

Abstract

Rosetta is a cornerstone mission of the European Space Agency (ESA). It was launched in March 2004 and will rendezvous with comet 67P/Churyumov-Gerasimenko (C-G) in 2014. Rosetta consists of an orbiter and a lander. Rosetta will meet Comet C-G early 2014 at a heliocentric distance of approximately 4 AU after wake up from a 2.5 year phase of deep space hibernation. The lander will be delivered to the surface in Nov. 2014 at around 3 AU from the sun, while the orbiter will continue to follow the comet on its orbit through perihelion until it reaches 2 AU outbound by end of 2015. The Science Operations and Data Handling Concept (SODH concept) deals with the 14 months between lander delivery and end of the nominal mission, the so called escort phase. That mission phase is extraordinarily complex: Approaching the sun the comet becomes increasingly active and its environment is expected to change dramatically and unpredictably. Therefore continuous monitoring of the comet (based on the science data returned) is required to mitigate risks on the spacecraft, mainly due to dust particles emitted from the nucleus. On the other hand, the evolving comet activity poses great scientific opportunities and payload operations are expected to react and adapt in response to these changing activities. In addition, the activity of the comet together with its small size (about 2 km radius) implies that the trajectory of the spacecraft relative to the nucleus may not be predictable for extended periods of time and that active orbit control will be required. The SODH concept foresees a closed loop system between operations planning and data analysis. Scientific operations planning is centralized at the Rosetta Science Operations Centre (RSOC), with an information repository at its core, containing operational inputs provided by the Principal Investigator (PI) teams that are responsible for the payload instruments. At the comet we expect to execute mostly predefined operation blocks. Changes in the comet environment and results of scientific observations feed back into the planning process. The planning process has already started with the baseline planning. It is based on the Rosetta Science Themes, representing the Science Objectives for Rosetta and the associated measurements by the various payload instruments. The instrument teams provide geometrical constraints (e.g. illumination requirements) and resource estimates (power, data volume, number of telecommands) needed for each measurement. The escort phase is divided into several phases. The proposed measurements are ordered based on their contribution to the science objectives to be covered during a given phase. The result will be the baseline plan of typical trajectories and pointing modes for each mission phase and an estimate of required resources, e.g. integration time and data volume. Expected conflicts and prioritization needs will also be identified in this stage. The baseline plan and the information repository are used to define the long term plan, a complete operations schedule for the escort phase. The actual operations planning will then be performed as a continuous adaptation and modification of the long term plan using predefined operational blocks. First the long term plan trajectory will potentially be modified according to latest information on the cometary environment and scientific results. At this point a conflict-free operations plan exists that can be executed on the spacecraft. If time permits, further iterations will be performed to further optimize the plan, fixing first the attitude profile and then the payload operations. © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.