Science Planning Implementation and Challenges for the ExoMars Trace Gas Orbiter

摘要

The ExoMars mission is a joint programme of the European Space Agency (ESA) and the Russian space agency Roscosmos. One element of the overall programme is the 2016 Trace Gas Orbiter (TGO) spacecraft which launched on 14 March 2016 and successfully entered Mars orbit on 19 October 2016. From this initial Mars capture orbit, the spacecraft has now completed an aerobraking phase in order to reduce the orbital period to approximately 2 hours and to a quasi-circular orbital distance of -400km from the Martian surface. The primary science phase of the mission is performed from this orbit and started in April 2018, lasting for a nominal duration of 1 Martian year. The primary scientific objectives of the mission are the detection and characterization of trace gases in the Martian atmosphere, plus the study of Martian climatology, surface geology and sub-surface ice detection. To this end the TGO spacecraft consists of the following 4 Principle Investigator (PI) led instruments: The Atmospheric Chemistry Suite (ACS), The Colour and Stereo Surface Imaging System (CaSSIS), The Fine Resolution Epithermal Neutron Detector (FREND) and The Nadir and Occupation for Mars Discovery instrument (NOMAD). The ExoMars Science Operations Centre (SOC) is located at ESA's European Space Astronomy Centre (ESAC) in Madrid, Spain and is responsible for coordinating the science planning activities for TGO in order to optimize the scientific return of the mission. The SOC constructs, in accordance with Science Working Team (SWT) science priorities, and in coordination with the PI science teams and ESA's Mission Operations Centre (MOC), a plan of scientific observations and delivers conflict free operational products for uplink and execution on-board. To achieve this, the SOC employs a planning concept based on Long, Medium and Short Term planning cycles. Long Term planning covers mission segments of several months and is conducted many months prior to execution. Its goal is to establish a feasible science observation strategy given the science priorities and the expected mission profile. Medium Term planning covers a 1 month mission segment and is conducted from 3 to 2 months prior to execution whilst Short Term planning covers a 1 week segment and is conducted from 2 weeks to 1 week prior to execution. The goals of Medium and Short Term planning are to operationally instantiate and validate the Long Term plan such that the SOC may deliver to MOC a conflict free spacecraft pointing profile request (a Medium Term planning deliverable), and the final instrument telecommanding products (a Short Term planning deliverable) such that the science plan is achieved and all operational constraints are met. With a 2 hour-400km science orbit, the vast number of solar occupation, nadir measurement, and surface imaging opportunities, combined with additional mission constraints such as the necessary provision of TGO communication slots to support the ExoMars 2020 Rover & Surface Platform mission and NASA surface assets, creates a science planning task of considerable magnitude and complexity. In this paper, we detail how the SOC is developing and implementing the necessary planning infrastructure, processes and automation in order to support science planning of this scale throughout the TGO mission. We also detail how the re-use and further development of ESA's multi-mission planning software tool is being implemented in order to provide the necessary additional functionality for the SOC's planning team to exploit, and to therefore ensure the optimum scientific return of the TGO mission. Finally, we provide an overview and status of the real science planning activities taking place in the first weeks of the nominal science phase in the first half of 2018.