June 24, 2014

Ground Segment

The Ground Segment is composed of several entities distributed in different geographical places :

CoRoT Ground Segment


    The Operational Ground Segment is in charge of the satellite housekeeping, the mission programming, the telemetry reception from the satellite, as well as data and services delivery to the scientific users (PIs and Co-Is). It is composed of the Mission Center, the Control Center, the communication network and a set of multi-mission 2 GHz ground stations completed by two secondary stations specific to the CoRoT mission. The CoRoT Mission Center and the CoRoT Data Center form the User Ground Segment.


      The Control Center is in charge of the satellite housekeeping, the environment auxiliary data delivery for the mission and of the uploading of the payload telecommands. The CCC is an element adapted from the PGGS multi-mission program. It is located in Toulouse and is operated by the joint exploitation teams for the mini- and micro-satellite series. In addition to the classical operations related to the PROTEUS bus housekeeping and monitoring, the CCC is responsible for the inertial pointing of the CoRoT spacecraft and management of its specifically developed AOCS modes.


        The Mission center is in charge of the observing runs preparation, the payload programming and the associated telecommands generation, the instrument performances follow-up, the calibration and the optimization of the processing at system level, the pre-processing of the scientific telemetry up to level 1, as well as the archiving and the cataloguing of the data delivered to the CoRoT users. There is no direct communication between the satellite and the Mission Center, but CMC is autonomous to retrieve the payload telemetry after reception in ground stations. The CMC is located in Toulouse. It uses the hardware and operating systems of the Computing Center of the CST. It is operated there for the telescope station acquisition activities (preliminary to each observing run) by a joint team gathering the CNES operation engineers and the scientific group responsible for calibration and instrument programming (group led by the Project Scientist). After commissioning, the CMC will product daily the level-1 light curves to be retrieved by the CDC.


          The main ground stations are there for the 2 GHz satellite-to-ground link with the satellite, this means : to receive the housekeeping telemetry (HKTM) and the payload telemetry (PLTM), to separate the telemetry flux, to send in real time to the CCC the pass-by housekeeping telemetry, to store locally the recorded telemetry, to upload telecommands to the satellite and to send in real time the acknowledgements received from the satellite. The main ground stations are a part of the ICONES stations network. This network is made up of two TTCET compatible with PROTEUS and Myriade programs. They are automatic stations, remotely managed by Control Centers, using the CCSDS standard in S band, with a 3-meter diameter dish antenna under a radome. It was verified that the gain performances of those stations is sufficient to maintain the link with the satellite in inertial pointing configuration (non geocentric). Those stations are located in Kiruna (Sweden) and Aussaguel (near Toulouse). The ICONES network is completed with PROTEUS base-band kits on the stations of the existing 2 GHz CNES network (Kiruna, Hartebeesthoek) or 3801-equipment upgraded for low rate communications with PROTEUS satellites in safe mode (e.g Kourou).


            The Data Communication Network is in charge of data exchange inside the operational ground segment as well as all the facilities linked to it. The network is an adapted element of the multi-mission PGGS program. During the critical operation phases, it includes interfaces with the 2 Ghz stations network compatible with PROTEUS (KRN, HBK, KRU) as well as the CNES support entities for launch countdown, launch and early operation phase: Network Coordination Center, Orbit Computation Center, Main Control Room. It is then connected to the ICARE network.


              The Operational Ground Segment is completed with a ground station, said secondary and located in Brazil. This station has the function to increase the volume of the scientific telemetry during the observing runs. The station, located in Alcantara, made available by the Brazilian partner, is of the same kind as the ones used by ICONES (TTCET compatible with all PROTEUS interfaces). It is operated by INPE and its control center is located in Sao Jose dos Campos. This facility talks to the CCC by the internet for the pass reservation and retrieval of the satellite ephemerides.


                To secure the scientific mission, CoRoT is also capable to download its telemetry flying over the MOST micro-satellite ground station in Austria. This back-up facility, operated by the Vienna University, was adapted to the CoRoT telemetry reception by doubling the radiofrequency part (work funded by Austria) and adding a CCSDS front-end (provided by CNES). Its interfaces with the CCC are in every way identical to those of the Brazilian station. Operational talks are through the internet.

                  THE CoRoT DATA CENTER (CDC)

                  Developed and operated by the French laboratories of the CoRoT mission, the CDC is the scientific part of the user ground segment. Spread out over several sites (Meudon, Orsay, Toulouse, Marseilles), it is in charge of building the stellar catalogues used by the mission, processing the scientific light curves (residual instrumental corrections and astrophysical corrections), archiving and distributing the data to the CoRoT community and beyond. The level-2 products archive is implemented at IAS and must benefit from the SOHO experience. The CDC teams participate in the validation and optimization of the CMC processings. Finally the CDC hosts the exoplanet alert function (at LAM), which consists in sending to the CMC the list of target stars requesting to be oversampled on board, when a transit is suspected in the data. The light curve then produced (with 1 light point every 32 s) will enable to thoroughly characterize the shape of the signal if the event occurs another time, to confirm its nature and, if need be, to reveal for brightest stars a number of physical and orbital properties of their planetary companion.