CHEOPS Launch and Operations

     

    CHEOPS was launched on a Soyuz rocket operated by Arianespace from Europe's spaceport in Kourou on 18 December 2019 at 05:54 locatl time (08:54 GMT/UTC). It shared the rocket with the Italian Space Agency's Cosmo-SkyMed Second Generation satellite, together with three cubestas ( OPS-SAT, EyeSat and ANGELS). The satellites separated into their own orbits soon after ascent, with CHEOPS operating in a low-Earth orbit at an altitude of 700 km and a Local Time of the Ascending Node (LTAN) of 6 a.m At this altitude the orbital period of the satellite is just under 99 minutes.


    Both the CHEOPS Ground Segment (GS) and the CHEOPS operational concept reflect the fast-track and low-cost nature of the mission, and follow two basic principles: 1) maximum reuse of existing infrastructure and operational tools, 2) high levels of both on-board autonomy and automation in the operations, in order to minimize the required manpower.

    The CHEOPS GS is under the responsibility of the CHEOPS Mission Consortium (CMC), and comprises:

    • the Mission Operations Centre (MOC), which is located at INTA in Torrejón de Ardoz, near Madrid (ES);
    • the Science Operations Centre (SOC), which is located at University of Geneva (CH);
    • Ground Stations (G/S) at Torrejon and Villafranca (ES). 

    Ground stations located in Kiruna (Sweden) and in Troll (Antartcic), were also used during Launch and Early Orbit Phase (LEOP). 

    Both the MOC and the SOC will operate on a 9-5 p.m/5 days-per-week basis during nominal operations.

    All operations, including LEOP and commissioning,  are to the executed from the MOC. The CHEOPS operational concept does not place stringent requirements on orbit control,and as a result, flight dynamics activities are minimal: in particular, no orbit maintenance manoeuvres are required after the initial launcher dispersion correction manoeuvre performed in LEOP, with the Local Transit of the Ascending Node remaining within the allowed range for the nominal duration of the mission. The orbit determination requirements can be fulfilled via Two Line Elements (TLE) available from NORAD/JSpOC. Doppler measurements will be used as a backup and to improve the orbit determination accuracy if needed. The satellite does not have a GPS receiver on-board, and so both the state vector and the On-Board Computer to Universal Coordinated time (OBC-UTC) time correlation coefficients will be computed on ground and uplinked to the spacecraft.

    The SOC is responsible for mission planning (tool provided by Deimos Engenharia (PT)), and will produce a weekly activity plan, with includes all platform activities and sequences of inertial pointing directions and associated instrument parameters for each observation. The activity plan will be sent to the MOC, where a check will be made to ensure that no critical spacecraft constraints are violated, and the plan converted to telecommands and uplinked to the spacecraft for execution in the Mission Timeline (MTL).

    The sequence of ground passes includes 5 to 6 daily passes over the G/S of Torrejon (or Villafranca, since the MOC plans to use both of them depending on their availability). Each pass has a duration of  7 to 10 minutes, with 2 to 3 of these passes taking place in the early morning (around 7 a.m. local time) and 2 to 3 passes in the early evening (around 8 p.m. local time). All passes will be used to downlink the spacecraft telemetry at a fixed downlink rate of 1143 Kbps, which is compliant with the daily science and instrument housekeeping data generation of 1.2 Gb. It is planned to use one pass per week to uplink the activity plan to the satellite MTL. A high degree of automation has been implemented in the Mission Control System (MCS) and the MOC, so that nominally only the uplink passes will require the presence of the operator.

    The Kiruna G/S was used duringLEOP to complement the Torrejon and Villafranca stations, providing additional passes (typically up to 10 per day) and enabling an earlier than otherwise possible acquisition of the spacecraft after the separation from the launcher. The duration of the LEOP was 4 days, leaving the spacecraft safely in the nominal operational orbit. In-Orbit Commissioning (IOC) started at the beginning of January 2020. The IOC Review will mark the end of the two month commissioning phase, after which  routine science operations will start.

    All science data will be processed at the SOC using an automated data reduction pipeline and will ba available to the Community via the CHEOPS science archive which will be also be at the SOC. Data access and download will be restricted to the PI of the observing programme to which the data belongs during the appropriate propriertary periods which are specified in the CHEOPS Science Management Plan and summarised at this link (link to  SMP).