October 1, 2015

Ground segment

Besides the space-segment, the other crucial part of a mission is its ground segment. The Merlin mission ground segment is composed of a Control Ground Segment (CGS) and a Payload Ground Segment (PLGS).

Control Ground Segment

The Control Ground Segment (CGS) includes the following components and services:

  • a Command and Control Centre (CCC) on the CNES site in Toulouse (CST),
  • an S-band and X-band telemetry and command function which uses the CNES network of TT&C ground stations,
  • additional support functions provided by CNES multi-mission services:
    • debris management service for collision risk computation,
    • orbit computation service,
    • main control room (used occasionally, mainly in LEOP and commissioning phases),
    • file exchange service.
  • a Numerical System Simulator

Command and Control Centre

The Merlin Command and Control Centre (CCC) will be built on the basis of the ISIS (Initiative for Space Innovative Standards) generic Command and Control Centre to be used by all future CNES missions. Its main tasks are to control and monitor the satellite and ensure it remains in good condition throughout the mission lifetime. The CCC is composed of seven specialised subsystems:

  • The Automation subsystem manages all the activities and orchestrates CCC operations,
  • The Monitoring and Control subsystem is responsible for the telemetry and command function and communication with the TT&C ground stations,
  • The Flight Dynamics subsystem is in charge of flight dynamics calculations linked to attitude and orbit control,
  • The Data Store subsystem is in charge of storing and managing all the data received and produced throughout the mission’s lifetime,
  • The Mission Operation Support subsystem provides dedicated services to support the mission including on-board software management, alert management, generation of reports and the management of external interfaces,
  • The Visualisation subsystem is the graphical interface dedicated to mission monitoring; it can display real-time telemetry and data available in the Data Store,
  • The Infrastructure subsystem comprises a set of general services, such as time management, hardware and software management or internal and external communication.

Station network

The CNES multi-mission stations network provides S-band and X-band data services. It will be used for satellite commands and the reception of satellite housekeeping telemetry (S-band), and, in X-band, for downloading science data. The location of the S- and X-band ground stations is shown on the map below. Network operations are managed by the Network Operations Centre in Toulouse.

Network of S-Band and X-Band Stations

Numerical system simulator

The Merlin “Training Operation and Maintenance Simulator” (TOMS) is a numerical simulator designed to simulate as realistically as possible the system’s behaviour in its operational environment, and in nominal and degraded working modes.

The Merlin TOMS aim to simulate the operational functions seen from the Ground Control Centre (CGS) through the housekeeping telemetry (TM) and the command (TC) in order to conduct the technical and operational qualification of the system.
TOMS simulates all the satellite units offering a full representation of the Merlin satellite.

PayLoad Ground Segment

In order to process and later on use the Merlin data collected, an efficient Payload Ground Segment (PLGS) is necessary.

The PLGS is responsible for payload operations, the end-to-end handling of Merlin data and the production, quality control, dissemination and archiving of mission products.

It consists of:

  • Payload Operation Centre (PLOC) dedicated to payload monitoring and control. Payload operations are conducted by the PLOC, which acts as the central hub for mission planning; it generates payload commands, manages payload calibration and monitors payload health. PLOC is composed of:
    • Payload Monitoring & Control (PLMC) which monitors and controls the payload. The PLMC generates commands to control the payload based on inputs from the PLEX, analyses payload behaviour, investigates payload anomalies and checks the Level 1a data produced by the PLDP. It provides information to the Scientific Products Expertise centres (SPEX) which can deliver a new version of the Level 1 processor to the PLDP.
    • Payload EXpertise (PLEX) which provides in-depth payload expert appraisal and off-line instrument support functions such as mission planning input, long-term monitoring, calibration, instrument configuration control, provision of procedures for off-line monitoring of housekeeping and measurement data.

  • The Payload Data Processing centre (PLDP) is responsible for processing and delivering science data, that is to say the generation of level 0 to level 3 data and products, and the dissemination of Merlin science data. The PLDP manages the data and product archives,

  • Scientific Products EXpertise centres (SPEX) dedicated to expert assessments of MERLIN science products. SPEX centres manage the science prototypes to support the development and testing of the reference processors. They deliver new versions of a reference processor to the PLDP and relay the reprocessing campaign required by the Science Advisory Group.