The Envisat Flight Operation Segment (FOS)

FOCC role
FOCC architectural elements
LEOP sequence

The FOS is composed of the flight operations control centre (FOCC) located at ESOC Darmstadt, Germany, and the associated command and control stations. It provides control of the Envisat satellite through all mission phases.

FOCC role

The flight operations control centre controls all FOS operations:

• satellite operation planning based upon the observation plans prepared at the payload data segment (PDS)
• mission planning interface with Artemis (see the Artemis document for background information)
• command and control of the Envisat satellite
• up-loading of operation schedules on a daily basis via the TT&C station at Kiruna-Salmijärvi;

Control room at the flight operations control centre
(FOCC) located at ESOC, Darmstadt

Furthermore the FOCC supports:

• the satellite configuration and performance monitoring;
• the software maintenance for the PPF and the payload elements;
• the orbit prediction, restitution and maintenance.

The FOCC provides also all the communication interfaces, internal to the FOS as well as external interfaces to the PDS and the specific entities supporting the mission operation.
The Kiruna Station upgrade, includes the refurbishment of the existing 15-m antenna, an upgrade of the TT&C part and the installation of the X-band receiving chains, including the demodulators.

FOCC architectural elements

The flight operations control centre (FOCC) hosts the following major subsystems:

	The flight operation control software
	The flight operation control software is based on the SCOS-1B system successfully used on the ERS missions; this approach presented minimum development risks with a system capable of fulfilling all specified user requirements.
	The flight dynamics system (FDS)
	The flight dynamics system is derived from the ORATOS system, already used on the ERS missions. The major upgrade was the addition of the star tracker control and performance monitoring.
	The mission planning  system (MPS)
	The mission planning system was a new development. The MPS functions and corresponding requirements are specific to the Envisat mission but the split of responsibilities between the FOS MPS and the PDS mission control facility is very similar to the ERS missions: The global mission planning, specified in the reference operation plan (ROP), is directly planned by the FOS; the regional mission scheduling, mainly driven by user requests, is built up at the PDS payload data control centre (PDCC) and transferred to the FOS as a preferred exploitation plan (PEP); The FOS MPS is in charge of building up the complete satellite scheduling sequence, verifying the compatibility between the satellite constraints and the operation requirements of the ROP and the PEP; The corresponding satellite operation schedule is delivered to the PDCC as a detailed mission operation plan and implemented via a set of time-tagged macrocommands routed from the FOS to the satellite via the TT&C station of Kiruna.
	The Envisat satellite simulator
	The Envisat satellite simulator software is built to be as representative as possible of the on-board software for all aspects related to satellite control in all mission phases (LEOP, routine operations, and contingencies). This simulator includes emulation of the flight software for the CCU and the PMC and simulations of the other satellite subsystems, including the Instrument Control Units. The main objective is to permit rehearsals of all critical operations as well as to train operators in nominal and contingency procedures.
	The performance archiving system (PAS)
	The performance analysis system permits to store and retrieve all satellite control and monitoring information through the complete mission lifetime.
	The satellite software maintenance facility
	The satellite software maintenance facility is based on software maintenance tools delivered by the satellite and instrument manufacturers. For the CCU software of the service module, due to its mission criticality and complexity, a significant part of the maintenance activities is planned to remain with the corresponding satellite contractor.

LEOP sequence

LEOP sequence

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry