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The attitude and orbit control (including propulsion)

Service Module attitude and orbit control (including propulsion)

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ESA / Applications / Observing the Earth / Meteorological missions / MetOp

The Attitude and Orbit Control Subsystem (AOCS) is in charge of:









  • automatic 3-axis control of the satellite attitude
  • orbit control for which the needed thrust impulses are provided by the propulsion subsystem
  • management of the propulsion subsystem
  • automatic 1-axis control of the solar array orientation
  • orienting the solar array towards the Sun in case of electrical anomaly
  • providing ancillary attitude data to the Payload Module

The AOCS architecture is composed of four main assemblies:


  • attitude measurement assembly comprising:
    • digital Earth sensors (STD) for roll and pitch
    • sun sensors (SSD) for yaw
    • four independent two-axis gyros (two being in cold redundancy)
  • wheels and magnetotorquers assembly comprising:
    • three 40 Nms reaction wheels (RW)
    • two magnetotorquers (MAC) able to generate a 315 Am2 magnetic moment
    • the associated monitoring and command unit (EAIM)
  • propulsion and solar array drive mechanism assembly:

    • the propulsion subsystem works in blow-down mode and it includes four pressurised tanks containing 300 kg of Hydrazine
    • two branches of eight 23.5 N (initial inlet pressure of 22 bar) thrusters located on the SVM
    • four latch valves, pressure transducers, fuel and gas valves for the propellant/pressurant loading/off-loading and pressurising/venting.

    This assembly also includes the solar array drive mechanism (SADM) and the propulsion drive electronics (EPRM).


  • safe mode assembly comprising:
    • the safe mode dedicated electronics unit (T4S)
    • the Sun Acquisition Sensors (SAS)
    • the safe mode software

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