Service Module attitude and orbit control (including propulsion)

• 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