Sener is responsible for the AOCS subsystem, under the direct coordination of Thales Alenia Space Italy (TASI), principal contractor for the mission.

Sener is in charge of the entire subsystem, which includes the equipment, functions and SW that control its attitude (pointing) and orbital position. The AOCS’s sensors include:

• Fine Guidance Sensor (FGS)
• Inertial Measurement Unit (IMU)
• Star Trackers (STR)
• Coarse Rate Sensors (CRS) and Sun Sensors (SS)
• Reaction Wheels (RWL)
• Micro Propulsion Subsystem (MPS) and Reaction Control Subsystem (RCS)

Eight Sener subcontractors from different countries are participating in the subsystem (including subcontractors from the Netherlands, France, Germany, Italy, Portugal, and the US), while the client itself is providing the FGS, MPS and RCS.

The operating logic includes multiple modes and functions which are implemented in the SW of the AOCS, while also integrated in the SW of the central computer. The functions of the AOCS include determining and controlling the satellite’s attitude in all the modes; orbital maneuvers; equipment management and control; fault management (FDIR); interactions with the central software; and management of the AOCS’s data, telemetry and telecommands.

The project includes the preliminary and detailed design, production, verification, classification, delivery, and in-orbit commissioning. The AOCS provides hitherto unseen levels of performance in terms of pointing and stability (75 milli-arcsec., 99.7% C.L.), which will also give the FGS, IMU, MPS, etc. the highest levels of performance. Furthermore, the RWL must compensate for any disturbances (including those caused by the actuation of the mechanisms), while also preventing the transmission of the characteristic (micro-)vibrations, meaning they require very special characteristics and operation.

The AOCS’s SW corresponding to its different modes will be generated using Model Based Design Tools, with subsequent automatic generation of code from these models for the first time on an ESA scientific mission.

At Sener, we develop the Secondary Mirror Refocusing Mechanism (M2M). The M2MM is a positioning mechanism with 5 degrees of freedom which allows the movement and adjustment of the secondary mirror (M2M) of the Euclid telescope to guarantee the optical quality required in orbit, necessary to recover telescope misalignment caused by the difference in conditions between the earth and space.

Characteristics:

• Radiation environment: The unit is designed to tolerate a uniformly distributed total dose of 22 krad inside the box.
• Mass: MDE 2.1 kg. Harness 1.6Kg. Mechanism 4.45 kg
• Thermal:
     – MDE operating range: 250K – 313K; non operating range: 230K – 313K.
  – M2MM operating range: 110K – 313K.
  – Harness operating range from 110K to 313K and support a gradient of 203K.
  – Special cabling to connect the mechanisms to the electronics with low thermal conductivity.
  – Max. dissipation by conduction for MDE < 8W .
  – Max. dissipation by radiation for MDE < 2W.
  – Harness transfer in cryogenic zone < 0.0005 W in non-operational mode
• Functional: Mechanical Resolution is half micron resolution over a travel of +/- 225 µm with stable positions and high load capability to withstand launch loads without losing a given position in a compact volume.
  – Positioning method based on a stepper motor.
  – Adjustment in 3 degrees of freedom of translation.
  – Adjustment in 2 degrees of freedom of rotation.
  – Linear resolution <0.050 μm.
  – Angular resolution <5μrad.
  – Range of linear operation 300 μm.
  – Range of angular operation 2mrad.
  – Precision of 2 μm for linear adjustments.
  – Precision of 30 μrad for angular adjustments.
• Redundancy: Two fully redundant sections in a single box.
• Power:  Each section powered by a 10W isolation converter.
• Control: Each section provided with an “intelligent” device capable of decoding all telecommands received via serial channels, (MIL-STD-1553, preferred) providing the switching sequences required by the motors, and encoding the status information to provide serial telemetry.
  Compact electronics for the operation and control of the twin mechanisms (up to 10 degrees of freedom).
• Motors drive: Ten independently biphased motors (with main and redundant wiring) can be managed by MDE main and redundant section in cold redundancy.