The different RSU models

The Euclid VIS shutter unit (RSU) is not directly built as a flight unit, but a number of preliminarily models are constructed in advance in order to progressively test the robustness and the maturity of the design.
According to the standard practices for the construction of flight hardware and the specific requirements of the Euclid VIS instrument, the following RSU models are being built:
  • The Engineering Model (EM)
  • The Thermal and Structural Model (STM)
  • The Bread-Board Model (BM)
  • The Qualification Model (QM)
  • The Flight Model (FM)
  • The Flight Spare (FS).
Here we present and discuss the STM model.

The Structural Thermal Model

The STM is mainly built to test the thermal and structural properties of the RSU.

The differences between the RSU STM and the final RSU FM are listed below:

  • The primary stepper motor is replaced by two mass dummies of cylindrical shape, one for the rotor and one for the stator. These dummies are representative of the FM motor in terms of mass, CoG and mechanical interfaces.
  • The HDRM is replaced by a mass dummy of block shape, representative of the foreseen FM HDRM in terms of mass, CoG and mechanical interfaces. A locking plate and a screw are used to simulate the HDRM primary function (locking the Hatch in place during launch). The preload in the screw will allow for proper adjustment of the preload applied to the Hatch. This preload will be representative of the foreseen preload implemented on the FM.
  • The Harness (including connectors) is replaced by mass dummies, representative of the foreseen FM design in terms of mass, CoG and mechanical interfaces.
  • The micro-switches are replaced by mass dummies, representative of the foreseen FM design in terms of mass, CoG and mechanical interfaces.
  • The F/H fasteners are replaced by standard issue industrial fasteners of similar materials.
  • The ball bearings are replaced by standard issue industrial units. Models were selected with a set preload value and stiffness characteristics as close as possible to the foreseen FM models.
  • The Flushing Cover encapsulating the gear is replaced by a stainless steel mass dummy, representative of the foreseen FM design in terms of mass.

All other elements are fully representative of the foreseen FM design at time of manufacturing, including materials and surface finishes. In terms of mass representativeness, the STM is designed to be representative of the FM predicted mass and MoI (i.e. without maturity margins).

Photos of the different STM parts (some of them have been painted in black) and of the entire STM assembled for tests (credits: APCO Technologies).