Mechanical Service Module

Diagram of the Gaia spacecraft, with parts made transparent to reveal different elements

The mechanical service module is optimised so as to guarantee the stability of the basic angle, necessary to meet science requirements. It comprises a flat and uniform deployable sunshield which prevents Sun illumination of the spacecraft - and specifically the payload module (PLM) - during the nominal mission. The thermal tent enclosing the PLM caters for additional protection of the scientific instruments.

The spacecraft main structure is of hexagonal conical shape. It is a sandwich panel structure with carbon-fibre reinforced plastic (CFRP) facesheets, and a central cone supporting the propellant tanks.

It also features the passive and active thermal control system, as well as the thrusters of the chemical propulsion system and the complete micro-propulsion system.

Electrical Service Module

The electrical service module design is driven by the science performance (attitude control laws with the hybridisation of star tracker and payload measurements, high rate data telemetry, and regulated power bus for thermal stability). It houses the AOCS units, the communication subsystem, central computer and data handling subsystem, and the power subsystem.
 

Diagram of the electrical service module. Image credit: EADS Astrium

Thermal Control