One element of the Gaia torus
One of 17 individual elements that make up the Gaia torus.
Starting on 28 April 2009 the 17 custom-built elements were assembled and aligned into the form of the torus. In preparation for brazing a special braze paste is then applied at each of the torus segments interfaces. When heated above 1000 °C this paste melts and seals the joints by capillary action - the torus then becomes one complete unit.
All elements of the torus are constructed from Silicon Carbide (SiC), a ceramic material whose physical characteristics make it the material of choice for structures which must be both light-weight and robust. The low thermal expansion coefficient and high thermal conductivity of SiC mean that it is a very stable material which can quickly dissipate thermal gradients, and with a Young's Modulus of about 420 GPa it is twice as stiff as steel. These are essential properties for the key hardware components of a mission whose scientific goals include obtaining microarcsecond astrometry of 1 billion celestial objects.
The individual segments of the torus were built by BOOSTEC, a subcontractor to the Gaia prime contractor EADS Astrium. BOOSTEC also performed the brazing of the torus.