The INTEGRAL Spectrometer Thermal Control: Design, Validation and Performances After One Year In-Orbit

The INTERnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) is an ESA observatory scientific satellite which was successfully launched on the 17^th of October 2002. The payload consists in four instruments : an optical camera (OMC), a X-ray monitor (XRM), an imager (IBIS) and a spectrometer (SPI).

The spectrometer (20 keV-8 MeV energy range, 2.3 m high, 1.1 m diameter, around 1300 kg) has been supplied by CNES where this instrument has been managed, assembled and tested before delivery to ESA for satellite level activities.

This paper describes the spectrometer flight model thermal design achieved thanks to the different international partners, gives and overview of the cryostat used to cool down the detection plane and exposes the thermal validation plan used at instrument level (thermal mathematical model and thermal test philosophy, cryostat thermal validation). We then focus on in-flight performances and compare them to expected ones.