SIGMA, a gamma imaging telescope, was successfully launched from BAIKONOUR on 1st of December 1989. It is the main experiment (1000 kg, D = 1.2 m, H = 3.5 m) of the GRANAT vehicle.
SIGMA thermal control heat rejection device is a variable conductance heat pipe (VCHP) radiator (0.9 m × 0.9 m).
The A 95 heat pipe technology has been developped and qualified by the Belgium firm SABCA under an European Space Agency contract (working fluid : NH3 ; control gas : N2 ; Dext = 9.5 mm). For SIGMA, six heat pipes are used with a L geometry, a total length of 2.3 m and a 140 cm3 reservoir.
Firstly, we remind design and ground thermal tests of SIGMA VCHP radiator. Secondly, we present detailed in-fligth performance during the first months of radiator operational life (18 months are specifieafor Telescope).