PREPARATIONS AND PERFORMANCE OF LARGE SPACE SIMULATION CHAMBER (LSSC) DURING INSAT-2E SOLAR SIMULATION THERMAL BALANCE AND THERMAL VACUUM PERFORMANCE TESTS

摘要

Solar simulation Thermal Balance and Thermal Vacuum performance tests on INSAT-2E (Indian National Satellite) were conducted in the Large Space Simulation Chamber (LSSC) available at ISRO Satellite Centre, Bangalore, India during October-Novemberl998. The performance of the chamber system was excellent. Both tests were conducted in stabilized environments of vacuum, temperature, solar beam and motion simulator operations as required. The good performance of the chamber can be attributed to a number of modifications, trial runs and performance reviews conducted prior to the above tests. Primarily, certain deterioration in the achievable chamber vacuum was noticed over a period of time since commissioning of the chamber in 1991. A study revealed that a major reason for these degradations are development of leaks at the inter panel connections of shrouds . The panel interconnection arrangements originally provided were reviewed and modifications to the panel interconnection and shroud anchoring incorporated. Subsequently an elaborate leak rate verification of each shroud panel was conducted keeping a bench mark for the acceptable leak level as less thanlxlOE-8 std cc/sec. Panels with higher leak levels were rectified identifying the degraded welds at the tubes inter connecting the panels . After rectification of leaks by re welding and qualification of each panel, vacuum trial runs were conducted to ensure that the overall vacuum performance of the chamber met specifications.During the analysis of some earlier tests conducted in the chamber it was noticed that there had been some vacuum fluctuation due to sudden release of gases by the cryo pumps. A study revealed the possibility of cryo pumps taking excessive gas load . To avoid this excessive loading and subsequent saturation of cryo pumps during extended chamber evacuation , an additional turbo molecular pump was incorporated to the pumping system of the chamber. This additional turbo molecular pump ensured a stable state lower order vacuum and an overlapped pumping regime with the cryo pumps thus relieving the cryo pumps from being loaded excessively due to out gassing from the shrouds or the test object during the pump down.Further during the INSAT-2E thermal balance test shrouds were cooled to the required temperature of less than 100 deg K in a gaseous Nitrogen mode. The temperature uniformity achieved was comparable with that achieved in LN2 mode using sub coolers during the earlier tests . The GN2 mode of operation was adapted on a trial basis as a safeguard against the power failure kind of test interruptions . The operation