BIRD 9 years microsatellite mission the experience of passive thermal control in space

Microsatellites are one of promising instruments to achieve near– Earth space research programs.. The aim of this paper is to present the experience gained by authors during thermal design of microsatellite BIRD and to give a summary of the thermal control system performance during almost 10 years of exploitation in the near – Earth orbit. Microsatellite BIRD (Bispectral InfraRed Detection, mass 95 kg, sizes 550 x 610 x 620 mm) was launched with Indian PSLV on October 22nd, 2001 into a sun-synchronous orbit. Payload consists of precise optical devices: VIS/NIR – Wide Angle Optoelectronic Stereo Scanner and MWIR/LWIR camera with activily cooled infrared sensors, operating within the MWIR range (from 3,4 to 4,2 µm) and within the LWIR range (from 8,5 to 9,3 µm wavelength). These cameras require an accurate control of optical axes geometrical parallelism and a faithful thermal control. The mean satellite power is about 35 – 40 W, with 10 – 20 min peak of 200 W power consumption in observation mode. The microsatellite thermal control system (TCS) has been designed to keep the satellite equipment within –10… +30° C for cold and hot cases. It includes a thermally stable design of the payload structure, heat transfer elements (conductors and grooved heat pipes), thermally connecting the satellite’s segments, two radiators, multilayer insulation and low-conductive stand-offs. More than 9 years of operation in space has brought an enormous volume of telemetric data about the performance of the TCS, based on information of temperature sensors, on power consumption and on the attitude relative to Sun and Earth. The TCS successfully maintained the required temperature level of satellite components. Nevertheless, the authors have set the task to analyze the temperature history during the satellite’s operation life. This concerns the main units of housekeeping equipment such as radiator, payload platform, power supply subsystem, board computer, solar arrays and communication setup. The authors intend to draw conclusions about apparently emerged changes in the thermal conditions and the performance of it. In order to realize that objective, an algorithm of initial telemetric data processing is proposed. A temperature survey is performed for the following time scales: short operation time (10 – 30 min), one orbit (96 min), one day, beginning of operation and actual time, the whole period – by now (from 10.2001 to 10.2010)