1997-07-01

A Comparison of INTELSAT VIII Spacecraft Thermal Vacuum Test Techniques 972525

The INTELSAT VIII / VIIIA program consists of six communication satellites (of two different designs) being produced by Lockheed Martin Astro Space for the International Telecommunications Satellite Organization (INTELSAT). Two spacecraft level thermal vacuum test facilities were required to test the first four spacecraft due to schedule constraints. The two facilities selected were the East Windsor, NJ (EW) 35 foot chamber and the 39 foot chamber at Lockheed Martin's Valley Forge, PA (VF) facility. INTELSAT 801 was tested in the EW 35 foot chamber which utilizes eight independently controlled shrouds to perform IR (hot wall) testing over an environmental temperature range of -180 to +80°C. INTELSAT 802 was tested in the VF 39 foot chamber which consists of shrouds flooded with LN2 at -180°C. Cal rods were used to independently control the thermal environments of the six spacecraft faces for this facility. A typical cal rod test approach measures cal rod fluxes via calorimeters at discrete locations and controls the applied fluxes based on a correction from the calorimeter to Optical Solar Reflector (OSR) or blanket thermo-optical properties. For INTELSAT 802, an equivalent sink test approach was developed for use with the cal rod test setup. A calibration of equivalent sink temperature to cal rod power was performed for each face of the cal rod test assembly. Three thermal balance cases, simulating equinox beginning of life, winter solstice end of life, and inverted spacecraft winter solstice end of life were common to the 801 and 802 test profiles. A comparison of these three balance cases confirms that the developed cal rod equivalent sink test technique is a good substitute for the hot wall test approach when chamber multiple zone temperature control is unavailable.

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