AGILE Satellite Thermal Control System Design: Thermal Model Uncertainty Reduction

The satellite AGILE (Astro-rivelatore Gamma a Immagini LEggero, “Light Gamma Ray Imaging Detector”) is a promising instrument for near-earth space research of the Italian Space(ASI) during the years 2007-2009: its scientific instrumentation has optimal imaging capabilities in both the gamma-ray energy range (30 MeV - 30 GeV) and hard X-ray range (15 - 45 keV). It will study the phenomena occurring in the high energy spectrum, such as: Active Galactic Nuclei, Gamma Ray Bursts, Gamma-ray Galactic Diffuse Emission, and more. The satellite was designed and built in years 2004-2006; this paper describes the design of the thermal control system of the satellite, with a survey of the flight prediction. As an example of uncertainty reduction, MLI performance characterization by test was done in an early phase of the AIV phase (i.e. well before the system level test), to meet stringent payload requirements in terms of temperature gradients and temperature stability. AGILE will fly in an equatorial orbit: dimensioning cases are presented in the paper. The satellite TCS has been designed modularly, with a bus/payload approach. AGILE Operational modes, design solutions and practical implementation (MLI, heaters/thermostats and passive radiators) are presented. Finally it is shown how the model uncertainty has evolved since the early design stage, to CDR design and to after tests-model correlation.