The microwave sensing in the Cassini Mission : the radar

Abstract

The spacecraft of Cassini Mission has been launched towards Saturn on October 1997 to study the physical structure and chemical composition of Saturn as well as all its moons. To this end many instruments have been mounted on the spacecraft ; one of these is the Cassini Radar. Cassini Mission is a cooperative mission between NASA (National Aeronautics and Space Administration), ESA (European Space Agency) and ASI (Agenzia Spaziale Italiana) to acquire scientific knowledge about the Saturnian system. Through many different scientific instruments, the Cassini Radar objective will be to investigate the nature of Titan : its optically opaque atmosphere and surface. Part of the Radar, the Radio Frequency Electronic Subsystem (RFES) has been developed by Alenia Aerospazio while the other parts have been developed from Jet Propulsion Laboratory (JPL). Cassini Radar is a multimode instrument able to operate in altimeter mode (4.25 MHz), an imaging mode (0.85 and 0.425 MHz bandwidth), a scatterometer mode (0.106 MHz bandwidth), and a radiometer mode (100 MHz bandwidth). These modes will be used to acquire images, topographic profiles, backscatter reflection coefficient, and sense brightness temperatures of the surface of Titan. A passive mode, i.e. radiometer, has been implemented to measure Titans surface emissivity in the ku-band. In the development of such an hardware, designers faced many requirements coming from the deep space environment and the specific features of a spacecraft designed to cruise in the Solar System to reach Saturn and its moons : e.g. reduced mass, low available room, low power consumption, severe environmental conditions, specific thermal control and on-ground test accessibility. The structure has been designed to survive high levels of vibrations at high frequencies (pyroshocks). Thermal design has to withstand wide range of temperature. Design avoids the genaration of magnetic fields, which could disturb magnetic sensitive sensor. Electronics have been shielded from natural and artificial radiation.