SMAP antenna feed radome: Design, development, and test

NASA´s proposed Soil Moisture Active and Passive (SMAP) mission would provide global soil moisture content and freeze/thaw state measurements with a minimum repeat period of three days at the equator. To do so, the SMAP instrument would employ a conically scanning synthetic aperture radar (SAR) and a radiometer operating at L-band (1.20 GHz - 1.41 GHz) through a common feed assembly. The proposed mission profile plans to employ a near polar sun-synchronous orbit that would periodically allow for solar impingement upon the internal surfaces of the feed horn, which could result in solar entrapment. If left unaddressed, this solar entrapment would cause the instrument to exceed its tight thermal stability requirements. These thermal stability requirements result from the sensitivity of the radiometer electronics and their proximity to the feed assembly. As a result of these stability requirements, a radome was incorporated into the design to act as a thermal barrier. As such, this paper will discuss the material selection process, design rationale, analysis, and material property test campaign for the SMAP antenna feed radome.