NISAR spacecraft concept overview: Design challenges for a proposed flagship dual-frequency SAR mission

NISAR (NASA-ISRO Synthetic Aperture Radar) would be the inaugural collaboration between National Aeronautics and Space Administration (NASA) and Indian Space Research Organization (ISRO) on an Earth Science mission, which would feature an L-Band SAR instrument and an S-Band SAR instrument. As partners, NASA and ISRO would each contribute different engineering elements to help achieve the proposed scientific objectives of the mission. ISRO-Vikram Sarabhai Space Centre would provide the GSLV-Mark II launch vehicle, which would deliver the spacecraft into the desired orbit. ISRO-Satellite Centre would provide the spacecraft based on its I3K structural bus, a commonly used platform for ISRO's communication satellite missions, which would provide the resources necessary to operate the science payload. NASA would augment the spacecraft capabilities with engineering payload systems to help store, and transmit the large volume of science data. The combination of two SAR instruments on one platform would challenge the capabilities of both ISRO and NASA. The following are some of the challenges that will be discussed in the paper. The desire to operate both radars simultaneously would lead to a several-kilowatt power system design. The need to point the radar antenna to within a tenth of a degree would drive the attitude control system design. At peak rates, each instrument would produce data at gigabit per second speeds, which would drive the data transfer and storage capabilities. Furthermore, these data volumes would require the transition from an X-Band telecommunication system to Ka-Band, which could support multi-gigabit data rates.