Low-Cost, Compact SAR System for Small-Satellite Constellation at LEO and vLEO

Since 2014, we have developed a unique, low-cost SAR (Synthetic Aperture Radar) for small-satellite constellations at LEOs and vLEOs (very Low Earth Orbits). Three SAR satellites have already been launched by a Japanese start-up company. The unique instrument in the SAR system is a deployable, two-dimensional slot array antenna consisting of multiple panels. The working system is X band SAR with 300MHz bandwidth, 1m ground resolution, where a series feeding, two-dimensional slot array antenna is applied. At present we are developing X band SAR with 1200MHz bandwidth, 0.25m ground resolution, where a corporate feed slot array antenna is utilized. All active instruments are in the satellite body. X-band microwave feeds from the satellite body to the antenna through waveguides embedded at the rear side of the antenna. A patented “non-contact microwave transmission technique with a choke flange” is applied at the hinge positions between antenna panels. Since there is no heat dissipation at the antenna panels, solar cells are installed at the rear surface of the plane antenna. The SAR satellite have only a deployed SAR antenna without any other deployment structures. Since our SAR system with deployable slot array antenna is very compact, we can make a flat small SAR satellite both in launching phase and on orbit. Aerospace Corporation in USA proposed a concept of a quasi-two-dimensional satellite, DiskSat in 2021, where DiskSats can be stacked vertically in rocket fairing for mega-constellation missions. Also, the flat shape of the satellite makes it possible to operate in vLEOs due to reduction of atmospheric drag. Signal-to-noise ratio of SAR is inversely proportional to cube of range (altitude). SAR observation at vLEO gives a significant advantage to SAR performances including system size or high ground resolutions. Our team collaborates with Aerospace Corporation to realize SAR DiskSat constellation. In the workshop we will summarize the unique SAR system and SAR missions at LEO and vLEO.