A Millimeter-wave Phased Array Radar for Hazard Detection and Avoidance on Planetary Landers

Safe, precise landing in difficult planetary terrain, including areas that are rocky, heavily sloped, or both, requires remote sensing of the surface in order to choose an appropriate landing site. While active or passive optical sensors might seem appropriate for this application, we are developing an alternate approach based on a millimeter-wave electrically scanned phased array radar. A radar offers several advantages over present optical sensors, including a substantial reduction in dust or engine plume susceptibility, a larger range of operating altitudes, and a coherent measurement of the platform velocity. In this paper, we describe the overall system design for a radar being developed for the NASA Mars Science Laboratory, set to launch in 2009. We discuss the terminal descent scenario, and the requirements imposed by the terminal guidance and landing vehicle hazard tolerance. We present the digital elevation and roughness map generation performance of our candidate sensor as derived from terminal descent simulations over synthetic Mars terrain, where roughness is derived from a optimal threshold crossing algorithm. We also present a novel, fast velocity vector retrieval algorithm that avoids the necessity of inverting the entire phase matrix, making it ideal for onboard computation. Finally, we describe our upcoming hardware development efforts, including the development of a system test bed that will be used in the prototype sensor. This system is capable of the required 1 GHz bandwidth and five hops in center frequency. Our future development and testing plans will use this test bed to develop a full millimeter-wave phased array, leading to a unique hazard detection sensor for this exciting mission.