Radar Technologies for Earth Remote Sensing From CubeSat Platforms

Space-based radar observations have transformed our understanding of Earth over the last several decades. Driven by increasingly complex science questions, space radar missions have grown ever more sophisticated with costs rising often to hundreds of millions of dollars. At the other end of the cost and complexity spectrum, CubeSats have emerged in recent years as a disruptive innovation in the satellite sector and are now considered a means to address targeted science questions in a rapid and affordable manner. CubeSats enable new kinds of constellation-based Earth science observations not previously affordable with traditional spacecraft. Constellations of low-cost sensors provide both global spatial and high temporal coverage. As such, CubeSats are not only viable platforms to address current Earth science goals, but they also open a new realm of possibilities for science advancement and unique applications. Radar instruments have often been regarded as unsuitable for small satellite platforms due to their traditionally large size, weight, and power (SWaP). Burgeoning missions such as Radar in a CubeSat (RainCube) and CubeSat Imaging Radar for Earth Science (CIRES), being developed by Jet Propulsion Laboratory and SRI International, respectively, and funded by NASA’s Earth Science Technology Office (ESTO), are slated to dispel this notion. The key to the simplification and miniaturization of the radar subsystems in a manner that still offers compelling science and applications is 1) component technological advancement; and 2) an integrated instrument architecture and mission design that exploits the capabilities offered by CubeSat platforms. This paper reviews the state-of-the-art and future developments of CubeSat radar missions for Earth remote sensing and the implications for NASA’s current and future Earth Science program. The key enabling technologies for radio frequency (RF), digital, and antennas are surveyed, as well as the evolution of the CubeSat avionics, in the aspects that mostly impact radar development, namely power, volume, and attitude control and knowledge and precision orbit determination (POD). We investigate various radar applications that could benefit from low-cost CubeSat platforms, such as altimetry, sounding, precipitation profiling, scatterometry, synthetic aperture radar (SAR), and interferometric SAR (InSAR). We also explore the science motivation and impact of future missions that are based on these technological advancements.