SmallSat Constellations for Earth Science – it’s about Timing

Constellations of SmallSats or CubeSats open up the fourth dimension – time – for scientists to remotely measure quantities of interest from space. As a striking (and ground-breaking) example, NASA’s CyGNSS ‘string of pearls’ constellation, led by University of Michigan PI Chris Ruf, tracks the variations in surface winds under tropical cyclones over short timescales. Similar concepts under development by NASA include TEMPEST (U. CO/JPL) which targets the time evolution of clouds, and TROPICS (MIT/LL), for time-resolved observations of precipitation structure and storm intensity. All three address the time-derivative of quantities of interest to Earth System scientists.

The National Academy’s 2017 Decadal Survey for NASA Earth Science calls for high temporal revisit frequency to address several challenges. Planet’s commercial satellite constellation is out in front, providing daily, global high-spatial resolution maps for a few spectral bands in the Visible and Near-IR, which scientists have begun to make use of. The author has conceived of an S-Band SmallSat SAR constellation to satisfy NASA’s need for rapid revisit surface deformation measurements. Others are studying SmallSat constellations to monitor volcanic hotspots using Thermal IR bands, 3-D Winds in the atmosphere, and variations in the Earth’s gravity field at higher temporal resolution than NASA/DLR’s GRACE missions.

The common thread for each of these SmallSat constellations is the importance of time sensitivity. Scientists may be willing to sacrifice spatial resolution, spatial coverage, and radiometric sensitivity for temporal resolution. The implication is that SmallSat and CubeSat instruments without large apertures can provide scientifically compelling measurements. SmallSat developers should therefore be encouraged to pursue methods to improve time sensitivity, resolution and even latency – for example through compact GPS, chip-scale clocks, retroreflectors, VLBI or other methods for precision orbit determination, and linking up with ComSat networks such as Oneweb, GlobalStar and Iridium to get data down quickly.