A SmallSat Mission to Track the Global Movement of Water, Carbon, and Sediment across Landscapes

Abstract:

This abstract presents early mission concepts for a SmallSat designed to complement the data collected by NASA’s SWOT mission by providing cotemporal water quality information. By pairing surface water quality data with hydrological observations, changes in water quality can be better understood. For example, the combination of satellite altimetry and optical remote sensing will allow for tracking of sediment in Earth’s rivers. The tradespace for this mission is particularly interesting because the overlap with SWOT observations must be maximized. Unless two satellites are in the same orbit, overlaps in coverage occur infrequently. In addition to the overlap, consideration of performance objectives such as spatial and spectral resolution, swath and revisit time creates a complex tradespace. It is impossible to satisfy the stakeholder requirements for all of these performance objectives from a SmallSat platform, so identification and comparison of reasonable architectures is necessary.

The decisions that define the design space are the satellite bus type, number of satellites, the instruments onboard each satellite, and the orbital parameters of the satellites. A satellite architecture evaluator propagates the orbit of the given satellite and calculates the performance objectives for each given combination of instrument and orbit, as well as the overlap with SWOT. Satellite bus operation is also simulated to provide a cost estimate and to eliminate architectures which exceed the limitations of the given bus type. For example, an extensive collection of instruments in one satellite would satisfy all scientific requirements but would not be feasible for a SmallSat platform given the mass and power use of the instruments. A wide variety of architectures on the Pareto frontier are feasible and merit detailed inspection. Intuitively, a satellite trailing SWOT seems to be an ideal architecture considering the overlap metric. However, since being in the same orbit poses a risk to the SWOT satellite, alternate architectures must be explored. Preliminary results show that a constellation of five 6U CubeSats, each carrying a VNIR hyperspectral imaging spectrometer with 324 spectral bands from 400-1000 nm, would have a spatial resolution of 18 meters, a swath of 44 km, and an overlap of 7.6 hours per week.