CubeSat Fully-Polarimetric Imaging Radiometer
Lead PI: Gregg Freebury, Tendeg, LLC
Start Year: 2018 | Duration: 2 years
Partners: California Institute of Technology Jet Propulsion Laboratory
The objective of this proposal is to study the feasibility of a low-mass, low-power fully-polarimetric imaging radiometer payload that can be hosted on a 12U Cubesat. The fully-polarimetric observations enable retrieval of ocean surface wind vector, as well as other key environmental parameters such as precipitable water vapor, cloud liquid water, precipitation rate and sea ice. Tendeg LLC and NASA’s Jet Propulsion Laboratory propose an innovative deployable aperture combined with a polarimetric radiometer system to achieve the stated objective.
The measurement of ocean surface vector winds using a polarimetric microwave radiometer was first demonstrated by the Naval Research Laboratory WindSat radiometer (launched in 2003). Because this was a first-of-its-kind measurement, the system minimized use of new technology to ensure successful demonstration of the new measurement technique and consequently had a large mass and power (450 kg and 350 W). NASA JPL has developed the Compact Ocean Wind Vector Radiometer (COWVR). The COWVR system utilizes a novel design to reduce the system complexity which in turn significantly reduces the cost, mass, power and volume from the heritage WindSat sensor, yet is predicted to maintain the same wind vector retrieval accuracy. COWVR has a mass of 60kg and power of 50W. The objective of this study is to evaluate the feasibility of shrinking a polarimetric radiometer payload down even further to fit within the resources of a 12U CubeSat.
Achieving this objective will require implementation of the COWVR instrument design into a compact multi-chip assembly. The integrated receiver assembly will feature internal calibration sources which enable fully polarimetric calibration and a compact highly integrated MMIC polarimetric combining receiver topology. In the COWVR technology demonstration sensor, these features were distributed among several electronics boxes and connected by transmission line. In this design, the components will be implemented in microstrip and integrated into a single, compact housing. This will require careful RF design and packaging to ensure sufficient isolation between the polarizations.
To achieve sufficient spatial resolution to meet the 50x200km sampling objective requires a reflector greater than 50cm. A rigid reflector of this size would obviously not be acceptable for a 12U Cubesat volume (approximately 20 x 20 x 30cm). To enable an adequate aperture that will package within a 3U portion of a Cubesat volume will require compaction ratios approaching 100:1 while still maintaining a precise reflecting surface up to Ka-band frequencies. The proposed design utilizes reflecting mesh integrated to a dual net architecture that is tensioned with radial ribs that spiral wrap around a central hub for packaging.
The overall objective of the Phase A proposal is to develop a novel Nanosat payload to address a Navy weather measurement need. The specific objectives of the program can be enumerated as follows:
1) Determine project feasibility and develop a novel payload concept design for nanosats to support measurement of Ocean Surface Vector Winds (OSVW) used for real-time littoral wind vector data and warnings of tropical cyclone position and analysis for assimilation into forecast models.
2) Use modeling and simulation to verify that the payload concept design can operate within the restrictions identified by the Navy for a 12U Cubesat payload.