Title: The CubeSat Radiometer Radio Frequency Interference Technology Validation (CubeRRT) mission
Presenting Author: Joel T. Johnson
Organization: The Ohio State University
Co-Author(s): J. R. Piepmeier, S. Misra, J. Kocz, R. Jarnot, S. Brown, D. Bradley, P. Mohammed, C. Chen, C. Ball, L. Garry, J. Lucey, J. Knuble, K. Horgan, C. McKelvey, M. Andrews, N. Miller, A. O'Brien, G. Smith,

Abstract:
Recent passive microwave measurements below 40 GHz have shown an increase in the amount of man-made interference, corrupting geophysical retrievals in a variety of crucial science products, including soil moisture, atmospheric water vapor, sea surface temperature, sea surface winds, and many others. Spectrum for commercial use is becoming increasingly crowded, accelerating demand to open the bands reserved for passive microwave Earth observation and radio astronomy applications to general use. Due to current shared spectrum allocations, microwave radiometers must co-exist with terrestrial RFI sources. As these sources expand over larger areas and occupy additional spectrum, it will be increasingly difficult to perform radiometry without an RFI filtering capability. Co-existence in some cases should be possible provided that a subsystem for filtering of RFI is included in future systems. Successful RFI filtering will not only open the possibility of microwave radiometry in an RFI intensive environment, but may also allow future systems to operate opportunistically over a larger bandwidth resulting in lower measurement noise. Initial progress in RFI filtering technologies for microwave radiometry has been achieved in the SMAP mission, which is currently operating in space a digital subsystem for this purpose in a 24 MHz bandwidth centered in the protected 1413 MHz band. RFI subsystems for higher frequency microwave radiometry over the range 6-40 GHz however require a larger bandwidth, so that the capabilities of RFI filtering backends in terms of bandwidth, processing power, and onboard operation must also increase. To demonstrate such technologies for future radiometer missions, the CubeSat Radiometer Radio Frequency Interference Technology Validation (CubeRRT) mission has been proposed and selected under NASA's In-space Validation of Earth Science Technologies (InVEST) program. The enabling CubeRRT technology is a digital Field-Programmable Gate Array-based spectrometer with a bandwidth of 1 GHz that is capable of implementing advanced RFI filtering algorithms such as the kurtosis and cross-frequency methods in real time on board the spacecraft. Though the technology can be demonstrated for any frequency band from 1 to 40GHz, CubeRRT will integrate this backend with a wideband radiometer operating over a 1 GHz bandwidth tunable from 6-40 GHz to demonstrate RFI detection and filtering in important microwave radiometry bands. Along with a wideband dual-helical antenna, the CubeRRT payload will be integrated into a 6U CubeSat for deployment in space. Although the spatial resolution to be achieved by CubeRRT will be coarse (~120-300 km, due to the limited antenna size possible), the goal of demonstrating observation, detection, and filtering of RFI should be achievable in this configuration. The CubeRRT project schedule plans for completion of the satellite by late 2017 with availability for launch beginning 2018. CubeRRT will act as an immediate risk reduction of new technologies that are necessary for future Earth science missions and directly relevant for future microwave Earth science missions such as SCLP, GMI follow on, SMAP follow on, and others.