Deployable W-Band Antennas for CubeSats, NanoSats, and SmallSats

Microwave sounding radiometers and imagers have a substantial influence on weather forecast error reduction, and according to a report by ECMWF the addition of ATMS, Metop-B, AMSU-A, and MHS between May 2012 and May 2013 increased the contribution of microwave sounders from 26% to 33%. Further, “every time additional microwave sounder data is added to the assimilation, some small additional positive impact is found. This is despite the system already using many microwave sounders” [English, et al. 2013]. In addition, the National Oceanic and Atmospheric Administration (NOAA) also considers data from microwave sounding sensors on polar orbiting satellites to have a large positive impact on reducing numerical weather prediction forecast errors. Traditionally these sensors are carried by satellites weighing several hundred kilograms or more, but the proliferation of smaller CubeSats, MicroSats, and NanoSats has the potential to change this trend. Earth observation (EO) and remote sensing satellites are expected to constitute a majority (64%) of nano/microsatellite launches in the future, and most of them (83%) will be orbiting on a sun synchronous or polar orbit [Doncaster, Williams, and Schulman 2017]. An antenna reflector with a diameter of 0.5m or larger that can be stowed in less than 1.5U, opens new possibilities in the design of passive and active microwave sensors. For example, a 12U CubeSat (~18.5 kg) with observational capabilities better than the Advanced Technology Microwave Sounder (ATMS) can be built, drastically reducing costs and facilitating the implementation of earth observing constellations, thus considerably improving EO capabilities.

Boulder Environmental Sciences and Technology (BEST) is currently developing deployable antennas for operation up to 100 GHz, intended for use on small earth observing platforms such as CubeSats, NanoSats, and SmallSats. This antenna utilizes an offset-fed, paraboloidal reflector to achieve a large aperture (0.25 – 2 m diameter) with minimal blockage due to the feed structure. For much larger apertures and much lower operational frequencies, the AstroMesh™ reflector, developed by Northrop Grumman, represents the current state of the art in weight, packing density, and robustness, with a perfect deployment record over multiple satellite missions including Thuraya, MBSat, Inmarsat 4, Alphasat, and SMAP. However, the AstroMesh™ reflector is intended for larger satellites, with a minimum deployed aperture of three meters advertised for their smallest configuration. Smaller paraboloidal antennas do exist, such as the KaDPA antenna developed by JPL, though the center-feed design blocks a portion the antenna aperture, reducing the efficiency of the antenna, and the umbrella-like design restricts operation to the Ka-band. Based on the flight-proven Astromesh™ design, our antenna utilizes opposing support nets tensioned between a collapsible perimeter ring truss to achieve the high surface accuracy required for the mesh reflector.

Preliminary design of a 550mm aperture offset-fed paraboloidal antenna operating up to 100 GHz has been performed resulting in an antenna that stows in 1.5U (stowed diameter of 55 mm and height 117 mm) weighing approximately 150 grams (reflector only). With deployed dimensions of 660 mm in diameter and 117 mm in height, the stowed to deployed volume ratio is approximately 1/144, or the stowed to deployed diameter ratio is 1/12. This reflector corresponds to a maximum gain of 55.2 dB at 100 GHz and a ground resolution at nadir from an altitude of 600 km of 8 km at 100 GHz. Apertures up to 2 meters can use a similar approach, with a 1.2 m aperture corresponding to an approximate stowed diameter of 120 mm, a height of 255 mm, and a weight of 0.33 kg, while a 2 m aperture corresponds to an approximate stowed diameter of 200 mm, height of 425 mm, and weight of 0.55 kg. These apertures are comparable to the GMI (GPM Microwave Imager with 1.2 m reflector) and AMSR2 (Advanced Microwave Scanning Radiometer with 2 m reflector) antennas.