Future NASA Astrophysics and Earth Science missions require submillimeter-wave remote sensing instruments to monitor air quality, climate variability and change, ozone layer stability, weather, and the global hydrological cycle. A key enabler for this technology is the F-band (106-114 GHz) solid-state power amplifier (SSPA) described in this proposal. This amplifier is need for the LO multiplier chain of the Scanning Microwave Limb Sounder and for the SOFIA (Stratospheric Observatory for Infrared Astronomy) airborne observatory. Currently available W/F-band SSPAs simply do not have enough power at this frequency, and further, their efficiency is poor. The efficiency SOA for amplifiers in the adjacent W-band is in the range of 10% and with practical packaged amplifiers including regulators, the efficiency is in the single digits. Our approach addresses this need by utilizing high-efficiency wide-bandgap (GaN) device technology and new high-efficiency power combining techniques to reach efficiency levels above 30%. Other NASA applications include planetary exploration missions which require W/F-band FMCW sensors to assist in planetary landings. Typical NASA applications require output power levels ranging from several watts to perhaps tens of watts at W/F-band frequencies.