The goal of this proposal is to extend Schottky receiver technology through the frequency range from 2 to 5 THz, with emphasis on the needs of future NASA missions. Initial examples include the SSOLVE receiver at 2.5 THz and a heliophysics mission concept at 4.7 THz. In general, the Schottky receiver technology will be useful for all missions in this frequency range that cannot make use of cryogenic receivers. Important examples will include planetary and lunar probes, atmospheric studies and heliophysics. Also, the source technology that will be demonstrated to pump the Schottky mixers can also be used as local oscillator sources for large arrays of cryogenically cooled hot electron bolometer receiver arrays, such as those planned for SOFIA and other platforms. Potential NASA Applications (Limit 1500 characters, approximately 150 words) The Schottky receiver technology will be useful for all missions in the 2-5 THz frequency range that cannot make use of cryogenic receivers. Important examples will include planetary and lunar probes, atmospheric studies and heliophysics. Initial examples include the SSOLVE receiver at 2.5 THz and a heliophysics mission concept at 4.7 THz. Also, improved source technology will be used to pump large arrays of cryogenically cooled hot electron bolometer receiver arrays, such as those planned for SOFIA and other platforms. Potential Non-NASA Applications (Limit 1500 characters, approximately 150 words) Molecular spectroscopy, plasma and accelerator diagnostics and materials science. Commercial test and measurement equipment will be extended to higher frequency. The receivers and sources will replace time domain terahertz systems for spectroscopy. The more powerful solid-state LO sources will also supplant vacuum tube technologies.