We propose the fabrication of large format, long wave infrared (LWIR) mercury cadmium telluride (HgCdTe or MCT) detector arrays where the cutoff wavelength is extended to 12 micron at cryogenic temperatures for use in missions to near earth objects, comets, and the outer planets. The MCT detector arrays will be a high performance improvement to meet the detector needs for future NASA missions. The MCT material for these detector arrays will be grown by molecular beam epitaxy on cadmium zinc telluride (CdZnTe or CZT) substrates to produce high quality semiconductor material with low defect densities. In this Phase I proposed effort EPIR, Inc. (EPIR) will fabricate a prototype focal plane array (FPA) where a 12 micron cutoff LWIR MCT detector array on a CZT substrate will be hybridized to a small format readout integrated circuit (ROIC) for capability demonstration purposes. EPIR will deliver this prototype FPA to the government for further evaluation. Should this effort progress to Phase II, then LWIR MCT detector arrays will be fabricated for hybridization to large format 1k x 1k ROICs for implementation into future planetary science space missions.