The purpose of this effort is to develop an instrument to accurately calibrate (1% k=2) the lunar spectral reflectance (350 to 2,300 nm) at relatively low expense from a small satellite. Assuming the TSIS missions are successful and the solar irradiance is known, the lunar spectral reflectance can be used to provide known lunar irradiance, thereby providing a stable exo-atmospheric calibration source for earth-viewing instruments on low earth orbit satellites. The proposed instrument has been designed specifically for calibrating the lunar irradiance. It is compact, simple in concept, and the data product is nearly immune to long-term degradation because it collects solar and lunar signals using the same optics in the same way. During this effort a prototype instrument will be developed, tested, and evaluated. Design reviews will be conducted and a plan will be made for a next-generation instrument.