Direct Momentum Accommodation Coefficient Measurements for Satellite Applications

Momentum Accommodation Coefficient (MAC) data, derived from experimental measurements, are required to predict atmospheric drag on satellites in low Earth orbit (LEO). Currently MACs are estimated from measurements of the velocity distribution of the incident and reflected molecules in a molecular beam facility. The reflected molecules velocity and flux must be measured in all directions; hence the measurement is difficult and inaccurate. Busek proposes a new technique that reduces or eliminates the present difficulties. A new atomic source invented at Busek is used to produce a stream or a beam of atomic oxygen that impinges upon the test article (satellite surface sample) whose drag is measured by a unique thrust stand that resolves micro Newton forces. The MACs are then calculated from the measured drag. The new source of atomic oxygen with adjustable energy appropriate for orbital conditions was successfully demonstrated during Phase 1 of the program. A complete, efficient, and widely manipulated direct force momentum accommodation coefficient measurement facility will be constructed and characterized in Phase II. Accurate drag measurements and concomitant accurate MAC predictions will lead to optimization of satellite design, including one or all of the following: increased orbital life, reduced propulsion requirements and/or increased payload.