Gaseous emissions from a spacecraft modify the orbital environment and degrade the observations of distant radiation sources. These emissions also provide contamination fluxes induced by self-scattering and scattering with ambient particles. Experiments were carried out on the orbiting Atmosphere Explorer D satellite (AE-D) to verify the calculated return fluxes of a neon source. Known rates of neon were emitted in the direction of the velocity vector on command from the MRMU (molecular return measurement unit). At 250 km the neutral mass spectrometer indicated a total neon return flux of 2.46¿10-2 times the emitted flux. The calculated fraction was 1.23¿10-2, including 9.14¿10-3 for the ambient scatter and 3.54¿10-3 for the altitude-independent self-scatter. The pressure gages indicated pressures less than 7¿10-8 torr at altitudes from 161 to 210 km. The maximum pressure for 161-km orbit was calculated as 7.4¿10-7 torr.