A spectrophotometer was flown on Spacelab 1 to study various mechanisms of Lyman-α emission in the upper atmosphere. The use of absorption cells filled with H2 and D2 gases allowed us to discriminate a number of weak Lyman-α emissions heretofore masked by the strong H geocoronal emission due to resonance scattering of solar photons. Preliminary results are presented on three topics: the first optical detection of the deuterium Lyman-α emission at 110 kilometers, with an intensity of 330 rayleighs indicating an eddy diffusion coefficient of 1.3 × 106 square centimeters per second; auroral proton precipitations seen on both the night and the day side; and an emission located above 250 kilometers of altitude, interpreted as the result of charge exchange of magnetospheric protons with geocoronal atoms.