alae

The objective of the ALAE experiment is to measure atomic hydrogen and deuterium in the terrestrial atmosphere. The instrument consists of a spectrophotometer with an atomic hydrogen absorption cell and an atomic deuterium absorption cell. Various combinations of switching the cells on and off allow observations of the atmospheric deuterium layer, the atomic geocorona, and the Lyman-alpha interplanetary medium. STS-45

The objective of the Atmospheric Lyman-Alpha Emissions (ALAE)
experiment was to measure atomic hydrogen and deuterium in the
terrestrial atmosphere. The ALAE was flown on the Space Shuttle as
part of the Atmospheric Laboratory for Science and Applications (ATLAS
1)

http://neonet.nlr.nl/ceos-idn/sensors/ALAE.html