Clementine, robotic U.S. spacecraft that orbited and observed all regions of the Moon over a two-month period in 1994 for purposes of scientific research and in-space testing of equipment developed primarily for national defense. It carried out geologic mapping in greater detail than any previous lunar mission; some of its data hinted at the possibility that water exists as ice in craters at the Moon’s south pole.

Clementine, launched on January 25, 1994, was a joint project of the Department of Defense’s Strategic Defense Initiative and the National Aeronautics and Space Administration (NASA). The ingenious mission design used the Moon as a “target” for testing various sensors and spacecraft components intended for ballistic-missile-defense applications and, in the process, returned a vast amount of scientific data. Its suite of remote-sensing instruments allowed imaging at various visible, ultraviolet, and infrared wavelengths (multispectral imaging); detailed topographic mapping by laser altimetry; and charged-particle measurements. Clementine’s multispectral imagery was used to create global and regional maps of iron and titanium concentrations in lunar soil, and radar studies employing its radio transmitting equipment suggested that water might be present in the form of ice deposits in permanently shadowed craters near the lunar south pole. Measurements of perturbations in the motion of the spacecraft were used to map the lunar gravity field and its anomalies (seemascon). Clementine was originally intended to observe a near-Earth asteroid after leaving lunar orbit, but a spacecraft malfunction canceled that portion of the mission.

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