On July 24, 1992, following EUVE's launch and in-orbit checkout, the all-sky survey phase of the mission began. Two different kinds of sky surveys were simultaneously conducted. The EUVE's three scanning telescopes systematically measured the positions and intensities of sources across the entire sky, while the deep survey telescope mapped faint sources along a narrow band on the Ecliptic.
Geometry of the Survey Phase Figure (47kbytes)To conduct the all-sky survey, the EUVE slowly revolved around its axis, sweeping its three scanning telescopes in great circles across the sky. These repetitive scans, combined with the Earth's orbital motion around the Sun, allowed the scanning telescopes to map the entire celestial sphere within about six months. Utilizing four band passes, the three scanning telescopes observed the sky over the entire extreme ultraviolet range (60-740Å).
Accomplishing the deep survey, however, was more challenging. The geocoronal glow, caused by sunlight that strikes the diffuse hydrogen and helium gas atoms surrounding the Earth, makes it difficult to observe faint EUV sources. Consequently, scientists configured the mission so that the deep survey telescope always pointed away from the Sun and only took measurements while viewing down Earth's shadow - the night portion of the orbit when the Earth blocks the Sun and shields the spacecraft from sunlight. This technique made the deep survey more sensitive by a factor of ten. Utilizing two band passes, the deep survey telescope observed a portion of the extreme ultraviolet range (70-365Å).