TIROS-ESSA Type

TIROS (Television TnfraRed Observations iSatellite) and ESSA (Environmental Survey Satellite of the United States Meteorological Bureau, Environmental Science Services ldministration) are well known satellites rotating on their own axes with the pet name - at the Meteorological Service - of Big Wheel. TIROS has its axis of rotation in the same position with respect to the plane of the ecliptic so that, during part of its orbit, it faces space, not Earth. On the other hand, the axes of the ESSA s are always directed towards the center of the Earth and, thus, always face our planet, which fills the whole field of view of the instruments. 

Country or agency In terrestrial orbits Lunar missions Solar orbits Total  

Still orbiting does not necessarily mean still working. 

Ten TIROS satellites were launched the first in 1960, and the tenth in 1965. With the exception of the last two, whose orbits were sub-polar, they were inclined 48 or 58° to the equatorial plane. All except four operate in the visible (TV) range the exceptions are TIROS 2, 3,4, and 7 which also work in infrared, but with very poor ground resolution. Though extremely useful for work in meteorological sciences, these satellites are of no interest to us. 

The ESS A satellites, nine in all, (the first launched on 3 February, 1966, the ninth on 1 April, 1969), are all sub-polar. All carry TV cameras and four also work in the infrared, but with unacceptable resolution for earth sciences (ESSA 3, 5, 7, and 9). 

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