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IRS
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The Indian Remote Sensing Satellite (IRS–1C)
was successfully launched into polar orbit
on December 28, 1995 by a Russian launch
vehicle. Its payload was activated in the
first week of January 1996. This satellite
was followed by a similar one that was
successfully launched into polar orbit
on September 29, 1997 by a PSLV launch
vehicle. Its payload was activated in mid-October
1997.
Orbit
The primary objective of IRS satellites
is to provide systematic and repetitive
acquisition of data of the Earth’s
surface under nearly constant illumination
conditions. IRS–1C operates in a
circular, sun-synchronous, near polar orbit
with an inclination of 98.69°, at an
altitude of 817 km in the descending node.
The satellite takes 101.35 minutes to complete
one revolution around the earth and completes
about 14 orbits per day. The entire earth
is covered by 341 orbits during a 24 day
cycle. Successive orbits are shifted westward
by 2820 km at the equator. IRS-1C and 1D
have slightly different orbits (see below)
and for this reason do not have the same
reference system.
The mean equatorial crossing time in the
descending node is 10.30 a.m. ± 5
minutes. The orbit adjust system is used
to attain the required orbit initially
and it is maintained throughout the mission
period. The ground trace pattern is controlled
within ± 5 km of the reference ground
trace pattern. |
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