Satgen 540 Satellite Inclination 2  by GM4IHJ (BID SGEN540) 1999-07-31

The inclination of a satellites orbit plane with respect to the earths
equator, is usually determined by the launch site and, the satellites
mission. So the need to launch a variety of satellite missions has
forced the Americans to use two quite different launch sites. Cape
Canaveral in Florida, is alongside the Atlantic Ocean , at latitude
28N. So the minimum inclination for a direct orbit is 28 degrees.
Which has the advantage of some earth rotation, but limits the earth
coverage of low altitude satellites . Eg most Space shuttles see no
further than 48N . While satellites going to geostationary orbits at 0
degs inclination need a second rocket burn to alter the orbit plane
from 28 to 0 degrees inclination.

However, some American shuttle missions require orbits around 52 to 57
degs inclination, in order to carry out support missions to the Mir or
ISS manned stations. While others need to go as high in latitude as
possible in order to observe sub arctic phenomena such as aurora or
ice conditions. These Canaveral missions must be restricted to
inclinations below 58 degrees , noting that their track as they climb
up to orbit just after launch cannot be allowed to go further west ,
because it would then be over the densely populated areas of the
Eastern Atlantic seaboard, where a launch failure could have tragic
consequences.

This restriction of Canaveral launches to a maximum inclination of 57
degrees means that almost half of American launches must go somewhere
else, where there is a clear launch path to orbits as high as 98
degrees inclination. Noting that a large number of satellites go to
these retrograde inclination orbits because despite the much larger
launch thrust required, this is compensated for by the fact that these
orbit inclinations allow the orbit to be Sun synchronous. That is, an
orbit which brings the satellite over the same part of the earth at
roughly the same time each day, and provides the satellite with a
fixed amount of solar illumination varying very little from day to day
for several years until other features gradually pull the orbit out of
sun sync.

A Sun synchronous orbit occurs when the pull of the earths equatorial
bulge shifts the orbit plane roughly 1 degree per day. Thereby
compensating for the gradual daily change of orbit plane angle versus
solar position , which varies about a degree per day because of the
earths 365.25 day orbit around the Sun. Satellites profiting from this
regular illumination pattern are the weather sats where solar angle at
the ground is important , ie afternoon or morning sun prefered with
the shadow detail it imparts, rather than a flat shadowless noon
picture. While in a different way a Sun synchronous orbit where the
satellite rises over the equator at 0600 local time and descends over
the equator at 1800 local time ensures almost continuous solar
illumination which gives stable power supplies from the solar cells,
with only very rare calls on the satellites batteries. Weather sats
etc therefore launch to high inclinations via paths down over the
South Pacific from the US West coast site at Vandenberg Air Force Base
about 130 miles NW of Los Angeles .