How do they get up there?
The vehicle used to launch a satellite varies with the kind of the
satellite being launched. Geostationary satellites are launched with cryogenic
rockets or space shuttle. On the other hand, the
rockets used to launch polar satellites (Just another way to say
sun-synchronous) are usually smaller and non-cryogenic.
A satellite cannot be put directly into its final orbit. This is
because the accuracy needed to place the satellite in the final orbit
cannot be achieved by the launching vehicle, which is geared towards
producing high thrust. So The satellites are placed in an intermediate
orbit called the Transfer orbit. The transfer orbit is
usually an elliptical one, having the apogee equal to the final height
and the perigee quite near to the earth. Then it is put into the final
orbit by firing the Apogee Kick Motor (which is a
smaller, but quite accurately controllable rocket).
So now we have the satellite into the orbit, and we are done. Are we?
No! because the satellite has to be continuously goaded back into orbit
as it continually strays away from it. And pray tell me, why does that
happen? Because there are many forces continuously acting on the
satellite which tend to change the orbit, its altitude, its inclination
and what not. These perturbing forces are courtesy
moon, sun and mother earth's oblateness. (The earth is not spherical in
shape. It is slightly fatter at the equator than it should be. So we say
that the earth is oblate.) So the satellite has to be continuously monitored
and its orbit needs to be continually corrected. We call it Station Keeping.
The satellite dies when we run out of fuel for the rocket motors (Those
used in station keeping), Since we can no longer use the
satellites data with any degree of ease and confidence, the satellite's
systems are then shut down. Note that other systems of satellite may
still be functioning because they draw power from the Solar
Panel which is usually a robust structure.
What do the satellites in the sky see from above? And how do they see it?
Find out!
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