johnnydeep wrote: ↑Thu Aug 03, 2023 3:48 pm
Also, from the geosynchronous orbit
in the text, we have:
A geosynchronous orbit (GEO) is a prograde, low inclination orbit about Earth having a period of 23 hours 56 minutes 4 seconds. A spacecraft in geosynchronous orbit appears to remain above Earth at a constant longitude, although it may seem to wander north and south. The spacecraft returns to the same point in the sky at the same time each day.
To achieve a geostationary orbit, a geosynchronous orbit is chosen with an eccentricity of zero, and an inclination of either zero, right on the equator, or else low enough that the spacecraft can use propulsive means to constrain the spacecraft's apparent position so it hangs seemingly motionless above a point on Earth. (Any such maneuvering on orbit, or making other adjustments to maintain its orbit, is a process called station keeping.) The orbit can then be called geostationary. This orbit is ideal for certain kinds of communication satellites and meteorological satellites. The idea of a geosynchronous orbit for communications spacecraft was first popularised by science fiction author Sir Arthur C. Clarke in 1945, so it is sometimes called the Clarke orbit.
But I'm having a hard time understanding the subtleties here. Geostationary is a sub-class of geosynchronous, that's clear. But:
Are all these orbits at the same height? (No, I guess not since it depends on eccentricity?)
Right. Unless the eccentricity is zero, the height varies.
Would there be any advantages in using a retrograde instead of a prograde orbit?
I believe satellites have occasionally been launched to the west to prevent launch debris from coming down over populated areas. But in general, no.
What about high inclination orbits?
What about an orbit that passes over a (geographic) north or south pole (inclination = 90 degrees)?
What about them? They are common, of course. Polar orbits in particular are popular for Earth observation satellites.
Isn't an inclination of zero identical to being "right on the equator" (by definition)?
How eccentric could an orbit be and still be either geosynchronous or geostationary?
There is no limit on eccentricity for a geosynchronous orbit (theoretically... there are certainly practical
limits). A geostationary orbit must
have an eccentricity of zero.