This should really be obvious to me as I’m in the mapping business.
OK. I’m watching the ISS on this site.
Why do satellites appear to make large S shaped orbits? I’ve seen this in other places too.
Is it because the map projection used, since the ‘map’ is flat and the earth is round?
I just followed It going SE right down the E coast of Australia, and now it’s nearly over South America. If you head SE from Australia, you would end up in Antarctica.
Basically, yes. If you took a globe and plotted the same course on it would see a great circle. Due the projection used on the map it looks like an sine wave. If it was an orbit that went around the equator it would be a straight line.
Thanks flight… Isn’t it also due to this…
The satellite is orbiting at an oblique angle. And since the earth is rotating, and the satellite is moving……. I ends up in over different areas.
Yes, this is also true.
The period of an Earth satellite depends on its alitude, e.g. a satellite at an altitude of 35800 km has a period of 24 hours. Lower altitude satellites have shorter periods, higher altitude satellites have longer periods.
A satellite with a period of 24 hours, orbiting in the same plane of the equator, is geostationary, it doesn’t track over the Earth’s surface. The “track” would just be a dot on the Equator.
A satellite with a period of 24 hours but not orbiting in the plane of the Equator tracks back and forth along a straight North-South line. I.e. it moves around the Earth at the same rate the Earth rotates, but sways north and south of the Equator.
A satellite with a period other than 24 hours, but not orbiting in the plane of the Equator tracks a sinusoidal path, which can be regarded as the North-South sway described above, superimposed on the Earth rotating below it.
(And finally, for completeness, the obvious - a satellite with a period other than 24 hours, in the plane of the Equator, tracks a straight line along the Equator!)
You can see live satellite orbits in 3-d here:
The ground track of highly elliptical orbits can cause quite a bit of head scratching. These sats exhibit retro-grade motion and can have significant hang time above a particular patch of the earth.
Ive been told that a “true” geostationary slot up there is very expensive, (and not many left ), slots just out of this desired plane will make little figure-eight ground tracks
>>A satellite with a period of 24 hours, orbiting in the same plane of the equator, >>is geostationary, it doesn’t track over the Earth’s surface. The “track” would >>just be a dot on the Equator.
Can’t you just send them up a bit higher and increase the speed of the satellite? It will still have a 24 hour period.
You can’t “increase the [orbital] speed” of a satellite; satellites are in a purely ballistic (unpowered) orbit, and every circular orbit will have a characteristic speed based strictly on its altitude and the mass of the body it orbits. The altitude of a satellite in geostationary orbit is 35,786 km…no more, no less. That’s a pretty high altitude to reach–higher than most communications satellites or Hubble–which takes a more powerful launcher to achieve.
The o.p.'s main question has already been answered, but it’s worth noting that there are a number of reasons, aside from the cost of getting it up there, to selecting a non-geostationary, and indeed, non-circular orbit. For communications or surveillence satellites, particularly those serving higher latitudes, it is preferable to orient the satellite at a significant angle to the ecliptic plane of the Earth, and in order to get significant dwell over high latitudes the orbit may be dramatically elliptical as well. Molniya orbits (designed to dwell over high latitudes and used for telecommunications satellites serving the former Soviet Union and Northern Europe) are an example of this.
Stranger
As Liver of Darkness points out, it won’t quite be a straight North-South line, but a figure 8. And if the orbit is inclined and eccentric, it can be an asymmetrical figure 8.