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Geostationary satellites are required to maintain their longitude (it's a license requirement to get their assigned orbital slot), but not their inclination. So

by Sanzig 2y ago

Geostationary satellites are required to maintain their longitude (it's a license requirement to get their assigned orbital slot), but not their inclination. Sometimes operators will let the inclination drift a bit to save fuel. Obviously it's a tradeoff, since if you let the inclination change to a non-zero value the satellite will move around in the sky. After a certain point it becomes unsustainable because it will start to drift outside the receiving beam of your customer's antennas.

ricksunny 2y ago
All soundng very reasonabke so far, thank you - yet why is the overall cylinder at an incline? If as you describe, why wouldn't the choice of inclination be relatively random across the entire population of only-somewhat-geosync satellites? i.e. why isn't the cylinder satellate constellation centered (and tberefore coaxial) about the true geosync hoop?
- thkru 2y ago
  The dead satellites sit at roughly 0 deg inclination initially and then the moon causes their inclination to shift. Depending on where the moon is in its orbit relative to the satellite it can pull the argument of perigee (lowest point) in different directions. The end result is that the inclinations are all roughly between 0-20 degrees but they all have different RAAN and argument of perigees.
  - ricksunny 2y ago
    Brilliant. As a result I'm reading up on graveyard orbits and end-of-life perturbations from various celestial sources. Also, this gem, whose longitude values roughly correspond to what I'm seeing: last line of: https://en.wikipedia.org/wiki/Geosynchronous_orbit#Geostationary_orbit https://en.wikipedia.org/wiki/Geosynchronous_orbit#Geostatio... : "Geostationary satellites will also tend to drift around one of two stable longitudes of 75° and 255° without station keeping.[21]" It cites SMAD, which on its face is more than good enough for me, but since I don't have a copy handy, it would still be interesting to know why those meridians would represent particularly attractive ones to drift into.
    - cfraenkel 2y ago
      *Dead* satellites are supposed to be boosted into a graveyard orbit so they don't clutter up the neighbourhood for everyone else. Of course if it just fails, and can't be commanded there's not much anyone can do, but that's relatively rare. Most will be drifting at a pretty good clip, +100 km or more above geosynch.

by Sanzig 2y ago

ricksunny 2y ago

All soundng very reasonabke so far, thank you - yet why is the overall cylinder at an incline? If as you describe, why wouldn't the choice of inclination be relatively random across the entire population of only-somewhat-geosync satellites? i.e. why isn't the cylinder satellate constellation centered (and tberefore coaxial) about the true geosync hoop?

thkru 2y ago
The dead satellites sit at roughly 0 deg inclination initially and then the moon causes their inclination to shift. Depending on where the moon is in its orbit relative to the satellite it can pull the argument of perigee (lowest point) in different directions. The end result is that the inclinations are all roughly between 0-20 degrees but they all have different RAAN and argument of perigees.
- ricksunny 2y ago
  Brilliant. As a result I'm reading up on graveyard orbits and end-of-life perturbations from various celestial sources. Also, this gem, whose longitude values roughly correspond to what I'm seeing: last line of: https://en.wikipedia.org/wiki/Geosynchronous_orbit#Geostationary_orbit https://en.wikipedia.org/wiki/Geosynchronous_orbit#Geostatio... : "Geostationary satellites will also tend to drift around one of two stable longitudes of 75° and 255° without station keeping.[21]" It cites SMAD, which on its face is more than good enough for me, but since I don't have a copy handy, it would still be interesting to know why those meridians would represent particularly attractive ones to drift into.
  - cfraenkel 2y ago
    *Dead* satellites are supposed to be boosted into a graveyard orbit so they don't clutter up the neighbourhood for everyone else. Of course if it just fails, and can't be commanded there's not much anyone can do, but that's relatively rare. Most will be drifting at a pretty good clip, +100 km or more above geosynch.