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https://en.wikipedia.org/wiki/Graveyard_orbit https://en.wikipedia.org/wiki/Graveyard_orbit puts the difference in delta V requirements for a geo-sync orbit at

https://en.wikipedia.org/wiki/Graveyard_orbit https://en.wikipedia.org/wiki/Graveyard_orbit puts the difference in delta V requirements for a geo-sync orbit at ~1500m/s to de-orbit vs 11m/s to get boost up to graveyard orbit.

penagwin 7y ago
Oh... Yeah that explains it for sure.
- zymhan 7y ago
  Essentially, you need a ton of fuel to take a satellite back down to earth.
staticautomatic 7y ago
So it's more expensive to design satellites that can de-orbit?
- mumblemumble 7y ago
  It depends on where they are. Take a look at the diagram on that Wikipedia page linked above - a geosynchronous orbit is very high; 50 or so times further out than the ISS, for example. And that's about as far out as we ever put satellites, so you've only got to boost it by a little bit to get out of the way of active space traffic.
- penagwin 7y ago
  From Geostationary Orbit yes, for other orbits it can be the opposite. Satellites in lower positions actually have to maintain their orbit due to orbital decay. Because Geostationary orbit is so far away, there's a lot less decay. For example SpaceX's starlink only has a lifespan of 5 years, and this is because of their low orbit.
dls2016 7y ago
What's the physical intuition here? Is it that you want the de-orbit to hit the atmosphere at a shallow angle instead of plunging to earth?
- jessaustin 7y ago
  A small change in momentum requires less energy than a large change in momentum.
  - jessaustin 7y ago
    Umm, wat? Does someone seriously disagree with this?
- Dylan16807 7y ago
  It doesn't de-orbit at all. For physical intuition, uh, the atmosphere is a hundred times further away than the graveyard orbit.
- pdonis 7y ago
  > Is it that you want the de-orbit to hit the atmosphere at a shallow angle instead of plunging to earth? De-orbiting to hit the atmosphere at a shallow angle would actually take slightly less delta-v than de-orbiting to a straight plunge to Earth. But both are much larger than the delta-v required to get to a graveyard orbit.
- penagwin 7y ago
  Geostationary orbit is REALLY far away from earth (and also the atmosphere) compared to other orbits, but it's very special and so we want to keep as little junk in it as possible. Other types of orbits are so low, that they have to keep maintaining their orbit or they'll decay into the atmosphere. So we're in a stable orbit with a high periapsis (closest part of our orbit to earth). To de-orbit we need to lower the periapsis so that it touches the atmosphere, and on each pass the satellite will slow down, further lowering the apoapsis and periapsis. The problem is that to do this we have to burn all that horizontal velocity that's keeping us in orbit in the first place, which is a crapload. An alternative is to instead change the orbit so it's no longer in geostationary orbit and potentially interfering with live satellites, so instead they just push the satellite further out into the "graveyard orbit". There's 100x difference in the needed energy for the two methods, and I'm sure you can see why most would opt for the graveyard orbit. EDIT: To add, it's actually rather difficult to "plunge into earth". To do this you need to burn all of your horizontal velocity (I think that's around 3.07 km/s in geostationary orbit?). Reaching the sun is actually really difficult as well for the same reason, you have to lose all of your horizontal velocity, and earth has a ton.
deleted 7y ago
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leni536 7y ago
Interestingly it takes slightly less delta v to send the satelite out of Earth's gravity well from a geo-sync orbit than to deorbit it.
- greglindahl 7y ago
  Yes, direct-to-GEO missions sometimes dispose of the upper rocket stage in solar orbit for this reason.
hanniabu 7y ago
Interesting, but then we also need to somehow fly through that when launching outer space rockets. Amazing how we can avoid the debris.
- DuskStar 7y ago
  The graveyard orbits are ~40,000km above the earth's surface - there's a LOT of space to avoid debris in. The issue with space debris is with orbits in the 500-5,000km range. Lower than that and the debris will reenter quickly, higher and you start getting spread out enough to not matter as much.
  - dreamcompiler 7y ago
    > The graveyard orbits are ~40,000km above the earth's surface They're also in a ring in the plane of the equator. Easy to avoid.
    - hanniabu 7y ago
      I had no idea about this. How do they get it aligned with the equator? (I'm assuming when the stuff is in operation that it's not just around the equator)
      - pacificmint 7y ago
        No, geostationary satellites actually are in a plane around the equator. That’s the only way geostationary orbit works. Otherwise they’d be moving with respect to the surface. So they already are aligned and just need to be moved to a higher orbit.
      - 0xffff2 7y ago
        Geostationary satellites are in fact in a ring around the equator. No other orbit would keep them stationary in the sky. Geosynchronous orbits are orbits at the same altitude, but not necessarily aligned with the equator. Most of what I know about orbital mechanics I learned from Kerbal Space Program, but given that it's very expensive to change orbital inclination, I would be shocked if geosynchronous satellites were returned to a flat inclination before being disposed of.

penagwin 7y ago

Oh... Yeah that explains it for sure.

zymhan 7y ago
Essentially, you need a ton of fuel to take a satellite back down to earth.

staticautomatic 7y ago

So it's more expensive to design satellites that can de-orbit?

mumblemumble 7y ago
It depends on where they are. Take a look at the diagram on that Wikipedia page linked above - a geosynchronous orbit is very high; 50 or so times further out than the ISS, for example. And that's about as far out as we ever put satellites, so you've only got to boost it by a little bit to get out of the way of active space traffic.
penagwin 7y ago
From Geostationary Orbit yes, for other orbits it can be the opposite. Satellites in lower positions actually have to maintain their orbit due to orbital decay. Because Geostationary orbit is so far away, there's a lot less decay. For example SpaceX's starlink only has a lifespan of 5 years, and this is because of their low orbit.

dls2016 7y ago

What's the physical intuition here? Is it that you want the de-orbit to hit the atmosphere at a shallow angle instead of plunging to earth?

jessaustin 7y ago
A small change in momentum requires less energy than a large change in momentum.
- jessaustin 7y ago
  Umm, wat? Does someone seriously disagree with this?
Dylan16807 7y ago
It doesn't de-orbit at all. For physical intuition, uh, the atmosphere is a hundred times further away than the graveyard orbit.
pdonis 7y ago
> Is it that you want the de-orbit to hit the atmosphere at a shallow angle instead of plunging to earth? De-orbiting to hit the atmosphere at a shallow angle would actually take slightly less delta-v than de-orbiting to a straight plunge to Earth. But both are much larger than the delta-v required to get to a graveyard orbit.
penagwin 7y ago
Geostationary orbit is REALLY far away from earth (and also the atmosphere) compared to other orbits, but it's very special and so we want to keep as little junk in it as possible. Other types of orbits are so low, that they have to keep maintaining their orbit or they'll decay into the atmosphere. So we're in a stable orbit with a high periapsis (closest part of our orbit to earth). To de-orbit we need to lower the periapsis so that it touches the atmosphere, and on each pass the satellite will slow down, further lowering the apoapsis and periapsis. The problem is that to do this we have to burn all that horizontal velocity that's keeping us in orbit in the first place, which is a crapload. An alternative is to instead change the orbit so it's no longer in geostationary orbit and potentially interfering with live satellites, so instead they just push the satellite further out into the "graveyard orbit". There's 100x difference in the needed energy for the two methods, and I'm sure you can see why most would opt for the graveyard orbit. EDIT: To add, it's actually rather difficult to "plunge into earth". To do this you need to burn all of your horizontal velocity (I think that's around 3.07 km/s in geostationary orbit?). Reaching the sun is actually really difficult as well for the same reason, you have to lose all of your horizontal velocity, and earth has a ton.

deleted 7y ago

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leni536 7y ago

Interestingly it takes slightly less delta v to send the satelite out of Earth's gravity well from a geo-sync orbit than to deorbit it.

greglindahl 7y ago
Yes, direct-to-GEO missions sometimes dispose of the upper rocket stage in solar orbit for this reason.

hanniabu 7y ago

Interesting, but then we also need to somehow fly through that when launching outer space rockets. Amazing how we can avoid the debris.

DuskStar 7y ago
The graveyard orbits are ~40,000km above the earth's surface - there's a LOT of space to avoid debris in. The issue with space debris is with orbits in the 500-5,000km range. Lower than that and the debris will reenter quickly, higher and you start getting spread out enough to not matter as much.
- dreamcompiler 7y ago
  > The graveyard orbits are ~40,000km above the earth's surface They're also in a ring in the plane of the equator. Easy to avoid.
  - hanniabu 7y ago
    I had no idea about this. How do they get it aligned with the equator? (I'm assuming when the stuff is in operation that it's not just around the equator)
    - pacificmint 7y ago
      No, geostationary satellites actually are in a plane around the equator. That’s the only way geostationary orbit works. Otherwise they’d be moving with respect to the surface. So they already are aligned and just need to be moved to a higher orbit.
    - 0xffff2 7y ago
      Geostationary satellites are in fact in a ring around the equator. No other orbit would keep them stationary in the sky. Geosynchronous orbits are orbits at the same altitude, but not necessarily aligned with the equator. Most of what I know about orbital mechanics I learned from Kerbal Space Program, but given that it's very expensive to change orbital inclination, I would be shocked if geosynchronous satellites were returned to a flat inclination before being disposed of.