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Kcorbyerd t1_it4mf6c wrote

Reply to comment by funkboxing in China looked at putting a monitoring satellite in retrograde geostationary orbit via the moon by OkOrdinary5299

Yeah the article seems misleading on this point. A retro-GEO orbit is silly, but what it actually says is “orbital informant satellite in retro-GEO.” This makes a huge difference as the informant satellite would be just outside of GEO and would just fly close to the actual GEO instead of in it. That way it could take a peeksie at the stuff in GEO and do a more rapid check on the things in it.

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msur t1_it4ykbl wrote

Wow, that's way different from a satellite that's at Geo-stationary altitude but going backwards. Thanks for clarifying.

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Kcorbyerd t1_it50j26 wrote

Yup, I was initially very confused at the idea, but then I realized what they were talking about and was like oh that is way different than what most people would assume it to be

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wnvalliant t1_it670js wrote

It's retro grade. They are talking about using the moon for a gravity assist to do it in the paper.

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Aceticon t1_it6nufi wrote

A satellite in a prograde GEO circles the Earth at the exact same speed as the Earth rotates so stands still over the same point of the Earth, which is very usefull.

A satellite at the same altitude (i.e. same apoapsis and periapsis) in a retrograde orbit circles the Earth in the exact REVERSE speed of the Earth's rotation, so it will pass over all points on the ground under its orbit two times a day, which is pretty much useless (specifically the "exactly two times a day" part is useless).

Somebody else explained this was meant to actually be a little higher than GEO orbit and going in the opposite direction, so its purpose was to watch the satellites in GEO orbit rather than anything on the planet Earth.

PS: Think I've posted this as answer to the wrong post, but the point still stands.

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wnvalliant t1_it7fkwm wrote

I understand what you mean about drifting above or below the ring but it would still be going pro-grade with respect to the spin of the earth.

Definitely the paper is saying this proposed satellite would be retro-grade. That would reduce visit times for spying on other satellites and other less nice things.

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Aceticon t1_it7nri9 wrote

I think I used the wrong terminology.

By "higher" I meant with a higher Apoapsis and Periapsis, so an orbit further out than GEO.

It's not possible to have an orbit fully above or below "the ring" (I presume you mean the orbital plane) - the best you can do is an orbit which is part of the time above and part of the time below, i.e. with an orbital tilt.

This makes sense if you think of the methaphor were you are rotating a bucket full of water at the end of a rope: if you try and make it go higher in relation to the hand which holds the rope you'll find it just goes down at the other end of the circle, making inclined circle, half the time above that point and half below.

The very same effects that keep an object in orbit by pulling it towards the Earth also pull it down when higher and up when lower, effectivelly forcing the orbit to be in a mathematical plane that includes the Earth, though a plane that can be different than the normal orbital plane.

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wnvalliant t1_itag82b wrote

Only thing I was trying to say to you was that the article from spacenews about the chinese paper was describing an orbit different than you were talking about.

I understood you about the drifting around the main geo belt satelites thing. "the ring" is me using bad terminology for the ring of satellites orbiting the earth, circular, at whatever it is, 42km or whatnot, over the equator, sorry to confuse. Note that those are pro-grade (spinning with the rotation of the earth) and that the Chinese article was talking about going the opposite direction (spining against the rotation of the earth).

It is possible to orbit the earth any way you want as long as you are not too high or low from the earth to get influenced by the atmosphere or the moon or whatever.

You sound like you are into the subject and did great describing things by the way! Sorry about the miscommunication Aceticon...

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