Advantages of geosynchronous orbits?

[Markotiks]

Hey everyone. Was just wondering if there were any advantages to putting objects (comm sats, space stations, fuel depots, etc.) into geosynchronous orbits. I'm getting ready to start a new save, which means setting up new comm sat relays (I use the RemoteTech mod) and building new space stations around Kerbin and Mun. Is there any reason to put these objects into gso or is it something that's just neat to do. For example, I believe a recalled the real ISS is in a gso around Earth. If it is, why is it so? Thanks.

[TheTriniFlyer]

Firstly, The International Space Station is not Geo-synchronous orbit.

GSO's are beneficial as the craft stays in the same place from Earth/Kerbin's perspective. Meaning that if you are In a GSO over KSC, there will be direct contact with KSC constantly 365 days a year. This is because your orbital velocity matches the speed at which the planet rotates on its axis, for further reading: http://en.wikipedia.org/wiki/Geo-synchronous_orbit

[Scotius]

No, ISS is not geostationary - it's in Low Earth Orbit about 400 km above our heads. Geostationary is 35 000 km (roughly). Advantages of GSO? Field of view - satellite placed there sees entire hemisphere of the planet at once. It's invaluable for comunications and meteorological satellites.

[deadshot462]

The real ISS is NOT in GSO around Earth, it's on an inclined Low Earth Orbit.

A few reasons I can think of as an advantage in real life:

-Constant line of sight for communications to a specific spot

-Constant view of the same area for weather monitoring

[drakesdoom]

They are also very nice in real life as you can tune a dish in for communication with one by hand and bolt it down. No fancy motors or tracking to deal with.

[stibbons]

I like to use geosynchronous orbit for my comms satellites because it's a nice way to make sure surface transmitters don't get periodic blackspots.

Putting a station in synchronous orbit, or at least an equatorial orbit, would be a nice way to make transit to and from the surface more predictable. But that's probably heavily negated by how far out it is. I'd rather wait for a transfer window for a low kerbin orbit station than have to get out to the much higher synchronous orbit.

[Markotiks]

Thanks for the reply guys. Can't recall where I heard that info on the ISS, but wow was I way off on that and feel pretty stupid about it. Anyway, I could definitely see the advantages for communications in real life and in KSP so I'll set my comm sat relay as such. As far as space stations I think I'll stick with a low Kerbin orbit and save my fuel.

[Xeldrak]

Well, advantage of GSO:

-You allways see the same spot of earth

Disadvantage:

-you never see anything else of earth

-also - quite far out, so is need a lot more fuel and heavier rockets than LEO

So, it's usefull for Communication or TV, because the Satelite is allways "on the same spot" in the night sky. Is also used for weathersurveilance (Meteosat are all in GSO)

[Motokid600]

No, ISS is not geostationary - it's in Low Earth Orbit about 400 km above our heads. Geostationary is 35 000 km (roughly). Advantages of GSO? Field of view - satellite placed there sees entire hemisphere of the planet at once. It's invaluable for comunications and meteorological satellites.

Sorry to go off topic here, but this has been on my mind since figuring out gso's. The space elevator concept(s). Are they bs? The station would have to be orbiting at 35000km with a cable just as long... No? Making it completely impractical.

[lyndonguitar]

Sorry to go off topic here, but this has been on my mind since figuring out gso's. The space elevator concept(s). Are they bs? The station would have to be orbiting at 35000km with a cable just as long... No? Making it completely impractical.

Nope, the elevator itself doesn't necessary have to reach 35000km. theoritically It can be 200km, 800km, 1123km, any distance as long as the structure can handle it. The problem is current designs and structural models need the elevator to be way above 35000km to be able to work. but theoretically, any distance will work.

the reason satellites need to reach 35000km because the orbital velocity there matches the rotation of the earth, so it would essentially move at the same rates, making you "stationary" at one point in the sky. It's like car racing. A car has a speed of 30mph, a car beside it matches that speed. the result is that they would "look" stationary in relative to each other.

The space elevator is different. It is tethered to the ground, therefore it has no velocity relative to the ground. It is literally stationary.

To make it easier to imagine. If you jump at the top of the space elevator. You would fall back to earth. where as if you are in a spacecraft orbiting geo-s and jump out, you would not fall back to earth.

Edited June 12, 2013 by lyndonguitar

[Brun]

The space elevator is different. It is tethered to the ground, therefore it has no velocity relative to the ground. It is literally stationary.

To make it easier to imagine. If you jump at the top of the space elevator. You would fall back to earth. where as if you are in a spacecraft orbiting geo-s and jump out, you would not fall back to earth.

Quite right, meaning that you couldn't dock a ship in orbit with a space elevator - it'd go whizzing by at an extremely high (orbital) speed. The advantage of having a space elevator is that you could carry rocket parts up there and launch from completely outside the atmosphere, which would save you a ton of delta-v (the end result would be smaller, less-expensive rockets).

EDIT: Now that I think about it, your second sentence is only true if the space elevator goes to a relatively low (on the scale of orbits) altitude. Taking one step off of a space elevator that reaches GSO (or slightly beyond) would put you into GSO. The same goes for anything above GSO (that is, you wouldn't fall back to Earth from a space elevator once you got above geosynchronous altitudes). In fact, a long enough space elevator would place you at escape velocity when you jumped from it.

Edited June 12, 2013 by Brun

[haltux]

Nope, the elevator itself doesn't necessary have to reach 35000km. theoritically It can be 200km, 800km, 1123km, any distance as long as the structure can handle it. The problem is current designs and structural models need the elevator to be way above 35000km to be able to work. but theoretically, any distance will work.

the reason satellites need to reach 35000km because the orbital velocity there matches the rotation of the earth, so it would essentially move at the same rates, making you "stationary" at one point in the sky. It's like car racing. A car has a speed of 30mph, a car beside it matches that speed. the result is that they would "look" stationary in relative to each other.

The space elevator is different. It is tethered to the ground, therefore it has no velocity relative to the ground. It is literally stationary.

To make it easier to imagine. If you jump at the top of the space elevator. You would fall back to earth. where as if you are in a spacecraft orbiting geo-s and jump out, you would not fall back to earth.

A space elevator is geostationary. 36000 km average. Otherwise it falls. Unless it is rigid enough and then it is called a tower.

Edited June 12, 2013 by haltux

[lyndonguitar]

EDIT: Now that I think about it, your second sentence is only true if the space elevator goes to a relatively low (on the scale of orbits) altitude. Taking one step off of a space elevator that reaches GSO (or slightly beyond) would put you into GSO. The same goes for anything above GSO (that is, you wouldn't fall back to Earth from a space elevator once you got above geosynchronous altitudes). In fact, a long enough space elevator would place you at escape velocity when you jumped from it.

Yup, I was talking about very low space elevator altitudes, which imo the only way space elevators could be useful.

Making Space elevators that run past GSO would be much much harder and useless, like motokid has said.

EDIT: Now that I also think about it, very, very long space elevators could actually useful in interplanetary explorations. The elevator would serve as the catapult, Launching ships to Sol Orbit without even using a single thrust. imagine the delta-v saved by it!

A space elevator is geostationary. Otherwise it falls. Unless it is rigid enough and then it is called a tower.

Exactly my point, current designs limit the elevator to geostationary orbits, but theoretically, as I said, If the structure can support it, It can be any distance. making it a tower as you said

Edited June 12, 2013 by lyndonguitar

[Nibb31]

The whole point of the space elevator concept is that it uses the properties of a GEO to stay up and to keep the cable in tension. If you're not in GEO, then you have a tower, not an elevator. A 200km tower cannot work, for (at least) two reasons:

- A construction material capable of supporting the weight of a 200km tower simply does not exist, and probably never will. It would have to be thousands of times larger than the largest thing we have ever built. It's simply impractical.

- Reaching orbit is about speed, not altitude. If you go up 200km with 0 velocity, you fall down. If you want to get to orbit, you still need to accelerate to 25000km/h from the top of your tower. You have solved nothing.

The space elevator, as it's usually envisioned, must actually have its center of mass in GEO, which means that it must reach down 36000km over the equator, but it must also reach up several thousand more with a counterweight on the end. The counterweight reaching up must have the same mass as the cable reaching down.

The idea is to use a very thin carbon nanotube fiber, which is the lightest and strongest material that we know of. You would need several tons of it on a reel to make up the first 36000km strand. You launch the reel to GEO, as well as a counterweight reel (which must have the same mass, but doesn't need to be carbon nanotube). You unreel the fiber down and the counterweight up, until the fiber reaches the ground, then you attach it to something solid. After this, you can start building your elevator by sending up climbers. Each climber carries more fiber strands, wrapped around the first one, until you've built a solid cable. Then you can build 3 or 4 more adjacent cables for redundancy.

That's the idea, and it can only work from a GEO orbit. The only problem is that the longest carbon nanotubes that we have made in a lab are 1cm long, so the technology isn't ready yet. There are still a lot of details to be ironed out, like anchorage, station-keeping, static electricity, reliability, climber design and transit time. It actually takes quite a while to travel 36000km, even if the climbers are fast... However, as soon as we get the nanotubes figured out, the concept will be much more practical than a tower, a railgun, or some of the other wacky concepts out there.

[UNSC]

Wouldn't your assent "pull" the orbital elevator out of orbit over time? Nothing is free...

[Nibb31]

Yes it would. Of course, the station at the elevator's CoM needs some sort station-keeping. That can probably be provided by SEP thrusters because you don't need high thrust. You can also adjust the counterweight on its own cable to compensate somewhat.

Personally, I find the Space Elevator a bit too ambitious, and the atmospheric part of the cable too problematic to be practical. I kind of prefer the "orbital trapeze" concept. This is how it works.

Instead of having your space elevator in GEO, imagine a rotating version in LEO. Its Center of Mass would be, for example, on a circular 200x200km orbit, with two 100km long cables extended either way and rotating on its axis like a giant cartwheel. It doesn't have to be equatorial. The end of each cable comes down to an altitude of 100km, at a suborbital speed, where a suborbital spaceplane (something like the XCOR Lynx or SpaceShipOne) would catch it, or dock with it. From there, you can climb a 100km elevator to the CoM station and get to orbit, or wait until the trapeze slings you up to your 300km altitude at a much higher speed.

I made a crude diagram (yeah, I suck !)

You lose some energy in the process, but again, you can use SEP to raise the orbit of the station because you don't need a high thrust and you can reboost over a longer period. Some energy is also fed back into the system by returning vehicles. Yes, it's wacky, and the actual engineering is complex, but it seems less ambitious than the space elevator.

Edited June 12, 2013 by Nibb31

[Latcarf]

@nibb This solves my thought experiment, thank you.

I have been thinking for a few months about a station that would serve as a Refuel Depot AND a kinetic...[i really cant think of the right word to use, lets call it a] kinetic-spaceship-tosser. My broken idea was a dense spherical station that could spin it's shell and throw a ship in the right direction in order to save transfer fuel. But when the ship leaves the station, the center of mass will shift too abruptly for the station to compensate.

The model you propose here is a good replacement. And even if the SCIENCE doesn't pan out, its fun to think about. Where does this concept come from?

Great thread:

http://forum.kerbalspaceprogram.com/showthread.php/30268-How-do-you-connect-a-spinning-centrifuge-to-a-non-rotating-central-collumn?highlight=centrifugal+force

[Nibb31]

@Latcarf, I just found the official name it, the skyhook: http://en.wikipedia.org/wiki/Skyhook_(structure)

Like many space things, the idea was fielded by Arthur C Clarke, but the first serious study on the subject was from this Boeing proposal:

http://www.niac.usra.edu/files/library/meetings/annual/jun01/391Grant.pdf

[Latcarf]

Awesome, thank you.