Space Elevators, Sky hooks and the like

[Ittiz]

So I've been experimenting with creating a space elevator. I found with the way the game is currently programmed it seems that it's not possible to have one on the planet Kerbin. I modded the KAS mod to make a space elevator. Then I tied it to the ground and try to launch a rocket to geostationary orbit. It doesn't work so well. It seems once you get too far away from the ends of the cable (about 10km) it disconnects. So I decided to attempt the same thing on Minmus due to it's low gravity and speedy rotation. I've only had marginal success. I managed to create a sky hook (by accident when the cables disconnected and flew straight up into space) that could hold my ship in low orbit at slow speeds (the cable extended upwards 10 to 15 km). I can land on Minmus, attach the cables, but I don't know how high geostationary is for that moon. If it's past 10km or so it probably won't work so well. Does anyone know? It would help a lot and I don't have the time to look at the math at the moment. Has anyone else tried this sort of thing with success? It'd be cool if I could hoist cargo into orbit on a KAS grapple!

[NASI Director]

If I'm not mistaken, Minmus' Geostationary orbit is beyond its SOI, so yeah.

EDIT: No, it's not. But it's much higher than 10km, ~357km.

[Ittiz]

Ahh crap ok. I tried it at 30 km, but I waited half an hour for the cables to descend to the surface in Minmus' low gravity but when I got impatient and descended to check how long they were they only made it to 5km. Also it's was extremely difficult to maintain that position while it descends, requiring second by second manual adjustments to my elevation.

[Geschosskopf]

Scott Manley's take on the subject:

[Ittiz]

Well I didn't use any hacks (per se, I only modded KAS to have a cable length as long as I wanted (Well I also turned down the springyness since the backlash on a 5km cable can tear a ship in two)). Some invincible tower that drops your ship right in to LKO is a little ridicules and unrealistic. I think the physics of the game are pretty solid (talking about orbital mechanics and not drag models), but loading and unloading of parts and ships from memory at a certain distance is the issue.

[Geschosskopf]

Well I didn't use any hacks (per se, I only modded KAS to have a cable length as long as I wanted (Well I also turned down the springyness since the backlash on a 5km cable can tear a ship in two)). Some invincible tower that drops your ship right in to LKO is a little ridicules and unrealistic. I think the physics of the game are pretty solid (talking about orbital mechanics and not drag models), but loading and unloading of parts and ships from memory at a certain distance is the issue.

Well, how realistic is it to have a cable as long as the altitude of geostationary orbit in a container about 1/2 the size of Kerbal?

In any case, assuming you can overcome all the technical difficulties imposed by both the game engine and KAS and actually get a KAS unit in geostationary orbit over KSC and hook onto payloads with it, and can hoist payloads fast enough to clear the mountains west of KSC without pulling said payloads apart or your winch down from the sky, you've still got a problem. Unless you take the time to hoist the payload all the way up to geostationary altitude, the payload will still require a lot of fuel because at any lower altitude, its orbital velocity upon release will be less than required for its altitude. The lower you release the payload, the more fuel and TWR it will need to get into a stable orbit before it falls back into the atmosphere. This kinda defeats the purpose of having a space elevator based on a cable hanging from above.

[SRV Ron]

The physic limits of the game prevents one from constructing a space elevator. In real life, it may be possible to make the cable from ultra strength carbon nanotubes. Getting the first strands of that cable into space and anchoring it to the Earth's equator and to a counterweight way beyond geosynchronous orbit is another matter. It also becomes a target for orbiting satellites that would promptly cut it dropping the cable to Earth and flinging the rest into a solar orbit.

[Tygroux]

An alternative solution would be to set up a Station in Geosynchronous Orbit with the Orbital Construction Mod.

Then we would need to be able to transfer ressources.

I think the lazor mod does that. Below craft unload point?

It would be like a Space Elevator, instead of using cables we would be use beams of [sciencemagic], converted back to matter in orbit..

[Ittiz]

Yeah using KAS is realistic if you're assuming the cables are nano tubes. However to make the game easier Squad increased all the planet densities by an order of magnitude. Making them much tinier and causing them to have a much smaller SOI. A good example of this is Jool is a gas planet in the game but has almost exactly the same size and density characteristics as the planet Venus IRL. So a space elevator could probably be built from the surface of Kerbin without using any fancy nano tubes. Also what I was doing was a test.

If the test had succeeded what I was going to do was attach cables to the ground at the KSC. Then have two ships attached to the cable in space. A smaller one below geostationary and a larger one beyond it, maybe a third one geostationary. When something was going to be hauled into space, the smaller one closer to Kerbin would release a cable which would descend to Kerbin. There would be a few cables attaching the stations together. One of which would actually be two cables attached to some kind of carrier with two winches attached to each station. That way objects could be ferried from one to the other. So the load could be transferred to the ferry and pulled up the rest of the cable by the station beyond geostationary. If you wanted to release it at geostationary you would just have to stop the winch at that point and release the cargo.

On the other hand my accidental sky hook did work around Minmus. Although I didn't use it to make any low energy orbital transfers. The gravity at Minmus is already so low anyway you could reach escape velocity with a sneeze just about.

Edited August 31, 2013 by Ittiz
grammer

[Epthelyn]

Yeah using KAS is realistic if you're assuming the cables are nano tubes. However to make the game easier Squad increased all the planet densities by an order of magnitude. Making them much tinier and causing them to have a much smaller SOI. A good example of this is Jool is a gas planet in the game but has almost exactly the same size and density characteristics as the planet Venus IRL. So a space elevator could probably be built from the surface of Kerbin without using any fancy nano tubes. Also what I was doing was a test.

Actually, you'd still need the nano tubes. The SoIs for each body are smaller than their real life counterparts, but the forces exerted by them are not. You'd still need incredibly strong materials even over 1/10 of the distance.