Is it possible to build a sky hook with KAS?

[RainDreamer]

I just read on some spacecraft proplusion methods today and found this on wiki: http://en.wikipedia.org/wiki/Skyhook_(structure)

It makes me wonder, can we replicate this using KAS with a lot of winches stack on top of each others, with a hook/magnet at one end? Then we can place that on some object with sufficient mass and velocity like an orbiting asteroid/space station, and we can just launch stuff to sub orbital trajectory, hookup, then get dragged along to orbit?

It would save a ton of fuel from not doing orbital burn. Though I suspect that the joint might not be strong enough.

[merendel]

I shudder at the thought of that but I'll do a quick rundown of the problems I see so far.

1. line length. No mater how you slice it you cant(baring a few mods) get around the 2.5km load limit. Even if you strung KAS winches togeather you cant get it longer than 2.5km long so you'd need to at least push the payload up that high.

2. Timeing. Asumeing you were fine launching the payload strait up to whatever orbital hight you still have to get to the right spot at the right time. On a vertical launch your hook is going to be blazing past at 2400 kph or a bit less depending on orbit hight. It will be in and out of physics window in 3-4 seconds. Your basicly trying to shoot an arrow through the head of a sewing needle from a hundred KM away. You can aliviate this somewhat by giving it some horizontal componant to the launch but the more you add to make the catch easier the closer you get to achieveing the orbit without the skyhook.

3. Boom. No other way to discribe whats going to happen if you make the catch. At the relitive velocities involved in this stunt I see 3 potential outcomes. First the magnet and your payload meet and mutualy anialate each other. Second it catches safely but the line stretches like a ruberband before snaping violently and most likely riping one or both objects (skyhook or payload) appart. You might get lucky and only loose the line but I doubt it. The third option, if you make the catch and survive the effects of hooking the two things togeather at that velocity your going to have the two ships springing wildly around eachother on the line.

I've seen this in action with skycranes lifting heavy loads off of minmus. Those lines are not ridged, they stretch and bounce. I had my skycrane try to tow a 200t container of metal (extraplanetary launchpads mod) and didnt dock fully first, just draged it to orbit on the rope. I was fine on the initial takeoff as I could carefuly get the slack out before applying more thrust. When I went to circularize however the payload had drifted a bit closer to the ship and caused a slight tug when I throttled up and it snaped taunt. It stretched then swung the 30ton ship violently backwards past the cargo container. They bounced back and forth for a while and developed massive phantom forces. Eventualy the force got bad enough that it snaped the crane off the ship. Dispite cuting thrust after controll was lost enough phantom force was generated that the 200t mass was flung clear out of the kerbin system on an eve crossing trajectory while the crane would have been destined for a steep reentry on kerbin, leaving minmus's SOI in the opposite direction from the other half.

[MarvinKitFox]

Basically, no.

KSP physics, erm I mean fizzics, only operates out to about 2400 meters from the centerpoint of your current vessel.

So Yes, you can build a Skyhook.

It will "forget" to rotate if you go more than 2.4km from it, or it you switch focus to another vehicle further than that.

You will not be able to build a skyhook longer than ~4.8 km, no matter what you try. (short of altering the physics engine's range-of-operation.. there are mods that can do that, but KAS doesnt)

A non-rotating Skyhook would also not work, as the physics engine does not apply a gravity gradient over its range, thus there is no tidal forces making the tether stabile radially, as one would otherwise expect.

Some fun things you *can* do, in the similar line of thought:

1) An orbital, electrically-powered, rotating slingshot. I've managed to get up to about 650m/s out of this.

2) An electrically-powered, rotating, self-climbing Jakob's Ladder with build-in antigrabbity device.

*To use: Link two tanks, half-full, with a nice looooong girder that allows fuel transfer.

*rotate in the plane of your orbit.

*when one tank is closer to the planet, pump its fuel out to the outer tank. Your orbital speed is unchanged but your center-of-mass(thus effective orbital altitude) rises.

*when the full tank rotates to be closer to the planet, pump its fuel out again. Repeat * repeat * repeat.

You get good orbital Altitude for free this way.

Combine these two methods, slap on some solar panels for electric power, and you have a completely free way to throw stuff from LKO almost to the Mun. (or de-orbit your ssto lander without using any fuel at all)

So basically, the spin-and-release bit is feasible, but the capture-a-passing-ship thing is not.

and the limit in tether length limits relative velocity to way under true orbital speeds.

Edited November 19, 2014 by MarvinKitFox

[RainDreamer]

Man, even when the idea is not possible, the explanation of why it is not possible is also fascinating. Rocket science is so fun! I will try to attempt the rotating sling shot method to launch satellites to higher orbit then.

[psyper]

I will try to attempt the rotating sling shot method to launch satellites to higher orbit then.

That would work. I had a similar experience to merendel. Had no docking port to match my payload on the surface of minmus so winched it up instead - it was too big to lock with the crane so I had it dangling there - it basically became a rotating mess with the center of gravity half way along the line - everytime the lifter was in the right direction I would hit the thrusters to eventually pull it up in to a circular orbit. Releasing the payload like a hot potato and sending it in to a higher orbit to collect later. If you meet the kraken just right you'll send your sat clear across the kerbin system - is eeloo a high enough orbit for you ??

[katateochi]

at a glance I'd say no, even if you got the concept working in KSP, actually managing to hook up (while only being able to control 1 vessel at a time) would be really hard I think. As others have said the 2.4km limit is a blocker, but there are mods that can extend that distance. Not sure if that is still true as its been a while since I used it but Romfarer's Lazor mod was able to modify the draw distance, but things can get weird if you make it too big, the game just isn't designed for it.

[TheScareCake!]

2,5, 2,5... Cmon, there are MODS. There, one problem solved, now we have to deal with timing...

[merendel]

2,5, 2,5... Cmon, there are MODS. There, one problem solved, now we have to deal with timing...

still a sticky widget that. worst case with a strait up and down accent your looking at a couple kilometers per second relative velocity. I was wrong in my analogy. not only are you trying to thread a needle from 100km away that needle is on the back of a bullet train Although looking back I futzed up the math too, I suspect I got m/s and km/h confused at some point and then did some converting with some strange results. My only excuse is its a bad idea doing napkin math just before passing out for the night. Either way you are not makeing the catch at that speed on anything but luck and will probably get riped appart for the effort. geting up to speed horizontaly first aliviates this problem somewhat but to get the speeds slow enough your geting close to orbital velocity already.

[RainDreamer]

Well, timing problems would be alleviated if there are just enough hooks to make essentially an orbital transportation ring around kerbin to make the chance that one of them will be a hit a bit higher. Sounds like a very kerbal solution though.

[MerlinsMaster]

Didn't Scott Manley stretch a launch clamp to orbital altitude on one of his Reddit challenges?

[merendel]

Didn't Scott Manley stretch a launch clamp to orbital altitude on one of his Reddit challenges?

I vaguely recall something like that but from memory it required manual editing of the craft file and it only worked in some old versions of the game as it exploited something that was eventualy removed. If you tried the same craft file in the wrong version it would either not load at all or just snap back down to a normal altitude.