Rotorvator

[Stevex]

A momentum exchange tether is a kind of space tether that could theoretically be used as a launch system, or to change spacecraft orbits. Momentum exchange tethers create a controlled force on the end-masses of the system due to the pseudo-force known as centrifugal force. While the tether system rotates, the objects on either end of the tether will experience continuous acceleration; the magnitude of the acceleration depends on the length of the tether and the rotation rate. 

https://en.wikipedia.org/wiki/Momentum_exchange_tether

I don't know if this possible in KSP currently but it is a device that could lead to cheap space access IRL although it needs very accurate  docking to use. IRL it could be solar powered  reacting against the atmosphere or a counterweight (alternative cable).

Compared with a space elevator it is much cheaper to build and is scalable, working with lengths of 1km to hundreds of km.

It would be a useful aid to regain orbit from somewhere like Venus , from a cloud city, where rocket fuel is in short supply.  It would also be cheap to build on planets and objects with no atmosphere where in theory you could walk into it from the ground and release in orbit.

 

[Bej Kerman]

Also called skyhook for those who were expecting something aircraft-related from the title

[pandaman]

 

1 hour ago, Bej Kerman said:

Also called skyhook for those who were expecting something aircraft-related from the title

I thought the title referred to gardening or terrain deformation.  

[K^2]

The problem with these, from perspective of replicating them in KSP, is that the more velocity you want to gain from it, the larger the arm has to be, since you want to avoid extreme centrifugal stress in the structure. There are some small moons in KSP for which this is viable, but they have no atmosphere. And if there is no atmosphere, you're better off building a catapult - and people have done that. The benefit of the skyhook is that it stays above the atmosphere and can boost a suborbital craft to orbital. And for that to make sense in KSP you'd need an arm many kilometers in length, which you can't dock with due to the loading range limits even if you could build one.

You could, potentially, mod the loading and physics ranges in KSP to make this work, but building multi-kilometer megastructures comes with all kinds of other problems there.

For KSP2, that's a more interesting question. We haven't really heard much about physics since a blog from a while back, and I don't think there was anything there that would address this particular kind of megastructure. We ought to be able to build things that are much bigger, but I don't know if we'd be able to build something this big, and whether it'd work as expected.

Other than that, though, so long as you can build a ship that's many kilometers long, get it spinning fast enough, and manage to dock with it, the principle is solid enough to work. Best part is that unlike the real world, you don't have to deal with tidal forces, so you don't have to worry about any kind of weird oscillations building up. It's really just a question of how big of a ship KSP2 can handle. It'd be an interesting thing to try out as soon as some form of orbital construction becomes viable in the game.

[Bej Kerman]

1 hour ago, K^2 said:

For KSP2, that's a more interesting question. We haven't really heard much about physics since a blog from a while back, and I don't think there was anything there that would address this particular kind of megastructure. We ought to be able to build things that are much bigger, but I don't know if we'd be able to build something this big, and whether it'd work as expected.

Other than that, though, so long as you can build a ship that's many kilometers long, get it spinning fast enough, and manage to dock with it, the principle is solid enough to work. Best part is that unlike the real world, you don't have to deal with tidal forces, so you don't have to worry about any kind of weird oscillations building up. It's really just a question of how big of a ship KSP2 can handle. It'd be an interesting thing to try out as soon as some form of orbital construction becomes viable in the game.

But, just like in the real world, you'd have barely a second of error margin to deal with. If you're too late, ten too many centimeters to the right, etc. the docking port is going back to space without you. An autopilot sounds somewhat necessary for the idea unless you don't mind having it happen in the background.

[K^2]

22 minutes ago, Bej Kerman said:

But, just like in the real world, you'd have barely a second of error margin to deal with. If you're too late, ten too many centimeters to the right, etc. the docking port is going back to space without you. An autopilot sounds somewhat necessary for the idea unless you don't mind having it happen in the background.

The margin is nowhere near that tight. You still have maneuvering engines to get into position and dock, no different than when you're docking with a station. You can't adjust your intercept by going to higher/lower orbit, so you have to be within a few hundred meters, but that's fairly reasonable. There's also a bit of an urgency to dock because the suborbital craft is being pulled down with nearly the full gravity, and the docking port of the skyhook is accelerating up at whatever the centripetal acceleration is. So you might be trying to, effectively, dock to a craft that's accelerating away from you at something like two gravities. That's obviously trickier, and you want to get through it fast so as not to burn too much fuel, but it's basically an identical problem, logistically, as trying to land on a small platform on a world with similar gravity - you are effectively performing the same maneuvers.

Under real world conditions, the fact that this leads to a very narrow margin for error is what makes the timing requirements so much more strict and leads to a need for precise automation. But that's a matter of safety. In KSP, if you fail on the first attempt, you reload a quick save. People do far more reckless landings in the game than what this would require.

[Stevex]

I put this in the KSP2 section as I am hoping the developers might pay attention and allow for this and I presume space elevators by having very long high strength cable. On a similar theme we might have a mission to build a sunshade for planets to terraform them using very large sails at the Lagrange point.

i agree the error margin for the skyhook is very small, so it would be time critical to be at the correct place at the correct time . This is something that could be automated. I have high hopes for KSP2 so what ever I can imagine and is scientifically possible I would expect could be added  by the developers or modders.

1 minute ago, K^2 said:

The margin is nowhere near that tight. You still have maneuvering engines to get into position and dock, no different than when you're docking with a station. You can't adjust your intercept by going to higher/lower orbit, so you have to be within a few hundred meters, but that's fairly reasonable. There's also a bit of an urgency to dock because the suborbital craft is being pulled down with nearly the full gravity, and the docking port of the skyhook is accelerating up at whatever the centripetal acceleration is. So you might be trying to, effectively, dock to a craft that's accelerating away from you at something like two gravities. That's obviously trickier, and you want to get through it fast so as not to burn too much fuel, but it's basically an identical problem, logistically, as trying to land on a small platform on a world with similar gravity - you are effectively performing the same maneuvers.

Under real world conditions, the fact that this leads to a very narrow margin for error is what makes the timing requirements so much more strict and leads to a need for precise automation. But that's a matter of safety. In KSP, if you fail on the first attempt, you reload a quick save. People do far more reckless landings in the game than what this would require.

I would imagine you would use two craft with a catch cable between them (or one craft with two arms supporting the cable), which would catch the skyhook when it came round (similar to the arrestor hook system on aircraft carriers). 

[magnemoe]

1 hour ago, K^2 said:

The problem with these, from perspective of replicating them in KSP, is that the more velocity you want to gain from it, the larger the arm has to be, since you want to avoid extreme centrifugal stress in the structure. There are some small moons in KSP for which this is viable, but they have no atmosphere. And if there is no atmosphere, you're better off building a catapult - and people have done that. The benefit of the skyhook is that it stays above the atmosphere and can boost a suborbital craft to orbital. And for that to make sense in KSP you'd need an arm many kilometers in length, which you can't dock with due to the loading range limits even if you could build one.

You could, potentially, mod the loading and physics ranges in KSP to make this work, but building multi-kilometer megastructures comes with all kinds of other problems there.

For KSP2, that's a more interesting question. We haven't really heard much about physics since a blog from a while back, and I don't think there was anything there that would address this particular kind of megastructure. We ought to be able to build things that are much bigger, but I don't know if we'd be able to build something this big, and whether it'd work as expected.

Other than that, though, so long as you can build a ship that's many kilometers long, get it spinning fast enough, and manage to dock with it, the principle is solid enough to work. Best part is that unlike the real world, you don't have to deal with tidal forces, so you don't have to worry about any kind of weird oscillations building up. It's really just a question of how big of a ship KSP2 can handle. It'd be an interesting thing to try out as soon as some form of orbital construction becomes viable in the game.

This, its also another problem docking with an skyhook with an suborbital plane has some challenges. First challenge is hitting something in orbit with an suborbital rocket is hard, its an anti satellite weapon. 
But that you need to do is match velocity with the hook at an very narrow window who is significantly harder than  hitting it. 

Yes at least one player has managed to intercept an suborbital craft on Eve, docket with it and then gotten up to orbital velocity but I say that is a skill few have. 

[Bej Kerman]

25 minutes ago, K^2 said:

The margin is nowhere near that tight. You still have maneuvering engines to get into position and dock, no different than when you're docking with a station. You can't adjust your intercept by going to higher/lower orbit, so you have to be within a few hundred meters, but that's fairly reasonable. There's also a bit of an urgency to dock because the suborbital craft is being pulled down with nearly the full gravity, and the docking port of the skyhook is accelerating up at whatever the centripetal acceleration is. So you might be trying to, effectively, dock to a craft that's accelerating away from you at something like two gravities. That's obviously trickier, and you want to get through it fast so as not to burn too much fuel, but it's basically an identical problem, logistically, as trying to land on a small platform on a world with similar gravity - you are effectively performing the same maneuvers.

Under real world conditions, the fact that this leads to a very narrow margin for error is what makes the timing requirements so much more strict and leads to a need for precise automation. But that's a matter of safety. In KSP, if you fail on the first attempt, you reload a quick save. People do far more reckless landings in the game than what this would require.

I think you are vastly overestimating how much help quicksaves are for a task that is literally best suited for a robot.

If you can dock a spaceplane to a rocket that's travelling through the atmosphere at supersonic speeds and accelerating upwards at 2g, and maybe post the recording here for everyone to witness, next drink is on me and I will take the idea of a manual skyhook docking seriously.

[K^2]

On 2/13/2023 at 3:46 AM, magnemoe said:

First challenge is hitting something in orbit with an suborbital rocket is hard, its an anti satellite weapon.

Anti-satellite weapon has a huge relative velocity on impact and full orbital speeds in absolute terms. A skyhook docking happens at relative speeds in tens of meters per second, allowing for terminal maneuvering, and the absolute speeds you are dealing with can be nearly half an order of magnitude lower. These two problems aren't even close.

On 2/13/2023 at 3:57 AM, Bej Kerman said:

If you can dock a spaceplane to a rocket that's travelling through the atmosphere at supersonic speeds and accelerating upwards at 2g, and maybe post the recording here for everyone to witness, next drink is on me and I will take the idea of a manual skyhook docking seriously.

You're on. Stock parts, airbreather jet plus 100m/s or so of orbital for maneuvering and docking sounds good enough? And I'll be using straight up save file hacks to create a skyhook I can actually dock with and probably some mods to extend the physics range.

I'm anticipating about 1km/s in suborbital just above Kerbin's atmosphere where I'm meeting the hook, and that's going to require a 200km arm to give me that 2g difference. On release, I should have escape from Kerbin plus about 400m/s, which is enough for a number of interplanetary missions.

Manual flight, using only stability assists available in the game, but I reserve the right to have some external calculator tools running to make quick estimates for corrections I'm going to need both for the rendezvous and the actual docking. It'd make for a tight departure window and some precise flying, but so long as I have a list of known checkpoints along the route, not harder than other missions I've flown before.

Edit: I'm realizing that modding a sky hook into KSP is not going to be this straight forward. Even with extended physics ranges, 200km+ is going to be troublesome for a physics object. I'm trying to make a fake "planet" for it with Kopernicus, but that has issues too, since I don't want to alter gravity in the area, and trying to make the hook be a landed part far outside the SoI is not going well. I might have to find another way to fake this. If anyone has ideas, I'm open to suggestions. All I need is a docking port in the correct trajectory that I can actually interact with.

Edited February 18, 2023 by K^2