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Comment by hirundo | Hacker News Reader

> But if you miss, boy are you fucked.

Imagine closing in on Mars knowing that if you fuck up a super-orbital speed, split second maneuver by more than a couple of meters you will drift in space until asphyxiated. It makes a carrier landing seem bland.

If you carry enough fuel to decelerate without the tether it defeats the purpose of the tether.

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The comparison between tethers and an aircraft carrier catch cable seems particularly apt. Thanks you. And yes, most times, you can initiate a go around if you fail a carrier landing. Not really an option with an orbital tether. Some sort of cable pair with a targeted coupler would probably work, each side with a heat emitter an heat seeker RCS system. Obviously, there would need to be slack in the system, (nearly local) winches a ways up-cable in the system, may be an answer.

Maybe don't open the tether until you have tugboat sufficient to retrieve a bolter.

The relative motion drops to zero though, at the moment of capture. So it's more like two cars on the highway that pull alongside each other just as they match speed. Might still be too precise for a human, but automated systems should have little trouble.

And it might be easier to store the emergency retrieval system on the tether's hub. That way it doesn't have to be hauled around to be used (hopefully) infrequently.

You have to get the distance and velocities to line up, and it’s challenging to change only one of those in a three body situation.

How is that different from aerocapture, which is what Starship is going to do?

You are coming in at hyperbolic velocity and have to use the thin and very variable atmosphere to break into an orbit.

At least the tether is completely predictable.

Hard to miss an atmosphere. If you're off to the side a bit, no big deal.

Actually it's completely plausible to skip on the surface of it. Bit easier to hit sideways, yes.

Because if you arrive with a full tank, it's useless and you vent it?

Maybe there could be uses for the fuel, if you succeed in getting it there.

You keep it for the next tether or you sell it at destination.

Bringing a few maneuvering thrusters to adjust the trajectory would still helpful and doesn't require tons of fuel.

If it works in KSP, it will probably work in reality.

I think the idea is brilliant, since you don't need rocket fuel to to generate the force you would transfer to the craft.

I’ve seen some proposals where there’s a low-mass extension to the cable that can change delta-v quickly and then reel in the real tether. Moral equivalent of bridging a ravine by tying a thread to an arrow, pulling a string across with the thread, pulling a rope across with the string, pulling a cable or two across with the rope, and pulling or building a simple bridge across using the cable.

But with the bridge, it’s just distance you’re crossing. With a tether you’re also dealing with velocity. And changing velocity changes distance...

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