> so how do we stop the rotation while reeling in for acceleration?

Thrust against the direction of travel, but angle the thrust appropriately to maintain tension on the cable or whatever?

I mean, this part sounds like it's a low-level college physics problem.

Thrusters require energy and reaction mass (or chemical propellants). For every course change of the spinning construct you'd need to stop the rotation, reel in the drum - now you suddenly need thrust to keep the bodies apart while reeling in, change course, reel out (requires thrust), spin up.

All of that requires reaction mass and energy (or chemical rockets).

On top of that you can't do work on the outside of the space ship since everything (including the space walker) would fly away. You need a double tether at least for safety, etc. Storing the propellants for the thrusters will be an issue: solid boosters won't do because they can't be stopped. Storing oxygen/hydrogen over long periods is an issue in itself.

It _is_ a low level physics problem, but the practical implications are massive.

> Thrusters require energy and reaction mass...

Yes, obviously. (Unless that microwave drive from earlier this year turns out to be really for reals).

> For every course change of the spinning construct you'd need to stop the rotation, reel in the drum...

I'm not convinced that this is entirely true. Doing so would simplify the math required to perform the course alteration, but I expect that altering the course of the craft while it is spinning is not impossible.

Regardless, as pavel_lishin mentioned in the first comment you replied to in this subthread, you can reel the tether in when making craft course changes.

> On top of that you can't do work on the outside of the space ship since everything (including the space walker) would fly away.

Unless -as you go on to say- you're attached to the outside of the craft.

> Storing oxygen/hydrogen over long periods is an issue in itself.

...if you're going to take a long journey in space, this is one of the problems you're gonna have to have solved, no?

So, I'm a little confused.

We go from:

> so how do we stop the rotation while reeling in for acceleration? Shortening the tether would accelerate the objects at the end...

to:

> Thrusters require energy and reaction mass (or chemical propellants). ... It _is_ a low level physics problem, but the practical implications are massive.

You're moving the goalposts. Your first question asked "How do we maintain the speed (and -thus- the g-forces in the craft) while altering the length of the tether?". Your follow-on comments to the answer to your question say -in a nutshell- "Gosh, solving that problem would make maneuvering too hard, and is thus kinda impractical.". :/

Thrusters mounted on the rotating components would be my first guess.

Or two counter-rotating tethers that can be braked against each other; the Arenauts could move to a non-rotating part of the ship for the procedure.

If you want to use the energy stored in the rotation you'd need stiff tethers, not a slack line - more mass, shear forces acting on the tethers, can't be reeled in. Moving to a non-rotating part of the ship requires a hub and a way to move to the hub - that would either require a space-walk up-hill against the artificial gravity (yay, climbing about a quarter of a km in space with an eternal fall if you loose grip) or a tether that's massive enough to move through - but then we're talking a very massive space ship, not about a rocket stage as counterweight.

Why not just a small vehicle attached to climb/drop down a small diameter tether? Similar to the space elevator idea?

Climbing the tether will change the center of mass and also increase the rate of rotation. It's going to be complicated.

Not if you have an equivalent mass climber on the other side mirroring your actions?

Admittedly, this is going to take energy to climb "up", but I'm assuming energy_to_climb << energy_to_alter_rotation.