[hoorayimhelping]

>The tricky bit is being able to launch enough mass to build something safe and comfortable to spin;

Is it? I might have a completely busted mental model, but I thought you only need a module-sized mass on one end of a rod the length of things we've already assembled in space (e.g. an ISS truss) and a motor to spin it.

[jerf]

It gets complicated, and the mass budget starts going up fast, if you want other things to be able to dock to it. Two space stations on the opposite side of a long rope (per the other reply) is also not a very compelling story to tell to Congress when you have to admit that astronauts won't be able to travel between those two space stations to speak of, unless, again, you really up the mass budget.

We're space-poor. It's just too darned expensive. Even relatively simple designs are out of our reach right now, if you have to manifest them in real designs with real safety margins and real practical applications, such as being dockable.

[nxzero]

What about grabbing mass from the surface of the moon, junk that's floating around, etc.?

Seems like this might be cheaper than getting it off Earth, right?

[akiselev]

Except then you'd need to launch a full blown transport, mining, and manufacturing facility from Earth and assemble it just like the space station. I wouldn't be surprised if such a ship is heavier than the station you're trying to build, even if you strip out life support because the gear necessary to make silicon chips or machine hard metals is massive and numerous.

[doikor]

At first we don't want 2 space stations spinning. We want 2 space crafts spinning and traveling to somewhere where we have enough gravity to survive (mars). All humans on one ship and cargo/return counter weight as other ship linked together by a tether and spinning for the travel duration.

But yeah we still need to lower the launch cost per kg to make it really feasible and super heavy launch vehicles which don't exist at all at the moment. Realistically we would want to launch 40+ tons directly to mars from earth (Falcon Heavy should be ~13 tons so we would need around 3x the power of that). We don't have anything with enough delta v to do that at the moment.

[thaumasiotes]

> Two space stations on the opposite side of a long rope (per the other reply) is also not a very compelling story to tell to Congress when you have to admit that astronauts won't be able to travel between those two space stations to speak of

I don't get the complaint. Assuming travel from one station to the other is impossible, what's supposed to be wrong with having two smaller stations that don't cripple the health of the inhabitants instead of one bigger one that does?

[jerf]

Congress won't fund two stations.

Again, the problem isn't physics or engineering, it's that we're poor in space. This, and a lot of the other posts, are basically saying "What's so hard about having a job 10 miles away? Just drive there!" to people too poor to own a car, too poor to even dream of owning a car. Yes, it is a simple problem... if space wasn't so expensive to us. (I mean, not trivial, we'd still have to redesign a lot of stuff, but there's no reason to believe there's a fundamental problem.)

[thaumasiotes]

This will serve as a reply to you and wlievens:

The objection I questioned was "when you have to admit that astronauts won't be able to travel between those two space stations to speak of". You and wlievens are both pointing out that the scheme is unworkable regardless of the necessity of traveling between one station and the other. That's fine, but it doesn't respond to my question of "who cares that you can't travel between the stations?" It means I was correct to wonder how it could be relevant that travel between one station and the other is impossible. The objection I questioned makes no sense.

On a separate note, if Congress will fund one station, they can't object to a two-station system at the same cost. The number of stations is, again, not relevant to much.

[wlievens]

Still can't dock. You need to be able to dock in the stationar center module.