It works in principle, but it's a very big engineering task, and an enormous expense to boot. To avoid noticeably different acceleration between head and foot,* it's going to have to be substantially larger than any spacecraft we've ever built, and the biggest spacecraft we've ever built cost over $100bn. It's also going to have to withstand stresses larger than anything we've done before.
There's no reason to doubt we could do it, but it's a very big step from where we are now.
* And if we don't do that, then we stray into the realm of untested biological issues. We have no idea if people can live safely and comfortably like that.
It is literally two things connected by a rope. A tether-based spun spacecraft is trivial from an engineering perspective, and can have as large a radius as you need to avoid differential “gravity” effects.
- What material are you making the rope out of? What data do we have of that material's behaviour under tension in a vacuum?
- How is the craft connected to the rope? Is it a fixed bond or is there freedom to move? What are the tradeoffs?
- What happens when one of the two ends is accelerated? How do you reestablish a stable rotation?
- How do you manoeuvre it? Can you?
- What happens in the event of a catastrophic failure of the rope? What safeguards need to be in place?
And this is all on top of the fact that we're discussing two things connected by a rope under conditions that rope has never been tested in, doing something that's never been done. Space exploration isn't in the habit of trusting that our untested models are reliable, especially where human life is involved.
It is unknown if it will be that easy. For obvious reasons, there have been no long-term studies in partial gravity. If 0.05g stops bone loss, great. If a full 1.0g and nothing less is required, then that's going to be a really onerous design constraint.
I wonder if this unknown may, in the end, turn out to be a great reason to motivate space exploration. A full G is the norm on Earth. Micro-G in orbital stations have known long-term negative effects on health. What if fractional-G actually has beneficial effects, like say, increasing average human lifespan a lot. The human circulatory system tends to fail early, causing a disproportional amount of deaths due to strokes or heart failure. It's far-fetched speculation on my part, but is not hard to imagine operating in a fractional-G environment could decrease wear and tear here, acting as a sort of medical treatment. In the end, people would have a great motivation for leaving Earth. Just dodging death, the ultimate enemy of all living things.
If a full 1.0g is required, that also makes it a much more difficult challenge on the moon. Spinning a module of a space station in zero g is one thing... trying to get a portion of a moon lab at 0.16g to 1.0g is a different challenge.
The advantage I see on the moon is that you have local mass to use. Yoy can build a large, banked circular track underground ground and then add cars as you expand.
It depends on how much gravity is needed for how much time to stave off the long term effects of zero gravity. If we're lucky, then just sleeping at a higher G may be enough and you just need the bunks built in a centrifugal train.
