Hacker News Reader

Comment by quickthrower2 | Hacker News Reader

Also is it possible to maintain muscle mass in space for over a year? What happens when you lose the bone density. Or could this been circumvented with a couple of hours of squats every day and other exercises using bands as resistance

View on HN

Muscle loss isn't too bad. The real killer is bone loss. You lose 1% of your bone mass per month in space. NASA still hasn't figured out how to fix it. Valeri Polyakov spent 437 days on Mir in 1995. Nobody has come close to that record since then, and nobody will until the problem is fixed.

And no one knows how much gravity you need to fix this. That's one reason a moon base would be beneficial.

Does 16% gravity let you do exercises that let you keep most bone density? Is it pretty much the same as microgravity? Or is it somewhere between-- just slightly less bad than orbit.

I have some hope that 16% + an aggressive exercise program could be OK.

As someone currently learning how to lift weights, I would love to be the guinea pig of a lunar exercise program.

At 16% gravity I should be able to deadlift over 1500 lbs and bench 1000 lbs!

I bet having 6 times as much inertia for the weight makes things strange.

In all seriousness, it's going to be mostly resistance exercises. But we can probably do better resistance exercises with gravity to help posture and alignment.

The Moon at least has 0.16g, which is a lot better than 0g.

The powerlifter in me hopes mooners will just be deadlifting 1000+ kilos for reps to stay in ship.

Interesting - I wonder if it would feel different, with conservation of momentum being a bigger portion of the effort than gravity vs. on Earth.

What I mean is it would be something between lifting 100kg and pushing a car in neutral and stopping it.

I suppose the force curve might resemble that of reverse band lift?

Wonder if it's a matter of slapping on some bands to make it feel "earthy" or need mechanism like vacuum tubes they use in the ISS gym (Advanced Resistive Exercise Device). From what I read, it simulates the 1G lifting pretty close.

Spin the spacecraft. Done.

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.

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.

Uh, if human habitation on the Moon requires living inside a centrifuge, then there won't be a human colony.

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.

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.

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.

Spinning a spacecraff is mostly hard because of the mass constraints, building a banked circular track on the moon should be much easier.

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.

Off the top of my head:

- 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.

I’m always leery of solutions to complex problems that take the tone of “all you’ve got to do is…”

“There is a solution to every problem: simple, quick, and wrong.”

Reply on news.ycombinator.com