LEO Space Station with Artificial Gravity (w/Discussion of effects on the human body)

Eric Berger: Meet the space billionaire who is interested in something other than rockets

McCaleb's space habitation company, Vast, emerged publicly last fall with a plan to build space stations that featured artificial gravity. This was significant because NASA and most other space agencies around the world have devoted little time to developing systems for artificial gravity in space, which may be important for long-term human habitation due to the deleterious effects of microgravity experienced by astronauts on the International Space Station. Vast boasted three technical advisers who were major players in the success of SpaceX—Hans Koenigsmann, Will Heltsley, and Yang Li—but did not offer too much information about its plans.

And there still isn’t much information but it’s fun to think about. I’ve been waiting over five decades now. It certainly won’t be this big, but it has to be at least several hundred meters in diameter.

 

[daniel]

I’m not a doctor, but do you really believe that slowed/limited gravity causes bone loss and degradation? Certainly, I could see slowed and mitigated bone formation, gestationally, among babies in utero in lower gravity environments, but I’m not convinced that any substantial bone degradation would occur amongst adults, even in substantially diminished gravity environments.

We know that there is very significant bone loss and muscle atrophy in microgravity, and that even regular vigorous exercise does not prevent it. Astronauts returning from an extended time in space have to be carried out of the return capsule and must undergo a long period of physical therapy before they are able to walk again.

We have no data on reduced gravity. The first people to go to Mars will be the first to experience any level of gravity between 1G and near-zero G. It's an experiment I certainly would not want to participate in. And, as noted above, having or attempting to have children in the reduced gravity of Mars is an experiment that would be highly unethical by any normal standards.

A couple who chose to have a child under such circumstances would be potentially condemning their child to a lifetime of extreme and possibly painful disability. Again, a barbarically unethical experiment.

Note also, that the first people to go to Mars will not be going in a gigantic rotating space station. They'll be going in a tiny space capsule with barely enough room to avoid bumping into each other when they move around. At best they'll be going in something like the SpaceX Starship. Still confined for a months-long trip, and without artificial gravity of any sort.

 

[ecarfan]

Note also, that the first people to go to Mars will not be going in a gigantic rotating space station.

True. And again, off topic for this thread. Note the title “LEO Space Station with Artificial Gravity”.

Thank you for staying on topic.

From my post that started this thread:

McCaleb's space habitation company, Vast, emerged publicly last fall with a plan to build space stations that featured artificial gravity. This was significant because NASA and most other space agencies around the world have devoted little time to developing systems for artificial gravity in space, which may be important for long-term human habitation due to the deleterious effects of microgravity experienced by astronauts on the International Space Station. Vast boasted three technical advisers who were major players in the success of SpaceX—Hans Koenigsmann, Will Heltsley, and Yang Li—but did not offer too much information about its plans.

As you can see, it is well known and accepted that microgravity is harmful to humans. No need to reiterate that fact.

 

[THEbuz]

You might want to do a Google search. Or talk to any doctor. Or pretty much anyone.. this is a well-established fact.

We were clearly designed to live in a 1G environment.

Suffice it to say that we agree that we were, in fact, “designed”. LOL

 

[wwu123]

And to get this back on topic, I'm worried about LEO and MEO debris for a large rotating station. According to Google, the ISS only has to maneuver once a year on average. So my fears are probably unjustified. That said, moving around a rotating large object is probably a bit trickier than a non-rotating object. I expect the maneuvering would need to happen at the hub.

Just slightly trickier if it's rotating, if it's a relatively rigid spacecraft as most have been discussing. One of the earlier solved problems really. Many spacecraft today have one to three axes of momentum/reaction wheels to maintain and stabilize attitude control (orientation), and perform stationkeeping or orbit-raising maneuvers all the time. A spinning space station is just itself a large one-axis momentum wheel, and whether thrusters are on the hub or elsewhere, maintaining attitude is a basic function - massive spinners were in fact the norm for commercial satellites for decades...

Now the alternate proposal for a station with two spinning bodies separated by 300m flexible tether - the overall station will have fairly stable momentum, but the dynamics are much more complicated, and I think still not well-studied, in space - e.g. when one body does attitude or stationkeeping adjustments, can cause complicated, unpredictable effects on both bodies and the tensioned tether....

 

[ecarfan]

If an LEO station with artificial gravity at 0.38 of Earth was established all sorts of research possibilities open up. Small mammals with short lifespans, such mice, could be bred and their offspring studied for abnormalities. In a few years a lot of information could be gained that would apply to humans. We are not that different.

Of course all species on Earth are adapted (not “designed”) to Earth gravity and do not do well in microgravity; it causes very serious problems after a relatively short time. 3.5 billion years of continuous life on Earth will do that.

But it is entirely possible that many Earth species could function reasonably well at 0.38 Earth gravity. If humans could reproduce on Mars and survive, the new “Martians” would almost certainly be different in many ways; better adapted to their environment and likely not able to return to Earth to live. But Mars would be all they know; it would be “normal” to them.

 

[daniel]

... it is entirely possible that many Earth species could function reasonably well at 0.38 Earth gravity. If humans could reproduce on Mars and survive, the new “Martians” would almost certainly be different in many ways; better adapted to their environment and likely not able to return to Earth to live. But Mars would be all they know; it would be “normal” to them.

We're still talking about a hellscape with virtually no atmosphere, no magnetosphere, and hardly any resources, where any breach in containment would be catastrophic.

 

[ecarfan]

We're still talking about a hellscape with virtually no atmosphere, no magnetosphere, and hardly any resources, where any breach in containment would be catastrophic.

Yes, I think you mentioned that earlier. More than once.

I suggest you post such comments in the relevant thread at https://teslamotorsclub.com/tmc/threads/mars-and-off-planet-colonization.24980/

 

[ecarfan]

From a pure research point of view, a rotating space station would be fantastic, especially if the spin rate could be adjusted to produce different levels of artificial gravity.

I wonder if it would be possible to connect two Starships in LEO with a rigid, pressurized tube that had a docking port in the center? Then use the RCS thrusters to spin it.

 

[henderrj]

If an LEO station with artificial gravity at 0.38 of Earth was established all sorts of research possibilities open up. Small mammals with short lifespans, such mice, could be bred and their offspring studied for abnormalities. In a few years a lot of information could be gained that would apply to humans. We are not that different.

Of course all species on Earth are adapted (not “designed”) to Earth gravity and do not do well in microgravity; it causes very serious problems after a relatively short time. 3.5 billion years of continuous life on Earth will do that.

But it is entirely possible that many Earth species could function reasonably well at 0.38 Earth gravity. If humans could reproduce on Mars and survive, the new “Martians” would almost certainly be different in many ways; better adapted to their environment and likely not able to return to Earth to live. But Mars would be all they know; it would be “normal” to them.

I agree with your proposal to have a station with gravity similar to Mars for testing. Perhaps we can agree to disagree on the design part. Especially as it's not really a part of this discussion. (Perhaps I shouldn't have brought it up. Many people get very upset about this.)

 

[ecarfan]

I agree with your proposal to have a station with gravity similar to Mars for testing. Perhaps we can agree to disagree on the design part. Especially as it's not really a part of this discussion. (Perhaps I shouldn't have brought it up. Many people get very upset about this.)

You are welcome to discuss how to design a rotating LEO station. That is one of the main topics in this thread. Please review my post #1 that started the thread.

 

[ecarfan]

This is an excellent video about how to create artificial gravity.

 

[Electroman]

This is an excellent video about how to create artificial gravity.

Excellent video.

Not so much about how to create, but goes into details on the various effects due to artificial gravity created through angular acceleration (aka rotation) as opposed to linear acceleration.

 

[ecarfan]

From that video, this graph shows station radius vs rotation speed and where humans could tolerate the various forces and effects at they would experience.

 

[Ben W]

Now the alternate proposal for a station with two spinning bodies separated by 300m flexible tether - the overall station will have fairly stable momentum, but the dynamics are much more complicated, and I think still not well-studied, in space - e.g. when one body does attitude or stationkeeping adjustments, can cause complicated, unpredictable effects on both bodies and the tensioned tether....

I would think that the dynamics of this setup should be fairly straightforward to model and solve for on a computer, so that e.g. stationkeeping or spinning up/down could be done without inducing instability. Probably much easier than keeping a Falcon 9 stable as it ascends to orbit, which (in simulators) has proven impossible for humans to do manually, but is "easy" for a computer. In the spinning-starships scenario, if the thrusters are placed at the rotational "sweet spot" of the combined system (the technical term is "center of percussion"), then firing them should not induce a wobble. But it will be very interesting to see it attempted in practice.

 

[daniel]

I suggest you post such comments in the relevant thread

Sorry. I was just responding to a comment about living on Mars.

 

[daniel]

I suggest you post such comments in the relevant thread at https://teslamotorsclub.com/tmc/threads/mars-and-off-planet-colonization.24980/

Looks like that thread has been inactive for two years.

 

[wwu123]

I would think that the dynamics of this setup should be fairly straightforward to model and solve for on a computer, so that e.g. stationkeeping or spinning up/down could be done without inducing instability. Probably much easier than keeping a Falcon 9 stable as it ascends to orbit, which (in simulators) has proven impossible for humans to do manually, but is "easy" for a computer. In the spinning-starships scenario, if the thrusters are placed at the rotational "sweet spot" of the combined system (the technical term is "center of percussion"), then firing them should not induce a wobble. But it will be very interesting to see it attempted in practice.

Computer is just a tool. No doubt there will be a control systems engineering team, not a software engineering team, whose first task will be to model and simulate the dynamics of the tethered system, on a computer. Their second task will be to design the sensors and actuators, and the closed-loop feedback control algorithms to stabilize the flexible system, the basic tenet of course is if it looks like it's moving in one unintended direction, nudge it back the other way - more complex than for a rigid body, using modern control theory, but yes, a computer can help. Easy part is done, could take as little as a few weeks or months.

Then the real work begins. Dynamic systems essentially have many low-frequency and high-frequency harmonics, of course you don't want to excite these with your feedback loop. Closed-loop feedback changes the system to have a different set of harmonics from the dynamic system alone. Your model will never exactly match reality, because of engineering and manufacturing tolerances in everything from the tether to the structure to the sensors and actuators, and it is the nature of closed-loop systems that even minute errors/deviations can shift a system from stable to unstable very quickly. For example, let's say one of these harmonics is starting to oscillate out of control, your sensors are saying everything's fine, because every interval when you're sampling, the structure is swinging through center so looks like it's fine. And maybe your corrective nudges that you think are dampening the oscillation, are delayed ever slightly from when you think they're happening, so they're actually increasing rather than decreasing the oscillation.

So you will spend years before the mission accounting for every possible little modeling error, tolerance, component error, failure that could occur and lead to instability, simulating, testing, correcting, in the hopes of avoiding any mission-critical control failures. So you don't end up with for example what happened with Launcher, the other startup that VAST acquired, and their one and only spacecraft mission. Unexpected GPS sensor measurement error (or failutr) -> unstable control algorithm -> uncontrolled spin -> solar panels not pointing to sun -> batteries can't recharge enough -> computer dead before you can upload new algorithm even if you knew what was going wrong -> mission-critical failure, game over in the first few minutes.

Not usually easier to design for a spacecraft vs a launch rocket, just different. And vastly more complicated with tether dynamics.

 

[Grendal]

Looks like that thread has been inactive for two years.

Moderator here. A thread jumps to the top of the discussions when you post something on it. I applaud someone reviving an old but relevant thread. There is a whole lot more to be said about off planet colonization.

 

[Ben W]

Not usually easier to design for a spacecraft vs a launch rocket, just different. And vastly more complicated with tether dynamics.

I certainly didn't mean to imply that it would be easy (because nothing in spaceflight or rocketry is); just that it should be solvable. One advantage of testing a space-based artificial-gravity system, unlike a rocket launch, is that it can be eased into arbitrarily gradually, starting at (say) 0.01g with extremely slow rotation, so if things start to go wrong, they will at least go wrong slowly. Once the system is stable at 0.01g, gradually spin it up to 0.02g, and so on. (The system will have to traverse all these regimes on the way to 1g anyway.) If signs of instability begin to appear at 0.03g, spin it back down to 0.02g and re-stabilize. Take weeks to do this; especially if uncrewed there's no rush. And in an emergency just detach the tether on one end, and now you have two much simpler systems to stabilize. Then re-rendezvous, reattach, and try again. (Even fully spun up at 1g with a 300m tether, the relative velocity of the two ships is only about 100 m/s; it's likely the ships could reach orbit with enough fuel for several such attempts, especially at partial-g spin.)

Obviously there are some tremendous design challenges: how to design the thruster system for all the necessary degrees of freedom and delta-v, how to autonomously deploy, attach, and extend the tether, how to emergency-detach the tether during spin without it recoiling and damaging the other spacecraft, how to damp out unwanted motion with minimal fuel waste, how to distribute mass in each spacecraft to ensure that the overall rotation is around a stable axis, and so forth. But given the huge advantages of making such a system functional, I'd be surprised if it's something SpaceX hasn't considered or may already be working on.

 

[daniel]

Moderator here. A thread jumps to the top of the discussions when you post something on it. I applaud someone reviving an old but relevant thread. There is a whole lot more to be said about off planet colonization.

Thanks for that. (On all the other forums I've been on, posting to a thread that's been inactive for that long is called "necroposting" and is frowned upon. Good to know that's not the case here.)

On the subject of a tethered two-module spinning space station in LEO, moving the station to avoid debris would be extremely complex. A rigid station can be pushed with a thruster at its center of mass (maybe that's not exactly right, but you get the idea). But a tether doesn't allow for that. Both modules would have to be pushed, in exactly the right way to maintain the exact right tension on the tether and keep the modules in exactly the right position, orientation, and spin.

I'm going to guess that that's one reason nobody has tried it.