Artificial Gravity: punctuated gravity using a centrifuge

[edzieba]

Pointless insults ignored.

So it is indeed "best" in extremely risk-intolerant environments.

Human spaceflight is such a risk-intolerant environment. Even SpaceX, the poster-child for moving-fast-and-breaking-things development, progress cautiously for their human spaceflight program. Lack of prudence in that environment is a good way to go from a rapid development programme to a stopped-dead development programme.

[Twark_Main]

So it is indeed "best" in extremely risk-intolerant environments.

Human spaceflight is such a risk-intolerant environment. Even SpaceX, the poster-child for moving-fast-and-breaking-things development, progress cautiously for their human spaceflight program. Lack of prudence in that environment is a good way to go from a rapid development programme to a stopped-dead development programme.

Anticipated and addressed. My very next paragraph was:

If the US with its current old guard is the leader in space, I do expect the field will remain extremely (paralyzingly?) risk intolerant. However it's a self-correcting problem, because it means we won't be the leader for long. 

Anyway, there's also a big difference between the kinds of (real) risks SpaceX is mitigating and the type of "risks" you're hand-wringing about in this thread. SpaceX is mitigating mountains, while you're moaning over molehills.

Astronauts will certainly be fine in 90% gravity, probably extending to <50% gravity, and perhaps punctuated gravity. Astronauts won't be fine if they blow up in a huge fireball on launch. SpaceX is very cleverly focusing on the latter, and avoiding wasted time on the former.

The same trade-off applies for punctuated gravity, hypogravity, or punctuated hypogravity. 

"In nature, the optimum is almost always in the middle somewhere. Distrust assertions that the optimum is at an extreme point." Constant 1G lies at one extreme end of the (biomedically motivated) AG spectrum.

[Coastal Ron]

...
I personally think AG systems will bifurcate into two or more G level optimisations: 1) mission/sortie-level gravity (which would be very convenient if it turned out to be around Mars G), suitable for keeping fully-grown adults comfortable and healthy for many years at a time, and 2) generational-level gravity, (probably much closer to 100% of G if not exactly 1x G), suitable for pregnancy & proper physical development of children.

While I have no evidence to support my assumptions, what you articulated is my current assumption for what the predominate future rotating space station population will look like, and for the mission/sortie-level gravity I am gambling that Mars level gravity will become that standard, since if Elon Musk can start Mars colonization there will be a huge amount of medical science focused on keeping humans healthy in Mars gravity.

Like salmon returning to freshwater to spawn, I expect people will have to commute back to full (or near-full) 100% of G for many generations to come. Evolution is usually slow like that.

Yes, as of today, for rotating space stations, I am assuming that Mars level gravity stations will be for work assignments, and Earth level gravity stations will be for long term living in space.

It makes sense to focus on the the mission/sortie level gravity spacecraft first though, for biomedical reasons, for critical equipment R&D reasons, and also for commercial/tourism reasons, so in the near-term I'll continue to argue for focussing on Mars-G level platforms in LEO.

I agree!

As for punctuated gravity for mitigating the effects of low gravity, I would suggest a second option. That instead of having a spin facility on a rotating space station that only produces far less than Earth gravity, you could have a second rotating "facility" stationed nearby where inhabitants of the rotating space station could go periodically for "gravity boosts".

And as already been stated, this idea might be worthy of testing out on a future artificial gravity testbed.

[Twark_Main]

Another part edzieba seems to have misclassified and forgotten to address (it's certainly no "insult"):

We don't pressurize planes to 0 feet MSL (or even 640 feet MSL, the average altitude where people live). By pressurizing cabins at 6000-8000 feet we trade off some discomfort for reduced operating cost. To do otherwise would be economically irrational.

Again the point I'm making applies to punctuated gravity, hypogravity, or a combination. In all cases you're trading off vehicle cost for the cost of accepting some biomedical impact, impact which can be compensated for in other (cheaper) ways  — eg scheduled exercise, body-worn weights, pharmaceuticals, etc

[Twark_Main]

As for punctuated gravity for mitigating the effects of low gravity, I would suggest a second option. That instead of having a spin facility on a rotating space station that only produces far less than Earth gravity, you could have a second rotating "facility" stationed nearby where inhabitants of the rotating space station could go periodically for "gravity boosts".

I don't get it.  If you need a second station anyway, why bother with low gravity at all? Just make it microgravity, instead of this "split baby" where you have all the design costs of spinning and you still need a second station with traffic between them. Seems like the worst (costliest) of both worlds.

Of course if you want, it's easy to have a higher-G "room" as part of a lower-G station. No centrifuge required. You just put your G Recovery Facility on the end of a long stick.   

[edzieba]

Another part edzieba seems to have misclassified and forgotten to address (it's certainly no "insult"):

We don't pressurize planes to 0 feet MSL (or even 640 feet MSL, the average altitude where people live). By pressurizing cabins at 6000-8000 feet we trade off some discomfort for reduced operating cost. To do otherwise would be economically irrational.

Again the point I'm making applies to punctuated gravity, hypogravity, or a combination. In all cases you're trading off vehicle cost for the cost of accepting some biomedical impact, impact which can be compensated for in other (cheaper) ways  — eg scheduled exercise, body-worn weights, pharmaceuticals, etc

Aircraft do not evacuate to altitude and then occasionally pressurise up to 1 Bar during flight. The fatigue cycles from ascent and descent pressurisation cycles are already the lifetime limiter for the airframe, so regular spinup/spindown would also apply new loads and lifetime fatigue constrains to space station structures.

[redneck]

Another part edzieba seems to have misclassified and forgotten to address (it's certainly no "insult"):

We don't pressurize planes to 0 feet MSL (or even 640 feet MSL, the average altitude where people live). By pressurizing cabins at 6000-8000 feet we trade off some discomfort for reduced operating cost. To do otherwise would be economically irrational.

Again the point I'm making applies to punctuated gravity, hypogravity, or a combination. In all cases you're trading off vehicle cost for the cost of accepting some biomedical impact, impact which can be compensated for in other (cheaper) ways  — eg scheduled exercise, body-worn weights, pharmaceuticals, etc

Depending on a lot of factors, it's possible that the exercise, weights, etc, could be more expensive than some level of spin gravity. What is the individuals time worth on that vehicle/station? Times how many man-hours per year for the extra workouts and such. Say thirty people times an extra hour a day for mitigation gets somewhere close to 10,000 man hours per year to offset the unfortunate effects. Probably still cheaper to have them doing the weights and exercise, but still a factor to consider.

I find it disturbing that the ISS crews have to spend so much of their time on maintenance of the station and themselves. It would seem to me that informed development going forward should have ships/stations with more focus on getting jobs done than just keeping it together.

[Lampyridae]

Another part edzieba seems to have misclassified and forgotten to address (it's certainly no "insult"):

We don't pressurize planes to 0 feet MSL (or even 640 feet MSL, the average altitude where people live). By pressurizing cabins at 6000-8000 feet we trade off some discomfort for reduced operating cost. To do otherwise would be economically irrational.

Again the point I'm making applies to punctuated gravity, hypogravity, or a combination. In all cases you're trading off vehicle cost for the cost of accepting some biomedical impact, impact which can be compensated for in other (cheaper) ways  — eg scheduled exercise, body-worn weights, pharmaceuticals, etc

Depending on a lot of factors, it's possible that the exercise, weights, etc, could be more expensive than some level of spin gravity. What is the individuals time worth on that vehicle/station? Times how many man-hours per year for the extra workouts and such. Say thirty people times an extra hour a day for mitigation gets somewhere close to 10,000 man hours per year to offset the unfortunate effects. Probably still cheaper to have them doing the weights and exercise, but still a factor to consider.

I find it disturbing that the ISS crews have to spend so much of their time on maintenance of the station and themselves. It would seem to me that informed development going forward should have ships/stations with more focus on getting jobs done than just keeping it together.

Not to mention making everyday tasks much simpler. Even with a small internal centrifuge, if you need to work on a piece of equipment you could do it there with a low spin setting. No need to find an anchor point to unscrew a panel. No need to worry about a loose bolt floating up your nose. No need to have velcro or duct tape everywhere to stick things to. I imagine it would increase productivity significantly.

[Twark_Main]

Another part edzieba seems to have misclassified and forgotten to address (it's certainly no "insult"):

We don't pressurize planes to 0 feet MSL (or even 640 feet MSL, the average altitude where people live). By pressurizing cabins at 6000-8000 feet we trade off some discomfort for reduced operating cost. To do otherwise would be economically irrational.

Again the point I'm making applies to punctuated gravity, hypogravity, or a combination. In all cases you're trading off vehicle cost for the cost of accepting some biomedical impact, impact which can be compensated for in other (cheaper) ways  — eg scheduled exercise, body-worn weights, pharmaceuticals, etc

Depending on a lot of factors, it's possible that the exercise, weights, etc, could be more expensive than some level of spin gravity. What is the individuals time worth on that vehicle/station? Times how many man-hours per year for the extra workouts and such.

"Some" level of gravity is what I advocate, yes. An informed and rational economic / engineering tradeoff, not a zealous compulsion to only accept solutions at one extreme of the spectrum.

I can see how the argument applies to scheduled exercise, certainly. I can't see how it substantially moves the needle on body-worn weights. That's one of their major advantages, in fact.


Without a time machine, in this thread we have two options: moan and lament the lack of biomedical data at punctuated gravity and/or infragravity, or speculate.  If intellectually risky and tenuous speculation (which accepts gravity lower than 1 G and punctuated instead of constant) is only met with conservativism and hand-wringing, might as well lock the thread now. 

[Paul451]

[...] not a zealous compulsion to only accept solutions at one extreme of the spectrum.
[...] is only met with conservativism and hand-wringing, might as well lock the thread now.

Jesus, dude, go outside.

[Twark_Main]

[...] not a zealous compulsion to only accept solutions at one extreme of the spectrum.
[...] is only met with conservativism and hand-wringing, might as well lock the thread now.

Jesus, dude, go outside.

Outside? Never heard of it. I live in Plato's Mom's Basement. With the ad hominem all settled, "Play the ball, not the man."

I didn't think "we should be allowed to actually discuss the thread topic instead of shutting down discussion in favor of constant 1G" would be so controversial. Let's discuss the topic rather than this.



...and don't call me Jesus!   

[mikelepage]

“It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so. “ – Mark Twain

The great irony is that you're running afoul of your namesake's quote in this thread Twark.

The reason disproving a null hypothesis is part of standard scientific best practice, is because it forces you to prove first what you "know for sure". It's core tenet of modern scientific theory, so ignore it at your own risk.

I don't usually play the "I have a phd" card, but maybe in this case it will help - if only to give an example of how badly it can bite you in the ass when you ignore this principle. For me, it was having my phd take over a year longer than it really needed to, because we saved money by not testing the thing we were sure we knew. Long story short: our friends and colleagues gave us the wrong reagent - one that was *so* similar to the one we were expecting that we only found out later when we finally put it through a mass spec after over a year of weird results. That's when our colleagues had their wtf moment - realised all *their* stocks had been accidentally switched - and took another 8 months to remake it from scratch and send us a new batch.

In that case it was human error as a root cause of the weirdness, but it's not like nature isn't capable of giving us weird results all by itself (see the results Lampyridae linked above). The point stands regardless: the scientific validity of an approach - test the thing you think you know first - is a standard approach for good reasons, and answers a qualitatively different question from those considered in a trade study, like cost. It's why you get so many news headlines of scientists "proving" obvious things, to which the usual response is "well duh!" - the obvious thing is never the actual point of the study.

One important exception to this rule is when the initial trades make it clear that this approach is so expensive, that it's the difference between whether the experiment gets done at all or not. That's the only reason why I'm pushing the Mars-G approach first. If the entire history of science is any guide, we will get weird results we weren't expecting, and the definitive interpretation of those results will only come once we build the 1G control^#, but with some luck by that stage we'll be much faster/better/cheaper at building spin-G habitats, and we'll have made some money and answered some interesting questions in the smaller model.

^#Technically the perfect control would be a crewed space habitat that could implement *linear* 1G acceleration for weeks or months at a time, (allowing us to properly control for the difference between the space environment and Coriolis effects) but good luck with that 

[Twark_Main]

“It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so. “ – Mark Twain

The great irony is that you're running afoul of your namesake's quote in this thread Twark.

The reason disproving a null hypothesis is...

This is basically the same misunderstanding I had with edzieba:

You're talking about the process. "How do you get there from here?"

I'm talking about the result. "Where will we eventually end up?"

The first is necessarily rigid, while the second is necessarily speculative.

One important exception to this rule is when the initial trades make it clear that this approach is so expensive...

My thinking precisely. It's weird that you're so vehemently...  agreeing with me.   

I too expect that Mars-G is probably a bit too low. Here I have been predicting (so please, no letters on epistemology or dead authors  ) that most cost-forward designs (which is the majority of all real-estate!) will eventually settle around 50% Earth gravity, with appropriate hybrid mitigations to match.

But I am confident that exactly 1 g is unlikely to be used for health reasons (other than the early experimental stations as mentioned), for the same boring rational economic reasons that commercial planes don't pressurize to the air pressure on the ground. There's always a trade-off.

^#Technically the perfect control would be a crewed space habitat that could implement *linear* 1G acceleration for weeks or months at a time, (allowing us to properly control for the difference between the space environment and Coriolis effects) but good luck with that 

True. The closest economical control environment would use an extremely long radius centrifuge, which is cheapest to build as a barbell (or even a tomahawk).

[mikelepage]

One important exception to this rule is when the initial trades make it clear that this approach is so expensive...

My thinking precisely. It's weird that you're so vehemently...  agreeing with me.   

That's the thing Twark, we're *all* largely on the same page regarding the pragmatic approach, but you've been misconstruing people's assertions that *ideally* we should start with a 1G control as saying that we *have* to do this, then combatively labelling it as hand-wringing and "infragravity phobia". Hence the complaints of straw-manning, and me calling you out on a lack of nuanced reading.

I'm just requesting better forum etiquette out of you really.

[Twark_Main]

you've been misconstruing people's assertions then combatively labelling it as "infragravity phobia".

Speaking of poor reading comprehension, my comment about "infragravity phobia" wasn't directed at any specific assertion made in this thread. I suggest going back and reading it again to understand the point I was making (vs your strawman).

And "hand-wringing?" That's because....  edzieba was hand-wringing. I stand by my accurate description.   


For the edification of any residual hand-wringers out there, here's a spoiler alert:

Will working in space destroy your body in the long-term? Yes.

Will we tolerate that? Yes. We'll tolerate it for the same reasons we tolerate it today with roughnecks on an oil derrick, roofers, plumbers, etc. These jobs already destroy your body, and working in space will be no different. Don't like this harsh reality? Tough. Not everyone can be born with "The Right Stuff."

Living in space is, of course, another matter. Then it simply boils down to how much you can afford. The equivalent of Elysium will be very nice, I'm sure.


This is why we shouldn't let perfect be the enemy of good when it comes to intermittent gravity. One day in the future we'll have all the biomedical data in front of us, and on that day we won't be choosing "there can be exactly zero health risks" for our final designs. In other words, the presence of non-zero biomedical risk is not a show-stopper, and we shouldn't treat it like one.

Hopefully it's clear now.  Let's move on, but we should keep this last point in mind.