Why artificial gravity?

[Vultur]

I've seen a lot written about artificial gravity on the trip to Mars.

But ... why? People have stayed in zero-g for more than a year (record 437 days), not just the ~8 months to Mars. And on Mars you only have to function in .38 g; even with spacesuits, that still probably comes out to carrying around less weight than on Earth. (And maybe you can use mechanical counter-pressure suits, which would weigh way less).

Is the real problem after return to Earth? Is it something physical theraphy can't deal with?

(And would something like 'Mars One' need to worry about it at all?)

What am I missing?

[QuantumG]

After all the long duration flights to-date the astronauts (and cosmonauts) have been incapable of getting out of the capsule themselves. Even under .38 g they'd be incapable of completing the mission.

However, the drugs and exercise regimes are improving and it looks like very soon the necessary fitness will be demonstrated.

Artificial gravity for a Mars mission isn't the must-have it once was perceived as being.

[gbaikie]

I've seen a lot written about artificial gravity on the trip to Mars.

But ... why? People have stayed in zero-g for more than a year (record 437 days), not just the ~8 months to Mars. And on Mars you only have to function in .38 g; even with spacesuits, that still probably comes out to carrying around less weight than on Earth. (And maybe you can use mechanical counter-pressure suits, which would weigh way less).

Is the real problem after return to Earth? Is it something physical therapy can't deal with?

(And would something like 'Mars One' need to worry about it at all?)

What am I missing?

I would say largest effect of 8 month in space is the psychological effects.
Next largest effect is the effects of radiation.
Followed by physiological effects of zero-g.

I don't think anyone questions there is big difference if Mars only require [the impossible] of 1 month
trip time as compared to 8 month.
Though even with one month trip time, you still have psychological effects, radiation effects and physiological effects of zero-g.
One could make the case that being at least one month allows enough time for astronauts
to get use to the space environment. Though recovery from acute symptoms 3 days could considered
a better length of time:
"The most common problem experienced by humans in the initial hours of weightlessness is known as space adaptation syndrome or SAS, commonly referred to as space sickness. It is related to motion sickness, and arises as the vestibular system adapts to weightlessness. Symptoms of SAS include nausea and vomiting, vertigo, headaches, lethargy, and overall malaise. The first case of SAS was reported by cosmonaut Gherman Titov in 1961. Since then, roughly 45% of all people who have flown in space have suffered from this condition. The duration of space sickness varies, but rarely has it lasted for more than 72 hours, after which the body adjusts to the new environment."
http://en.wikipedia.org/wiki/Effect_of_spaceflight_on_the_human_body

But to sort of "forget you are in space" takes about month- in order to "feel" fully adapted to environment.
So anyways, after only month in space, one probably has some recovery time if going to 1 gee or 1/3 gee of Mars. Such recovery time could be minutes or within one day one can get back feeling normal in gravity environment.
But the longer in space more the physiological effects are going to occur with your body, getting back to feeling normal and actually being normal takes a lot longer.
From radiation effects you may never recovery, and same goes for bone loss from long periods in zero-g, couple with knowledge that you have repeat the same duration back to Earth is going to effect you when at Mars. Plus you aren't going to feel well and closest hospital is +8 months trip time distance.

It's the combination of these factors which makes me put psychological effects as most severe factor of long travel time. Psychological effects not just affect how crew reacts with other crew and mission control,
and how well to perform their tasks, but it can affect the physical health of the crew.

So it seems to me that you spending billions of dollars to put crew on the surface of Mars- it's not good idea just in general terms to have these crew impaired. And impairment of one crew, makes harder on the rest of the crew. And crew morale is important.

And reason put radiation as next important is because that crew being damaged with radiation, and will affect them psychologically.
So if you have 1.8 milliSieverts of GCR per day:
"NASA has established a three percent increased risk of fatal cancer as an acceptable career limit for its astronauts currently operating in low-Earth orbit. The RAD data showed the Curiosity rover was exposed to an average of 1.8 milliSieverts of GCR per day on its journey to Mars. Only about three percent of the radiation dose was associated with solar particles because of a relatively quiet solar cycle and the shielding provided by the spacecraft. "
http://www.nasa.gov/mission_pages/msl/news/msl20130530.html#.UoBYSifU3zY

240 days times 1.8 is 432 milliSieverts. And:
"Long-term population studies have shown exposure to radiation increases a person's lifetime cancer risk. Exposure to a dose of 1 Sv, accumulated over time, is associated with a five percent increase in risk for developing fatal cancer."
So 8 months there and 8 month back is putting pretty close to 1 Sv. This not an accident, but it's rather planned minimum of exposure. You essentially having agency making policy which is deliberately increasing the risk of cancer on it's crew.
Plus you have "other needs" [or margins of risks] of crew being expose to additional radiation. You have solar flares [variable], time spent on Mars surface [and decisions one has to make regarding what are "safe" levels of additional radiation].
Plus any crew training prior to going to Mars which could add radiation exposure adding to career life time exposure.
So, this quite different than some individual deciding to take such a risk, because one has make a policy, and follow this policy. And with 8 month trip, it seems NASA would have to change it's current policy.
It's one thing to use a rocket that fails 1 in a 100 times, it's another thing to design a rocket that will fail 1 of 100 times. And an astronaut may decide it's worth it to go a rocket that has 1 in 10 chance to fail [or unknown risk which may be kind of risk or higher].

So the affect of zero gee for 8 months trips *might be* getting rid a factor which added to all the risks.

But I think answer, is getting crew to Mars within 3 months and that this worth a lot money spent to do this. So my view of a lot money is a additional cost of 1 billion dollar per crew.
Or would have 3 crew sent, so total cost of 3 billion spent to get this which is upfront cost.
So I don't mean 30 billion spend on program which must completed before to sending 30 crew over decades of time. Or in terms total cost, say it's 10 billion to entire program cost of 100 billion.

Or saying differently, sending crew should viewed as special delivery, not the normal mail or book rate mail.
 

[Vultur]

After all the long duration flights to-date the astronauts (and cosmonauts) have been incapable of getting out of the capsule themselves. Even under .38 g they'd be incapable of completing the mission.

But don't they recover in a reasonable time? And you'll probably be on Mars for months and months. So what makes a few weeks of recuperation-only unacceptable? The lander being too small for enough exercise to recuperate?

I would say largest effect of 8 month in space is the psychological effects.

I think these are handleable by proper crew selection alone. People have dealt with much more extreme isolation in much worse conditions (look at some of the guys on early Antarctic expeditions cramped into small winter quarters to conserve heat -- with no strong lighting for months and months) without psychological damage.

You have tons of people to choose from. Be very very very selective on the psychological aspects.

Next largest effect is the effects of radiation.

Well, let's distinguish between mission risk and lifetime risk. As I understand it -- not an expert -- only solar flares are a mission risk since only they may produce radiation levels high enough to cause acute problems.

(And if we do manned Mars in say the 2030s I think it pretty likely that by the 2060s or so cancer will be far far less of a risk due to personalized medicine/advances in biotech.)

Anyway -- the risk of cancer is not nearly high enough to be beyond what a reasonable and informed adult could sensibly accept for something as significant as going to Mars.  I thought the Curiosity stuff suggested 5% or so.

From radiation effects you may never recovery,

Barring solar flares (which DO need shielding -- I never questioned that) 95% of people will never have any radiation effects and those that do will develop them decades later.

So, this quite different than some individual deciding to take such a risk, because one has make a policy, and follow this policy. And with 8 month trip, it seems NASA would have to change it's current policy.

Well, yes. But IMO applying risk limits used for "standard" ISS operations to the first mission to a new planet is silly.

This is why I don't think NASA will be the first entity to land humans on Mars. (Or the next entity to land humans on the Moon.)

[IRobot]

Also some things are simplified with artificial gravity, for example toilets and personal hygiene.

[gbaikie]

gbaikie on Today at 04:03 AM

    -I would say largest effect of 8 month in space is the psychological effects.-

I think these are handleable by proper crew selection alone. People have dealt with much more extreme isolation in much worse conditions (look at some of the guys on early Antarctic expeditions cramped into small winter quarters to conserve heat -- with no strong lighting for months and months) without psychological damage.

You have tons of people to choose from. Be very very very selective on the psychological aspects.

I think we can assume all astronauts have already had some some degree of screening, but you seem to suggest there high level precision about this, and I have no reason to suppose there can be such accuracy.
So the skill of such predictions can be tested, and imagine some where and some time it has been tested.

But I need the reference or some reason to agree that is such predictive ability of people future behavior which could be adequate to remove this risk.  Very very very selective doesn't help unless you can successful select with skill.
Here example:
http://www.forbes.com/sites/crossingborders/2013/09/18/nasa-will-pay-18000-to-watch-you-rest-in-bed-for-real/
"Those who are short-listed in the application round go through a modified Air Force Class Three physical, which is a rigorous physical exam. In addition, there is a psychological screening in which subject candidates fill out a battery of tests, followed by ninety minutes one on one with a psychologist.

“We want to make sure we select people who are mentally ready to spend 70 days in bed. Not everyone is comfortable with that. Not every type of person can tolerate an extended time in bed,” says Dr Cromwell."

Now after all this testing how many finished? If they can get 100% on this that would indicate some skill.
Though this is pretty easy in comparison.

So, right, found it:
"Applicants are earning while lying down on the job – getting $10 per hour for the 16 hours per day they are awake during the study. Ciaciura said he was paid $16,800 for his most recent study of 105 days – 70 of which were spent horizontally. Yarbrough said approximately 85 percent of test subjects complete the study once they begin."
https://bedreststudy.jsc.nasa.gov/
And if was it harder can we assume more would quit.
You could use such test to improve the ability to screen.
I don't know if they attempting to do this.

[QuantumG]

After all the long duration flights to-date the astronauts (and cosmonauts) have been incapable of getting out of the capsule themselves. Even under .38 g they'd be incapable of completing the mission.

But don't they recover in a reasonable time? And you'll probably be on Mars for months and months. So what makes a few weeks of recuperation-only unacceptable? The lander being too small for enough exercise to recuperate?

People laid up in bed can't take care of themselves.. doubly so on Mars.

[Andrew_W]

Is the cost of artificial gravity going to be so great that the inconvenience of zero g and the time to adjust to the return to gravity are justified?

[Vultur]

People laid up in bed can't take care of themselves.. doubly so on Mars.

Is the effect that extreme? I agree that people who get back from long stays can't just walk away as soon as they get back to Earth... but that's in 1 g, not .38. That should be much more manageable, no?

And how long is the recovery time likely to be? If it's fairly brief, couldn't you set up the necessary controls for the first bit to where they could be operated sitting down?

Is the cost of artificial gravity going to be so great that the inconvenience of zero g and the time to adjust to the return to gravity are justified?

It seems to me that it requires pretty much untested techniques (tethers on a much bigger scale -- I know there was a Gemini experiment but it wasn't nearly this scale, didn't really produce noticeable gravity).

I think we can assume all astronauts have already had some some degree of screening, but you seem to suggest there high level precision about this, and I have no reason to suppose there can be such accuracy.
So the skill of such predictions can be tested, and imagine some where and some time it has been tested.

But I need the reference or some reason to agree that is such predictive ability of people future behavior which could be adequate to remove this risk.  Very very very selective doesn't help unless you can successful select with skill.

Yeah but the Antarctic guys were able to do it with basically no formal psychology.

“We want to make sure we select people who are mentally ready to spend 70 days in bed. Not everyone is comfortable with that. Not every type of person can tolerate an extended time in bed,” says Dr Cromwell."

Now after all this testing how many finished? If they can get 100% on this that would indicate some skill.
Though this is pretty easy in comparison.

Not sure I agree on that last part -- it's less time but much more restriction. And not the degree of "reward" going to Mars would be.

[QuantumG]

Is the effect that extreme? I agree that people who get back from long stays can't just walk away as soon as they get back to Earth... but that's in 1 g, not .38. That should be much more manageable, no?

It's getting less and less "extreme" over time as it is learnt how to keep astronauts healthy in zero-g.

And how long is the recovery time likely to be? If it's fairly brief, couldn't you set up the necessary controls for the first bit to where they could be operated sitting down?

If you stayed sitting down, the recovery time would be forever.

[sanman]

What happens if astronauts are kept in some kind of suspended animation? Would that also retard or suspend their skeleto-muscular atrophy?

[gbaikie]

Yeah but the Antarctic guys were able to do it with basically no formal psychology.

Because they know each other.
And people have getting along with each other for thousands of years.
Humans as an animal are very good at doing this.
And in the Antarctic it's a shorter time period- nor are people locked in a small room for months.

"Despite winter-over studies that date back to the 1950s, researchers say there's no single archetype that can define a winter-over. "Our analyses of the human experience in Antarctica suggest that there are few, if any, traits that serve as useful predictors of performance during the austral winter," Palinkas wrote in a paper called "The Psychology of Antarctic Research."
http://spaceref.com/news/viewnews.html?id=1113

"However, "research has consistently demonstrated that interpersonal conflict and tension is the greatest source of stress in the Antarctic," Palinkas wrote. While winter-overs seem to agree there can be an inordinate amount of drama, they're also steadfast in their belief that the community is one of the best things about living down south. "

So perhaps one could say, mad hatters but happy about it

[Vultur]

Yeah but the Antarctic guys were able to do it with basically no formal psychology.

And in the Antarctic it's a shorter time period- nor are people locked in a small room for months.

Perhaps not technically locked -- but the winter quarters of the early guys (Shackleton era, 1900s and 1910s) were pretty close as I understand it, because an Antarctic winter is so cold you can't do much outside. They may have gone out occasionally to get seals or something, but...

"Despite winter-over studies that date back to the 1950s

I don't think we are talking about the same thing. I'm talking about the "heroic age" antarctic exploration of the 1900s and 1910s. Totally different (and MUCH more severe!) conditions than post International Geophysical Year "modern" Antarctic science.

Is the effect that extreme? I agree that people who get back from long stays can't just walk away as soon as they get back to Earth... but that's in 1 g, not .38. That should be much more manageable, no?

It's getting less and less "extreme" over time as it is learnt how to keep astronauts healthy in zero-g.

OK but my real question is 'would the severe effects, eg inability to walk, seen when you go from 0g to 1g still apply when you go from 0g to 0.38g'?

If you stayed sitting down, the recovery time would be forever.

Yeah, that was probably poorly phrased...

[guckyfan]

OK but my real question is 'would the severe effects, eg inability to walk, seen when you go from 0g to 1g still apply when you go from 0g to 0.38g'?

Of course not. And they can stand up even in earth gravity if they have to. They just won't jump out of their seats after landing to fight venusian swamp monsters. Anyway they are not on Venus but on Mars which does not have swamp monsters. Just artificial gravity elephants in the room.

Edit: fixed quote

[RanulfC]

AG is nice because as mentioned some things get a lot easier to do. (Zero-G toilets suck.. Pun highly intended However the most often noticed long term "adapation" problem when someone returns to gravity after a long stay in microgravity seems to be habitual... Simply "forgetting" for quite a while that the things you learned to do and adjust to in microgravity no longer apply.

For example, Valeri Polyakov was at a formal dinner/party over two years after he came back and while telling a story to several people he habitually, and without thinking set his tea-cup in mid air to free both hands to expound a point. Gravity works

Of course even with AG that 'habitual' problem is not going to go away as there are going to be noticable and "adapted-to" issues with most proposed AG schemes.

The "main" problem with landing on Mars after a long period in microgravity is the very LACK of time between micro and adverse gravity during landing. Going from nothing to upwards of 6Gs during the landing (possible in some scenerios) might be more than the astronauts can take after a long trip. (This doesn't seem as likely as it once did given the number of times long duration astro/cosmo-nauts have been exposed to purely ballistic recoveries on the Soyuz) But still it would probably take at least a few weeks to fully adapt back to gravity after a long trip. The major reason for AG being needed was for the most part because the STAY on Mars for most early missions was only a few weeks meaning there wasn't enough "adapt" time built in to allow much actual work. This may no longer be the case.

Randy

[RanulfC]

OK but my real question is 'would the severe effects, eg inability to walk, seen when you go from 0g to 1g still apply when you go from 0g to 0.38g'?

Of course not. And they can stand up even in earth gravity if they have to. They just won't jump out of their seats after landing to fight venusian swamp monsters. Anyway they are not on Venus but on Mars which does not have swamp monsters. Just artificial gravity elephants in the room.

Edit: fixed quote

No Venusian Swamp Monsters of course, but they may face the dreaded Mars Meme's and their Princess! And what is it going to say about the reputation of Men from the Planet Earth if we can't even stand defiently in front of the  Princess, impressing her with our prowess and Earthly strength! Why it could topple the whole balance of interplanetary diplomacy and relationships in one fell swoon!

Randy

[Patchouli]

Though AG increases the complexity of the vehicle in some ways it can simplify the design of other parts.

Even partial G makes liquid gas separation a lot easier.
This would simplify at lot of the ECLSS design eliminating a lot of small high speed centrifuges and small passageways increasing it's reliability.

Another benefit you can now have a real shower on the ship and cook normally.
These are small things that can go a long way in keeping crew morale up on a long voyage.


From what I seen of the bearing on Nautilus-X  the system could be very reliable.
Yes it has a seal and a bearing but it's low speed.

Spacesuits BTW have similar moving seals.

Some designs simply spin the ship about it's long axis these would probably be the easiest .
Since a chemical or NTR ship already has to be structurally capable of handling sizable accelerations the mass penalty may be quite small.

[JasonAW3]

AG is nice because as mentioned some things get a lot easier to do. (Zero-G toilets suck.. Pun highly intended However the most often noticed long term "adapation" problem when someone returns to gravity after a long stay in microgravity seems to be habitual... Simply "forgetting" for quite a while that the things you learned to do and adjust to in microgravity no longer apply.

For example, Valeri Polyakov was at a formal dinner/party over two years after he came back and while telling a story to several people he habitually, and without thinking set his tea-cup in mid air to free both hands to expound a point. Gravity works

Of course even with AG that 'habitual' problem is not going to go away as there are going to be noticable and "adapted-to" issues with most proposed AG schemes.

The "main" problem with landing on Mars after a long period in microgravity is the very LACK of time between micro and adverse gravity during landing. Going from nothing to upwards of 6Gs during the landing (possible in some scenerios) might be more than the astronauts can take after a long trip. (This doesn't seem as likely as it once did given the number of times long duration astro/cosmo-nauts have been exposed to purely ballistic recoveries on the Soyuz) But still it would probably take at least a few weeks to fully adapt back to gravity after a long trip. The major reason for AG being needed was for the most part because the STAY on Mars for most early missions was only a few weeks meaning there wasn't enough "adapt" time built in to allow much actual work. This may no longer be the case.

Randy

Randy,
     It seems the less time spent in Microgravity the less likely those bad habits will be established.  Establishing a .5 to .75 Gee centripedal force should prevent much of the physiological issues involved with microgravity, but still won't resolve the radiation issues.  (Whose brilliant idea was it to convert to Servets from Rads?  This new system still confuses the heck out of me and I'm actually suprised I heard nothing about the change over until the Fukashima disaster).
     Regardless of whether we take the long chemical rocket trail or a faster nuclear trail, the Health (physical and Mental) of the crew is going to be paramount.  if we can get them to Mars and back in a total of about 6 months, while stressfull, it shouldn't be a mission breaker.  Two years or more, you'll not only want a larger habitat and a larger crew, but definately AG.

[alexterrell]

Though AG increases the complexity of the vehicle in some ways it can simplify the design of other parts.

Even partial G makes liquid gas separation a lot easier.
This would simplify at lot of the ECLSS design eliminating a lot of small high speed centrifuges and small passageways increasing it's reliability.

Partially true though bear in mind the ECLSS has to be able to work in zero-g as well. You cannot guarantee spin gravity for the entire voyage.

[alexterrell]

Bear in mind the delta v penalty for a fast transit (2-3 months, compared to 8 months) to Mars is massive - like from 5km/s to 40km/s from low Earth orbit.

If the choice is, a small fast ship with low mass and no artificial gravity, versus a large slow ship with artifical gravity and a larger crew number, then I'd go for the latter, despite the radiation (GCR) issue.

[savuporo]

The real problem is that we dont know the effects of spin gravity at all.
Effects of prolonged micro-g are well quantified, we have no data on what spin G does to humans over a prolonged period. Trying it out for the first time on a martian sortie with no way to turn back would be a Bad Idea - maybe they will all co crazy from prolonged sea sickness or something.

Engineering related effects on mechanisms etc are much easier to test and quantify, but even that might have some hidden risks.

This is what OCT technology roadmap says on the subject

Artificial-Gravity Systems (TA06, TA07)

Artificial Gravity spacecraft has been researched for years as an option for reducing the detrimental effects of long-duration 0-g on the human physiology. It would also benefit LEO and HEO commercial facilities. Artificial Gravity includes technologies and research of Artificial Gravity spacecraft for long-duration deep space missions.
Examples of technologies required include Coriolis counter-effects technologies; deployable and retracting mechanism for A-G spin-up & down in zero-G; power and/or propulsion for spin-up/spin-down; tethers (momentum exchange); light weight high-strength tension cables; slip-rings for high efficient power transfer on rotating joints; counter rotating docking mechanism; and magnetic force suits (body suits that would experience a downward force due to localized magnetic field).

[JohnFornaro]

What happens if astronauts are kept in some kind of suspended animation? Would that also retard or suspend their skeleto-muscular atrophy?

There is no such a thing at the present time.

[JohnFornaro]

The real problem is that we dont know the effects of spin gravity at all.
Effects of prolonged micro-g are well quantified, we have no data on what spin G does to humans over a prolonged period. Trying it out for the first time on a martian sortie with no way to turn back would be a Bad Idea - maybe they will all co crazy from prolonged sea sickness or something.

I had not considered the idea that spin gravity would be different from gravitational gravity at all just yet.  I would like to see a roughly 900m dia, 1rpm ring station, which would generate one gee at the rim.  There could be lunar and martian rings inside of it.  If the station were at L1, the trip to and fro would be just a few days.

Assuming as always in these speculations, money would not be the main problem, but would have to be considered.

The building of such a station would take at least ten years, assuming greater launch capability than was required for ISS.  It would be started from two habs on a tether, so the spin gravity effects could be studied from the very beginning of construction.  Intuitively, I feel it wouldn't be a problem, thinking that the inner ear, after a day or two, would be well acclimated to that lazy spin.

Smaller, faster rotating components would certainly have deleterious effects.

My approach suggests that the easiest thing on the body be attempted, even though that means more mass to space.   After all, I reason, mass is your friend.

[kkattula]

Apart from toilets, there are a lot of things that are easier and safer in even fractional g, e.g. cooking, cleaning, personal hygiene, sleeping, equipment maintenance & repair, air circulation, water recycling, fire fighting.

Zero g can be designed for as a temporary, transitional state during maneuvering. The crew can be exposed to Mars and Earth gravity levels for weeks before each respective arrival to acclimatise them.

I'm a fan of rotating and non-rotating sections. I'd put the bearing inside the pressure vessel so it can be easily maintained, with several layers of non-load bearing rotating air seals outside that, and scavenging air pumps between some of the seals to reduce air losses to a tiny amount.


Of course it should be tested in cis-lunar space before committing to a Mars trip. It's just a great shame that almost nothing in this field has been tested in space in the last 40 years.

[neviden]

The only good reason why we should have 0g is that it makes design simpler, you can use aerobreaking and you save 5% weight.
1g would keep crew healthy and make many other things simpler. I don't think that it is "ok" for crew not been able to walk after a multi-year mission in space.
 `
Any mission that would take more then few weeks to complete, should be 1g, by default.

[JohnFornaro]

Of course [AG] should be tested in cis-lunar space before committing to a Mars trip. It's just a great shame that almost nothing in this field has been tested in space in the last 40 years.

More supporting evidence regarding the theory of intention regarding HSF that I raise from time to time.

It's more than a "shame". Necessary work is simply not being done, and there's no data whatsoever being offered as to why AG, plant growth, propellant manufacture, etc. are not now, and have not ever, been studied to the extent that they need to be studied.

[RanulfC]

The real problem is that we dont know the effects of spin gravity at all.
Effects of prolonged micro-g are well quantified, we have no data on what spin G does to humans over a prolonged period. Trying it out for the first time on a martian sortie with no way to turn back would be a Bad Idea - maybe they will all co crazy from prolonged sea sickness or something.

Engineering related effects on mechanisms etc are much easier to test and quantify, but even that might have some hidden risks.

There does need to be more research on a LOT of things before we go to Mars, just to retire a large amount of risks that we don't have a lot of practical knowledge base for at the moment.

Of course it should be tested in cis-lunar space before committing to a Mars trip. It's just a great shame that almost nothing in this field has been tested in space in the last 40 years.

Didn't they schedule an experiment during Gemini that had to be called off because of a malfunctioning Agena rocket? Still not much "excuse" for not doing "something" in the last half century, but given the numerous constraints on hardware and finances its not hard to see "why" it hasn't happened but it's frustrating none the less.
(Vibration is a bugaboo for many experiments on the ISS, movement, thruster-kicks and mechanical transients all are bad enough without a rotating section attached )

The only good reason why we should have 0g is that it makes design simpler, you can use aerobreaking and you save 5% weight.

"Simpler" somewhat and you DO save mass but you can "aerobrake" with a ring habitat sized aerosheild if you really want to. Since such a ship would have to be "put-together" building a large areobraking shield is actually easier.

Randy

[neviden]

Those limitations are kind of the worst things about AG that I could find. Some people (big rocket guys mostly) don't like an idea of an assembled shield. I think that it would work just fine.
The same with ekstra complications. 5% isn't that much of a deal either.
`
1 G should be default preference, but that goes against the whole "we must build 0 G laboratory in space, so that we can learn to live in 0 G, that's why we need $100B" idea.. 

[daveklingler]

I would like to see a roughly 900m dia, 1rpm ring station, which would generate one gee at the rim.

Long before that happens, I'd like to see an 893m tether with a hab on one or both ends, spinning at 1 rpm.  It's not a very tall order - the tether would be virtually off-the-shelf and the hab could be a station module modified to hang at 1G.  Berthing could be done either by clamping at the center of the tether, followed by a move down toward the hab, or at the hab itself.

Testing of artificial gravity on human subjects has been done.  Human beings seem to put up with 1 rpm without problems, but 2 rpm was too much.

[JohnFornaro]

It would be started from two habs on a tether, so the spin gravity effects could be studied from the very beginning of construction.

You must have missed that part:

I would like to see a roughly 900m dia, 1rpm ring station, which would generate one gee at the rim.

Long before that happens, I'd like to see an 893m tether with a hab on one or both ends, spinning at 1 rpm.

Hopefully, you see 893m as being "roughly" 900m.  Seems like we agree on the rpm.

[RanulfC]

Those limitations are kind of the worst things about AG that I could find. Some people (big rocket guys mostly) don't like an idea of an assembled shield. I think that it would work just fine.
The same with ekstra complications. 5% isn't that much of a deal either.
`
1 G should be default preference, but that goes against the whole "we must build 0 G laboratory in space, so that we can learn to live in 0 G, that's why we need $100B" idea.. 

There is a lot of resistance to in-space and on-orbit assembly, some based on some not-so-good previous work and some based on a lot of false assumptions

You've got the "zero-g" lab part wrong though, it was and is mostly to learn what we can DO in microgravity rather than if we can "live" there for prolonged periods. We've already proven the former but are still looking for the former

Randy

[JohnFornaro]

You've got the "zero-g" lab part wrong though, it was and is mostly to learn what we can DO in microgravity rather than if we can "live" there for prolonged periods. We've already proven the former but are still looking for the former latter.

Fixed that for ya?

[neviden]

Well, some of that learning involved observing what happens to astronauts living in 0 G.

[nscali]

Without using a tether how big would a rotating hab "ring" have to be to generate comfortable artificial gravity? Are there any concrete studies on this? From what little I've read on the subject you would need a very large diameter ring to create a gravity effect that doesnt make the astronauts want to lose their lunch. Definitely much larger than we could launch in a single piece right?

[neviden]

There are some studies, but nothing definitive. Tens of meters seems to be the minimum.

[nscali]

Even something like this seems far off at around 12-15m, could you imagine the BFR needed to launch it? Not to mention the speed at which it would have to spin...Doesn't seem worth it.....

[JasonAW3]

What happens if astronauts are kept in some kind of suspended animation? Would that also retard or suspend their skeleto-muscular atrophy?

There is no such a thing at the present time.

Not entirely true.

     Over the last few years surgeons have been using a form of deep hibernation for many more complex operations that require the Heart to stop beating.  This usually lasts about 45 minutes.  They have also been able to induce a hibernative state with the use of low quantities of Sulfur dioxide and low temperatures, but have only maintained this for a few hours at best.

Jason

[alexterrell]

Testing of artificial gravity on human subjects has been done.  Human beings seem to put up with 1 rpm without problems, but 2 rpm was too much.

This is not what I've read. I can google for research but I recall that:

- The Stamford Torus chose 1rpm because just about all humans won't notice this (except when playing ball games).
- Most humans are quite happy at 2rpm, but some sensive people may feel the effects.
- Many are quite happy at 4rpm, and may get used to it, but more research is needed.

The difference between 1 and 4 is a 16 fold reduction in radius.

More experimentation is needed - I'd like to see a variable tether experiment. But you can get something into a near term inflatable volume.

[alexterrell]

Even something like this seems far off at around 12-15m, could you imagine the BFR needed to launch it? Not to mention the speed at which it would have to spin...Doesn't seem worth it.....

You could launch an inflatable ring - that would fit in most fairings.

However, to be useful, you need a radius of about 20-25m. The inflatable structure for that could fit into SLS, or even F9 Heavy. But the impact shielding would be very heavy. Plus such a radius is useful for hundreds of passengers. Not the dozen or so who could go on a first mission.

[QuantumG]

All rotation experiments that have been done have been done in Earth gravity.. with the exception of the minor tether experiments done on the Gemini flights.

For all we know humans have no problems with 10 rpm.. if there isn't a gravity field messing with the inner ear.

[Vultur]

My approach suggests that the easiest thing on the body be attempted, even though that means more mass to space.

I think that ends up being an argument for not doing it since you can always come up with more improvements to make it safer or easier.

Early exploration is always hazardous, there's little point in trying to get around that. Choose an acceptable risk level (probably much higher than we accept for ISS say... more on the level of early Antarctic exploration) and go.

[JohnFornaro]

My approach suggests that the easiest thing on the body be attempted, even though that means more mass to space.

I think that ends up being an argument for not doing it since you can always come up with more improvements to make it safer or easier.

Yes, it ends up being that argument if you don't want to go.  If you do want to go, you'll find a way to deal with the additional mass and its accompanying margin.

[JohnFornaro]

What happens if astronauts are kept in some kind of suspended animation? Would that also retard or suspend their skeleto-muscular atrophy?

There is no such a thing at the present time.

Not entirely true.

Over the last few years surgeons have been using a form of deep hibernation for many more complex operations that require the Heart to stop beating.  This usually lasts about 45 minutes.  They have also been able to induce a hibernative state with the use of low quantities of Sulfur dioxide and low temperatures, but have only maintained this for a few hours at best.

"A few hours at best" in the confines of a terrestrial hospital sounds like "no such thing at the present time" in space.

[alexterrell]

All rotation experiments that have been done have been done in Earth gravity.. with the exception of the minor tether experiments done on the Gemini flights.

For all we know humans have no problems with 10 rpm.. if there isn't a gravity field messing with the inner ear.

I wonder if they could knock up an outdoor experiment at the ISS.

What would be the cheapest format? You could have two freeflying modules, each big enough for 1 astronaut for 12 hours at a time. Or would it just be easier to use 2 manned Dragons away from the ISS? (One on the way to ISS, and one returning, for like 4 days of testing).

[Patchouli]

Though AG increases the complexity of the vehicle in some ways it can simplify the design of other parts.

Even partial G makes liquid gas separation a lot easier.
This would simplify at lot of the ECLSS design eliminating a lot of small high speed centrifuges and small passageways increasing it's reliability.

Partially true though bear in mind the ECLSS has to be able to work in zero-g as well. You cannot guarantee spin gravity for the entire voyage.

I thought about that and you just simply make use of a Skylab style open ECLSS during the microgravity parts of the flight.

The consumables would be sized to allow an abort back to Earth or the Martian surface hab if needed.

[Vultur]

My approach suggests that the easiest thing on the body be attempted, even though that means more mass to space.

I think that ends up being an argument for not doing it since you can always come up with more improvements to make it safer or easier.

Yes, it ends up being that argument if you don't want to go.  If you do want to go, you'll find a way to deal with the additional mass and its accompanying margin.

Except that missions will exist within financial limitations, which means limited numbers of launches thus limited mass. So you can't just "deal with" more mass. Early Mars missions will probably need to be minimalist.