Author Topic: Why artificial gravity?  (Read 13046 times)

Offline Vultur

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Why artificial gravity?
« on: 11/11/2013 12:46 AM »
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?

Online QuantumG

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Re: Why artificial gravity?
« Reply #1 on: 11/11/2013 01:33 AM »
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.
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Offline gbaikie

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Re: Why artificial gravity?
« Reply #2 on: 11/11/2013 04:03 AM »
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.
 
« Last Edit: 11/11/2013 04:21 AM by gbaikie »

Offline Vultur

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Re: Why artificial gravity?
« Reply #3 on: 11/11/2013 06:41 AM »
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.
Quote
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.


Quote
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.

Quote
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.)

Offline IRobot

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Re: Why artificial gravity?
« Reply #4 on: 11/11/2013 07:41 AM »
Also some things are simplified with artificial gravity, for example toilets and personal hygiene.


Offline gbaikie

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Re: Why artificial gravity?
« Reply #5 on: 11/11/2013 11:48 AM »
gbaikie on Today at 04:03 AM

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

Quote
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.
« Last Edit: 11/11/2013 11:58 AM by gbaikie »

Online QuantumG

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Re: Why artificial gravity?
« Reply #6 on: 11/11/2013 08:44 PM »
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.


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Offline Andrew_W

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Re: Why artificial gravity?
« Reply #7 on: 11/11/2013 10:56 PM »
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?
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Offline Vultur

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Re: Why artificial gravity?
« Reply #8 on: 11/12/2013 03:30 AM »
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.

Quote
“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.
« Last Edit: 11/12/2013 03:34 AM by Vultur »

Online QuantumG

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Re: Why artificial gravity?
« Reply #9 on: 11/12/2013 03:43 AM »
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.

Quote from: Vultur
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.
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Online sanman

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Re: Why artificial gravity?
« Reply #10 on: 11/12/2013 04:44 AM »
What happens if astronauts are kept in some kind of suspended animation? Would that also retard or suspend their skeleto-muscular atrophy?

Offline gbaikie

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Re: Why artificial gravity?
« Reply #11 on: 11/12/2013 06:05 AM »
Quote
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 :)
« Last Edit: 11/12/2013 06:14 AM by gbaikie »

Offline Vultur

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Re: Why artificial gravity?
« Reply #12 on: 11/12/2013 06:22 AM »
Quote
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...


Quote
"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'?



Quote

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

Yeah, that was probably poorly phrased...

Online guckyfan

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Re: Why artificial gravity?
« Reply #13 on: 11/12/2013 07:21 AM »

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
« Last Edit: 11/12/2013 07:21 AM by guckyfan »

Offline RanulfC

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Re: Why artificial gravity?
« Reply #14 on: 11/12/2013 04:44 PM »
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
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British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline RanulfC

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Re: Why artificial gravity?
« Reply #15 on: 11/12/2013 04:49 PM »

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
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline Patchouli

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Re: Why artificial gravity?
« Reply #16 on: 11/12/2013 04:58 PM »
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.


« Last Edit: 11/12/2013 05:10 PM by Patchouli »

Offline JasonAW3

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Re: Why artificial gravity?
« Reply #17 on: 11/12/2013 06:22 PM »
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.
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Offline alexterrell

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Re: Why artificial gravity?
« Reply #18 on: 11/13/2013 10:17 AM »
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.


Offline alexterrell

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Re: Why artificial gravity?
« Reply #19 on: 11/13/2013 10:20 AM »
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.