Artificial Gravity

Ian · 2003-04-20 14:59:12

Hi. I was just reading Einstein's theory's of gravity and I just wanted to say that I know that 1 g could be simulated if you travel at a certain speed. I also want to say that this might be usefull considering people might or might not want to feel "weightlessness" on the long trip to mars.

Fishbowl236 · 2003-04-20 15:13:43

Exactly, It cna be simulated by centrifugal foce if the craft was spinning. If it was in a Ring design habitats could be located on the ring would have artificial gravity.

RobertDyck · 2003-04-20 15:41:11

Artificial gravity is produced by ACCELERATION, not SPEED. That means you require a 1g acceleration to simulate 1g of gravity. 1g is defined as the acceleration of gravity on Earth at sea level, which is 9.78 metres per second per second (9.78m/s^2) at the equator. Producing continuous acceleration requires continuous thrust, and continuous acceleration at that level requires a great deal of fuel. It would certainly get you there quickly; in fact it could take less than 4 days if you timed it when Earth and Mars are at the closest position in their orbits. However, fuel expended would be immense. If your spacecraft has a dry mass of 25 tonnes, including propellant tanks and engines, and you expect to use 100 tonnes of propellant, then the specific impulse would have to be somewhere around 1,000,000 seconds (1 million kgf?s/kgm). The solid rocket boosters (SRB) of the space shuttle achieve 269 seconds in vacuum, the shuttle main engines (SME) produce 455 seconds in vacuum, the Nerva nuclear thermal rocket developed 1950-1974 produced 825 seconds in vacuum, the Nerva-2 engine designed in the late 1980s had 925 seconds, the Timberwind nuclear thermal rocket developed in the late 1980s/early 1990s had 1,000 seconds in vacuum, the NSTAR ion engine on Deep Space One produced 3,100 seconds, the 50cm high-power ion engine currently under development at the Glenn Research Center is estimated to achieve 8,300 seconds at 10kW of power. A specific impulse of 1 million seconds is orders of magnitude above this. Don't expect to achieve that within your life time.

Gennaro · 2003-04-20 18:43:18

Ian, you don't need Einstein to prove artificial gravity. Maybe you confused the notion of artificial gravity from acceleration, with Einsteins theory of mass increase as a relativistic effect? If that sounded like I meant to impress you, forget it! If there's one thing I fail to understand it's the logic behind the theories of relativity.
Anyway, if your spaceship accelerates with the constant equivalent of 1 g, that is 9.78 m/s, you will be pressed in reverse to the direction you are going, resulting in the bottom of the spacecraft becoming the floor upon which you can stand. This is a simulated gravitational effect, resulting from linear acceleration (ordinary newtonian physics). The layout of the ship with its floors can maybe best be compared to a sky scraper, rocketing through space.
As a certain kind of antimatter propulsion concept can reach specific impulse levels of around 10 million seconds, it's at least theoretically possible to build such a spaceship as you propose. When deaccelerating, you simply turn your ship around and fire its engines for the same effect.
However, within less than a year of 1 g constant acceleration (disregarding eventual relativistic effects) you will have surpassed light speed which according to Einstein is a physical impossibility.
A much simpler way of creating 1 g of artificial gravity would instead be to utilize centrifugal force (centripetal acceleration), that is a habitation section constructed as a big revolving cylinder. In this case the floor becomes the curvature of the outer hull, with upper floors directed towards the center of the cylinder like the peels of an onion or rings on a tree trunk. This option is of course only really effective when our spaceship moves without accelerating.
The nearer you get to the center of such a cylinder, however, the gravitational effects will decrease, making upper/inner floors of a cylinder close to useless and a waste of space.
Now, please all tell me what you think of this solution! If you fill this center area with vertically arranged floors, like in a sky scraper and you have a spaceship that can accelerate at the level of 1 g, I suggest this section of living quarters could be used during the acceleration/deaccelleration phases of the journey to say, Alpha Centauri, and the outer onion peel arranged area during mean speed phases, when you are not firing your big antimatter boosters.

Algol · 2003-04-25 13:22:26

unfortunately this method cannot be used on the passage to mars as our ship would be too small. The size of the spinning habitat would be restricted and so any induced artificial gravity would vary to greatly over the length of the body of a person standing, thus inducing nausea. Put simply, gravity may be 1g at his feet, but it might be as low as 0.5g at his head.

One way to counter this is to simply only apply as much g as would be necessary to maintain muscle/bone mass. They are currently studying this at nasa and esa Also a lower applied artificial g would drop of slower (it drops of exponentially) so the difference of g over an area would be less.

Also it should be noted that if you go for too high a induced g, there are problems of balance that might induce a wobble in the space craft (like a washing machine but less violent ) which would disastorous in terms of applying your thrust in the right direction.

nick

dickbill · 2003-04-25 14:36:55

I am not convinced that rotating structure cannot do the job.
Go to http://www.labcentrifuge.com/gforce5.html
for g calculation (use cm, not meters)
A 30 meter radius structure rotating at 4 rpm gives 0.536g for the feet.
at 28 meters, you get 0.500g for the head if you are 2 meters tall. There is only a 0.036g difference. Maybe the coriolis effect would be acceptable in this condition.
I think it's preferable to have such a relatively compact structure, I mean compared to the 900 meters radius rotating at 1rpm and 1g gravity.
A trip to the 30 meters tunnel would allow to reach the center of the rotating ship and the manoeuvrability is preserved. It seems safer. On the other hand, a 900 meters tether seems poorly manoeuvrable and difficult to set up and down. This is just a feeling, I am not a specialist.

Algol · 2003-04-26 03:42:12

This was exactly my point, if you aim for a reduced induced 'g' the drop accross the length of the body will be less, the same affect can be achieved from using a larger rotating structure.

A radius of 30 meters is extremely unrealistic for our first mars mission. If we assume a radius of 10m, generous in my opinion, and wanted to maintain 1g (worst case) then the drop of by head height would be just over 0.2g.

The idea for the 900 m rotating tethered structure is that it negates any discernable effect from drop off by being extremely large whilst not requiring any prohibitively expensive construction in space, and the slow rpm will reduce the 'woble' effect of any imbalances.

However the tether idea does fill me with unease due to possible complications involving letting the tether out and being seperated from your engine, as well as the stopping it all at the end ???

A 30m radius rotating colony ship makes more sense, (cant wait to see them! ) but it would simply be too large for the mars direct/NASA reference mission

nick

dickbill · 2003-04-26 09:12:19

A 30m radius rotating colony ship makes more sense, (cant wait to see them! ) but it would simply be too large for the mars direct/NASA reference mission

For the first mars mission, as said Zubrin, 'iron men in wooden ship" etc, the security and comfort might not be as primordial than in the subsequent missions.
If there is Mars settlement one day, we won't call that a "mission" anyway.
But, for the first "mission" maybe there won't have any gravity at all, and the guys in the wooden ship might get more radiation than "necessary". When they come back to earth, they might very well be "cooked", but hey, they have been the first one ! (I hope it's not gonna be like in life, nice guys finish last).
For the next trip, again not a mission but rather like a cruise, couch potatoes like me request a comfortable 0.5 g , with minimum coriolis, and with no radiation. And I don't want to be 1 km away from the center of gravity of the ship. In "mission to mars" the movie, they had to transfer in space and one of them was frozen alive because he missed the target 1 km away!

So, but you said 30 meters is unrealistic, why's that ?
The rotating device could be 2 space shuttle tanks separated from 60 meters and linked trough the central ship where they could transfer trough an elevator. No need for a pressurized tunel. And 4 rpm is just one turn in 15 seconds, it's not very fast.

Algol · 2003-04-26 10:46:04

My point was that the first mission to mars will want to involve minimal construction in space (keeping in line with the mars direct plan and assuming it is in the near future, <touch wood>, ie there is inadequate in-orbir infrastructure for this at the moment), thus a 60 meter diameter ship or two shuttle boosters connected via an elevator or any other rigid means is unrealistic.

nick

dickbill · 2003-04-26 15:04:33

I understand the lack of space infrastructure NOW, but in 20 years ?
If it was to be now, say in the next following 5 years, I would say that they will do the trip in zero gravity, but with a lot of exercise and a compressing exosqueletton. That won't mimic the gravity for the blood flow and the heart pumping to the head, but that will very well simulate the pressure on the bones and the muscles. For a first mission, that's the best IMO, after all, the first ones need some challenge.
A vaincre sans peril, on triomphe sans gloire !

MarsGuy2012 · 2003-04-26 20:02:39

Algol,

"However the tether idea does fill me with unease due to possible complications involving letting the tether out and being seperated from your engine, as well as the stopping it all at the end."

I know the Mars Direct plan by heart. 'The Case for Mars' is my favorite book. I've read/studied it five to ten times. So trust me when I say your unease is unfounded. First, the counterweight at the other end of the tether is just the burnt out upper stage that threw you to Mars. It has no fuel and is useless except as dead weight. Your engines for orbit correction and landing are on the Hab itself. Second, to stop the rotation and get ready for Mars aerocapture all you have to do is cut the line. The counterweight will fly off and the rotation will stop.

The tether system is extremely simple, but if for some unexpected reason the counterweight can just be cut off and the mission can continue in zero-g. I suggest testing the tether on the first ERV that is sent out 2 years before the first manned mission. That will help work out any bugs. With the manned mission I say hope for the best and prepare for the worst. Try the tether and if something goes wrong and you have to cut it just use the excersize equipment that you brought along as a backup.

RobertDyck · 2003-04-29 07:00:35

Well, actually if you cut the tether the hab will continue to spin. During rotation the hab would rotate about the centre of gravity for the hab/spent stage system. However, both the hab and stage spin at a rate of one spin for each rotation. After all, you don't want the roof of the hab to become the floor every half rotation. Once you cut the tether the rotation will stop, but not the spin. (Differentiating "rotation" from "spin" is a bit arbitrary, but it was the easiest way of referring to the two types of rotation.) You will have to use thrusters or a very big flywheel to stop spinning. A flywheel is not practical, so that leaves thrusters. Controlling spin with thrusters is pretty easy, but it is more than just cutting a cable.

By the way, if you tried to "reel in" the cable after releasing the stage, it would increase the spin of the habitat. This is the same as a figure skater spinning slowing with arms extended, then increasing her spin by pulling her arms in; it is conservation of angular momentum. That problem is prevented by just releasing the cable from the hab.

Bill White · 2003-04-29 10:46:14

This is exactly why I believe it would be worthwhile to practice with a Soyuz/Progress combination in LEO.

Ian · 2003-04-29 11:43:02

Woud't it be easier to first simulate zero g in freefall and then the tether system and artificial gravity using centrifugal force in freefall and also some experiments that are related to this on the ground.

Algol · 2003-04-29 12:36:40

I believe students in europe have already conducted experiments on tethered systems in freefall, using the ESA parabolic flight campaign.

This is one link a quick search pulled up.

http://esapub.esrin.esa.it/bulletin/bullet85/ocke85.htm

nick

Bill White · 2003-04-29 12:48:12

Woud't it be easier to first simulate zero g in freefall and then the tether system and artificial gravity using centrifugal force in freefall and also some experiments that are related to this on the ground.

In my opinion, one key question is whether astronauts can maintain safe control of a spacecraft while manuevering in a tethered configuration. Yes, we can sim the heck out of this but sooner or later two spacecraft will need to accomplish a large range of flight manuevers while tethered together.

The potential for astronaut disoreintation is a major concern - IMHO - that would be ruled out or confirmed by a Progress/Soyuz test flight.

If this is *NOT* feasible then we can pretty much toss MarsDirect on the scrap heap and wait for some nice new fast nuclear rockets to travel fast and avoid the health risks of extended exposure to microgravity.

Is there a downside to tethering a Progress nose to nose with a Soyuz and then rotate the pair and attempt various flight manuevers? Am I missing something?

Shaun Barrett · 2005-04-30 22:18:08

NASA is doing some work using this set-up:-

For the initial study this summer, 32 test subjects will be placed in a six-degree, head-down, bed-rest position for 21 days to simulate the effects of microgravity on the body. Half that group will spin once a day on the centrifuge to determine how much protection it provides from the bed-rest deconditioning. The "treatment" subjects will be positioned supine in the centrifuge and spun up to a force equal to 2.5 times Earth's gravity at their feet for an hour and then go back to bed.

For the full story, see http://www.spaceref.com/news/viewpr.html?pid=16783]THIS ARTICLE.

GCNRevenger · 2005-05-01 00:02:56

Woud't it be easier to first simulate zero g in freefall and then the tether system and artificial gravity using centrifugal force in freefall and also some experiments that are related to this on the ground.
In my opinion, one key question is whether astronauts can maintain safe control of a spacecraft while manuevering in a tethered configuration. Yes, we can sim the heck out of this but sooner or later two spacecraft will need to accomplish a large range of flight manuevers while tethered together.
The potential for astronaut disoreintation is a major concern - IMHO - that would be ruled out or confirmed by a Progress/Soyuz test flight.
If this is *NOT* feasible then we can pretty much toss MarsDirect on the scrap heap and wait for some nice new fast nuclear rockets to travel fast and avoid the health risks of extended exposure to microgravity.
Is there a downside to tethering a Progress nose to nose with a Soyuz and then rotate the pair and attempt various flight manuevers? Am I missing something?

Nah, we don't need fast rockets or zero-G to get to Mars, humans can handle a 5-6mo trip in zero-G all the way.

The biggest problems I think are the damage that would be sustained from the sudden change in dynamics... for the ship or the crew... if the cable were to break. A serious risk going from 0.3G to 0G in a fraction of a second. Liquid tank sloshing?

Secondly, the possibility that the cable could be "whipped" when it fails, such that the vehicle would enter an end-over-end spin. Bad news for the crew if they can't quickly correct.

Thirdly, communication with Earth would be difficult, since you could not so easily align a high-gain directional antenna with Earth.

Fourthly, all parts of the vehicle must resist the 0.3G acceleration deployed. That means no light weight extendable radiators, solar pannels, or radio antennas. How are you going to get power when spinning? ...One of the many failings of MarsDirect that Bob glosses over I think.

Fifthly, if you are using an NTR engine for upper stage & escape burn, like MarsDirect would need to have sensible mass margins, then you will be tied not far away from one big hot nuclear reactor for extended periods. Not a small RL-10 sized nuke, but a big SSME-sized one... radiation hazard and all.
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"Is there a downside to tethering a Progress nose to nose with a Soyuz and then rotate the pair and attempt various flight manuevers? Am I missing something?"

-Costs ~$100M+
-Unessesarry
-Manevuers are easy
-Unsafe for Soyuz crew
-Progress/Soyuz solar pannels/radar/antenna would snap off
-Not reprisentative of the Mars vehicle
-Russia is broke and can't afford it, but NASA can't pay Russia to do it

Yeah, you missed something.

Shaun Barrett · 2005-05-05 04:56:57

GCNR:-

...humans can handle a 5-6mo trip in zero-G all the way.

Yes they certainly can handle a 6-month zero-g trip to Mars.
The question is, can they handle 6 months in zero-g, 18 months in 0.38g, 6 more months in zero-g, and then a sudden return to 1g (after 2.5 years)?
My guess is no, they can't.

The biggest problems I think are the damage that would be sustained from the sudden change in dynamics... for the ship or the crew... if the cable were to break.

Sure. Big problem. But why should the cable break?
Why not worry about a large meteor impact?
What if you have a car crash ... what if your airbag doesn't deploy?
What if you have a heart attack tomorrow?
Why don't we just make a reasoned evaluation of the risks and understand that the rotation-cable breaking on the trip to Mars is an extremely low risk?

Thirdly, communication with Earth would be difficult, since you could not so easily align a high-gain directional antenna with Earth

Have a small communications pod, with antennae, on the cable, at the centre of gravity. It would have no problem aiming toward Earth.

Fourthly, all parts of the vehicle must resist the 0.3G acceleration deployed. That means no light weight extendable radiators, solar pannels, or radio antennas. How are you going to get power when spinning? ...One of the many failings of MarsDirect that Bob glosses over I think.

Put the solar panels on the centre-of-gravity pod, too. And, with the modules rotating once per minute, or faster, heat build-up should be controllable.

Fifthly, if you are using an NTR engine for upper stage & escape burn, like MarsDirect would need to have sensible mass margins ..

If we have comfortable 1g living quarters for the trip, by utilizing centripetal force, do we need to use an NTR for a faster trip? Why not increase our margins by taking a month longer to get there?
Admittedly, the less time in interplanetary space, the less the radiation dose. But I believe radiation is a far lesser danger to the crew and the mission than the deleterious effects of bone and muscle wasting during 12 months in zero-g and 18 months in 0.38g. And then there's the PR disaster of astronauts being dragged off the ERV, incapacitated, on stretchers and life-support.

Just a few thoughts to counter GCNR's regular doom-and-gloom scenarios.
[No offence GCNR, but your pessimism and tut-tutting can get depressing at times. No doubt you call it 'realism'. ]

BWhite · 2005-05-05 07:41:21

Why would it cost $100 million to tether a Soyuz to a Progress? Both ships are up there already, fully depreciated on the bean-counter ledger books. The spacecraft are FREE as we are merely adding tasks to vessels that have already finished their primary mission

Marginal cost would be the flight controllers and the tethers. But the staff at Korolev is on salary, I imagine.

= = =

Risk of cable failure? Use two, or three each independently capable of handling the load.

Edited By BWhite on 1115300676

GCNRevenger · 2005-05-05 12:31:00

I think that they can probobly be just fine for the round trip without artifical gravity on either inbound or outbound leg. As long as they have a little gravity, the body's "self destruct" isn't triggerd and the skelaton shouldn't weaken, so then the concern is the muscular/cardiovascular systems, which can be maintained by excercize. Plus, if the crews are going to be working outside in heavy suits much of the time, then their effective weight won't be much different then Earth.

The one time a real space tether has been tested (Shuttle tried it) it failed. A long space tether is much less of a sure thing than Bob makes it out to be. And yes, the cable should have to be able to take micrometeoroid impact, just like the rest of the vehicle should. You are going to be putting several tonnes of strain on this cable for months on end, and bad things would happen if it were to break (see above).

I am not happy about the idea of a pod-anything. Aligning it with the center of gravity won't be a trivial task, and if the cable DOES break, it is a pretty heavy piece of equipment that could hit the ship like a wrecking ball in the worst possible place, the aerobrake shield.

Putting the solar arrays, which will be fairly large (like a pair of SAFE arrays), on the central pod is a lousy idea too. They will still have to spin, unless you fancy a complicated powerd bearing with rotating wire connections and regular re-spinups of the vehicle and the spent boost stage, just not as fast. Running a heavy multikilowatt electrical cable from the pod to the ship is a mass concern too... Oh, and you will need at least some radiator capability most likly.

In such an arrangement, the spent booster stage would also need to remain functional, at least the RCS thrusters, attitude sensors, and control mechanisms, through the whole flight.

If you are going to use a nuclear engine, as you would have to in order to make MarsDirect fly most likly, the trouble is you are going to have a big, hot reactor tied to your ship and not far away. The mass of the extra shielding to protect the crew from this continuous threat would be nontrivial. For MarsDirect to work, the NTR engine is non-negotiable, an all-chemical design will never push enough payload to even safely get the crew there and back. The NTR engine is about payload margins, not speed.

You can't trade too much speed for mass either, otherwise you will never even sufficently escape Earth's gravity nor skirt the Sun's well enough to actually get to Mars. The six-month trajectory is already about as slow as you can go without switching to the Conjunction class mission, which basically eliminates your stay and takes you much closer to the (radiation-spewing) Sun. And there are the psychological concerns to worry about being cooped up for so long.

And, frankly, your suggestion sounds like another desperate try to save the fatally flawed MarsDirect by sacrificing something that you really, really shouldn't. We HAVE to get away from this "cut off the toothbrush handles" thinking if we are ever to get anywhere safely, weight creep will kill the design dead. If we "just barely" get there, then it was a waste of time and money from the beginning... "Just getting there" is NOT the goal, after all.
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Bill: I could see the cable, winch, additional docking equipment all adding up to a few tens of millions. Plus, the extra mass for such will take up the whole Progress payload, which means you'll need a whole fresh vehicle just for this. A few more million for Progress RCS/attitude control modifications, and you are well on your way to a nine-digit project when you throw in crew training and ground support.

Shaun Barrett · 2005-05-05 17:57:02

GCNR:-

I think that they can probobly be just fine for the round trip without artifical gravity on either inbound or outbound leg. As long as they have a little gravity, the body's "self destruct" isn't triggerd and the skelaton shouldn't weaken, so then the concern is the muscular/cardiovascular systems, which can be maintained by excercize. Plus, if the crews are going to be working outside in heavy suits much of the time, then their effective weight won't be much different then Earth.

Your comment about even "a little gravity" sufficing to prevent loss of skeletal strength is interesting. I didn't know that. This information will serve to allay many fears about the maintenance of healthy human physiology on the Moon and Mars. Excellent news!
Can you direct me to a site which compares gravitational acceleration with bone loss over time?

Despite this good news you've mentioned, I still have serious reservations about the cardiovascular systems of our astronauts. I'm no physician, by the way, but it worries me that the blood is so much easier to pump around the body if it's weightless, or is only 38% of its usual weight. Even if the astronauts spent all their time exercising vigorously, their hearts will be having an extended vacation from the stress of pumping 'heavy' blood around the body. And also, many of the muscles which are constantly in use in 1g, such as the neck muscles and various other postural muscles, will not be exercised (or not exercised sufficiently), despite your gym regime.
It seems likely to me that any human in zero-g for 6 months, 0.38g for 18 months, then back in zero-g for another 6 months, will have grave difficulties adjusting to 1g at the end of it.

And, frankly, your suggestion sounds like another desperate try to save the fatally flawed MarsDirect ..

I haven't entered into the fray regarding Mars Direct to any great extent because I don't feel comfortable arguing strongly about spacecraft masses and mission feasibility. I haven't the appropriate engineering background to make sensible comments - beyond the ones I've made above, which I notice you've rejected anyway. (I didn't find that surprising, by the way.) But I'd be interested to see Dr. Zubrin himself engage you in a debate regarding the figures you dispute.
Nevertheless, I don't think you need either an engineering or medical degree to foresee serious health issues if we don't provide gravity for a Mars Direct based mission of the kind of duration we're talking about.

My point is much more to emphasize what I see as the necessity of artificial gravity, and finding ways to provide it, than to defend Mars Direct, as such.
I'm concerned that you seem, at least to me, to find any number of ways to decry plans to get humans to Mars. There are always many more problems than answers in your posts and I find that unhelpful. (Right or wrong, that's the feeling I get.)
America got where it is today on quite a different premise; a 'can do' premise that a tired Old World found refreshing and invigorating. By all means, let's be realistic about the difficulties of manned Mars exploration and colonization, but do we have to be so damned pessimistic all the time?
???

GCNRevenger · 2005-05-05 21:45:55

Ah I'm sorry if I have jumped on you too hard, I have been doing that too much lately (especially with Publiusr...).

I am not trying to be a pessimist despite the way it looks, mainly I am trying to be a realist and move the discussions of various systems, technologies, and goals from "neat idea" to reality. Lots of ideas sound great on paper, but turn out to be impractical, unessesarry, or untrue.

Imparticularly, MarsDirect is one of these things... it is a neat idea on paper, but its not practical as a serious way to get to Mars. Nor is it a good idea in the first place if it did, since its capabilities are so limited and has no real upgrade options. And finally, its creator has permitted his zealousness and pride to bring him to tell lies to try to irrationally rush to Mars to "save" humanity.

...Anyway, if astronauts keep their hearts in good shape, then the muscle will be stronger and not need to "beat" as fast when exerting, right? Well, if the problem with blood being "too light" for too long is that the heart muscle is no longer strong enough to cope with 1G, then excercise to maximize the hearts' strength will counteract that problem entirely, as demonstrated by Mir and ISS crews. With at least a third of your weight on Mars, this should be even less of a problem.

It is much the same way for all the major muscles, and I bet that with a (by our standards) unusual excercise regimine, most of the muscles can be properly kept conditioned, or if nessesarry employ electronic stimulus to prevent aptrophy... NASA is also right now testing drugs on the ISS to reduce muscle loss if memory serves.

We don't need astronauts climbing out of the return capsule ready to run a marathon, they don't even need to be in average-joe shape, they just have to be able to get that way again without long-term difficulty. The need for artifical gravity is simply dubious. Even with no more then excercise, Russian Cosmonauts have climbed and walked out of their Soyuz capsule after a zero-G length of stay almost as long as the entire time a Mars crew would be gone.

Shaun Barrett · 2005-05-05 22:12:13

GCNR:-

Even with no more then excercise, Russian Cosmonauts have climbed and walked out of their Soyuz capsule after a zero-G length of stay almost as long as the entire time a Mars crew would be gone.

I seem to remember cosmonauts being carried from their craft after 12 or 13 months in orbit (?). What if we add an 18 month interval at 0.38g into the middle of a similar period in zero-g, going to and from Mars?
No. I think I'm just going to have to agree to disagree with you on this one.

Incidentally, I'm still intrigued by your reference to this:-
"As long as they have a little gravity, the body's "self destruct" isn't triggerd .. "
Does this mean a prolonged stay on Mars, or even Luna, won't trigger bone loss? I'm genuinely interested in seeing any research articles about this that you may have come across.
Thanks.

Michael Bloxham · 2005-05-06 00:54:56

I agree with GCNR. Zero gravity isn't a show stopper. However, I do think that creating artificial gravity using a tether system would be easy enough to do, and should be utilized nevertheless. I heard once that astronauts hearts decrease to half or so of their natural size after prolonged stints in orbit. Shocking? Not really, because while they work in zero gravity, they don't actually require a terrestrial-strength heart. In fact their whole bodies change, adapting, not deteriorating as some would believe, to zero-g. It would be interesting to see how the human body would adapt after many years in zero-g. The real issue, of course, is bringing them back to earth. Six months should be alright; they don't have to come back kicking, so long as they come back alive. But I think the real benefit of creating an artificial-g environment enroute would be psychological. Not only is a familiar work environment good for morale, but a healthy familiar-looking body is good too: The crew probably won't want to watch themselves wither as they get closer to their destiny.

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