I've arrived on Mars. Argggh, my back! New research brings more bad news to astronauts thinking about long-haul space flights as spinal muscles shrink after months in space, scientists have found. Floating around in space in an environment with little or no gravity is not good for the human body. Along with decreased bone density, nausea, a puffy face, possible …
Just give the poor sods a rowing machine. Shirley!
(Not that I can see any reason why arriving with c. 80%* of normal muscle mass need necessarily be considered a problem when travelling to a destination with just 37.8% of "normal" gravity... I'd have thought it'd still be quite a surplus)
*?: Or whatever? The pertinent figures in the article seemed strangely encapsulated in a peculiar relativistic cipher. Really most odd.
While it's useful to know the long-term effects of exposure to zero-g, why hasn't anyone explained why people haven't started using different ways to actually provide some gravity?
Robert Zubrin tells the story (possibly apocryphal, I haven't found any details on-line) of the late 30's, as fighters started to get up into the high atmosphere, the pilots blacked out and planes and pilots were lost. Doctors wanted to study the effects of low oxygen and things continued until the Generals got fed up and called in the engineers who added a small tank of oxygen, a hose and a mask and solved the problem.
NASA has spent huge sums of money on the study of zero-g but surely astronauts on their way to Mars would at least spin their ship to provide some g? Zubrin himself talks about tethers and rotating your people-carrier with a counterweight.
So, problem going to Mars? This is the story of the dog that didn't bark...
I think this is mainly a cost problem really. To do proper, long term, research into artificial gravity (and I mean something more involved than say Gemini 11 where they tethered two capsules together) would require putting a huge amount of infrastructure into orbit. A rotating space vehicle would have to have a large enough radius to generate 1g (or even half a g, that would probably do) through centripetal force without causing disorientation in the occupants via the Coriolis effect. Keeping the spin fairly slow, say about 2 rpm, would require a radius of some 50-60 meters at least.. a diameter comparable to the length of the international space station.
Whilst it's certainly achievable, that's a lot of stuff to put into orbit for just an experiment. It's certainly well within the reach of some future rockets though, SpaceX's ITS booster, for example, would probably make it financially feasible within two / three launches. I certainly feel it would be a research benefit. With proposed transit times to mars around an average 115 days though (to quote SpaceX) I think the impact of this would be fairly minimal, especially considering Mars gravity is a third of Earths. Less time in microgravity for a start, and less of a shock to adjust to on arrival.
Coming back to Earth after a two years stay in 1/3rd g and then three months in 0g however.. I can't see that being a pleasant experience!!
"Keeping the spin fairly slow, say about 2 rpm, would require a radius of some 50-60 meters at least.. a diameter comparable to the length of the international space station."
Early science fiction authors often had large rotating space stations with the "tyre" being the occupied bit. The problem of getting all that mass up there was ignored, so it was still really a "magical" solution. 2001 was still fantasy rather than science fiction, not because of the monoliths but because of the size of spacecraft required - rather as Gormenghast passed over in silence how a pre-industrial society could build and maintain such a huge edifice given the apparent human resource constraints.
Obviously we need a magical drive to push the craft at 1g to the half way mark and then decelerate at 1g all the way to landing. The journey would also be an awful lot shorter.
Perhaps the real solution to manned spaceflight is to stop messing about with inadequate vehicles and work seriously on physics to identify an energy supply which will actually get enough stuff up there to make things really feasible.
We definitely should work seriously on physics, but there's the distinct chance that an energy supply capable of getting enough stuff up there is simply impossible. We should also work on how to get and use resources that are already out of the gravity well.
"but there's the distinct chance that an energy supply capable of getting enough stuff up there is simply impossible"
Personally, I consider that is most likely the case, but I'm a miserable old git. There may be an extremely good reason why we haven't heard from other civilisations - that the energy requirements to get to the level at which it becomes possible either exceed the capabilities of any habitable planet, or exceed what is politically possible (e.g. if it was concluded that in order to build and maintain a Mars colony we would need to exterminate 99% of the human race to lift enough stuff without catastrophic climate change.)
There's a reason why economics is called the "dismal science". If economics hadn't got there first, the same label could be applied to thermodynamics, whose laws state roughly:
1. You have to play in the casino.
2. You can only lose or break even.
3. You can only break even if you're dead.
could be applied to thermodynamics, whose laws state roughly:
1. You have to play in the casino.
2. You can only lose or break even.
3. You can only break even if you're dead.
"Heat can't move from the cooler to the hotter,
You can try it if you like, but you'd far better notta"..
(Flanders & Swann)
Perhaps the real solution to manned spaceflight is to stop messing about with inadequate vehicles and work seriously on physics to identify an energy supply which will actually get enough stuff up there to make things really feasible.
Like a nuclear powered rocket maybe? up to 8,000,000 tons enough? https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)
nuclear rockets are an _AWESOME_ idea, until the protesters and enviro-wackos show up and sue you into oblivion...
(stupid anti-technology protesters and enviro-wackos - they need a CLUE BAT)
seriously, though, the ideal propellant would be super-heated steam made from ocean water, heated with some kind of nuclear reaction. A nuclear rocket could make that happen. Great for deep space, too.
"seriously, though, the ideal propellant would be super-heated steam made from ocean water"
Think about it. The specific impulse of water is not high - you need a large volume. And ocean water contains a large amount of dissolved stuff that becomes corrosive when hot - which is why steam ships rapidly stopped using sea water in the boiler feed, and why direct cooled Diesel engines are limited to about 60-70C for cooling water. The same problems apply in space only more so, because you can't easily send people into the boiler to clean it out.
Incidentally I believe Feynman had the original patent on the nuclear engine, which he considered a joke because it wasn't really feasible.
The specific impulse of water is not high - you need a large volume.
That depends on the exhaust temperature. Low temperature steam rockets might achieve 180Isp. But hydrogen-oxygen rockets achieve relatively high exhaust velocities with (mostly) water exhaust - Isps of 460 have been demonstrated. Engines like solid core nuclear rockets, which run cooler than chemical rockets to avoid melting their fuel, should get better than 400. The Rooskies tested ammonia and ammonia-alcohol mixtures (similar to water in molecular mass) with nuclear rockets and were estimating 500-550Isp. Of course, ammonia dissociates at those temperatures, lowering the exhaust's molecular mass and raising specific impulse. Water's too stable for that so it's specific impulse would be a bit lower for a given temperature.
But, as you noted, water brings a problem with corrosion even if it's salt-free. Ammonia was selected because it didn't bring those oxidation problems.
"nuclear rockets are an _AWESOME_ idea, until the protesters and enviro-wackos show up and sue you into oblivion...
(stupid anti-technology protesters and enviro-wackos - they need a CLUE BAT)"
Yep, the way round the bodily degradation issue due to lack of gravity is to get to Mars and back by a quicker and more efficient propulsion method such VASIMR and NERVA rocket engines, both of which are do-able with current technology.
Yes, we do need a better energy supply, that's for certain.
However, putting the materials up into space to build a "2001" type space station is not fantasy. Those who read the rest of Clarke's books would tell you the material came from the moon and was launched into orbit using an electromagnetic catapult, which is not at all fantasy. There are plenty of materials there, and the moon's lack of air and lower gravity make such a scheme very feasible for getting materials into Earth orbit.
One would have to figure in the cost of setting up a lunar colony (not cheap) and mining and building a catapult there, but once it was a going concern, the per kilo cost of putting material into Earth orbit would be a fraction of using rockets (even SpaceX ones) from Earth.
Launching material off the moon might be relatively easy, and maybe even mining it won't be to hard, but most of our ore refining methods rely heavily on gravity separations (at least at some point). That's a whole lot of new (and heavy) equipment to design and ship to the moon before you get your first batch of moon-metals.
The cost in rockets of putting the material up is massive. The cable materials have to be extended from the geosynchronous platform. Also we have no proven material for the cable.
The Space Elevator's ongoing maintenance is considerable too. A fusion / plasma torch rocket is frankly more believable than a space elevator on Earth.
An Elevator WILL work on the Moon.
Kevlar might actually be strong enough for a space elevator on Mars.
Why a wheel? Why not a module tethered to a large asteroid by space-age cables?
Spin it up, reel out the module on the cables and Bob's your Capcom. No problems with shifting mass as you engineer things so the big rock is many times the mass of the system at the end of the cables.
Reel out far enough and Coriolis forces won't have everyone throwing up when the turn their heads too.
".....Why not a module tethered to a large asteroid by space-age cables?...." Because (a) asteroids don't come as neatly balanced packages, they're usually odd-shaped masses of materials of differing density and rigidity, making the task of controlling their trajectory and spin a complex task; and (b) because an asteroid might disintegrate under the strains of both being spun, pulled on by the cable's anchor, and driven through space by the main engine.
A better idea might be a spun central core with the main engine and supplies, plus two counter-balancing modules for the crew on tethers. A mini gymn in each crew module for exercising and retaining muscle density and job done. The problem I do foresee is that non-rigid tethers mean you would have to reel the modules in before braking the core at your destination.
No need for two living modules, one is enough. With the bulk of the ship mass on one end of the tether, the living module will do most of the spinning, and feel most of the centripetal force.
In answer to those who suggest massive cables are required for the system, that's not correct. Quite modest cabling can withstand very large loading. If you let it out to several hundred meters you smooth out the negative effects a lot, and there's no need to move between living modules 'cause there's only one.
In fact, the main module would have a slight g-force, perfect for 'light' sleepers. ;-)
Actually two modules tethered with a cable, orbiting a common centre has been suggested.
Wheels and rings
1G isn't feasible due to Coriolis forces if too small, and no strong enough material existing if it's large!
However perhaps 1/3G or a bit more might be enough. Coupled with a clever elastomer structured bodysuit.
"Actually two modules tethered with a cable, orbiting a common centre has been suggested."
The apparent simplicity of this idea hides the unpleasant problems that crop up as soon as an astronaut in one pod moves, even slightly, changing the centre of mass of the module he's in and therefore the rotational velocity of it relative to the other module. You can only really use dampers to correct motion along the axis of the cable, leaving the relative movements of the two modules in 2 translational and 3 rotational degrees of freedom undamped.
i.e. unless you want to be constantly firing thrusters to keep the motion of each module stable, don't try this design for your spaceship.
It could perhaps work with something that looked like an Eagle from "Space 1999" turning end over end and flying sideways.
Another reason to use a ring is that it allows people to walk from one place to another. If you put two modules on the ends of a beam, then to get from one to the other you have a long "climb" to get from one module to the centre and then a long "decent" to get to the other module. Climbs and descents significantly increase the risk of injury from falls compared to something where you can walk "on the flat".
Rings are better/best, but need to be quite big to reduce Coriolis forces, thus materials limit you to about 1/3 G to have a safety margin.
Realistically in terms of shielding, gravity, materials etc, we are still at remote probe stage of exploration, even a moon base would be challenging, and people wouldn't be able to stay much longer per person than on ISS. It would have to be underground for shielding (see "The Moon is a Harsh Mistress" and many other decent moonbase stories. Not Space 1999)
Mage, The moon would be an excellent test bed to study the effects of reduced gravity on the human body as well as ISRU (in-situ resource utilization). The Moon is a Harsh Mistress is one of my favorite books. RAH presents many things as a fait accompli, but he does suggest some very interesting ideas. I have a feeling that a moon base will be less expensive and complicated to construct than an orbiting ring proposed by Gerard K. O'Neill. There might even be some commercial possibilities that could help pay for the endeavor at some point.
"A rotating space vehicle would have to have a large enough radius to generate 1g (or even half a g, that would probably do)"
And that's a fundamental question right there that needs answering eventually. Just how much gravity does the human body need so as not to degrade more than usual over a the months or year(s) of a mission? Say they make it to Mars and find that a long stay in 1/3rd G is bad for them too?
Maybe sometime soon we will see a couple of large Bigelows joined by a tether or even a tube people can get up and down with a docking module in the centre point. (why am I hearing The Blue Danube Waltz in my head?)
Two Bigelow B330 units, one manned, and with an additional orbital manouvering unit docked, in case of emergencies. The other with autonomous scientific experiments and ballast, joined by a dozen kevlar/carbon fibre/whatever latest best tether material is cables; add spin. Investigate effects of LOW gravity (maybe start with 0.1G then go to 0.2G, etc, perhaps)? - that'll get some kind of handle on whether less than 1G mitigates the effects felt in 0G, and to what extent. We could do this now with currently available technology, although I wouldnt; blame 'them' one bit for being cautious re planning for astronaut rescue in all situations (eg: catastrophic failure of all tethers simultaneously), plus how does one regain control of a unit the size of B330 unit that's one of a pair flung apart by centrifugal force?
many science fiction authors have written about viable artificial gravity solutions. Perhaps the more obvious one could be the 'gemini tether' someone else mentioned.
OK here's the idea: Extend two "gravity modules" 10 to 20 meters, using very strong cables [like the ones used for elevators on Earth]. Provide an inflatable tunnel between them, made of the same stuff you might find on a typical work site, going down a manhole or something. It all collapses nicely for launch, acceleration, and deceleration. For the bulk of the trip, it's extended. Careful use of thrusters cold provide the spin, and get rid of it when it's time to decelerate. And sliding weights (computer controlled) could be used for balance, something you might find in an industrial washing machine for the spin cycle [if they're not just using water for the same purpose].
you don't need a full 1G, either. 1/4G or 1/2G would be better than 0G. And you can just minimize the disorientation that fast-spin might cause, rather than trying to eliminate it entirely. [many engineering choices are compromises between multiple ideals, like rounding off at 'enough' digits instead of calculating to ridiculous precision...]
In any case I remember reading books written in the 1950's that seemed to have most of these details worked out. Most likely some bright bulb could come up with a workable solution for a reasonable cost.
but, there's more MONEY in "researching", and the scientists who do the research will get to play with lots of cool toys at (public?) expense...
Do the math, the effect of spinning a small diameter spacecraft is negligible and can lead to some undesirable effects like different amount of "G" on your feet and head.
To spin up and have a reasonable approx to 1G means a really large diameter spacecraft and big engineering problems.
Lets get to Mars first, after all "G" on Mars is less so you don't need as big back muscles.
What do you mean you want to come back?
I think the problem is "how fast".
To achive 1G requires a minimum inside diameter of about 32 feet. Of course this means it has to rotate over 9.5 times per minute.
Then you have to put it inside something else... and deal with bearings between the rotating part and non-rotating part, rotation balance (you don't want it to act like an unbalanced washing machine - it would tear the ship apart).
If you rotate the entire ship - now you cant service anything from the outside without first stopping the rotation (need a lot of fuel). You can't go outside except at the axis of rotation or you get thrown away from the ship... You have a harder time making cource corrections (the ship is a gyroscope). Trouble with fuel balances, pumps...
If you try to make only the sleeping quarters rotate, you don't get the full benefit of the gravity (less than 1/3 time there), you have to deal with bearings, navigation issues, balances...
You also end up with a MUCH larger ship required .
The most likely thing to happen is that you get three ships. One to get to the transport before departure, one mother ship for the transport, another to go from the transport to surface.
And you get to make the transport as large as you need, with all the shielding you need. Live inside a rotating cylinder (bigger than 32 feet in diameter) inside non-rotating shielding, and gimbal mounted so the external propulsion can move around it for navigation purposes.
There is a "spin" calculator that provides a lot of information about simulating gravity. (You also have to be large enough not to cause vertigo).
http://www.artificial-gravity.com/sw/SpinCalc/SpinCalc.htm
Two part solution,
A spin that provides somewhat less than 1g, say 1/3 g
+ lead-lined helmets and shoulder pads!
Just try not to look down too much..or topple over... or move too fast and forget it takes longer to stop with a few 10's of kgs of lead about your person.
Still, might be something in it!
Alternatively, several sizes too small (in the vertical direction) rubber onesies might serve to put some gravity like pressure on the spine.
If you rotate the entire ship - now you cant service anything from the outside without first stopping the rotation (need a lot of fuel). You can't go outside except at the axis of rotation or you get thrown away from the ship...
If you ignore the life support suit that the spacewalkers wear, this is the same as working on high bridges/buildings etc, like a Steeplejack. The SteepleJack can climb on the outside of a high building with the right equipment, just as I can walk across the Millau viaduct without plummeting to earth.
You don't need to stop the rotation to, for example, connect to a supply / refuelling ship; you can either have a section on the axis that turns (relative to the main body of the ship) on bearings, but is stationary as seen from outside; or you can spin the supply ship before docking.
Propellor-head icon, because they'll be good at managing all these rotating and counter-rotating and co-rotating things.
"...deal with bearings between the rotating part and non-rotating part" Why have a non-rotating part, what would you want to dock with en route to Mars?
"...unbalanced washing machine..." this only happens because the centre of rotation does not align with the fixed point that the washing machine's drum is rotating about. A spinning spacecraft isn't attached to anything (and there are no aerodynamic effects) so it will spin around it natural C of G. It will not be unbalance.
I'd go for a simple design - a spinning system that uses a steel cable to tie a crew module at one end of the cable and with a counterweight** on the other end.
If the cable is 100m long and of negligible mass, and the crew model is 10 times the mass of the counterweight, then the whole lot only needs to spin at about 9.5 rpm to get 1G (if my 35 year old O level physics is right*). This doesn't sound too difficult to achieve.
I'd start with the counterbalance attached to the space module and get the whole lot pointing towards Mars at the correct velocity. I'd then get it spinning perpendicular to the direction of travel and slowly pay out the cable attaching the module & counterbalance.
{*Posting anon because my 35 year old physics O-level is probably wrong}
{**Can something be a counterweight in the absence of gravity?}
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