Artificial gravity in long term space travel

[Yuri_Armstrong]

My apologies, Yuri - I don't mean to be dragging the dialog away from your original theme. I'll try to make up for my digression in another post.

I stand by my original post- though it's fun to think about, long term space travel for intelligent life will never be economically practical, let alone the generation of gravity through means other than accumulating mass. But it doesn't matter, because there's no place economically interesting for intelligent life to to travel to anyway. Let's stick with probes and robots. They don't need gravity.

I said that it will be expensive, but I don't think that economics will be on people's minds when our sun goes red giant and its time to leave the solar system.

You say there are no interesting places to go to, but how could you say this when we know so little about even our local area of the galaxy? All we can do is map out stars, identify a few gas giants, but I bet there's lots of exotic yet habitable locations out there for humans. Billions of years from now I bet our descendants will have a very good idea of the planets of Alpha Centauri and other nearby star systems.

And my question about the artificial gravity machien still stands, wasn't someone talking about carrying gravitons onboard a ship to produce its own gravity? I believe it was in the unexplained forum.

 

[MeteorWayne]

Well this thread is about the multiple ways of producing gravity for long term spaceflight. Centrifugal effect is one, but the only other alternative is to have an object large enough to produce its own gravity field.

uhh, yeah, something the size of Mars. But that seems a bit impractical...

Also, I seem to recall someone talking about a gravity machine in the unexplained forum. Is it possible to make such a thing?

No, there's a reason it's in The Unexplained...

 

[Yuri_Armstrong]

uhh, yeah, something the size of Mars. But that seems a bit impractical...

In what other way do you think we could travel to a star system and carry enough people and equipment for them to survive not just the trip but also supplies for when they land, and to make repairs. A gigantic "world" ship is probably the best option.

No, there's a reason it's in The Unexplained...

But wasn't he saying something to the effect that gravitons can be carried on board a ship? I think he said he created a machine which could capture gravitons and carry them around.

 

[MeteorWayne]

uhh, yeah, something the size of Mars. But that seems a bit impractical...

In what other way do you think we could travel to a star system and carry enough people and equipment for them to survive not just the trip but also supplies for when they land, and to make repairs. A gigantic "world" ship is probably the best option.

Yeah, maybe in a few dozen generaions...

No, there's a reason it's in The Unexplained...

But wasn't he saying something to the effect that gravitons can be carried on board a ship? I think he said he created a machine which could capture gravitons and carry them around.

Yes, it's total BS, which is why it's in The Unexplained. Fools can say anything they wish before being ripped apart there.

 

[Yuri_Armstrong]

Yeah, maybe in a few dozen generaions...

Well, nobody expects manned interstellar travel for a while anyway. So that will probably end up being the best option.

Yes, it's total BS, which is why it's in The Unexplained. Fools can say anything they wish before being ripped apart there.

So there's only two ways to simulate gravity in space?

 

[vulture4]

There is no known limit to the time adult humans can spend in weightlessness; people have spent up to 14 months in orbit and returned to 1G on earth without any serious problems. However if it ever should really be necessary to produce Marian gravity on the spacecraft, most people can tolerate rotation at 4 revolutions per minute without getting sick, so using the centripital equation:

a= r*w^2
where a=centripital aceleration (meters/sec^2), r=radius (m), w=angular velocity (radians/sec)
if
a= Martian gravity = 3.7 m/sec^2
w= 4RPM= .41 radians/sec
then radius r=~22 meters, which could easily be achieved by linking two sections of the spacecraft with a telescoping boom or simply a cable and setting them rotating about each other.

 

[MeteorWayne]

vulture4,
Got any evidence to support your statement that people can tolerate 4 RPM? Just curious.

 

[Yuri_Armstrong]

4 rpm? Ugh That's not very comfortable. I'd prefer 2 rpms with .3 Gs... how big would the radius need to be for that?

 

[James_Bull]

4 rpm? Ugh That's not very comfortable. I'd prefer 2 rpms with .3 Gs... how big would the radius need to be for that?

Radius, 28 meters with 3RPM would give 0.3G. I find this really fun: http://www.artificial-gravity.com/sw/Sp ... inCalc.htm

Studies have found 4RPM can be entirely livable with. I remember seeing that somewhere...

 

[Yuri_Armstrong]

4 rpm? Ugh That's not very comfortable. I'd prefer 2 rpms with .3 Gs... how big would the radius need to be for that?

Radius, 28 meters with 3RPM would give 0.3G. I find this really fun: http://www.artificial-gravity.com/sw/Sp ... inCalc.htm

Studies have found 4RPM can be entirely livable with. I remember seeing that somewhere...

This thread was mainly created for the astronauts on the mars mission. If they went the whole way there in zero-G then it would take them a while to get used to martian gravity which is a little higher than .3 Gs. If the ship spun for .3 Gs then they would be used to martian gravity as soon as they got there and wouldn't have to worry about adjusting to the new gravity.

Also, another way to generate artificial gravity, is by having the ship go fast enough to create Gs on the ship. Understandably though this would take a lot of thrust.

 

[scottb50]

Also, another way to generate artificial gravity, is by having the ship go fast enough to create Gs on the ship. Understandably though this would take a lot of thrust.

And you also have to slow down.

 

[HopDavid]

Obviously, a mission to mars will take a few months at least. Is it possible that the spacecraft going there will have one section spinning around enough to create aritifcial gravity on the same level that they will face on Mars? If so they could become acclimated to the martian gravity while on the trip, instead of recovering from a long period of zero g when they get to mars.

Centrifuges are commonly used in science fiction to protect space travellers from the health effects of long term zero g, but wouldn't the constant spinning make you dizzy and nauseous when you tried to get up and walk around?

Some believe humans can grow accustomed to high angular velocity just as sailors grow accustomed to the movement from ocean waves.

If so, this could have a big impact on how small a spin hab can be.

Given a hab of a given diameter, the "gravity" you feel goes with the square of angular velocity. A hab rotating 4 revolutions per minute would have 16 times the spin gravity of a hab rotating 1 revolution per second.

Another unknown is how much gravity we need to stay healthy. If lunar gravity (1/6 G) suffices, the diameter could be 1/6.

Depending on the tolerance to angular velocity and minimum gravity needed, spin habs could be much smaller than the Stanford Torus or O'Neill Cylinder portrayed in science fiction.

 

[HopDavid]

vulture4,
Got any evidence to support your statement that people can tolerate 4 RPM? Just curious.

http://chamberland.blogspot.com/2006/07 ... avity.html

http://www.graybiel.brandeis.edu/histor ... ntier.html

http://www.ncbi.nlm.nih.gov/pubmed/14501105

http://jn.physiology.org/cgi/reprint/80/2/546.pdf

 

[vulture4]

vulture4,
Got any evidence to support your statement that people can tolerate 4 RPM? Just curious.

The Bioastronautics Data Book - it has a few errors but even after 30 years there is really no higher authority. It is freely available online and should be the first thing anyone interested in space medicine reads. The direct testing by experiment on almost every question is a breath of fresh air in a world where even the highest managers argue interminably based on opinion.

This specific problem was considered long ago by the ancient space medicine researchers.

http://articles.adsabs.harvard.edu/full ... 4.000.html

 

[Yuri_Armstrong]

Obviously, a mission to mars will take a few months at least. Is it possible that the spacecraft going there will have one section spinning around enough to create aritifcial gravity on the same level that they will face on Mars? If so they could become acclimated to the martian gravity while on the trip, instead of recovering from a long period of zero g when they get to mars.

Centrifuges are commonly used in science fiction to protect space travellers from the health effects of long term zero g, but wouldn't the constant spinning make you dizzy and nauseous when you tried to get up and walk around?

Some believe humans can grow accustomed to high angular velocity just as sailors grow accustomed to the movement from ocean waves.

If so, this could have a big impact on how small a spin hab can be.

Given a hab of a given diameter, the "gravity" you feel goes with the square of angular velocity. A hab rotating 4 revolutions per minute would have 16 times the spin gravity of a hab rotating 1 revolution per second.

Another unknown is how much gravity we need to stay healthy. If lunar gravity (1/6 G) suffices, the diameter could be 1/6.

Depending on the tolerance to angular velocity and minimum gravity needed, spin habs could be much smaller than the Stanford Torus or O'Neill Cylinder portrayed in science fiction.

I'm sure lunar gravity would be fine. Your bones only completely wither away if there's no gravity. I'm sure that .16-.36 Gs, combined with a healthy diet and a couple of hours of exercise a day would suffice. The gravity of the ship though should be equal to that of the surface the mission plans to land on so the astronauts can become accustomed to it.

People may be able to go with 4 RPMs for a certain amount of time but I'm not so sure for months on end. I wouldn't put it over 2 RPMs, and 1 or less RPMs is always preferable. The lower the RPM the better so you don't take a chance with the crew getting sick.

 

[scottb50]

I wouldn't put it over 2 RPMs, and 1 or less RPMs is always preferable. The lower the RPM the better so you don't take a chance with the crew getting sick.[/quote

It would be fairly simple to have a gravity section, but most of a vehicle would not need gravity. Habitation areas would be primary.

 

[neutrino78x]

Obviously, while the ship's main drive is in operation, the torus would be stationary, and people would be strapped into their seats, or liquid acceleration beds, or whatever.

Hm. That's not so obvious to me. For one thing, it would take years of constant acceleration to achieve any practical velocity for useful space travel.

This is not necessarily true. There is no reason you can't accelerate at say 15 G. The human body cannot handle that acceleration, so you would have the crew immersed in some kind of liquid.

See this wikipedia article.

Having said that, yes, if you accelerated at 1 G, it would take a year to achieve (99.999% of) the speed of light. Not multiple years. But if you are accelerating at 1 G, there is no reason to remain strapped in a seat or to spin the torus. You are already feeling the acceleration of Earth gravity. You can walk around the torus with no issues. It would feel normal, although, at certain points in the torus, it would probably feel like you are upside down, since your feet would be pointing the opposite direction from the acceleration of the ship.

As SteveCNC said, if you're using a low thrust main drive, like an ion drive or something, you could build up speed over time with a negligible acceleration, and under those conditions, you would spin the torus.

That's a long time to be strapped down to a seat. Accelerating at a faster rate would destroy the torus or crush the intelligent inhabitants.

I'm not an engineer, I don't even have a college degree, but I question that; if the torus is unable to sustain the forces of accelerating at 1 G, how can it provide said acceleration to people inside?

As an aside, I've enjoyed trying to imagine the kind of seat to which one would be strapped in your scenario.

You have never seen the movie 2001: A Space Odyssey?

On some level, the inside walls of this crazy torus idea would have to, what, rotate is some weird way to stay orthogonal to the acceleration vector de jour?

The walls would do nothing. I suppose you could rotate the bed in your quarters or something.

I stand by my original post- though it's fun to think about, long term space travel for intelligent life will never be economically practical

Never is a long time. I think by the time we are seriously considering such a mission of colonization, building a torus 1.6 km in diameter will not be especially difficult.

, let alone the generation of gravity through means other than accumulating mass.

Dude, this has been studied by so many competent engineers. You just spin the ship. That's how you generate the feeling of artificial gravity.

--Brian

 

[neutrino78x]

The Atomic Rocket page on Artificial Gravity mentions a way to allow the torus to rotate so that the floor is where expected while the ship is under thrust. You would divide the torus into modules, and each module can be pivoted independently, so the ideal orientation is maintained. You have to click on the above link and scroll down about half way.

--Brian

 

[neutrino78x]

Speaking of 2001, when they were in the shuttlebay, shouldn't they have been floating?

--Brian

 

[uberhund]

Neutrino78 writes:
Speaking of 2001, when they were in the shuttlebay, shouldn't they have been floating?
Exactly, Neutrino. This is one of the many, many, visualization failures in the movie which, in spite of its hopeless optimism is nonetheless my favorite Kubrick epic. I can think of many failures, but not one correct prediction either Kubrick or Clarke made in that movie. There my be some, none just come to mind at the moment. And they were only trying to visualize 5, 10, and 20 years in the future. Again, predictions are difficult, especially about the future.

Neutrino78 continues to write:
The Atomic Rocket page on Artificial Gravity mentions a way to allow the torus to rotate so that the floor...
Thanks for the link, Neutrino78. As I said, I've enjoyed thinking about a crazy torus that would permit continuously variable adjustments to changes in acceleration vectors. This was certainly fun.

When a wall becomes a floor that becomes a wall again and then becomes the ceiling is a tricky environment in which to do useful work, especially when the walls have to shrink and expand based on their rotational position (the inner torus circumference would be less than the outer torus circumference). The "ezekiel" wheel would solve this by sectioning the torus into, what, piece-wise linear components I guess you'd call them. Make a great movie prop. Expensive, but entertaining.

More from Neutrini78
it would take a year to achieve (99.999% of) the speed of light. Not multiple years
Overlooking other issues and realities, somewhere around April or May, your spaceship would have attained a mass, and therefore an increasing requirement of fuel, that would eventually approach infinity, in order to maintain the 1G acceleration. The relativity physicists who monitor this site can no doubt greatly correct my profile of the increase in mass as velocities approach significant fractions of L.

In any case, engineers hate designing infinitely capable technology, and taxpayers/business people hate paying for it.

 

[kk434]

On Skylab one astronaut did run in circles around the stations wall, running this way for a while would create a brief period of artificial gravity.

 

[Yuri_Armstrong]

On Skylab one astronaut did run in circles around the stations wall, running this way for a while would create a brief period of artificial gravity.

The ISS could use a big huge module for the astronauts to move around instead of the ant tunnels they've got now.

 

[MeteorWayne]

Are you paying for them? If not, who is?

 

[Yuri_Armstrong]

Are you paying for them? If not, who is?

In a way we're all paying for this through tax dollars. We could use politicians who are more bold when it comes to space though, they cancelled one of the ISS's most useful modules.

 

[MeteorWayne]

That's not correct. We (the taxpayers) pay for (not enough) well justified missions. Beyond that, rich people with money to spare need to step up.