Artificial gravity in long term space travel

[aaron38]

I've settled on 3rpm, 50m radius and 0.5g as a good standard design for artificial gravity. It's relatively compact, low spin rate and probably all the gravity that's needed. We've already built a 100m truss on the ISS. Attach a hab module to each end, spin it and there you go. It's not complicated and it's not heavy. In spin, everything is in tension and a structure in tension can be built very light. It's compression that's heavy.

The reason for gravity isn't that zero gravity problems are insurmountable, but that zero gravity creates so much more work for the crew. Gravity does a ton of work for us by holding everything in place. And a lot of mass goes into a ship to hold everything still.

Just think of a repair workstation that needs magnetic plates and air current screens to keep small parts from floating away. And can you imagine trying to solder when little balls of molten solder are floating around? With gravity, all you need is a flat space. No pouches with straws for every drink, no chasing after a loose glob of water before it floats into a computer's cooling fan. Everything stays where you put it. And the human body gets most of it's exercize by just standing up and walking around.

All that time saved gets put to better more productive use. If there can be gravity, there will be gravity.

 

[uberhund]

If there's a hab module at each end, where would the propulsion unit go? Just curious.

In any case, regardless where the source for thrust is placed, developing the delta-V needed for interplanetary travel would create some compression, would it not?

 

[EarthlingX]

If there's a hab module at each end, where would the propulsion unit go? Just curious.

In the centre of mass rotation.

In any case, regardless where the source for thrust is placed, developing the delta-V needed for interplanetary travel would create some compression, would it not?

It would, but no worries. If it is a short burst and a long cruise, than beam is unpacked after the pulse, if it's a long push, it will be a very little force to worry about.

 

[neilsox]

Hi Aaron: Yes some tasks are easier and faster with 0.5 g than 0.0001g, but likely not a lot faster after the crew learns to deal with free fall. An advantage of free fall is each room has 6 floor surfaces (sort of) instead of one. This makes for better utilization of space especially for rooms with 3 dimensions of about 3 meters. What dimensions were you thinking for the end habs? 5 meters by 5 meters by 2.2 meters tall perhaps? 2 meter radius spheres have a about the same usable space in freefall, but poor utilization at 0.5g. Spheres reduce the probability of blowout considerably, for the same total mass. Spheres with less than 2 meters radius would likely stress some of the crew long term, but 3 meters radius would be less noticeable, except a person could be stranded near the center of the sphere with no easy way to move off center in free fall. Perhaps one railing though the diameter of a 3 meter radius sphere would be desirable and could provide electrical outlets, air circulation and an additional place to mount small equipment?
If the spheres are of different mass the gravity will be inversely proportional and the system can be variable g, such as 0.38 g just before landing at Mars, or 1/6 g just before landing at the moon. Items rarely requiring human attention can be mounted any where on or in the truss, which will have very slightly less air pressure. Neil

 

[uberhund]

Aaron38 writes
In spin, everything is in tension and a structure in tension can be built very light. It's compression that's heavy.

Given that the structure will need to endure compression stresses (and worse, torque and torsion) after all, is it now possible to guesstimate the total mass of chemical propellant required to make the round trip, to, say Mars? An energy density of 3Mj/kg for the chemical propellant might be a reasonable starting assumption.

 

[neilsox]

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

I'm unsure that is necessary, as a torus is donut shape.If the axis of rotation is the same as the direction of acceleration and both are 0.5 g then the net gravity is 0.707 g and down is shifted about 45 degrees from the direction of down with either acceleration alone? Neil

 

[uberhund]

Yes. In a toridal configuration, the hab units would need to swivel like the people buckets on some amusement park rides.

This configuration introduces horrific complications for plumbing high pressure gasses, fluids, and movement of humans between hinged units, not to mention the torque and torsion issues introduced when accelerating to Mars travel speeds.

Toroids are non-starters. Though not as hollywood-like, the rotating stick concept removes many of the problems inherent with toroids.

 

[SteveCNC]

I would assume that if your using a high yield liquid fuel rocket motor to accelerate to speed for a mars target , then you would deploy your artificial gravity system after you reach speed . If your using a ion or plasma drive , it wouldn't cause enough G's to be a real problem you could deploy the artificial gravity system before you leave orbit , just build the floor at a slight angle to compensate for the acceleration and the line of force is then perpedicular to the floor .

 

[uberhund]

To help visualize the mass, and therefore the fueling requirements of a Mars capable ship, it might be helpful to base estimates on the only space habitat now in existence - the ISS.

For example, if one intends to build a rotating stick with a hab at each end, and an engine in the middle, a reasonable estimate of the total mass would be five or six ISS equivalents. I.e.: Each hab = 1 ISS each for a total of 2 ISS. The bus structure along which the stick would expand = 1 ISS. The radiation shielding, in all its forms (concrete, water, electromagnets) = 1 ISS. Engine and landers = 1 ISS. Intermodule plumbing and other stuff: 1 ISS.

If we assume that the mass of the fuel = the mass of the structure, as it is with many terrestrial flying machines, then we can estimate that the "wet" mass of a Mars ship would approach as much as 12 ISS for each leg of the journey on average. (Nuclear will not be possible for political, cost, and safety reasons).

To support two delta-V bursts outbound, and two delta-V bursts on the return, the ship would attain a fully loaded mass of, let's see, carry the one... 6 ISS dry + 12 ISS outbound fuel + 6 ISS return fuel = 24 ISS.

If one intends to build a torus, instead of a stick, multiply the number of spokes in the torus by 12 ISS.

That's an intimidating amount of mass. And remember, there'd have to be three of these beasts. That represents the cost and time required to build 72 International Space Stations.

 

[SteveCNC]

Sadly the ISS build technology is old and not efficient , where as the bigelow moduals seem to be far more practical (more volume with less mass and shielded to boot) . The shield could be improved upon for beyond earths magnetic field but it's already better than the ISS .

To me the ISS looks like it is built upon the Apollo technology which was doable back in the day but we have better materials now and designs . Speaking of designs , with software like Solid Works , Catia and Pro-E designing things with complex moving parts has become so much faster and easier than the old days it's truely amazing (that's what I do for a living , deal with things like this) , so that's why new designs can go from concept to reality so much faster . I'm really looking forward to the next 5-10 years in space flight (hope I live that long) at least from the private sector , after that I think many things will change (technology,direction,who knows) .

edit * Ohh and BTW there are two bigelow modules in space as we speak and have been there since 2006/2007 respectively .

 

[aaron38]

Given that the structure will need to endure compression stresses (and worse, torque and torsion) after all, is it now possible to guesstimate the total mass of chemical propellant required to make the round trip, to, say Mars? An energy density of 3Mj/kg for the chemical propellant might be a reasonable starting assumption.

If you want chemical propulsion just use Mars Direct. The hab is spun against the spent upper stage on a cable, and if anything goes wrong, just cut the cable. The cable reels out after the primary burn is done, and none of the course correction burns are strong enough to slack the cable. The hab is designed to be used in a gravity field on Mars, so no one will be sitting on the walls and ceiling anyway.

Anything larger is going to be built in orbit and can use the VASIMR drive. Thrust is low enough that it won't buckle the truss.

As for useable volume being less, that's a good point. The entire habitable volume doesn't need to spin though, so the impact isn't necessarily that great.

 

[uberhund]

My original question was, assuming your rotational computations, whether it was now possible to determine the mass of the whole rotating stick thing, given your vision of a hab at each end.

I kind of answered it myself after thinking about it a bit - about 24 times the mass of the current configuration of the ISS for each of the three craft, at least according to the back of *my* envelope. Your envelope may differ.

But since you mention VASMIR, this poses a new question: what would the acceleration profile be for a trip to Mars using VASMIR? Or, another way to put it: how long to get to Mars and back under VASMIR propulsion?

 

[Floridian]

Using a dwarf planet or moon as an inter-solar generational ship is remotely feasible. It would just take a longggg time.

Ideally it would contain large amounts of water and energy already present.

We'd need quite a few fusion/fission hybrid reactors set up on its surface to start generating speed.

First you would slowly de-orbit it from its planet (in the case of a moon).

Then you would just keep accelerating until it escaped the sun. It would already be moving at like 13km/second.

If you could aim it correctly you could be leaving the solar system at 13km/second + whatever thrust you added.

Moving towards your target.


My target would be the Gleise star system.

At 20.3 light years away, (This is not correct at all, just an estimate) thats 300,000km/s x 20.3 years.


Also assume your median speed for the trip would somehow be 5000 km/second (thats pretty freaking fast for a moon or dwarf planet but you'd have a long time to deccel and accel).

100/1.66 = 60.24 x 20.3 = 1223 years

Methods of entertainment: Studying things along the way
Reproducing
Organizing everyone into playing a massively multiplayer online RPG (LOL)


The good news is, once you got there colonization would be much easier as you would of had 2000 years to prepare. And would have large energy sources available.

 

[uberhund]

Thanks, Floridian. Interesting analysis.

Which brings me back to my original point. Speculating on long term or interstellar travel is fun if you're doing a Hollywood movie. But spending resources preparing for a journey of 1,223 years is not remotely economic or ethical.

Since this forum is on Space.Com, not ScienceFiction.com, let's shelve discussion of human space flight and focus resources on real science. Probes and rovers do not require Hollywood movie props, and because they're more efficient than human visitors, they will bring us more knowledge about the Universe with the least invested.

Building our knowledge of the Universe in the most efficient manner will come in handy when the time finally arrives for us to regret in earnest our tenuous position on this planet, though anyone reading this will be long dead before that happens.

 

[EarthlingX]

Last time i checked this forum was on 'www.space.com'.

Machines can not expand human civilization, only people can, they are just tools, and not the most efficient in every case.

There are some of us who already know about human caused climate change, probably one the biggest mass extinction caused by us, limits of terrestrial resources and so on.

We have to go, not robots, and time is now, or we might loose our chance, not in 200 years, more like 20-30.

Here are some very nice ideas for space settlements :

http://settlement.arc.nasa.gov/Contest/

 

[uberhund]

EarthlingX writes:
Last time i checked this forum was on 'www.space.com'.
Oops. Good catch. Sorry for the confusion. The original post has been edited.

We have to go, not robots, and time is now, or we might loose our chance, not in 200 years, more like 20-30.
Thanks for the link. Good to see kids taking an interest in science. Sadly, though, there's no place *to* go, no matter how many high school kids may trot out papers on Dyson spheres, terraforming Mars, or light speed travel.

If the goal is to preserve the human race, perhaps humans should start by not invading random countries for no reason. Controlling population would be better for the environment than any number of Al Gores traveling by private jet to so-called green pep-rallies, but no one expects to see either of these happen.

In the end, all things must die, including the human race. Let's try to understand the universe before it's our time to go, since there's no other choice.

 

[Yuri_Armstrong]

Thanks, Floridian. Interesting analysis.

Which brings me back to my original point. Speculating on long term or interstellar travel is fun if you're doing a Hollywood movie. But spending resources preparing for a journey of 1,223 years is not remotely economic or ethical.

Since this forum is on Space.Com, not ScienceFiction.com, let's shelve discussion of human space flight and focus resources on real science. Probes and rovers do not require Hollywood movie props, and because they're more efficient than human visitors, they will bring us more knowledge about the Universe with the least invested.

Building our knowledge of the Universe in the most efficient manner will come in handy when the time finally arrives for us to regret in earnest our tenuous position on this planet, though anyone reading this will be long dead before that happens.

Actually astronauts could learn a lot more about the solar system than a tiny, inefficient robot. The Hayabusa mission only returned a few specks of asteroid dust for pete's sake. If all you are interested in is the science of our solar system, then astronauts going on science/exploration missions to the worlds of our solar system would be the best thing to do because they can deploy lots of science experiments and return plenty of samples. Probes are not capable of handling very much. And for all your talk of science fiction, robots are not the perfect accurate machines depicted in sci fi movies. Their exploration and sampling capabilities are few. Heck, 2/3 of the probes sent to Mars have been failures.

We've been sending probes throughout the solar system for decades now and we still can't confirm or deny life elsewhere. We've just begun to scratch the surface in that area with these probes. If we had been sending manned missions instead, we would know a lot more. Yes, the costs would be greater but expense is a necessary part of spaceflight. You can't expect to advance our understanding of our solar system and the universe on the cheap and easy. These science probes do have their merits but I see them mostly as taking the easy route instead of sending a team of astronauts to do much better work and return many more samples.

 

[uberhund]

Yuri writes:

"Actually astronauts could learn a lot more about the solar system than a tiny, inefficient robot."

I know this is the popular notion, particularly closely held by those who get to travel to space on my tax dollars, but we don't have to leave it there. I believe this can be settled scientifically, rather than emotionally. I have a few ideas, but perhaps MeteorWayne knows a way to measure the efficiency of one over the other.

Yuri also writes:

"robots are not the perfect accurate machines depicted in sci fi movies. Their exploration and sampling capabilities are few. Heck, 2/3 of the probes sent to Mars have been failures."

Exactly. And they never will be. The more complex a man-made object, the more likely it is to fail. Life support systems increase complexity by orders of magnitude. Gladly, the numerous failures to Mars were probes. Imagine if there were humans aboard.

Speaking of, do they have that DEXTRE thing working yet?

 

[vulture4]

You can't expect to advance our understanding of our solar system and the universe on the cheap and easy. These science probes do have their merits but I see them mostly as taking the easy route instead of sending a team of astronauts to do much better work and return many more samples.

If the goal is science, robotic systems are far more effective. We can send a hundred probes for the cost of a manned flight. The Mars Rovers have taught us far more about Mars than a few samples would. Human flight to Mercury? Venus? Jupiter? Saturn? Pluto? Human capability is the same today as it was a thousand years ago, while robotic systems improve every year. Moreover, robotic vision gives those of us who cannot physically go (which is everyone but a lucky few) the sense of being there.

 

[Yuri_Armstrong]

Yuri writes:

"Actually astronauts could learn a lot more about the solar system than a tiny, inefficient robot."

I know this is the popular notion, particularly closely held by those who get to travel to space on my tax dollars, but we don't have to leave it there. I believe this can be settled scientifically, rather than emotionally. I have a few ideas, but perhaps MeteorWayne knows a way to measure the efficiency of one over the other.

Yuri also writes:

"robots are not the perfect accurate machines depicted in sci fi movies. Their exploration and sampling capabilities are few. Heck, 2/3 of the probes sent to Mars have been failures."

Exactly. And they never will be. The more complex a man-made object, the more likely it is to fail. Live support systems increase complexity by orders of magnitude. Gladly, the numerous failures to Mars were probes. Imagine if there were humans aboard.

Speaking of, do they have that DEXTRE thing working yet?

You're arguing hypotheticals there. I think that a manned science mission would have a higher chance of success due to the enormous importance of keeping the crew safe. That being said all manned missions to the moon brought back not only important scientific data but also all the astronauts back alive. Robotic probes are useful for preliminary explorations and reportings, but if you sent a manned science expedition we could learn a lot more because humans are infinitely more nuanced than machines. Sometimes when docking a spacecraft's computer can't handle it, so it requires an astronaut's skill to complete the docking.

Robotic probes are cheaper but you won't be able to learn as much as you could with a manned mission. I think we could settle once and for all the issue of life on Mars with the first manned mission, whereas we have been sending probes there for decades, most of which fail, and none of which could confirm or deny presence of fossils or microbial life.

 

[neutrino78x]

I'm unsure that is necessary, as a torus is donut shape.If the axis of rotation is the same as the direction of acceleration and both are 0.5 g then the net gravity is 0.707 g and down is shifted about 45 degrees from the direction of down with either acceleration alone? Neil

Well if you have a significant acceleration, you wouldn't run the torus. If you're coasting, or if you're using a low acceleration to build up speed over time, then you would run the torus.

--Brian

 

[neutrino78x]

Thanks, Floridian. Interesting analysis.

Which brings me back to my original point. Speculating on long term or interstellar travel is fun if you're doing a Hollywood movie. But spending resources preparing for a journey of 1,223 years is not remotely economic or ethical.

You're talking about the concept of a "generational ship". People are born, live their whole lives, have children, who become crew members, and die aboard the ship, for thousands of years. It is not unethical, but there are questions as to whether the crew will mutiny, forget the mission, or forget that they are on a spacecraft. That's not the only way to do it.

You could also put the crew in suspended animation, or freeze them at cryogenic temperatures. Other options are to colonize via cloning (seed ship), or computer simulations of a crew, but I don't count those, because I want to send the actual people.

However, by the time we get ready to colonize a planet beyond this solar system, we will presumably have created a space drive that allows the craft to accelerate to 90% the speed of light or so. In which case it wouldn't take thousands of years. Such a ship would want a torus, or some form of artificial gravity, as there would be a long coasting phase, or a low thrust drive would be used, which applies a small acceleration over a long period of time, in which case you would still want artificial gravity.

See the slower than light section on Atomic Rocket.

Since this forum is on Space.Com, not ScienceFiction.com, let's shelve discussion of human space flight and focus resources on real science.

Uh, real science allows you to travel 99.9999999% the speed of light, as close as you want, as long as you don't reach or exceed it. If you claim otherwise, I suggest you read The Evolution of Physics by Albert Einstein. It is an excellent book. I am not familiar with calculus, or really anything beyond algebra, but I know that relativity does not prohibit travel just below the speed of light (yes I am familiar with the lorentz transformation, gaining mass etc. point still stands).

Probes and rovers do not require Hollywood movie props, and because they're more efficient than human visitors, they will bring us more knowledge about the Universe with the least invested.

Well, yes, if all you want to do is observe, but we can't stay on the Earth forever. People want to get out and explore and colonize. We colonized North America, and we will do the same with Mars and beyond. Ad Astra!

--Brian

 

[uberhund]

Without getting circular in our discussion here, it's not the PowerPoint slide physics of attaining near-light speeds that's the problem, it's the engineering and economics that prevent attainment of even small fractions of light speed.

Unfortunately, outside of Hollywood, one must toe the line of all three taskmasters - physics, engineering, and economics.

But I get the Ad Astra thing. If I weren't touched by the romance of space travel, I would not have wanted to be an astronaut (in the real, Mercury 7 sense of the term) since I was old enough to talk. I have had to give up on that dream, as reluctantly as I have come to realize that humans will never colonize again, this side of Armageddon.

 

[Yuri_Armstrong]

Without getting circular in our discussion here, it's not the PowerPoint slide physics of attaining near-light speeds that's the problem, it's the engineering and economics that prevent attainment of even small fractions of light speed.

Unfortunately, outside of Hollywood, one must toe the line of all three taskmasters - physics, engineering, and economics.

But I get the Ad Astra thing. If I weren't touched by the romance of space travel, I would not have wanted to be an astronaut (in the real, Mercury 7 sense of the term) since I was old enough to talk. I have had to give up on that dream, as reluctantly as I have come to realize that humans will never colonize again, this side of Armageddon.

You can't say never on that sort of thing because NASA is not the only space program looking at manned missions BEO. It will just take a lot of hard work, funding, and political commitment from the people of America if we are to return to the moon and establish a long term permanent base there. As JFK said if we are not willing to fully devote ourselves to it then perhaps it is better that we don't go at all.

 

[uberhund]

As JFK said if we are not willing to fully devote ourselves to it then perhaps it is better that we don't go at all.

Regardless whether he actually said it, I vigorously agree.

A culture fully devoted to a wrong headed venture will destroy itself.

Hitler's Germany comes to mind. The bird man culture of Rapi Nui fully dedicated to the construction of large statues is another fascinating example.