Author Topic: Artificial Gravity - Why Weight?  (Read 27369 times)

Offline Elmar Moelzer

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Re: Artificial Gravity - Why Weight?
« Reply #20 on: 05/15/2016 07:34 PM »
Gas stations in space with prepositioned supplies and propellant are the fastest way to send crew to Mars, but it appears to be limited to about 3 months one way with existing technology.
I think there was a concept for a VASIMIR based mission with a slightly over 30 day trip time. MSNW is also working on a new fusion drive that could result in 30 day trip times with a space craft that fits into a single BFR launch (with payload to spare) or a single SLS launch (with no margin).

Offline launchwatcher

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Re: Artificial Gravity - Why Weight?
« Reply #21 on: 05/15/2016 10:47 PM »
Gas stations in space with prepositioned supplies and propellant are the fastest way to send crew to Mars, but it appears to be limited to about 3 months one way with existing technology.
I think there was a concept for a VASIMIR based mission with a slightly over 30 day trip time. MSNW is also working on a new fusion drive that could result in 30 day trip times with a space craft that fits into a single BFR launch (with payload to spare) or a single SLS launch (with no margin).
There's a 39-day VASIMR mission described here:

http://www.adastrarocket.com/Andrew-SPESIF-2011.pdf

If I'm reading the paper correctly, the 39 day mission requires a 200MW nuclear reactor with power density of around 0.8kg/kW.   It mentions in passing that 4kg/kW is the best that's currently achievable.


Offline Elmar Moelzer

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Re: Artificial Gravity - Why Weight?
« Reply #22 on: 05/15/2016 10:59 PM »
There's a 39-day VASIMR mission described here:

http://www.adastrarocket.com/Andrew-SPESIF-2011.pdf

If I'm reading the paper correctly, the 39 day mission requires a 200MW nuclear reactor with power density of around 0.8kg/kW.   It mentions in passing that 4kg/kW is the best that's currently achievable.
Not "achievable", but that has been designed and built. Mind you that most current reactors are quite small and the power increases volumetrically. There are also concepts for solar power that could reach as little as 1kg/kWh. And then there is still MSNWs fusion drive (which is arguably a bit further out).
Anyway, my point was that there are conceivable ways to get to such short trip times if the funding and will is there. So you can spend the money on artificial gravity or on faster trip times. I feel like faster trips gain us more for Mars.
« Last Edit: 05/15/2016 11:02 PM by Elmar Moelzer »

Online philw1776

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Re: Artificial Gravity - Why Weight?
« Reply #23 on: 05/16/2016 06:08 PM »
Artificial gravity has a high probability of actually working and is a low capital investment R&D.  VASIMR with its way beyond state of the art power requirements costs $$$ to develop and has a good chance of under or not performing.  More so for the fusion approach.  Solar can get you a few megawatts but not nearly enough even with HUGE arrays.

Those believing that the also as yet non-existent BFR will happen have an easier "fast" 100-120 day transit solution.  Load 'er up with an extra couple hundred tons of propellant, a few more tanker launches to LEO refueling, and fire away with a couple extra Km/sec.  Brute force but large scale works for you here.  Don't add complexity of additional vehicles and waste propellant entering Mars orbit but EDL directly to the landing, as is planned for Red Dragon.

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Offline JasonAW3

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Re: Artificial Gravity - Why Weight?
« Reply #24 on: 05/16/2016 07:12 PM »
Interesting thought here;

     If using the Tether With Spent Stage Counter-Mass technique, one could, in theory, DRASTICALLY reduce the velocity of the approaching craft by simply cutting away the counter mass when it is approaching the direction of flight, assuming the rotation is parallel to the direction that the craft is traveling.

     Of course one would have to kill the tumble that would result from cutting loose the mass, but this shouldn't be too great of an issue.   
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Offline WindyCity

Re: Artificial Gravity - Why Weight?
« Reply #25 on: 05/16/2016 10:33 PM »
On the subject of artificial gravity for long duration space flight, NASA researchers Dr. Michael Schmidth and Dr. Thomas Goodwin, in an hour and a half interview for The Space Show, presented a history of artificial gravity research and summarized their own work on OMICS analysis pertaining to the human factors of exposure to microgravity and how artificial gravity might mitigate its effects on human physiology. They also outlined parameters for possible missions to Mars (or other transorbital deep space flights) involving artificial gravity, including SpaceX's MCT plans. It's worth a listen. Go to http://www.thespaceshow.com/show/01-mar-2016/broadcast-2657-dr.-michael-schmidth-dr.-thomas-goodwin. One interesting speculation they mentioned, based on animal studies, is that Mars' 0.38G gravity field might not be strong enough to prevent harm to human health over long stays on the planet.
« Last Edit: 05/16/2016 10:36 PM by WindyCity »

Offline Aussie_Space_Nut

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Re: Artificial Gravity - Why Weight?
« Reply #26 on: 05/17/2016 06:21 AM »
(snip) One interesting speculation they mentioned, based on animal studies, is that Mars' 0.38G gravity field might not be strong enough to prevent harm to human health over long stays on the planet.

And this is why we must have at least a system whereby we can simulate Mars gravity for extended stays. I mentioned this in the past but it is only reasonable to assume that if you sent people somewhere knowing it MAY BE HARMFUL then surely you open yourself up to legal claims. I can see the lawyers standing in the court rooms showing all the wonderful concept pictures of idyllic mars bases, of how the believers got the hopes up of the decieved thereby condemning them to a sorry end..........on mars! :-)

For the record I want to go to Mars but it just freaking does my head in why we will not simulate the Mars environment in a reasonably safe manner in Earth orbit, close enough for a quick trip home should any problems occur. I mean, you can make an argument for just about anything but surely what is reasonable should prevail.

Offline guckyfan

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Re: Artificial Gravity - Why Weight?
« Reply #27 on: 05/17/2016 09:10 AM »
For the record I want to go to Mars but it just freaking does my head in why we will not simulate the Mars environment in a reasonably safe manner in Earth orbit, close enough for a quick trip home should any problems occur. I mean, you can make an argument for just about anything but surely what is reasonable should prevail.

So for the record. Based on one speculation you want to stop going to Mars, the only place where you can fully "simulate" Mars conditions and spend billions (and how many years?) to simulate a less authentic environment for studies?

Offline JamesH65

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Re: Artificial Gravity - Why Weight?
« Reply #28 on: 05/17/2016 11:12 AM »
(snip) One interesting speculation they mentioned, based on animal studies, is that Mars' 0.38G gravity field might not be strong enough to prevent harm to human health over long stays on the planet.

And this is why we must have at least a system whereby we can simulate Mars gravity for extended stays. I mentioned this in the past but it is only reasonable to assume that if you sent people somewhere knowing it MAY BE HARMFUL then surely you open yourself up to legal claims. I can see the lawyers standing in the court rooms showing all the wonderful concept pictures of idyllic mars bases, of how the believers got the hopes up of the decieved thereby condemning them to a sorry end..........on mars! :-)

For the record I want to go to Mars but it just freaking does my head in why we will not simulate the Mars environment in a reasonably safe manner in Earth orbit, close enough for a quick trip home should any problems occur. I mean, you can make an argument for just about anything but surely what is reasonable should prevail.

Everyone going to Mars will know EXACTLY what they are letting themselves in for. The lawyers will have their signatures in blood confirming it. I'm not seeing any lawsuits in the near future.

Offline RonM

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Re: Artificial Gravity - Why Weight?
« Reply #29 on: 05/17/2016 03:31 PM »
(snip) One interesting speculation they mentioned, based on animal studies, is that Mars' 0.38G gravity field might not be strong enough to prevent harm to human health over long stays on the planet.

And this is why we must have at least a system whereby we can simulate Mars gravity for extended stays. I mentioned this in the past but it is only reasonable to assume that if you sent people somewhere knowing it MAY BE HARMFUL then surely you open yourself up to legal claims. I can see the lawyers standing in the court rooms showing all the wonderful concept pictures of idyllic mars bases, of how the believers got the hopes up of the decieved thereby condemning them to a sorry end..........on mars! :-)

For the record I want to go to Mars but it just freaking does my head in why we will not simulate the Mars environment in a reasonably safe manner in Earth orbit, close enough for a quick trip home should any problems occur. I mean, you can make an argument for just about anything but surely what is reasonable should prevail.

Everyone going to Mars will know EXACTLY what they are letting themselves in for. The lawyers will have their signatures in blood confirming it. I'm not seeing any lawsuits in the near future.

Exploration missions to Mars will be dangerous and everyone knows that. No lawsuits afterwards.

The big issue is whether or not it is possible to colonize Mars. We need to know if 0.38g is enough for long term health before we start building a colony. Artificial gravity studies will be important.

Offline guckyfan

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Re: Artificial Gravity - Why Weight?
« Reply #30 on: 05/17/2016 04:42 PM »
Exploration missions to Mars will be dangerous and everyone knows that. No lawsuits afterwards.

Yes.

The big issue is whether or not it is possible to colonize Mars. We need to know if 0.38g is enough for long term health before we start building a colony. Artificial gravity studies will be important.

I am of the firm opinion that artificial gravity on a large scale has no place in such a scenario. We can and should build a base on Mars regardless. That base is the place to find out about long term health, including reproduction. First with animals and then soon with humans.

Offline WindyCity

Re: Artificial Gravity - Why Weight?
« Reply #31 on: 05/17/2016 06:30 PM »
The big issue is whether or not it is possible to colonize Mars. We need to know if 0.38g is enough for long term health before we start building a colony. Artificial gravity studies will be important.

The same issue would affect permanent bases on the moon, but even more so. Schmidth and Goodwin also talked about surface-based centrifugal gravity simulators that people could spend time in to ward off the ill health effects of low gravity. That would add considerable complexity to living permanently on the surface of Mars (assuming that 0.38G is insufficient to prevent muscle and bone loss over time), but it could make it doable.

Obviously, human studies in LEO are essential in order to move  in a rational manner toward long-duration deep space flight or surface colonization of the moon or Mars.
« Last Edit: 05/17/2016 06:34 PM by WindyCity »

Online philw1776

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Re: Artificial Gravity - Why Weight?
« Reply #32 on: 05/17/2016 11:57 PM »
Why do we NEED to do artificial grav studies in LEO before Mars?
Where did we do zero grav studies before we sent people into LEO?
Send people on round trips and animals on longer trips to Mars. Disect them.  The animals, not the people.
If incurable side affects, then no Mars colony until medicine advances.
Else, continue.

Not against AG studies in LEO, just against that they are NEEDED before proceeding.
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Offline QuantumG

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Re: Artificial Gravity - Why Weight?
« Reply #33 on: 05/18/2016 12:07 AM »
One argument why you might want to know the reduced gravity effects of surface stays on Mars is to reduce the amount of reduce gravity mitigation assurance you need for a mission. If you conservatively assume that 0.38 gravity is no better than zero gravity for bone mass depletion, then you need to show that ~900 days in zero-g is survivable. Obviously, being able to show that Mars gravity is not as debilitating as zero-g will reduce the mitigation requirements. That said, a long duration mission to the lunar surface may be just as effective as an artificial gravity experiment, and more attractive to whoever is footing the bill.
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Offline WindyCity

Re: Artificial Gravity - Why Weight?
« Reply #34 on: 05/18/2016 11:33 PM »
Why do we NEED to do artificial grav studies in LEO before Mars?

NASA is cautious is my guess. (Isn't astronaut health and safety the agency's preeminent concern?) Schmidth and Goodwin would like to study how much (or how little) artificial gravity is needed to prevent ill health effects. They call that the "sweet spot". Such studies would compare incremental levels of artificial gravity to zero in on it. If 0.38G doesn't cause problems, that would be good to know for mission and vehicle design purposes. The slower the centrifuge turns, fewer vestibular problems arise from the Coriolis effect. The strength of a centrifugal force is determined by the length of the centrifuge arm and its speed.

These guys also would like to bring nuclear thermal propulsion on line to reduce transit time to Mars (or other deep space destinations). Wouldn't we all? And good luck with that.

I should also mention that they're not asserting that artificial gravity would have the same beneficial effects as a gravity field. Animal studies suggest that it would, but shy of actually conducting human studies on orbit, it's a question mark. Centrifuge studies on earth are inconclusive.
« Last Edit: 05/19/2016 05:44 PM by WindyCity »

Offline guckyfan

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Re: Artificial Gravity - Why Weight?
« Reply #35 on: 05/19/2016 12:27 AM »
Why do we NEED to do artificial grav studies in LEO before Mars?

NASA is cautious is my guess. (Isn't astronaut health and safety the agency's preeminent concern?)

That's why I am somewhat surprised that they plan orbital missions. They are not shorter than landing missions and they are continuous zero g. That does not sound like overly concerned to me. They must be very confident that that time is acceptable. Spending part of that time under martian gravity cannot be worse than microgravity the whole time.


Offline WindyCity

Re: Artificial Gravity - Why Weight?
« Reply #36 on: 05/19/2016 05:49 PM »
That's why I am somewhat surprised that they plan orbital missions.

No studies are planned as of now, I believe. The researchers spoke in favor only of conducting them. I do recommend listening to their Space Show interview. That would be better than my trying to relay what I recall from it. These fellows have detailed knowledge of the history of artificial gravity research, especially from the point of view of the physiological effects of weightlessness and artificial grav's ameliorative value.

As to your concern about why LEO studies would be preferable in their minds to studying low gravity's effects on the surface of Mars,  the reason might be that they wouldn't want to send people on a 2-yr plus mission without knowing in advance what the possible dangers of low-grav exposure are. If they could determine what the "sweet spot" is from studies in zero-G, that could save money in terms of mission design while preventing harm to the astronauts. That would seem to make sense to me.

I think that before planners talk seriously about what the challenges are in colonizing Mars they ought to have some idea of whether 0.38G is enough gravitational force to prevent harm to human health. If it's not enough to keep people healthy, then perhaps astronauts could spend a period of time each day in a surface centrifuge, in the manner of  a daily exercise regimen, to keep them healthy. Meanwhile, advances in medications or genetic modification could solve the problem in the future.
« Last Edit: 05/19/2016 06:03 PM by WindyCity »

Offline CuddlyRocket

Re: Artificial Gravity - Why Weight?
« Reply #37 on: 05/20/2016 01:33 AM »
These fellows have detailed knowledge of the history of artificial gravity research, especially from the point of view of the physiological effects of weightlessness and artificial grav's ameliorative value.

Be wary of experts promoting "further studies" in their field; it is in their interests after all!

Quote
I think that before planners talk seriously about what the challenges are in colonizing Mars they ought to have some idea of whether 0.38G is enough gravitational force to prevent harm to human health.

The best, possibly only, way of finding that out is to send people to Mars; especially if you're talking about really long-term exposure to 0.38g - we can hardly expect to keep people in orbital centrifuges for decades!

At least some of the first people on Mars will come back and can then be tested; with steadily increasing periods spent on the surface. And you can always send data, even samples, back to Earth. Once there's sufficient capacity on Mars they can do their own biomedical research.

Offline muomega0

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Re: Artificial Gravity - Why Weight?
« Reply #38 on: 05/20/2016 01:45 AM »
These fellows have detailed knowledge of the history of artificial gravity research, especially from the point of view of the physiological effects of weightlessness and artificial grav's ameliorative value.

Be wary of experts promoting "further studies" in their field; it is in their interests after all!
Corollary:  Be wary of experts promoting 'further studies' of decades old LVs and capsules, without developing any technology; it is in their interests after all!

Yet all this 'detailed' knowledge is now extended by the first U.S. data point of almost a year in space.  Why not get one or two data points at fractions of gravity to try and bound the problem?  Ahhh...must not be in the interests of propulsion and capsule operations.

Offline guckyfan

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Re: Artificial Gravity - Why Weight?
« Reply #39 on: 05/20/2016 06:04 AM »
Once there's sufficient capacity on Mars they can do their own biomedical research.

That would likely be from day one of the first landing. I do expect a permanent presence from that day on and individual people staying 2+ years.

That is if the first landing is done by SpaceX which I see likely.

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