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#11
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Orbital Gravity Lab?
David Spain wrote on Fri, 4 May 2018 09:22:30
-0400: Another thing we just don't know, is whether it is good enough to have limited exposure to 'g' to overcome the deficits of long duration in 0g or low g. Thus it becomes routine to spend some time working out in a centrifuge and the rest of the time in 0g or Mars gravity or whatever. Call it extra-terrestrial PE.... I remember the classic video of one of the Skylab astronauts (was it Conrad?) getting their exercise by 'running' around the inner circumference of the Skylab habitation module. I seem to recall some sort of bungee contraption with a treadmill, too, but I can't imagine that would be adequate. We need something that can do variable gravity so we can see if the effects diminish linearly, just how much exposure per day to what g level works, etc. Right now we're talking about 'fast' Mars trajectories to minimize radiation and g effects, but that doesn't get you to the 'live and work in space' place. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
#12
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Orbital Gravity Lab?
David Spain wrote on Fri, 4 May 2018 09:39:09
-0400: On 5/4/2018 6:14 AM, Fred J. McCall wrote: You'll need some reaction wheels to control pointing and some engines to unload the reaction wheels when they become saturated. Think about the mass of the station when compared to the mass of a human being... As an aside apropos of nothing, I remember reading an elaboration I think it was by A.C. Clarke himself about how the centrifuge would have worked on the Discovery in 2001 A Space Odyssey. It may have been from the book "The Making of 2001: A Space Odyssey". In it he mentions a reaction wheel used to contain the angular momemtum of the centrifuge when it was spun down and to assist in its spin up. I suppose if mass is no object, it could also be used to counter-rotate against the centrifuge if it was massive enough. On the Discovery the centrifuge was completely contained within the spherical pressure hull. The problem, as you mentioned, is vibration unless the station is truly massive and the centrifuge is incredibly well isolated. You really need a trio of stations; a habitat that rotates so you're living in gravity, a nearby free-flyer for microgravity experiments, and a more distant free-flyer for optical work (so you're not getting contamination from outgassing from the other pieces). -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
#13
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Orbital Gravity Lab?
On May/4/2018 at 1:34 AM, Fred J. McCall wrote :
Alain Fournier wrote on Thu, 3 May 2018 20:56:01 -0400: On May/3/2018 at 8:30 PM, Fred J. McCall wrote : 'Spinning' a BFS makes a lot of things too hard and it's not really big enough to let you have appreciable spin gravity without making people sick. I agree with you. But one of the things that would be interesting to investigate is whether a small gravity would help. I don't think a one percent of a g would help much. But it would be nice to know that, not just think it. If you want a real 'gravity lab', I would suggest something other than B330 modules attached to a tether so that they can change the distance between them. Then you give them enough propulsion so that they can keep a reasonable rotation rate to adjust for angular momentum effects from moving them closer together or further apart. Then you can select the gravity level you want to test at, do that for however long you need to, then adjust the distance and test at a different level of gravity. The only thing I don't like about that is that it wasn't done 20 years ago. Alain Fournier |
#14
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Orbital Gravity Lab?
JF Mezei wrote on Sun, 6 May 2018
15:27:18 -0400: On 2018-05-04 09:12, David Spain wrote: concrete. If I recall, a major objection to these being attached to the ISS is the vibrations they would induce that would interfere with other experiments. One could argue ISS should have been primarily a spinning station, with 0G experiments at the centre. This would have given crews a better environment and I have to assume that crystal growing experiments that really require 0G don't take that much space and the module at centre of the circular station would provide that environment. One could argue anything. The question is whether the argument makes sense and is executable. From the things you say, I assume you're thinking about the old 'wheel' design for a station. Think about how big such a station would have to be. ISS can use all the 'walls' of the modules, since the whole works is in 0g. That wouldn't be true on a spinning station. How many launches to get the pieces up? How do you assemble it? How long before first occupancy? You're also confused about 0g at the center. You'd have some small amount of gravity with angular forces. Not a good place to do things like trying to grow 0g crystals. HOWEVER: while growing crystals is one aspect, one more important aspect was studying whether humans can live in 0G for a long time and what measures/exercises rediuce or eliminate the negative impacts. If ISS human experiments have shown it is not possible to eliminate 0g problems with long duration flights, this is a very important finding. 'IF'? Do you bother to know ANYTHING about the things you bring up? And ISS has allowed to quantify body performance degradation, so that on a flight to Mars, they can predict what conditions humans would be in when they arrive, if they follow similar exercise regime as on ISS. To some extent this is true. So not having artificial gravity on ISS is/was an important step in learning about living in space. (even if the end result is a failure to learn how to stop body degradation). But it also prevents any follow-on research. I need to do the math on this hand-wave of mine. It'd be interesting to see, given the dimensions of BFS, how much spin could be induced before ill crew effects and to what degree of 'g' that would yield. You also need to consider ECLSS. O2 gnerators, toilets and anything else that uses liquids. There are vast differences how they work n 0g versus gravity. If a component is designed with assumption bubbles don't rise, but with artificial gravity, bubbles move, then how it is mounted matters because bubbles may be flowing to the bottom or sides, not nessessarily to the "top" of the unit. So if BFS is gonna spin, it really needt to be designed as such. (and also consider whether it will have one large burst of accelerationa and then coast for 6 months, or use slow but constant acceleration and then slow but constant deceleration once more than halfway to Mars). It's not big enough. Spinning around its long axis you get a couple hundredths of a g at the outer skin for rotation rates that humans can tolerate. Spinning it around its short axis isn't particularly useful, either. In either case, you'd need everything built so that 'up' could be two different directions; through the tail when landed or under acceleration and some other direction when spinning. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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Orbital Gravity Lab?
JF Mezei wrote on Tue, 8 May 2018
04:05:43 -0400: On 2018-05-07 01:00, Fred J. McCall wrote: You're also confused about 0g at the center. You'd have some small amount of gravity with angular forces. Not a good place to do things like trying to grow 0g crystals. The centre lab could rotate relative to the rotating station to give it a neutral position relative to space. So now you've got the same vibration problem that you get with a treadmill. If you're going to play that game, there are easier ways. The vibration isolation racks developped by NASA would eliminate any vibration from the station retating around the structure. Yeah, sure. And if frogs had wings they wouldn't bump their asses when they hopped. -- "Ignorance is preferable to error, and he is less remote from the truth who believes nothing than he who believes what is wrong." -- Thomas Jefferson |
#16
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Orbital Gravity Lab?
JF Mezei wrote on Tue, 8 May 2018
15:36:53 -0400: On 2018-05-08 07:57, Fred J. McCall wrote: So now you've got the same vibration problem that you get with a treadmill. If you're going to play that game, there are easier ways. Which is why they have vibration isolation racks for stuff that really needs vibration free environment. Said racks being in a largely vibration free environment. Believe what you want. You're too stupid to try to educate. -- "Ignorance is preferable to error, and he is less remote from the truth who believes nothing than he who believes what is wrong." -- Thomas Jefferson |
#17
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Orbital Gravity Lab?
JF Mezei wrote on Tue, 8 May 2018
15:36:53 -0400: On 2018-05-08 07:57, Fred J. McCall wrote: So now you've got the same vibration problem that you get with a treadmill. If you're going to play that game, there are easier ways. Which is why they have vibration isolation racks for stuff that really needs vibration free environment. How cute. You probably think your waterproof watch is actually waterproof, too. Hint: That **** is very limited and certainly won't isolate from the sort of thing you're talking about. -- "Ignorance is preferable to error, and he is less remote from the truth who believes nothing than he who believes what is wrong." -- Thomas Jefferson |
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