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#60 by Robotbeat on 09 Nov, 2012 13:16
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If nothing is unthinkable, then we can consider other options like just increasing the limit or combining it with drugs or an antioxidant cocktail to deal with the limits or use older astronauts with a higher limit.
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#61 by muomega0 on 09 Nov, 2012 14:02
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[No wonder the document opens with the statement that limiting the amount of exposure to Galactic Cosmic Radiation (GCR) is "the sound-barrier to break" before real BEO exploration can take place.
It's clear that it's the elephant sitting in the middle of the room.
IMHO, as no-one is seriously talking about an aircraft-carrier-sized DSH with most of its mass made up of shielding, it makes the EML spacelab even more important. That would allow for testing of mitigation methods and technologies in the BEO environment but also with an easy Earth return in the event of an emergency. The NEO missions simply wouldn't provide that.
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Just an additional point: This is only going to be possible if there is a standing rule of: "Nothing is unthinkable". Flying with huge unfurling sun-shades (as on JWST)? Composite-hulled inflatable habs with a water layer on the inside? It's clear that this is a big unknown area and it's going to take a lot of effort (and money - horror of horrors!) to fix.QuoteAlthough SPE shielding in the form a specific storm shelter area will be incorporated into the DSH, we would not expect to generically use dead mass shielding as a primary go forward solution for GCR
At least the studies are starting to acknowledge that while a thick layer of suitable material is effective for SPE, it is impossible to provide protection from GCR without active shielding.
However, no provision is included in the architecture for mass:
Total wet mass estimates of 34,009 kg including cargo radiation protection of 2,055 kg. Launch Cost estimates at $5000/kg of the SPE shielding only range from ~$100M to $1B.
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NEA will not provide GCR protection?! Good luck with that requirement change.....
What is the cost to train crew that can only have a 14 day tour of duty at L2 before their careers are over given the lack of GCR protection cited in these studies? Time to reach NEA?
Drugs? name them and the effectiveness. FDA approved?
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The good news is that active system estimates are in the 30,000kg range for the size stated. (Before you ask: No, it can be sent in pieces, so don't start talking about 70,000 kg HLV requirements.) Multiply by either SLS like ~$100,000/kg or $5000/kg with depot centric. The GCR reduction would be about an order of magnitude.
Active systems will require cryocoolers, and likely much colder than LOX (90K) when the optimal trade of cryocooler weight versus active system weight is considered, despite assertions that the low temperatures can be achieved passively. IOW: a sunshield is not going to be sufficient--the solution requires active cryocoolers. Subscale systems of course, would be deployed first--sound exciting, lots of R&D + mission ops for repair and replacement.
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Will active systems work? No one is sure, no one will try, but somehow folks can still type on keyboards. That is why a L2 stepping stone is critical: it focusses NASA on its key challenges (well not exactly...see below...). If it does not work, i suppose NASA's destination is to the moon to live like a mole. what is the hurry? Afraid to try? try again? So once the L2 habitat is in place, it gives NASA a critical R&D facility, and the lunar missions can commence. It would seem to be that HSF finally has a long term critical science goal other than the wrong g-level bone loss studies and guaranteed spinoffs back to earth. Milli-g may be the answer for the trip to Mars. Of course, taking a spin in LEO is the first step because GCR protection is not required.
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A lot of money?
Even better is that the dollars spent on GCR protection will have numerous benefits back on earth. More on this later. Development costs will be substantially less than a new (unnecessary) engine program for this critical area to enable Exploration. Is this "alot of money"?
With R&D, there are known areas ripe to reduce the weights further from the SOA, which appears to be cost effective R&D to meet a critical need. Authorized but not appropriated.
Depot centric architectures are most cost effective with ZBO LEO depots, not passive depots, so common cryocooler technology can both bring launch costs down and help solve the critical crew health issue with GCR. Recall that with a depot, the launch vehicle size can be reduced dramatically and the flight rate is increased reducing IMLEO costs. Likely need a cryocooler for all that ISRU product too. Does the depot spin and could a tether be attached to a 100,000+ kg (when fueled) piece of hardware to study constant milli-g health affects? Authorized but not appropriated.
Oh well, back to reality: 99% of the funds are spent on J2X, 5-seg, SSME to RS68 to SSME, liquid strap ons, Orion without GCR, ...... nothing to do with the NASA technology challenges, all thanks to the 2000 to 2008 fiscally conservative Congress and the 2010 NASA Authorization Act. Authorized and appropriated. congrats.
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Also note that even the
NASA Technology Grand Challenges do not include radiation under Space Heath and Medicine, but it appears to be a problem for robotics.
QuoteSurviving Extreme Space Environments
Enable robotic operations and survival......
Problem: Space travel can present extreme environments that affect machine operations and survival. Like humans, machines are impacted by gravity, propulsive forces, radiation,....
Space Health and Medicine
Eliminate or mitigate the negative effects of the space environments on human physical and behavioral health, optimize human performance in space and expand the scope of space based medical care to match terrestrial care.
Problem: Space is an extreme environment that is not conducive to human life. Today’s technology can only partially mitigate the effects on the physical and psychological well-being of people. In order to live and effectively work in space for an extended period of time, people require technologies that enable survival in extreme environments; countermeasures that mitigate the negative effects of space; accommodations that optimize human performance; comprehensive space-based physiological and physical health management and prompt and comprehensive medical care in a limited infrastructure. -
#62 by ChileVerde on 09 Nov, 2012 14:42
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attached is a document with full NASA briefs on the DSH as of 12/2011
I don't recall this being posted before.
Also attached is a sensitivity analysis for DSH radiation issues - its not pretty.
Thanks for that. For reference, here's a table giving a general orientation to radiation effects.
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#63 by MikeAtkinson on 09 Nov, 2012 14:51
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attached is a document with full NASA briefs on the DSH as of 12/2011
I don't recall this being posted before.
Also attached is a sensitivity analysis for DSH radiation issues - its not pretty.
Thanks for that. For reference, here's a table giving a general orientation to radiation effects.
That table says that the make career astronaut dose is 1,500mSv, while the Lora Bailey report above says 150mSv for lifetime limit "goal". Quite a difference. -
#64 by ChileVerde on 09 Nov, 2012 16:01
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attached is a document with full NASA briefs on the DSH as of 12/2011
I don't recall this being posted before.
Also attached is a sensitivity analysis for DSH radiation issues - its not pretty.
Thanks for that. For reference, here's a table giving a general orientation to radiation effects.
That table says that the make career astronaut dose is 1,500mSv, while the Lora Bailey report above says 150mSv for lifetime limit "goal". Quite a difference.
Yes, it is. I don't know the ins and outs of radiation medicine, but note that 150 mSv is what we old guys used to call 15 rem, which is considerably below the threshold of noticeable effects for "radiation sickness." Of course, the study under discussion here is concerned with increased cancer risk, a totally different thing.
Is there a radiologist in the house? -
#65 by MikeAtkinson on 09 Nov, 2012 16:46
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There are many contributing factors to cancer, including diet, exercise, stress, immune system health and many others. When becoming an astronaut all these factors change. Singling out radiation is a mistake in my opinion.
If you get cancer probability of death depends on how early the cancer is discovered and standard of treatment. Astronauts and ex-astronauts will have the highest level of health care.
Death rates from cancer are falling (by 16% in Britain in the last decade, partly due to reduction in smoking, partly better treatment). Using the death rate now (even if they have used up-to-date figures) will lead to an overestimate for when the missions are planned for. -
#66 by Robotbeat on 09 Nov, 2012 17:02
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How to solve this problem? Send smokers without their cigarettes (plentiful patches). Net decrease in cancer risk.
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#67 by Robotbeat on 09 Nov, 2012 17:09
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Actually, that's false. Do you know just how large of a magnetic field is necessary to block GCR? I calculated it, once... It'd be like being INSIDE of an MRI machine. If you move too fast, you'll get a metal taste in your mouth (and possibly a headache?) because your body is conducting and moving a wire through a magnetic field causes a current to flow. No. Active shielding is better for solar particle radiation, and except at extremes is worthless for GCR.[No wonder the document opens with the statement that limiting the amount of exposure to Galactic Cosmic Radiation (GCR) is "the sound-barrier to break" before real BEO exploration can take place.
It's clear that it's the elephant sitting in the middle of the room.
IMHO, as no-one is seriously talking about an aircraft-carrier-sized DSH with most of its mass made up of shielding, it makes the EML spacelab even more important. That would allow for testing of mitigation methods and technologies in the BEO environment but also with an easy Earth return in the event of an emergency. The NEO missions simply wouldn't provide that.
[edit]
Just an additional point: This is only going to be possible if there is a standing rule of: "Nothing is unthinkable". Flying with huge unfurling sun-shades (as on JWST)? Composite-hulled inflatable habs with a water layer on the inside? It's clear that this is a big unknown area and it's going to take a lot of effort (and money - horror of horrors!) to fix.QuoteAlthough SPE shielding in the form a specific storm shelter area will be incorporated into the DSH, we would not expect to generically use dead mass shielding as a primary go forward solution for GCR
At least the studies are starting to acknowledge that while a thick layer of suitable material is effective for SPE, it is impossible to provide protection from GCR without active shielding.
...
If you use a thick enough (passive) shield, you can block GCR. It's absolutely not impossible. The lightest way to do this is liquid hydrogen.
I wish people who don't actually know what they're talking about would stop strongly asserting things about space radiation. It adds unnecessary confusion and is quite counter-productive. -
#68 by truth is life on 09 Nov, 2012 18:48
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I wish people who don't actually know what they're talking about would stop strongly asserting things about space radiation. It adds unnecessary confusion and is quite counter-productive.
I, for one, am presently extremely confused about everything GCR, at least so far as their impact on spaceflight is concerned. -
#69 by Robotbeat on 09 Nov, 2012 19:19
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Some clarity:I wish people who don't actually know what they're talking about would stop strongly asserting things about space radiation. It adds unnecessary confusion and is quite counter-productive.
I, for one, am presently extremely confused about everything GCR, at least so far as their impact on spaceflight is concerned.
The effect is not acute. In other words, the effect of GCR is long-term and doesn't (for the most part) affect the capability of the astronauts to perform the mission. The effect, if any, is on future cancer incidence rates (and isn't worse than smoking).
Also, it takes a lot to shield from GCR. The atmosphere of Mars shields part of GCRs, and regolith piled on top of a habitat on the Moon, on Mars, or on an asteroid could reduce GCR incidence.
GCR doses are higher during Solar Minimum (i.e. when there are fewer solar particle events) and lower during Solar Maximum. The solar cycle repeats every 11 years (essentially... it's actually a ~22 year period, but the effect for GCR is a repeat every 11 years), and we are entering Solar Maximum right now. The difference is roughly a factor of 2.
GCRs are made of charged ions at high energy (many relativistic, i.e. near the speed of light).
To first order, more shielding mass means less radiation. But hydrogen is a few times more effective than other elements for shielding. (and for a small range of metal shielding thicknesses, total radiation dose can increase slightly with increasing shield thickness... but that is a small range). GCRs produce much of their damaging effect through secondary particles... I.e. the big charged ions hit some matter and produce a secondary shower of particles... but usually, adding more shielding will still reduce total dosages.
GCRs come in from all directions essentially evenly (except when on or near the surface of a large body, of course). Because of their high momentum, they are only barely affected by magnetic fields. If the Earth had no atmosphere, we would experience a very large flux (though still somewhat attenuated flux) of GCRs on the Earth's surface, in spite of the Earth's large geomagnetic field... It is the Earth's atmosphere that does the most heavy lifting when it comes to shielding us from space radiation. -
#70 by strangequark on 09 Nov, 2012 19:31
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Actually, that's false. Do you know just how large of a magnetic field is necessary to block GCR? I calculated it, once... It'd be like being INSIDE of an MRI machine. If you move too fast, you'll get a metal taste in your mouth (and possibly a headache?) because your body is conducting and moving a wire through a magnetic field causes a current to flow. No. Active shielding is better for solar particle radiation, and except at extremes is worthless for GCR.
If you use a thick enough (passive) shield, you can block GCR. It's absolutely not impossible. The lightest way to do this is liquid hydrogen.
I wish people who don't actually know what they're talking about would stop strongly asserting things about space radiation. It adds unnecessary confusion and is quite counter-productive.
There are magnet windings around a torus that allow you to have arbitrarily high magnetic field strength that fades to a uniform zero in the "donut hole" of the torus. Not saying it's easy, but that's one solution. -
#71 by Robotbeat on 09 Nov, 2012 19:35
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That is true. But it's not terribly practical, since you're still talking about several Tesla fields, and even the residual field is likely to be large in that case.Actually, that's false. Do you know just how large of a magnetic field is necessary to block GCR? I calculated it, once... It'd be like being INSIDE of an MRI machine. If you move too fast, you'll get a metal taste in your mouth (and possibly a headache?) because your body is conducting and moving a wire through a magnetic field causes a current to flow. No. Active shielding is better for solar particle radiation, and except at extremes is worthless for GCR.
If you use a thick enough (passive) shield, you can block GCR. It's absolutely not impossible. The lightest way to do this is liquid hydrogen.
I wish people who don't actually know what they're talking about would stop strongly asserting things about space radiation. It adds unnecessary confusion and is quite counter-productive.
There are magnet windings around a torus that allow you to have arbitrarily high magnetic field strength that fades to a uniform zero in the "donut hole" of the torus. Not saying it's easy, but that's one solution. -
#72 by Robotbeat on 09 Nov, 2012 19:39
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One benefit of high magnetic field gradients is another potential form of artificial gravity...
(but again, not practical... You can get a headache from moving your head around too fast in a field that large) -
#73 by strangequark on 09 Nov, 2012 19:47
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There are magnet windings around a torus that allow you to have arbitrarily high magnetic field strength that fades to a uniform zero in the "donut hole" of the torus. Not saying it's easy, but that's one solution.
That is true. But it's not terribly practical, since you're still talking about several Tesla fields, and even the residual field is likely to be large in that case.
I may still have a circa-2005 MATLAB code kicking around that covers the geometry I'm thinking of. I had thought that the internal field is completely independent of the surrounding field strength, but I'm reaching back to a sophomore year research task, back when I was bright-eyed, bushy-tailed, and didn't know any better. You're the physicist, you ever read anything by Rainer Meinke on double helix superconducting coils? -
#74 by Robotbeat on 09 Nov, 2012 20:46
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I have no doubt you are correct, but what you are saying rings no bells. (I'm taking a 500-level ENM course next semester, though.)There are magnet windings around a torus that allow you to have arbitrarily high magnetic field strength that fades to a uniform zero in the "donut hole" of the torus. Not saying it's easy, but that's one solution.
That is true. But it's not terribly practical, since you're still talking about several Tesla fields, and even the residual field is likely to be large in that case.
I may still have a circa-2005 MATLAB code kicking around that covers the geometry I'm thinking of. I had thought that the internal field is completely independent of the surrounding field strength, but I'm reaching back to a sophomore year research task, back when I was bright-eyed, bushy-tailed, and didn't know any better. You're the physicist, you ever read anything by Rainer Meinke on double helix superconducting coils? -
#75 by JohnFornaro on 10 Nov, 2012 01:39
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Not the scrawny little arms again!
No, NO, NO, NO, Hee-haw, hee-haw.
But otherwise, pretty good presentation. -
#76 by Ben the Space Brit on 10 Nov, 2012 19:07
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I read that Bigelow were talking about adding a water layer to the inside of their composite habs to increase their BEO radiation tolerance. How effective would a water layer be against GCRs?
I might be wrong, but I'm thinking that solar radiation, if not licked, is at least understood well enough to mitigate the risk to acceptable levels. GCRs are a different matter as no-one has really had the cause to look seriously at the issue yet. I'm hoping that I misunderstood the presentation and that NASA isn't seriously thinking of tap-dancing around the problem by using astronauts old enough that the exposure isn't likely to increase their statistical likelihood of cancer. That's the worst kind of pretending to deal with a problem without actually doing so.
I'm thinking that any eventual physical solution will be a kind of multi-layer sandwich using polyethylene and water as an easy-to-use low-maintenance hydrogen-rich fluid. You might also be able to add that to the water cycling system and let the radiation purify the water (if not ionise it
). Even so, we are probably looking at a 20-inch or more hull thickness. Add a separate sun-shield for solar radiation and a storm shelter for solar radiation spikes. That's going to be bulky, so something SLS-class or FH-class with a wide-body PLF is sounding necessary, as is EOR Assembly.
Non-physical solutions must be dependent on developing a mag field generator where the inside the diameter of the generator ring, the mag flux isn't significantly different. It will probably also require flying with a nuclear power pile. Once again, the ol' brain might be playing tricks but I seem to remember reading about someone claiming to have done the no flux inside the torus trick. -
#77 by clongton on 10 Nov, 2012 19:22
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I'm hoping that I misunderstood the presentation and that NASA isn't seriously thinking of tap-dancing around the problem by using astronauts old enough that the exposure isn't likely to increase their statistical likelihood of cancer.
Sounds like the makings of a good sci-fi story. Imagine if NASA actually did that and it backfired; the GCR didn't diminish their lifespan but instead hardened it so that the astronauts became all but immortal! Imagine the civilian pressure to get people into space for "hardening"! What a story that would make!
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#78 by Patchouli on 10 Nov, 2012 19:24
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I read that Bigelow were talking about adding a water layer to the inside of their composite habs to increase their BEO radiation tolerance. How effective would a water layer be against GCRs?
I might be wrong, but I'm thinking that solar radiation, if not licked, is at least understood well enough to mitigate the risk to acceptable levels. GCRs are a different matter as no-one has really had the cause to look seriously at the issue yet. I'm hoping that I misunderstood the presentation and that NASA isn't seriously thinking of tap-dancing around the problem by using astronauts old enough that the exposure isn't likely to increase their statistical likelihood of cancer. That's the worst kind of pretending to deal with a problem without actually doing so.
I'm thinking that any eventual physical solution will be a kind of multi-layer sandwich using polyethylene and water as an easy-to-use low-maintenance hydrogen-rich fluid. You might also be able to add that to the water cycling system and let the radiation purify the water (if not ionise it ). Even so, we are probably looking at a 20-inch or more hull thickness. Add a separate sun-shield for solar radiation and a storm shelter for solar radiation spikes. That's going to be bulky, so something SLS-class or FH-class with a wide-body PLF is sounding necessary, as is EOR Assembly.
Non-physical solutions must be dependent on developing a mag field generator where the inside the diameter of the generator ring, the mag flux isn't significantly different. It will probably also require flying with a nuclear power pile. Once again, the ol' brain might be playing tricks but I seem to remember reading about someone claiming to have done the no flux inside the torus trick.
Water is one of the best radiation shielding materials you can get if you can afford the mass.
As for mitigating the huge magnetic fields with a mag shield you can add a second coil to neutralize most but not all of the magnetic field inside the habitat.
There really is not much research on the affects of exposure to large magnetic fields for long duration.
A third option might be an electrostatic shield. -
#79 by MATTBLAK on 10 Nov, 2012 19:52
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I'm hoping that I misunderstood the presentation and that NASA isn't seriously thinking of tap-dancing around the problem by using astronauts old enough that the exposure isn't likely to increase their statistical likelihood of cancer.
Sounds like the makings of a good sci-fi story. Imagine if NASA actually did that and it backfired; the GCR didn't diminish their lifespan but instead hardened it so that the astronauts became all but immortal! Imagine the civilian pressure to get people into space for "hardening"! What a story that would make!
Didn't something similar happen to 'The Fantastic Four?' But to dent my analogy - they were young Astronaut/Scientists.
). Even so, we are probably looking at a 20-inch or more hull thickness. Add a separate sun-shield for solar radiation and a storm shelter for solar radiation spikes. That's going to be bulky, so something SLS-class or FH-class with a wide-body PLF is sounding necessary, as is EOR Assembly.