[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.
Although 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.

Surviving 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.