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#40 by RocketmanUS on 04 Apr, 2013 18:44
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Latest 500 day pretty picture of the DSH from Paul Bookout's April 2013 presentation.
Were is that image from?
Note the solar panel rotary joints and Orbital Cygnis-like (looks stretched) logistics module -
#41 by RanulfC on 04 Apr, 2013 21:40
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For long-duration missions Galactic Cosmic Radiation, or GCR, shielding remains the unresolved issue. Passive GCR shielding would be extremely heavy and costly. If active shielding can be made to work, it may require a DSH with a very different design.
You need to stay current with your own postings... You already addressed this issue when you cited this report:
http://spirit.as.utexas.edu/~fiso/telecon/Bailey_10-31-12/Bailey_10-31-12.pdf
Which shows a distinct increase in GCR protection can be achieved by a simple change in design to a "surrounded" rather than an "in-line" configuration and that's BEFORE additions to the passive shielding which NASA is considering. (Note that the Skylab-II configuration has an even better protection cross-section)
Randy -
#42 by HappyMartian on 05 Apr, 2013 02:58
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For long-duration missions Galactic Cosmic Radiation, or GCR, shielding remains the unresolved issue. Passive GCR shielding would be extremely heavy and costly. If active shielding can be made to work, it may require a DSH with a very different design.
You need to stay current with your own postings... You already addressed this issue when you cited this report:
http://spirit.as.utexas.edu/~fiso/telecon/Bailey_10-31-12/Bailey_10-31-12.pdf
Which shows a distinct increase in GCR protection can be achieved by a simple change in design to a "surrounded" rather than an "in-line" configuration and that's BEFORE additions to the passive shielding which NASA is considering. (Note that the Skylab-II configuration has an even better protection cross-section)
Randy
Randy, the study showed "the GCR reduction afforded by the surrounded structure, was minimal (~10%)" which is the opposite of the "distinct increase" you claim it showed. Note also that the "weight of the 'surrounded' architecture is essentially twice the in-line architecture."
Doubling your DSH's mass, complexity, and costs to gain a modest 10% increase in protection against GCRs is not the most affordable and useful way to shield against GCRs.
Deep Space Habitat Project Radiation Studies for a Long Duration Deep Space Transit Habitat
By Lora Bailey Engineering Directorate NASA Johnson Space Center 10/31/2012
At: http://spirit.as.utexas.edu/~fiso/telecon/Bailey_10-31-12/Bailey_10-31-12.pdf
Page 13 "Shielding is not conducive for protecting against GCR." "GCR radiation does not respond very favorably to shielding. Shielding has much less effectiveness against GCR."
Page 16 "SRAG recommends 150 mSv as crew lifetime exposure limit goal"
Page 21 "The DSH ISS-derived concept is an in-line architecture that was analyzed for GCR protection performance at EML1/L2 for 365 consecutive days of exposure" • Five “dose points”/locations inside this type architecture, using actual ISS module models, resulted in a range of internal dosage from 394 to 456 mSv"
Page 22 "Assumes crew has no prior occupational radiation exposure" "Males about 47 years old or older
are in range" "Females about 57 years old or older are in range"
"Recall: design target GCR exposure of 150 mSv Effective Dose --- these dose values are 2–3 times higher"
"Far away from arriving at 150 mSv" "values are a 'broke' for Mars/NEA space travel meeting the 3%REID
at 95% CL at solar minimum levels"
Page 31 "'Surrounded' Architecture Data/Results" "The 'surrounded' architecture was analyzed for GCR protection performance"
"Three 'dose points'/locations examined inside the center Node showed a range of dosage from ~ 385 to 435
mSv for the surrounded architecture"• "This is essentially very little change from the ISS-derived results which were a range from ~ 394 to 456 mSv for the in-line architecture"
Page 32 "About a doubling of the effective shielding thickness was successfully achieved using the surrounded architecture concept. However, the corresponding crew radiation dose reduction is only by about 10%, due
to the Node shielding alone being somewhere along the knee of this curve, thus placing the additional shielding
provided on the flatter part of this curve."
Page 35 "GCR: DSH Conclusions Summary"
"Two architectures were analyzed for crew radiation (GCR) protection capability
1) The ISS - derived, baseline architecture
2) A surrounded architecture, to evaluate the GCR protection benefit afforded by surrounding a core working/living module with logistics and less trafficked modules
Results showed approximately a doubling of the effective shielding provided by the surrounded architecture over the simpler ISS-derived (“in-line”/exposed) architecture
However the GCR reduction afforded by the surrounded structure, was minimal (~10%)
Note also, that the weight of the 'surrounded' architecture is essentially twice the in-line architecture, and the large total volume of the surrounded architecture may not necessarily be needed"
The item in bold was in bold in the original source.
Surround the L1/L2 DSH with massive amounts of effective GCR shielding and the costs go up dramatically.
Two meters of regolith is far cheaper GCR shielding and is widely available on the Moon's surface. Land the DSH on the Lunar surface and test it out there.
If we are in a stable high orbit around the Moon and are going to an asteroid or Mars, then the robust DSH vehicle needs to be surrounded by very large propellant tanks and filled with Lunar derived propellant.
Rocket engine braking, and thus using up the DSH vehicle's GCR shielding', into orbit around the asteroid or Mars, requires that propellant has already been prepositioned or made at those locations.
Refill all your propellant tanks, or 'drop' them and dock your DSH inside the prepositioned 'new' propellant tanks, and you are ready to go home. Near the Moon use your rocket engines to brake into a stable high Lunar orbit.
Deep space, such as L1 and L2, is a GCR rich and risk multiplying environment. Active shielding may someday be doable. For now, if we want our international crews to have robust safety margins in such a hostile environment, we need to devise affordable and effective GCR shielding. Currently, hauling propellant up from the Lunar surface and storing it in large tanks surrounding the DSH is about the only affordable option.
And someone may wonder about the best propellants for the DSH's GCR protection on a long-duration deep space mission. Hydrogen is a very efficient propellant, but it isn't very dense and may be difficult to store.
One might suspect that dual propellant rocket engines that burn hydrolox for the initial delta-v burn and then burn liquid propane or liquid methane, with liquid oxygen for the subsequent burns might be doable. The very large tanks for the liquid propane could be somewhat lighter than those for liquid methane. Propane may also be easier to store than methane.
"Another interesting feature of a LOX/H2 expander-bleed cycle engine is that, based on a recent study, the cycle can potentially be designed to function as a dual fuel engine utilizing LCH4 or LH2. This capability can facilitate the use of in-situ propellant systems for space exploration applications. The purpose of this paper is to discuss progress and background towards the development of these expander-bleed cycle engine improvements and capabilities."
And, "In spite of the “open” nature of the expander-bleed cycle, its performance exceeds or remains comparable to that of a conventional closed cycle engine."
From: Excellence of the Japanese Expander-Bleed Cycle Rocket Engine and Enhancements for Future Engine Applications By William Sack, Koichi Okita, Akihide Kurosu, Akira Ogawara, Kimito Yoshikawa, Masahiro Atsumi, Kenji Kishimoto, Kevin Lunde 2008
At: http://archive.ists.or.jp/upload_pdf/2008-a-03.pdf
Randy, did liquid propane/liquid oxygen ever get tested in a modified RL10 rocket engine? If so, was it compared to liquid methane/liquid oxygen? -
#43 by HappyMartian on 05 Apr, 2013 06:59
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Found it.
"The RL10 has actually been run on a very wide variety of things. For fuels, hydrogen, methane, and propane have all been used; for oxidizers, they've fired it on LOX, liquid fluorine, and FLOX (LOX/fluorine mixture). Mixture ratio has been varied extremely widely, including successful tests
running severely oxidizer-rich. And it's been throttled down to 1%. An amazingly tolerant engine."
From: Henry Spencer Wed, 23 Apr 1997
At: http://yarchive.net/space/rocket/rl10.html
The Deep Space Habitat module concepts outlined for BEO exploration are about two real options. Going somewhere interesting to explore. Or burying the hab to protect it from varying thermal loads, hyper velocity micrometeorites, and nasty radiation.
If we want our DSH to travel to somewhere interesting we need it to be lightweight so as to go as fast as possible. For GCR shielding the DSH would use propellant required for braking into whatever orbit we need at our destination.
Propellant tanks for the initial departure are located to the exterior of the tanks used for the braking burn. Note that the Orion is not rocket braked into orbit on the return to cislunar space and it does aerobraking in the Earth's atmosphere.
Propellant at our destination orbit has to be prepositioned by other means or made near our destination by ISRU robotic systems. We immediately 'load up' our DSH vehicle's massive tanks with more propellant once we arrive at our destination orbit.
That very large 'new supply' of propellant that was immediately loaded up at our destination is our GCR shielding while exploring at our destination's neighborhood and a ticket home if the mission has to be aborted early.
The DSH vehicle burns some of the propellant for the delta-v burn to head home, but retains a very large supply of propellant in the inner tanks closest to the DSH and Orion for GCR shielding and its braking burn into a high Lunar orbit.
After a deep space mission or two, a DSH would be buried somewhere interesting and useful, such as in Stickney on Phobos, or somewhere in the Moon's polar regions, where it can serve for several decades as part of an emergency shelter or permanent base.
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#44 by deltaV on 10 Apr, 2013 15:03
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When Orion is docked with a deep space hab would Orion be doing anything (other than waiting) such as navigation or communications? If so how much would this reduce the cost of the hab (compared to leaving Orion near Earth and having the hab do everything)?
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#45 by BrightLight on 10 Apr, 2013 16:00
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When Orion is docked with a deep space hab would Orion be doing anything (other than waiting) such as navigation or communications? If so how much would this reduce the cost of the hab (compared to leaving Orion near Earth and having the hab do everything)?
Looking at the latest power-point-pretty-picture I posted shows at least 5 antenna on the DSH; 4 on the solar array mounts (I assume they are rotary mounts) and one on the docking (node?) module, I would conclude that the DSH would be the prime comms. link. The position of the MPCV might suggest that it can do some maneuvering of the DSH. Also on the DSH solar "joints" are small thrusters for position maintenance? -
#46 by Ben the Space Brit on 10 Apr, 2013 16:12
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When Orion is docked with a deep space hab would Orion be doing anything (other than waiting) such as navigation or communications? If so how much would this reduce the cost of the hab (compared to leaving Orion near Earth and having the hab do everything)?
Looking at the latest power-point-pretty-picture I posted shows at least 5 antenna on the DSH; 4 on the solar array mounts (I assume they are rotary mounts) and one on the docking (node?) module, I would conclude that the DSH would be the prime comms. link. The position of the MPCV might suggest that it can do some maneuvering of the DSH. Also on the DSH solar "joints" are small thrusters for position maintenance?
A lot depends on the overall alignment of the DSH relative to the propulsion section. From this, it looks like Orion is on the node's Zenith CBM, so the most it would be able to do is add a little power to the DSH's RCS.
I imagine it's main role would be a redundant GNC platform with its navigation computer running in parallel to that on the DSH so that guidance data can be preserved in the event of a catastrophic computer failure. -
#47 by BrightLight on 10 Apr, 2013 16:21
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This brings up another question - If the DSH is built in LEO, how will it be moved to EML-1/2 or other BEO positions?When Orion is docked with a deep space hab would Orion be doing anything (other than waiting) such as navigation or communications? If so how much would this reduce the cost of the hab (compared to leaving Orion near Earth and having the hab do everything)?
Looking at the latest power-point-pretty-picture I posted shows at least 5 antenna on the DSH; 4 on the solar array mounts (I assume they are rotary mounts) and one on the docking (node?) module, I would conclude that the DSH would be the prime comms. link. The position of the MPCV might suggest that it can do some maneuvering of the DSH. Also on the DSH solar "joints" are small thrusters for position maintenance?
A lot depends on the overall alignment of the DSH relative to the propulsion section. From this, it looks like Orion is on the node's Zenith CBM, so the most it would be able to do is add a little power to the DSH's RCS.
I imagine it's main role would be a redundant GNC platform with its navigation computer running in parallel to that on the DSH so that guidance data can be preserved in the event of a catastrophic computer failure. -
#48 by Robotbeat on 10 Apr, 2013 16:33
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When Orion is docked with a deep space hab would Orion be doing anything (other than waiting) such as navigation or communications? If so how much would this reduce the cost of the hab (compared to leaving Orion near Earth and having the hab do everything)?
Some have suggested leaving Orion at EML1/2 (perhaps at the gateway) while the Deep Space Hab does its mission. That's an attractive idea to me, as it reduces the mass of the Deep Space Hab, assuming we want to reuse it.
But others have suggested using Orion to perform other tasks such as communication or even some RCS/ACS (this is an interesting idea to me... to use a docked spacecraft to perform maneuvers, potentially reducing the cost of the hab... I think Progress is capable of serving as a sort of service module for a small space station, providing attitude control...). -
#49 by Robotbeat on 10 Apr, 2013 16:35
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SEP tug has almost always been mentioned in the different proposals, at least for the gateway built at ISS. But you could also potentially use a large in-space chemical stage launched on SLS (it has been suggested).
This brings up another question - If the DSH is built in LEO, how will it be moved to EML-1/2 or other BEO positions?When Orion is docked with a deep space hab would Orion be doing anything (other than waiting) such as navigation or communications? If so how much would this reduce the cost of the hab (compared to leaving Orion near Earth and having the hab do everything)?
Looking at the latest power-point-pretty-picture I posted shows at least 5 antenna on the DSH; 4 on the solar array mounts (I assume they are rotary mounts) and one on the docking (node?) module, I would conclude that the DSH would be the prime comms. link. The position of the MPCV might suggest that it can do some maneuvering of the DSH. Also on the DSH solar "joints" are small thrusters for position maintenance?
A lot depends on the overall alignment of the DSH relative to the propulsion section. From this, it looks like Orion is on the node's Zenith CBM, so the most it would be able to do is add a little power to the DSH's RCS.
I imagine it's main role would be a redundant GNC platform with its navigation computer running in parallel to that on the DSH so that guidance data can be preserved in the event of a catastrophic computer failure. -
#50 by BrightLight on 10 Apr, 2013 18:33
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The SEP concept is widely espoused. MSFC is building the DSH simulator, where is the SEP simulator being built? I'm really glad to see the DSH simulator evolve and hopefully will be integrated with the MMSEV work being done at JSC. I look forward to the SEP simulator as that would suggest a more serious movement towards a workable in-space architecture.
SEP tug has almost always been mentioned in the different proposals, at least for the gateway built at ISS. But you could also potentially use a large in-space chemical stage launched on SLS (it has been suggested).
This brings up another question - If the DSH is built in LEO, how will it be moved to EML-1/2 or other BEO positions?When Orion is docked with a deep space hab would Orion be doing anything (other than waiting) such as navigation or communications? If so how much would this reduce the cost of the hab (compared to leaving Orion near Earth and having the hab do everything)?
Looking at the latest power-point-pretty-picture I posted shows at least 5 antenna on the DSH; 4 on the solar array mounts (I assume they are rotary mounts) and one on the docking (node?) module, I would conclude that the DSH would be the prime comms. link. The position of the MPCV might suggest that it can do some maneuvering of the DSH. Also on the DSH solar "joints" are small thrusters for position maintenance?
A lot depends on the overall alignment of the DSH relative to the propulsion section. From this, it looks like Orion is on the node's Zenith CBM, so the most it would be able to do is add a little power to the DSH's RCS.
I imagine it's main role would be a redundant GNC platform with its navigation computer running in parallel to that on the DSH so that guidance data can be preserved in the event of a catastrophic computer failure. -
#51 by strangequark on 10 Apr, 2013 18:42
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The SEP concept is widely espoused. MSFC is building the DSH simulator, where is the SEP simulator being built? I'm really glad to see the DSH simulator evolve and hopefully will be integrated with the MMSEV work being done at JSC. I look forward to the SEP simulator as that would suggest a more serious movement towards a workable in-space architecture.
It's called a Boeing 702SP. -
#52 by BrightLight on 10 Apr, 2013 18:54
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It looks like the 702SP series can move about 6000kg, uses roughly 18KW, can they be scaled up to DSH mass of roughly 50,000Kg?The SEP concept is widely espoused. MSFC is building the DSH simulator, where is the SEP simulator being built? I'm really glad to see the DSH simulator evolve and hopefully will be integrated with the MMSEV work being done at JSC. I look forward to the SEP simulator as that would suggest a more serious movement towards a workable in-space architecture.
It's called a Boeing 702SP. -
#53 by A_M_Swallow on 11 Apr, 2013 07:48
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This brings up another question - If the DSH is built in LEO, how will it be moved to EML-1/2 or other BEO positions?
The asteroid catching mission is proposing a spacecraft with a large bag on one end and a SEP able to move 500-tons. Make a second one replace the bag with say a NASA Docking System (NDS) and we have a tug able to push the DSH around. -
#54 by BrightLight on 14 Apr, 2013 00:06
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After looking at the Keck document found on the "capture asteroid mission"
This brings up another question - If the DSH is built in LEO, how will it be moved to EML-1/2 or other BEO positions?
The asteroid catching mission is proposing a spacecraft with a large bag on one end and a SEP able to move 500-tons. Make a second one replace the bag with say a NASA Docking System (NDS) and we have a tug able to push the DSH around.
http://www.kiss.caltech.edu/study/asteroid/asteroid_final_report.pdf
I think you have a good point, the concept looks to be well within the available technology and without being a engineer, looks reasonable. The DSH would take a while to get to EML-2 but if its unmanned, so what. -
#55 by Lar on 14 Apr, 2013 01:32
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That's actually a Really Good Idea. One of my beefs with NASA is the tendency to only make one of certain kinds of things...
The asteroid catching mission is proposing a spacecraft with a large bag on one end and a SEP able to move 500-tons. Make a second one replace the bag with say a NASA Docking System (NDS) and we have a tug able to push the DSH around.
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#56 by BrightLight on 15 Apr, 2013 20:44
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Latest DSH internal configuration from the P. Bookout April 2013 presentation. The port and starboard ends do not allow for easy access to the solar array modules from inside the DSH, this drawing would suggest no access.
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#57 by kkattula on 16 Apr, 2013 10:09
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"150 mSv as crew lifetime exposure limit goal"
That's an extremely conservative goal. Current ESA and Russian lifetime limits are 1000mSv.
Note there is little data for low level exposure over long duration. These limits are extrapolated from the effects of high doses of short duration, e.g. Hiroshima. There is some speculation and anecdotal evidence that long duration exposure at many times the background level is not harmful.
So an estimated dose of around 500mSv on a multi-year mission seems reasonable.
IMO, it is in the interests of the people who want funding to work on space radiation mitigation, to emphasize the danger. Similarly those in many other fields. They're not being paid to actually build a DSH yet, so they may feel the need to justify being paid to study it. -
#58 by BrightLight on 16 Apr, 2013 15:27
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"150 mSv as crew lifetime exposure limit goal"
I think your in the right track but I don't want to get off topic
That's an extremely conservative goal. Current ESA and Russian lifetime limits are 1000mSv.
Note there is little data for low level exposure over long duration. These limits are extrapolated from the effects of high doses of short duration, e.g. Hiroshima. There is some speculation and anecdotal evidence that long duration exposure at many times the background level is not harmful.
So an estimated dose of around 500mSv on a multi-year mission seems reasonable.
IMO, it is in the interests of the people who want funding to work on space radiation mitigation, to emphasize the danger. Similarly those in many other fields. They're not being paid to actually build a DSH yet, so they may feel the need to justify being paid to study it.
but
50mSv is the yearly dose for a radiation worker, 400 mSv in a short period dose that might show some symptoms of radiation poisoning in some people (not all!). In short, good shielding; 2.5cm polyethylene with an addition of lithium hydride walls will be adequate for most people most of the time. Clearly there is risk and older people with existing families is reasonable for astronauts on the DSH.
my short rant is over, please forgive me. -
#59 by strangequark on 16 Apr, 2013 19:47
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It looks like the 702SP series can move about 6000kg, uses roughly 18KW, can they be scaled up to DSH mass of roughly 50,000Kg?The SEP concept is widely espoused. MSFC is building the DSH simulator, where is the SEP simulator being built? I'm really glad to see the DSH simulator evolve and hopefully will be integrated with the MMSEV work being done at JSC. I look forward to the SEP simulator as that would suggest a more serious movement towards a workable in-space architecture.
It's called a Boeing 702SP.
Not directly, but my point is that the technology is pretty mature. A tug that can deliver 50mT through 6 km/s in 250 days uses about 300kW. We've built and tested 100kW thrusters. Using modern solar cells the required array size is less than half that on the ISS. There's no point to building a non-flight simulator. You might as well work on flight hardware. You would certainly want to build an integrated flight-grade propulsion bus (PPU plus thrusters plus propellant feed). However, at that point you're doing a qual program. The required tech is already high TRL. so there's no point in spending the money until you actually have funding committed to go off and build the real deal.
