The MSL reported measuring 1.8 milliSieverts/day radiation dose during cruise to Mars. One Sievert total dose increases risk of fatal cancer by 5%. ...
...It must be correct that halving the trip time would halve the total radiation dose on any crew. How much shielding did the MSL provide to the instrument and is it necessary to double the shielding to halve the dose with shielding? ...
...How much shielding did the MSL provide to the instrument and is it necessary to double the shielding to halve the dose with shielding? ...
Quote from: aero on 12/31/2013 05:15 am...How much shielding did the MSL provide to the instrument and is it necessary to double the shielding to halve the dose with shielding? ...Basically, there was no specific radiation shielding in MSL design, just whatever was provided by construction withstanding launch loads, nothing more.Therefore, it's incorrect to transfer directly the dose measured by RAD in MSL to human-rated spacecraft.For instance, if we put Apollo CM in trans-Mars injection with RAD inside - I would expect the cumulative trip dose to get lower by factor of 2.
......Elon Musk should know that his idea of shielding just with a column of water pointed at the Sun won't work for many reasons. I should shoot him an email.
I have been a long time proponent of short trip times as opposed to a more complex spacecraft. The collumn of water makes sense for solar radiation and events. The rest is IMHO better solved with reduced trip times. A technological breakthrough in the area of propulsion should IMHO be a focus of research, much more than shielding and in situ resource use.
typical Mars mission plans have round-trip flight times of 400 to 450 days.[21] A fast Mars mission of 245 days round trip could be possible with on-orbit staging.
^ Forget about a reactor. SpaceX would probably go bust fending off legal actions and other politically-instigated regulatory actions!Not much you can do about GCRs. As for solar flares; point the engines at the Sun - those, together with the propellant tanks should provide sufficient shielding.
Quote from: CuddlyRocket on 01/01/2014 10:44 am^ Forget about a reactor. SpaceX would probably go bust fending off legal actions and other politically-instigated regulatory actions!Not much you can do about GCRs. As for solar flares; point the engines at the Sun - those, together with the propellant tanks should provide sufficient shielding.Considering I haven't seen NASA get sued for flinging plutonium-fueled RTGs up into orbit (mounted on various probes), your point remains just a hypothesis.
We would need to see Spacex actually go forward with that approach to test it.
Also, given that Big Tobacco is still in business today despite losing a huge lawsuit, I remain dubious about Spacex getting sued out of existence.
If they're dominating the world launch market with their Falcon 9 family in 5 years, the worst that could possibly happen is they'd have to file for bankruptcy and reorganize. Much like Sea Launch they'd probably be right back in business, only far more successfully.
In an interesting possibility, you might be able to use the reactor shielding to also protect the crew from solar flares. Think of it as a 2 for the price of one deal.
Quote from: Robotbeat on 12/31/2013 05:19 am......Elon Musk should know that his idea of shielding just with a column of water pointed at the Sun won't work for many reasons. I should shoot him an email.It's not that simple although, I'm going to present simplified picture too (softly speaking There are TWO major radiation threats for a trip to Mars: GCR and Solar flares******* GCR *******= constant level, low fluctuations (or "no events");= isotropic (comes from all directions);= VERY high energy (makes passive shielding ineffective);= while present serious health hazard at long exposures, it is not life-threatening in short-term.*** SOLAR FLARES ***= catastrophic events (up to 4 orders of magnitude in range);= uni-directional (from the Sun, roughly - plus/minus magnetic field distortion for p+ and e- fluxes);= low-mass particles, mostly - n, p, e, and gamma (makes common light liquids like LOX, RP1, CH4 highly effective shields);= deadly dangerous - can kill in a matter of minutes.Considering the above two lists (simplified, yes, but correct in the first approach) - the idea of Sun-pointed liquid shield is reasonable and working ( and btw - it is not Elon's ).Yes, it's working, just like body armor - it won't make you 100 % safe in battlefield, but it protects you from deadly hits of small arms fire and shrapnel.
Solar flare particles are most definitely NOT unidirectional. They spiral around the magnetic field lines at various angles, thus end up fairly isotropic (though certainly not perfectly so).It's like shielding from light on a clear day versus a cloudy day.
I sincerely doubt Musk is planning nukes.I agree it'd be helpful vs solar on the surface, but NOT in transit. For high-thrust rockets, NTRs aren't worth it compared to hydrolox. For electric propulsion, solar beats nuclear until you get to Jupiter. This is BEFORE politics has anything to do with it.And even with surface power, if you're using a nice lithium-sulfur rechargeable battery (they're starting to enter the market) with unrollable solar arrays, you still get very close to nuclear power. Personally, I think nuclear power is still quite useful for a colony (it's a very stable, low-maintenance power supply that could be designed to last a century before needing a fill up or maintenance http://terrapower.com/ ), but you could certainly still do it with solar power.