mheslep said:Mars surface radiation is 30 uSv/ hr,
Even then you have to shift everything by 2 years if there is a problem with the reactor.mheslep said:One might well send a single reactor for the unmanned fuel production mission.
99% of direct sunlight. There is also indirect sunlight, especially with so much dust around.. About 1/2, with a worst case of about 1/4 light left, we had the numbers earlier in the thread.mheslep said:Supposedly the dust storms encountered by the rovers blocked up to 99% of sunlight during the storm
30µSv/hr for unshielded components (number from above, didn't check it). Humans would be shielded at least by a space suit, but most of the time by their habitat, and probably some regolith on top of that.gleem said:This would result in almost five time the yearly maximum permissible dose for radiation worker on Earth. I have seen figures of abut 10uS/hr. for ISS so the astronauts can be brought back before them reach the 0.05Sv limit. How will the Mars surface dose let alone the transit dose to and from Mars be justified?
gleem said:... How will the Mars surface dose let alone the transit dose to and from Mars be justified?
First, the 30 µSv/hr (263 mSv/yr) is on the surface, is not a dose, and is not inside a vac suit/habitation/vehicle where some amount of the radiation won't penetrate. Second, the US radiation worker limit is 100 mSv/yr, though Fukushima workers use 250 mSv/yr. Third, these limits are in terms of dose, absorbed by the body, not simply incident on the skin. The ESA has a total career limit of 1000 mSv for its astronauts, which gives a "5-percent increase in lifetime fatal cancer risk".gleem said:This would result in almost five time the yearly maximum permissible dose for radiation worker on Earth. I have seen figures of abut 10uS/hr. for ISS so the astronauts can be brought back before them reach the 0.05Sv limit. How will the Mars surface dose let alone the transit dose to and from Mars be justified?
Redundancy should be used with a high bar of overall improved mission performance and reliability. Adding another 4.5 tons of a #2 reactor means at least 4.5 tons less of something else, in a context where every kg on board has a high or critical value. Often, it will be better to take one of something made very reliably with lots of performance margin and well tested. After all, I've not seen it suggested that two loads of hydrogen fuel are transported in case the first is lost.mfb said:...Even then you have to shift everything by 2 years if there is a problem with the reactor..
mfb said:... the thread.30µSv/hr for unshielded components (number from above, didn't check it).
Use two 2.25 ton reactors, unless they scale too bad for that. If one fails, you make slower progress, but at least you don't lose all power in the station. In particular, you can keep cooling the fuel you already have, and if the failure doesn't happen too early you still might get the job done in time.mheslep said:Adding another 4.5 tons of a #2 reactor means at least 4.5 tons less of something else, in a context where every kg on board has a high or critical value.
A nuclear reactor is more prone to issues than a simple fuel tank.mheslep said:After all, I've not seen it suggested that two loads of hydrogen fuel are transported in case the first is lost.
There is a high risk, but the cancer risk is not the largest part.stefan r said:
mheslep said:First, the 30 µSv/hr (263 mSv/yr) is on the surface, is not a dose, and is not inside a vac suit/habitation/vehicle where some amount of the radiation won't penetrate.
mheslep said:First, the 30 µSv/hr (263 mSv/yr) is on the surface, is not a dose
mheslep said:Second, the US radiation worker limit is 100 mSv/yr, though
mheslep said:which gives a "5-percent increase in lifetime fatal cancer risk".
I like that idea for the prelim-unmanned fuel production mission, when time has little cost in the case of a single failure. On a manned mission, I doubt two-half size reactors prevent calamity if up to twice the food and other supplies are required for the period on the surface.mfb said:Use two 2.25 ton reactors, unless they scale too bad for that. If one fails, you make slower progress, but at least you don't lose all power in the station.
I don't know that this is the case for a simplified 100 kW reactor on a Mars mission: sealed, no-refuel of fuel removal. I don't believe many radioisotope power generators have failed in the history of spacecraft , relative to fuel/oxidizer tanks. A single spark won't destroy a reactor and everything around it, as a spark in an O2 tank might do.A nuclear reactor is more prone to issues than a simple fuel tank..
How do you know the radiation type? Gammas, neutrons are highly penetrating, alphas, protons, not as much. I don't know the make up, other than that cosmic is higher energy than solar.gleem said:The 30 uSv/hr is most likely due to rather penetrating radiation ...
Yes, my mistake, max annual whole body dose is 50 mSv.When did we increase the MPD? https://www.osha.gov/SLTC/radiationionizing/introtoionizing/ionizingattachmentsix.html OSHA still lists it at 50 mSv/year, i.e. 5 Rem/yr in the old units listed on their site.
Right, radiation of one Sv gives excess cancer risk of 5%.Just to clarify this statement at 1 Sv whole body dose equivalent the lifetime probability of cancer is 0.05. The lifetime probability of cancers from non radiation causes is about 0.39..
For comparison, a current smoker has an excess risk of 20% (Figure 4). I would not call smokers brave.The bottom line is that we can (must) relax the dose limits for a few brave explorers for relatively short stays. Will tourists be exempt from the MPD requirement for the general public currently at 0.5mSv/year? What about large populations for a lifetime especially those born there?
Desperate about what, in relation to a Mars mission?Actually not a problem in desperate times with desperate situations we must take desperate measures,
Isn't it a bit early in the day to be making judgements like that? Is your background value consistent all over the surface?mheslep said:How are nuclear materials, even if some escaped from a tiny reactor, harmful to the Martian environment? Mars surface radiation is 30 uSv/ hr, 120 times that of Earth background levels.
Radioisotope generators are not nuclear reactors. At least not the type discussed, that could power a Mars settlement.mheslep said:I don't know that this is the case for a simplified 100 kW reactor on a Mars mission: sealed, no-refuel of fuel removal. I don't believe many radioisotope power generators have failed in the history of spacecraft , relative to fuel/oxidizer tanks. A single spark won't destroy a reactor and everything around it, as a spark in an O2 tank might do.
The manned mission will need more nominal power than normally used to account for failures. There is no way to avoid that.mheslep said:On a manned mission, I doubt two-half size reactors prevent calamity if up to twice the food and other supplies are required for the period on the surface.
As Mars doesn't have a relevant magnetic field and the atmosphere is quite thin everywhere, I would not expect a strong dependence on the location. Lower points and points closer to the poles will have slightly lower dose rates.sophiecentaur said:Isn't it a bit early in the day to be making judgements like that? Is your background value consistent all over the surface?
mheslep said:How do you know the radiation type? Gammas, neutrons are highly penetrating, alphas, protons, not as much. I don't know the make up, other than that cosmic is higher energy than solar.
mheslep said:For comparison, a current smoker has an excess risk of 20% (Figure 4). I would not call smokers brave.
mheslep said:Desperate about what, in relation to a Mars mission?
That measurement is presumably of surface radiation levels and most of that would presumably be from space, due to the lack of magnetic field. I mentioned environmental damage and the environment goes below the surface. If nuclear materials get into the surface, the result is very different from radiation from space, which will not penetrate far below the surface. Now is the time to consider such matters and avoid over simplistic comparisons of the two risks. It's that attitude that confirms my doubts about the viability of humans Terraforming Mars, in which absolutely everything possible needs to be taken into account. It certainly hasn't been like that for Earthly development.gleem said:Whoever measured/quoted 30uSv had to make an assumption since all they could measure would be the absorbed dose with would be quoted in Grays.
stefan r said:Was that 1% energy efficient conversion?
The leaf does gas separation by conversion from CO2 to carbonic acid, H2CO3. Martians can use minerals that react with water. However, if there is already a 2 story sand dune of hydrated mineral nearby then it is easier to use a bulldozer instead stressing the distillation plant.
And thin atmosphere.sophiecentaur said:That measurement is presumably of surface radiation levels and most of that would presumably be from space, due to the lack of magnetic field.
Cosmic radiation creates dozens of radioisotopes in the Earth's atmosphere, and so too the surface of Mars and Ceres, which is how in part that the Dawn probe performs gamma spectroscopy on Ceres to determine it's surface composition, and to some depth.I mentioned environmental damage and the environment goes below the surface. If nuclear materials get into the surface, the result is very different from radiation from space, which will not penetrate far below the surface. Now is the time to consider such matters and avoid over simplistic comparisons of the two risks.
Yes humans have flaws, one of which is dogma. For instance, to declare environmental disturbance A okay, but type B bad.It's that attitude that confirms my doubts about the viability of humans ...
You seem very confident that the little we know about the surface (and below) of Mars is enough to predict the effect of anything we might do to it. That is surely as much a "dogma" as any wariness I might be expressing about the possible risks. Doesn't experience of the effects of human careless treatment of Earth give you any worries about possible damage on other planets? Disturbances A and B should each be treated with care. Out record is not impressive down here and not surprising, bearing in mind the priorities that are applied.mheslep said:Cosmic radiation creates dozens of radioisotopes in the Earth's atmosphere, and so too the surface of Mars and Ceres, which is how in part that the Dawn probe performs gamma spectroscopy on Ceres to determine it's surface composition, and to some depth.
I pointed out the mistaken assertion that there is no radiation penetration below the surface, but I've never indicated omiscience about Mars. The discussion above was about you singling out a particular disturbance ("nuclear materials") with no particular basis.sophiecentaur said:You seem very confident that the little we know about the surface (and below) of Mars is enough to predict the effect of anything we might do to it.
No, not about rocks in space. Yes people have done Foolish Things, more to come. At the same time, space exploration also conjures up, "What a piece of work is a man! How noble in reason, how infinite in faculty! In form and moving how express and admirable! In action how like an angle"Doesn't experience of the effects of human careless treatment of Earth give you any worries about possible damage on other planets?
The nature of life, and of exploration, is to disturb the surroundings. To focus on the trivial is to miss the disasterous.Out record is not impressive down here and not surprising, bearing in mind the priorities that are applied.[/QUOTE]Disturbances A and B should each be treated with care.
You are assuming that your priorities are not open to challenge then?mheslep said:Out record is not impressive down here and not surprising, bearing in mind the priorities that are applied.
So Mars is just a 'rock in space'? From the title of this thread, I though we were discussing the possibility of a future home for colonists. But I guess they would not be you so you are insulated from their consequences.mheslep said:No, not about rocks in space.
I cannot get fired up by language like that, I'm afraid. Politicians dish it out all the time and it's very often the strongest when their cause is weakest. (Second Gulf War was a good example) Let's have some evidence based policies and not policy selected evidence.mheslep said:At the same time, space exploration also conjures up, "What a piece of work is a man! How noble in reason, how infinite in faculty! In form and moving how express and admirable! In action how like an angle"
UW-PurpleHusky said:I don't understand why we would want to look at a planet in our solar system...
Exploration, discovery. I don't care to live at the top of Everest or the bottom of the deap ocean, but I think it would interesting to visit.UW-PurpleHusky said:I don't understand why we would want to look at a planet in our solar system...
I was making assumptions about your priorities, perhaps. (I missed the \QUOTE thing.) But, from your statements, I think I have divined your priorities correctly - no?mheslep said:You're responding to your last sentence in #796, which I failed to trap correctly in quotes for some reason.
Because it would be hugely expensive to supply and maintain unless it produced something valuable that could not be done on Earth.Jim777 said:Why not build a HUGE space station off planet earth.
The colony ship needs to produce colony ships.rootone said:Because it would be hugely expensive to supply and maintain unless it produced something valuable that could not be done on Earth.
Jim777 said:A HUGE Space Station/Colonizing Space Ship
The difference for Earth is that the conditions were just right for us to survive with very little conscious effort. Our nature has been to 'improve' things and it has worked in as far as the human population has increased and increased. Nonetheless, I think it is still true to say that we rely more on what Earth is doing for us than on what we are actually doing. Our agriculture only works because farming has replaced existing species of flora and fauna to produce more food than was available from the indigenous organisms of a few millennia ago. The rest is still 'laid on' for us.anorlunda said:SF writers will point out that we already have one of those, called Earth.