Why colonize Mars and not the Moon?

[gleem]

Mars surface radiation is 30 uSv/ hr,

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?

 

[mfb]

One might well send a single reactor for the unmanned fuel production mission.

Even then you have to shift everything by 2 years if there is a problem with the reactor.

Supposedly the dust storms encountered by the rovers blocked up to 99% of sunlight during the storm

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.

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?

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.

 

[stefan r]

... How will the Mars surface dose let alone the transit dose to and from Mars be justified?

http://www.theverge.com/2016/9/27/13080836/elon-musk-spacex-mars-mission-death-risk
3:45

 

[mheslep]

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?

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".

 

[mheslep]

...Even then you have to shift everything by 2 years if there is a problem with the reactor..

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.

... the thread.30µSv/hr for unshielded components (number from above, didn't check it).

27 µSv/hr from here, via the instrument on Curiosity: "RAD's data show that astronauts exploring the Martian surface would accumulate about 0.64 millisieverts of radiation per day."
I had 29 uSv/hr from somewhere else which I can't recall.

 

[mfb]

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.

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.

After all, I've not seen it suggested that two loads of hydrogen fuel are transported in case the first is lost.

A nuclear reactor is more prone to issues than a simple fuel tank.

http://www.theverge.com/2016/9/27/13080836/elon-musk-spacex-mars-mission-death-risk
3:45

There is a high risk, but the cancer risk is not the largest part.

 

[stefan r]

They probably want one power supply for the main site and one with the rover. Going to Mars and sitting in a hole does not sound like the inspiring adventure people were hoping for.

 

[gleem]

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.

Since the skin is rather insensitive to radiation exposure it is the deeper "critical organs" that is of more interest. The 30 uSv/hr is most likely due to rather penetrating radiation to assess the dose to these organs. I think the ISS dose data indicates that the space suit provide minimal protection.

First, the 30 µSv/hr (263 mSv/yr) is on the surface, is not a dose

Actually it is what is referred to as a dose equivalent, the standard quantity used in radiation safety programs. Dose equivalence takes into account, as a rather rough approximation, the relative biological effects of different types of radiation. It differs from absorbed dose which only determines the energy per gram deposited in tissue. The rate of deposition of energy as measure by the Linear Energy Transfer produces increasing biological effects as it increases.

Second, the US radiation worker limit is 100 mSv/yr, though

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.

which gives a "5-percent increase in lifetime fatal cancer risk".

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..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? Actually not a problem in desperate times with desperate situations we must take desperate measures,

Initially living accommodations will be on the surface similar to ISS I would suppose. Living underground at least 12 feet to get the equivalent protection of our atmosphere will probably require heavy machinery complicating the establishment of a colony.

 

[mheslep]

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 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.

A nuclear reactor is more prone to issues than a simple fuel tank..

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.

 

[mheslep]

The 30 uSv/hr is most likely due to rather penetrating radiation ...

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.

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.

Yes, my mistake, max annual whole body dose is 50 mSv.

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..

Right, radiation of one Sv gives excess cancer risk of 5%.

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?

For comparison, a current smoker has an excess risk of 20% (Figure 4). I would not call smokers brave.

Actually not a problem in desperate times with desperate situations we must take desperate measures,

Desperate about what, in relation to a Mars mission?

 

[sophiecentaur]

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.

Isn't it a bit early in the day to be making judgements like that? Is your background value consistent all over the surface?

 

[mfb]

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.

Radioisotope generators are not nuclear reactors. At least not the type discussed, that could power a Mars settlement.

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.

The manned mission will need more nominal power than normally used to account for failures. There is no way to avoid that.

Isn't it a bit early in the day to be making judgements like that? Is your background value consistent all over 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.

 

[gleem]

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.

I don't. 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.

For comparison, a current smoker has an excess risk of 20% (Figure 4). I would not call smokers brave.

Nor do I. They are tolerant of the latent risk because for the immediate perceived benefit(?). Astronauts really do not have many benefits but say for curiosity or glory if they succeed.. Sitting on top of thousands of pound of explosive chemicals or using technology that has been minimally tested does elicit a certain amount of bravery since much of the risk is imminent. The increased risk of cancer from radiation exposure is probably not even statistically significant for a few dozen persons.

Desperate about what, in relation to a Mars mission?

I am led to believe that at some point in the probably distant future it is expected that the Earth will not be a fit place to live and humanity must be preserved at any cost. The Mars mission is the first step for the establishment of a colony for the anticipated emigration.

Remembering the small asteroid that exploded over Chelyabisk Russia might be one reason that some are thinking about our demise.

 

[sophiecentaur]

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.

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.

 

[nikkkom]

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.

Practice will tell.
In any case, this discussion is useful by highlighting (especially for the "Moon first" crowd) the issue of having various volatiles available. It's very important for any colony.

 

[mheslep]

That measurement is presumably of surface radiation levels and most of that would presumably be from space, due to the lack of magnetic field.

And thin atmosphere.

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.

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.

https://en.m.wikipedia.org/wiki/Cosmic_ray#Changes_in_atmospheric_chemistry

It's that attitude that confirms my doubts about the viability of humans ...

Yes humans have flaws, one of which is dogma. For instance, to declare environmental disturbance A okay, but type B bad.

 

[sophiecentaur]

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.

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]

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.

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.

Doesn't experience of the effects of human careless treatment of Earth give you any worries about possible damage on other planets?

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"

Disturbances A and B should each be treated with care.

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]

 

[UW-PurpleHusky]

I don't understand why we would want to look at a planet in our solar system... In order to increase the probability of human existence remaining in the universe, we need to both terraform and colonize another planet orbiting a different star. A younger star preferably.

 

[sophiecentaur]

Out record is not impressive down here and not surprising, bearing in mind the priorities that are applied.

You are assuming that your priorities are not open to challenge then?
You seem to imply that 'enough' work has been done on establishing the situation and possible risks in Mars. I can't think of the basis for this. Humans have been aware of situations on Earth in great detail and made decisions which have been based on a selected sample of evidence, to support their cause. Do you really think that things would be different on Mars?

No, not about rocks in space.

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.

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"

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.

 

[glappkaeft]

I don't understand why we would want to look at a planet in our solar system...

Because while sending a lot of people to Mars or the Moon ain't easy going to another star system is completely infeasible for the foreseeable future.

 

[mheslep]

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.

 

[mheslep]

You are assuming that your priorities are not open to challenge then?...

You're responding to your last sentence in #796, which I failed to trap correctly in quotes for some reason.

 

[sophiecentaur]

You're responding to your last sentence in #796, which I failed to trap correctly in quotes for some reason.

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?
This thread is getting very tired and we're not going to be convincing each other, are we? I would just suggest that there is more to this than 'to boldly go' and your "rocks in space" description is worrying to me.

 

[Jim777]

Why not build a HUGE space station off planet Earth and then another and then another, if survival and colonization are the goals. When we get a HUGE space station colonized and self-sustaining, then we can send these stations into deep space searching for planets that have the conditions to sustain life. Mars is a dead planet with unhospitable conditions for long term survival. To Terraform Mars would take centuries, if even possible.

 

[rootone]

Why not build a HUGE space station off planet earth.

Because it would be hugely expensive to supply and maintain unless it produced something valuable that could not be done on Earth.

 

[stefan r]

Because it would be hugely expensive to supply and maintain unless it produced something valuable that could not be done on Earth.

The colony ship needs to produce colony ships.

 

[Jim777]

The cost of colonizing Mars or the Moon will be huge, but in the end we may have NOTHING for our money and efforts. It could be a colossal failure due to the unknown risks that will be actually involved. A HUGE Space Station/Colonizing Space Ship will give us the time to deal with living in space, and working in space, and raising a family in space. It has to be constructed in space because it will be too HUGE to ever get off the planet, if buit on Earth. It will have to accommodate thousands of doctors, engineers, astrophysicists, welders, mechanics, machinists, metal fabricators, cooks. It will have to be a City in Space, and when it is completed, and colonized to the point that it is self-sustaining, it will take years, maybe decades, before all the 'bugs' are out and then it can move out of the nesting place above Mother Earth toward the Asteroid Belt to begin mining operations to get the necessary materials that are needed to build more Space Colonies. Workers will use smaller work vessels to land on the asteroid predetermined to begin mining raw ore, and smelters, whether on the Mother Ship or built on the Asteroid will convert the raw materials into a material or materials they can machine into parts for the new stations or repair the Mother Ship if damaged while on it's journey there.

 

[anorlunda]

A HUGE Space Station/Colonizing Space Ship

SF writers will point out that we already have one of those, called Earth.

 

[sophiecentaur]

SF writers will point out that we already have one of those, called Earth.

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.
Any other environment in the form of a massive spaceship or a nearby planet would need more work than most people could imagine, to make it more than just barely habitable. I can't help feeling that an environment with a significant gravity field would be easier to develop on - despite being a long way from Earth. The species on which we rely (all except microbes) are mostly suited to 1g. Every plant or animal would need to be developed specially to cope without its reliance on geotropism. You'd even need to be giving cows a daily workout if their meat were to be what we like to eat on Earth.