Why colonize Mars and not the Moon?

[nikkkom]

Water is only trace in that cold atmosphere, and that only near the poles. Maybe mine the soils for ice and/or recycle for human needs.

Mining requires a lot of additional equipment. Additional equipment needs to be designed and built or imported, and needs additional maintenance. Mining can't be done just in any location - you need to actually have the desired material at the mining location (as opposed to air which is everywhere).

Instead of messing with all that, if you already have air processing plant which produces some H2O anyway, it may make sense to use _it_ to get H2O.

Mars colony is likely to have closed-loop life support systems (developed from space station technology) and need not that much water to top up losses.

 

[nikkkom]

Why not colonize both the Moon and Mars?

Sure, I agree.
The discussion exists because the $$$ available for space programs is limited. Thus, the question is more like "which colony - Moon or Mars - should be prioritized?"

 

[sophiecentaur]

Im not a chemist either, but a change in pressure doesn't not necessarily effect Haber;

I thought that Haber was all about the appropriate working pressures. Perhaps we'd only be talking about a few more Watts of compressor on low pressure atmospheric N on `Mars. Probably not the biggest problem up there.

 

[mfb]

The Haber process needs the right pressure range, but once you have purified the inputs (probably via distillation), you are decoupled from the atmospheric pressure anyway.

 

[stefan r]

Mining requires a lot of additional equipment. Additional equipment needs to be designed and built or imported, and needs additional maintenance. Mining can't be done just in any location - you need to actually have the desired material at the mining location (as opposed to air which is everywhere).

Instead of messing with all that, if you already have air processing plant which produces some H2O anyway, it may make sense to use _it_ to get H2O.

Mars colony is likely to have closed-loop life support systems (developed from space station technology) and need not that much water to top up losses.

I think they will hauling/piping water from the polar caps. At least until Ceres gets their elevator and mass driver built.
For colony #1 they are likely to drop the lander directly on the water deposit. http://www.space.com/31143-manned-mars-landing-sites-workshop.html

They will need to top up water much more than they will need nitrogen or argon. Data from viking mission has nitrogen 2.7% and water at 0.03%. Distillation would give you a cheap run separating CO₂ from the Ar/N₂. The water would be bound up in the dry ice at a little over 315 ppm. I suspect using a molecular sieve would be easier than distilling. Gypsum might be much more available than molecular sieves.
Maybe bulldoze the gypsum into a large solar bake oven or use nuclear waste heat oven. After extracting the water spread the gypsum out and let it pick up trace water for a few years. Maybe pile it on the habitats for extra radiation shielding. Helps if any water leaked reacts on location. then throw it back in the heat oven.

 

[mfb]

They found vast amounts of water ice at intermediate latitudes on Mars, just a few meters below the ground. A small digging or drilling tool can deliver as much as water as necessary. Digging gives water, the atmosphere provides CO2 and a bit of nitrogen. Water and CO2 are needed both for the station and to produce rocket fuel (and potentially as emergency energy storage), while nitrogen is only needed to cover losses in the station ecosystem.

 

[sophiecentaur]

The Haber process needs the right pressure range, but once you have purified the inputs (probably via distillation), you are decoupled from the atmospheric pressure anyway.

OK That's a reasonable reply, thanks. Nitrogen will just be a bit more expensive - fair enough as everything else would be the same. There is always the possibility that mineral Nitrate deposits exist, from a time when there was more of an atmosphere.
[Edit: it looks like they would have to be of biological origin so that's a non starter . . . . . unless. . . .]

 

[nikkkom]

Water and CO2 are needed both for the station and to produce rocket fuel (and potentially as emergency energy storage), while nitrogen is only needed to cover losses in the station ecosystem.

CO/O2 is a good fuel/oxidizer pair too, and this pair can be made from only CO2.
Nitrogen also is needed for plastics.

 

[mfb]

CO/O2 would give a bad I_sp. Wikipedia mentions 250 s without reference, that is at the level of bad solid rocket fuels. The Raptor engine using methane and oxygen has 380 s.

With 380 s, you can go from the Martian surface to Earth with a single stage easily (mass ratio ~5-6).
With 250 s, you probably want a second stage (mass ratio ~12-14). What do you do with the first stage then? And how do you get the now much larger and more complex rocket to Mars?

 

[nikkkom]

CO/O2 would give a bad I_sp. Wikipedia mentions 250 s without reference, that is at the level of bad solid rocket fuels. The Raptor engine using methane and oxygen has 380 s.
With 380 s, you can go from the Martian surface to Earth with a single stage easily.

Fuel is useful not only for rockets. It might be the way how to store PV-generated energy for night consumption. Also, vehicles.

You don't have to go from Mars surface to Earth using a single rocket. A developed colony can have dedicated LVs for ferrying cargo and people to low Mars orbit. Earthbound passengers then change the ship. CO/O2 is adequate for LMO launch vehicle.

Here is a thread about CO/O2 fuel in NS forum - https://forum.nasaspaceflight.com/index.php?topic=21544.0
A few snippets:

"""
Here's a few technical reports:
Experimental evaluation of the ignition process of carbon monoxide and oxygen in a rocket engine
http://hdl.handle.net/2060/19960045922

Carbon monoxide and oxygen combustion experiments: A demonstration of Mars in situ propellants
http://hdl.handle.net/2060/19910014990
(This one says that 260-280s is a realistic Isp for a pressure-fed engine, while 290-300s is realistic for a pump-fed engine.)
"""
Use the right tool for the right job. The low Isp of the CO/O2 propellant combo is actually optimal from an energy standpoint (presuming you get really good mass fraction), which is relevant if you have to produce all that propellant from local power sources.
"""

 

[stefan r]

CO/O2 would give a bad I_sp. Wikipedia mentions 250 s without reference, that is at the level of bad solid rocket fuels. The Raptor engine using methane and oxygen has 380 s.

With 380 s, you can go from the Martian surface to Earth with a single stage easily (mass ratio ~5-6).
With 250 s, you probably want a second stage (mass ratio ~12-14). What do you do with the first stage then? And how do you get the now much larger and more complex rocket to Mars?

Colony #1 uses the same rocket. Earth to LEO with methane is much harder than Mars to MEO using CO. That would not work with H₂/O₂ engines.
ISP measurements vary depending on liquid vs gas going into the engine and the atmospheric pressure outside of the rocket nozzle. Wikipedia lists ISP 369 and ISP 309 for methane on the same chart.

You can do a single stage to orbit CO/O₂ rocket on Mars ISP 250 is enough. But you can make engines that burn both methane and CO. So launch with CO to haul CH₄ and Oxygen to the orbiting station and return using CH₄. You can switch tanks fuel tanks mid flight while using one LOx tank and one rocket. Would not be 2 stages but similar effect. Elon Musk said something about using natural gas instead of pure methane to further cut costs for launch from earth. That opens up options for CO mixed into CH₄ and/or mixtures with C₂H₄ and C₂H₂.

 

[mfb]

Use the right tool for the right job. The low Isp of the CO/O2 propellant combo is actually optimal from an energy standpoint (presuming you get really good mass fraction), which is relevant if you have to produce all that propellant from local power sources.

Let's calculate. For fuel that combust to CO2 and H2O, the reaction releases as much energy as we put in. Then, neglecting efficiency issues, the energy we need scales with $(\mathrm{mass factor} - 1) I_{sp}^2$ where $\mathrm{mass factor} = \exp(\Delta v / (g\cdot I_{sp}))$. For every $\Delta v$, this leads to a curve with a minimum at $g I_{sp} = 0.628 \Delta v$.

For Mars orbit, 3.5 km/s, the most energy-efficient I_sp is 225 s. If you get fuel from Earth in Mars orbit, then a low energy density can be an advantage. For return to Earth, 6 km/s, the most energy-efficient I_sp is 385 s, and CO/O₂ is significantly worse due to the staging issue.
This is neglecting gravity losses, which favor higher I_sp. It is also neglecting that a lower I_sp will need a larger rocket, again favoring higher I_sp. CO has a higher density than methane, but we need more of it compared to methane, the effective density is similar. CO has a lower boiling point, making cooling more difficult.

You don't have to go from Mars surface to Earth using a single rocket. A developed colony can have dedicated LVs for ferrying cargo and people to low Mars orbit. Earthbound passengers then change the ship. CO/O2 is adequate for LMO launch vehicle.

Why would a developed colony want to rely on fuel sent from Earth? Or do you suggest electric propulsion or something similar to leave Mars orbit? Or multiple fuel launches as pseudo-second stage? All that increases the complexity. With methalox you can launch from Earth, land on Mars, refuel, and fly back in the next launch window.. You don't need a rocket infrastructure on Mars.

Earth to LEO with methane is much harder than Mars to MEO using CO.

Yes, but you have to get to LEO, and Earth to LEO with CO is not going to happen. With methalox you can use the same engines to get to Mars and to get back.

But you can make engines that burn both methane and CO.

Different temperature range, completely different fuel mixture ratios, different temperatures... I don't think that would lead to a good performance. Mixtures might work, but I don't see why CO should be in the mixture.

 

[mheslep]

The risk is tiny for everyone involved apart from the few astronauts that would go to Mars. Space missions are not just the astronauts.

Sure. ? And the topic is moot if the astronauts are removed from the mission. Unmanned missions continue as before, for a $billion per go, with no concern about flight time, radiation, return, and relatively little concern about failure.

 

[stefan r]

...Yes, but you have to get to LEO, and Earth to LEO with CO is not going to happen. With methalox you can use the same engines to get to Mars and to get back.
Different temperature range, completely different fuel mixture ratios, different temperatures... I don't think that would lead to a good performance. Mixtures might work, but I don't see why CO should be in the mixture.

CO should be in the mixture because it is excessively abundant. Splitting CO₂ to make O₂ creates CO. Using the CO means no added infrastructure.
It is certainly not going to be ideal performance. The question is how much performance is lost. The oxy-fuel mix is easy to adjust. The valves to control flow are already in the engine. I have never built a turbo-pump. If I was buying a pump for a lab I would likely use the same model on CO or CH₄.
I would worry about the engine getting hot enough to crack the CO. Would be easy to test for that.

 

[mfb]

For 1 liter of oxygen, you need 3.1 liters of CO, or 0.8 liters of methane. That is a factor 4 difference. An engine that can burn both needs horribly oversized fuel pumps and probably two separate injection systems. Not to mention the problem how to design the tank. Do you want to keep it 3/4 empty in methane operation? Or keep the oxygen tank 3/4 empty in CO operation?
The optimal chamber pressure and the optimal expansion ratio will be different for the two fuels, again you misdesign your engine for at least one of them. A thermal system good for CO is overdesigned for methane. You would need a gigantic benefit to outweigh all these disadvantages.

I'm sure it is possible to design a methalox engine to accept 1% CO or vice versa. But where is the point? You just add complexity for no reason.

 

[mheslep]

f you already have air processing plant which produces some H2O anyway

H20 is only trace in the air, except for small periods near the poles.

 

[mheslep]

I thought that Haber was all about the appropriate working pressures. Perhaps we'd only be talking about a few more Watts of compressor on low pressure atmospheric N on `Mars. Probably not the biggest problem up there.

Right, whatever Haber requires, additional power can make the conditions Earth like.

 

[rootone]

Right, what ever Haber requires, additional power can make the conditions Earth like.

In principle yes, but where is additional energy to come from?
With useable technology at present the only feasible option is to set up several fission power plants on Mars.
These will have to be shipped, installed, and maintained from Earth.
That seems unlikely at best.

 

[mheslep]

In principle yes, but where is additional energy to come from?
With useable technology at present the cheapest option is several fission plants set up on Mars.
These will have to be shipped, installed, and maintained from Earth.
That seems unlikely at best.

Any power source on Mars must be shipped from Earth, of course. Small nuclear power plants have been proposed for missions, both by in the Mars Direct proposal in NASA's "90 Days Study". Either radioisotope (already used multiple times in space missions) or fission are considered.

Immediately after landing, the propellant factory/ERV would deploy a robot “utility truck” rover carrying a 4.5-metric-ton SP-100 nuclear reactor. The rover, which would burn methane fuel and oxygen oxidizer, would carry the reactor a few hundred meters away and place it into a natural crater or one blasted “with the aid of a few sticks of dynamite.” The crater wall and rim would prevent the reactor from irradiating the landing area. Thermal radiators would deploy from the SP-100, then the rover would run a cable from the reactor back to the propellant factory/ERV.

The SP-100 would supply 100 kilowatts of electricity to compressors in the ERV. These would draw in martian air, which is mostly carbon dioxide. The carbon dioxide would be reacted in the presence of a catalyst with 5.8 metric tons of liquid hydrogen brought from Earth, yielding 37.7 metric tons of methane and water...

I believe the deployment of the reactor to make fuel in Mars Direct occurs before arrival of the manned mission, i.e. is all robotic.

 

[mfb]

Solar panels are considered as well. They have a nice power to mass ratio and space is not an issue.

 

[mheslep]

Solar panels are considered as well. They have a nice power to mass ratio

Yes, apparently 1.7 tons of solar panels http://www.uapress.arizona.edu/onlinebks/ResourcesNearEarthSpace/resources30.pdf to accomplish the same fuel production mission as the four ton nuclear reactor in Mars Direct.

and space is not an issue.

Same source has an array 1850 m^2, less than on the ISS. Space craft arrays don't need much structural support, but one on Mars would need some. Assuming, 2 cm thick strings of cells, that's 37 m^3 of solar panels. Its not clear to me how that volume competes with the reactor on Mars transit.

 

[sophiecentaur]

Solar panels are considered as well. They have a nice power to mass ratio and space is not an issue.

I would have thought solar panels would be an ideal solution. Totally flexible modular design where a single problem with nuclear generation would mean no electricity supply. And we wouldn't want to mess up the Martial environment die to a crash or other unforeseen accident.
The issue of batteries for night time is not there if the panels are for fuel production. They deffo get my vote.

 

[nikkkom]

H20 is only trace in the air, except for small periods near the poles.

On Earth, CO2 is only 0.04% in the air. Look at any tree. Its carbon came _entirely_ from that CO2.

 

[stefan r]

On Earth, CO2 is only 0.04% in the air. Look at any tree. Its carbon came _entirely_ from that CO2.

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.

 

[sophiecentaur]

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.

We're discussing a very involved industrial process here, for which the small details affect the choice of the optimum system. It's hardly worth discussing the beauty contest without much more information about the real situation and the actual costs involved.

 

[mfb]

I would have thought solar panels would be an ideal solution. Totally flexible modular design where a single problem with nuclear generation would mean no electricity supply. And we wouldn't want to mess up the Martial environment die to a crash or other unforeseen accident.
The issue of batteries for night time is not there if the panels are for fuel production. They deffo get my vote.

Everything has to be redundant. No one would rely on a single nuclear reactor - you would send at least two or three, where the failure of one or even two is not mission-critical. Same for the electronics for solar panels.

Batteries are useful if no nuclear reactor is present - you need electricity at night, and burning fuel for that has a bad efficiency.

 

[sophiecentaur]

Everything has to be redundant. No one would rely on a single nuclear reactor - you would send at least two or three, where the failure of one or even two is not mission-critical. Same for the electronics for solar panels.
Batteries are useful if no nuclear reactor is present - you need electricity at night, and burning fuel for that has a bad efficiency.

I get all that; redundancy goes without saying, along with loads of reconfigurability. A solar farm would be producing much more fuel than would need to be stored in the basic overnight batteries. The best economy is to run with minimal dark time requirements and a big proportion of the solar output would go towards rocket fuel and daytime manufacturing activity. Vast thermal storage systems would be the way to provide heating. Life would revolve around such regimes - which is why I have always said that life on Mars would be no picnic ( same as in the Antarctic stations but much worse - no penguins to provide light relief. I would foresee the need for a lot of Psychoanalyists up there.

 

[mheslep]

On Earth, CO2 is only 0.04% in the air. Look at any tree. Its carbon came _entirely_ from that CO2.

I know. However, the need of plant life for water and CO2 is considerably different. A mature tree might uptake .1 or .2 kg of CO2 per day in its growing season, but use almost half a ton of daily water. I doubt collecting the scant water vapor in the Martian atmosphere is effective compared to mining the soil for ice.

. No one would rely on a single nuclear reactor

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

Supposedly the dust storms encountered by the rovers blocked up to 99% of sunlight during the storm, and the dust cover remaining afterwards significantly reduced power. I doubt solar (plus batteries) is suitable, either for a manned mission with 24 power needs or an earlier unmanned fuel production mission that might be permanently impaired.

https://en.m.wikipedia.org/wiki/Spirit_(rover)#Global_dust_storm_and_Home_Plate

And we wouldn't want to mess up the Martial environment die to a crash or other unforeseen accident.

There have been several unmanned Mars mission accidents strewn around the planet, such as the Mars Polar Lander impact. There will be more. Curiosity's sky crane retro rocket was by design destroyed on the surface after landing Curiosity.
https://marsmobile.jpl.nasa.gov/msl/mission/technology/insituexploration/edl/skycrane/

 

[sophiecentaur]

There have been several unmanned Mars mission accidents strewn around the planet, such as the Mars Polar Lander impact. There will be more. Curiosity's sky crane retro rocket was by design destroyed on the surface after landing Curiosity.
https://marsmobile.jpl.nasa.gov/msl/mission/technology/insituexploration/edl/skycrane/

. . . .but none involving nuclear materials, which was what my post was referring to.

 

[mheslep]

. . . .but none involving nuclear materials, which was what my post was referring to.

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.

 

[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.