New Mars Forums

So, in summary:  You propose that, rather than using aerobraking for atmospheric entry, we should instead do a breaking burn followed by powered descent; and that further, rather than importing Hydrogen for use in ISRU that we should import methane.  You also propose a reusable launch/descent vehicle for crew and (am I reading this correctly?) for cargo.  Rather than starting in LEO you instead suggest that the mission should start in L2.

Your justifications for this (which I intend to argue, once I can be sure that I'm arguing with what you actually said ) are of course contained in your introductory post.

This seems like a good technology, not just for Mars, but also for Earth.  I hope it gets the funding to be used in the near future!

GW-

I just read your blog post.  We've been thinking very much along the same lines for structures.  I hadn't thought about windows, particularly.  My thoughts tended towards having regolith on the side, for radiation protection reasons.  Seeing as the quantity of regolith atop the structure will reduce the radiation load to negligible-ish levels, given your proposed structure the majority of the radiation would actually come in through the sides.  Now, cosmic rays are not unidirectional, though they are blocked the worst in the vertical direction.   In any case, I would expect that the elimination of windows in favor of shielding in that direction would result in an approximate halving of radiation dosage within the enclosed area.  I have no calculations or evidence to support this, and obviously it depends on the geometry of the building as well as the attenuation effects of the atmosphere, and any number of other factors.

I was also thinking that the supports would only be on the outside, and a truss would hold the regolith up in the center.  Po-tay-to/Po-tah-to, really.  Temporary supports could be used to hold the roof up before pressurization, and then removed when the structure is fully pressurized.  Depressurization beyond a certain level would subsequently pose a structural hazard, but I'm not sure that this represents any additional mortality risk, beyond that already posed by significant depressurization.  One would have to do a cost-benefit, of course; I suppose in that case one could still use the building afterwards, which is at least something.

I think it's also important not to discount the possibility of multi-story structures.  Some stories could have windows and others could be shielded, meanwhile one wouldn't have to move as much regolith.  By use of excavators and explosives, one could also imagine buildings that go down.

Midoshi does plan to attend the Banquet, by the way, so I look forward to seeing you all there.

I like it!  I suspect that that procedure may actually be used more to make glass than to make the chemical precursor for Aluminium, but I don't think that's a big problem.  It would be better if we can find some white silica somewhere but no guarantees, of course.

I do question whether it's a good idea to have external windows in every apartment.  One can't shield with 5m of regolith where there is a window, after all.  I would say that sufficient artificial light, creative use of coloring, and internal windows, to common areas and the like, should be enough to keep people happy.  I also tend to be of the opinion that, given that people spend more time in their beds than in any other single location, that should be the place that has the lowest amount of radiation out of anywhere that person spends in a day.

Oh, one objection:  That apartment is too roomy!  It's got more room than where I live

Edit:  Oh, and no limestone.  Limestone on Earth is the remnant of long-extinct crustaceans, and all signs point to there being none on Mars.

Robertdyck-

I would suggest that the numbers you gave are basically the same as the numbers I gave, to within the margin of error and accounting for the potential variation in different parts of the solar cycle.

I think you're under a false impression regarding the source of the particles from spallation.  Spallation can happen even when the impactor is a proton, so long as the nucleus that it is impacting consists of more than a proton.  Subcritical, spallation-based nuclear reactors have been proposed in which protons are accelerated to 1 GeV to impact with Uranium atoms.  They fracture the nucleus and the particle fragments are energetic enough to cause fissions in other nuclei.  As you said, light element shielding would do a lot to alleviate this-- but not just light elements.  It has to be Hydrogen.

Secondly, regarding "High energy radiation" protons can be every bit as energetic as other particles, be they heavier or lighter.  Momentum is pretty irrelevant in this context, it's energy that matters.  For our purposes, Cosmic Ray protons are just as energetic as other kinds of particles to be found in cosmic rays.  By the way, some cosmic ray particles are moving so quickly that, due to relativistic time dilation, they experience time at rates that near zero.  It's not inconceivable that we could get neutrons from other stars but I would think, and evidence seems to bear me out, that most of them are not moving quite that rapidly.

Most kinds of radiation are not particularly penetrating.  Solar protons and x-rays, while a huge threat to a totally unprotected individual, are not nearly as hard to shield from as Cosmic Rays.  I would imagine that any shielding that is sufficient to deal with cosmic rays would also be enough to deal with X-rays, even if it is composed of light elements.

The problem, again, is cosmic rays.  I would simply use regolith.  If you're using it in the dual function of pressurization and shielding, it will be more than enough to reduce radiation risk to acceptable levels.

GW and Robertdyck:

This really feeds into what GW was saying in his post: Given that simple and common-sensical measures can reduce radiation to acceptable levels, our response to anyone outside the scientific community with regards to radiation is (and ought to be) simple: Not a problem.  No issue at all.  Not dangerous.  Perhaps our colonists will be subject to statistically higher rates of cancer or other diseases later in life, and this is unfortunate; It may sound callous but that's not unreasonable for a group of people who will be carving out a new society.  If someone believes that people should be allowed to smoke then someone should certainly be allowed to colonize another planet (for much greater gain, to oneself and society) at comparable risk to theirself.

GW-

Regarding TMS Convention, when will your presentation be?  I'd like to make sure that I attend.  I'll be there that weekend, as will the user Bobunf and Midoshi.

The issue with that kind of shielding for greenhouses is that Mirrors aren't very good at capturing natural light like that at all hours of the day.  In fact I'd suspect they're pretty bad at it.  You'd need a good amount of land area and large greenhouses (good for thermal efficiency reasons) aren't really practical.  Please recall that in a general sense agriculture is more productive when plants have more light to work with.

I've always been a fan of aeroponics to grow plants-- given that we'll want to economize on space and energy it seems like it is by far the most efficient way to do so.  The basic method is that you suspend a plant with its roots in darkness and continuously spray them with a nutrient solution.  Because the plants aren't in dirt it's relatively easy to move them, and the harvesting and planting (presumably the most labor-intensive parts of farming, given automation where possible) can be done by transferring racks of plants to a shielded location.  Actual human presence in the greenhouse is unnecessary, and indeed providing for human access to the plants while they're in there could be seen as a waste of space.

MCP suits need to be revived, and I'd imagine that this could happen at low cost.  I know it's been brought up before, but how different are they really from a full-body bathing suit?  These "supersuits" as they were called prior to being banned certainly did not have price tags in the tens of millions of dollars.

For ease of human access in fixing machinery, etc. I favor a greenhouse atmosphere that is the same as the habitat environment as a whole.  I think that this also makes it easier to use the greenhouse to regulate the atmosphere of the habitat, specifically with regards to CO2 levels and humidity.

Assuming that 18 hour warning can be given, I would imagine that a sheet of lead/iron/whatever could be pulled over the greenhouse to shield from X-rays.

Just because heavy ion Cosmic Rays have been blocked doesn't mean that all of the high energy particle radiation has.  Specifically, protons, which according to Wikipedia compose 90% of Cosmic Radiation (With a further 9% Helium, putting metals in the cosmological sense at just 1% of the radiation), and thus blocking of heavy ions is not that important in the context of radiation shielding, be it from primary or secondary radiation.  I don't know exactly what is considered "heavy" in the context of radiation shielding but I would have to imagine that it would be the same as "heavier than Helium."  If you can point me to the paper in which the claim was made I would love to look at it.  In any case, this image (reproduced below) suggests that the annual radiation dose decreases from about 22 rem/year at the top of Olympus (where the pressure is nearly zero) to about 16 rem at the datum, where the pressure averages 610.5 Pa, by definition.  At martian gravity of 3.7 m/s^2, this is 165 kg/m^2 (16.5 g/cm^2).  These 165 kg of CO2 serve to reduce the radiation from Cosmic Rays by about 27%.  Assuming exponential decrease, one would need 363 kg/m^2 (3.63 g/cm^2) of Carbon Dioxide to halve the cosmic radiation.  Water ice is presumably better and regolith perhaps worse.

Hyperphysics suggests that this secondary radiation has three primary components about which we care:  Energetic Protons, energetic Neutrons, and more exotic particles known as Pions and Kaons, each of which comes as a positively charged particle, a negatively charged antiparticle, or a neutrally charged particle.  The charged Pions and kaons have half-lives of 2.6e-8 s for the Pion and 1.2e-8 s for the Kaon, and negligibly small (~1e-16 s) for the neutral particle.  These decay into various combinations of electrons, positrons, and gamma rays (we don't care about neutrinos).

Unfortunately, I have no idea of the branching ratios for the formation of various particles.  However, I would like to forward the following points for each: Protons will have lower energy than the particle that produced them, probably by a pretty significant amount.  They should be stopped in short order by whatever shielding is in the way.  Neutrons will also be stopped in a reasonable distance, depending on the material.  Pions and Kaons will presumably have higher energies than protons or neutrons, since they are the result of subnuclear reactions as opposed to spallation.  Between decay and impacts with shielding material, I would expect that they would have mostly decayed by the time they pass through the shielding.  This will release gamma rays, which are also difficult to shield against.  Note that this is the case for both heavy and light materials.

I wonder how low you could get the costs.  Say a small chemical thruster to spin and de-spin, a couple mice or rats or whatever, three to six months of food, water, and oxygen.  I bet it could weigh under 100 kg and be developed for a minimal cost.

That said, to crowd fund the interest would have to be there.

RobertDyck, I absolutely agree that further experimentation with and development of M2P2* units is a good idea.  In addition to its potential as a radiation shield, it is also quite good as far as electric propulsion goes, insofar as the Sun provides most of the energy input to the system. 

That said, I would like to see more development before M2P2s are settled upon as the prime method of radiation shielding.   First off, I haven't seen any studies (be they physical experimentation or computer simulations) that say that an M2P2 unit has a strong enough or large enough magnetic field to have a significant effect on cosmic radiation.  These particles are, after all, much higher in energy than the Solar Wind, and the simulations that I've seen suggest that even for the Solar Wind deflections won't be too large.

Beyond that, I have to call BS on the "Secondary Radiation" argument.  Not because the physics is wrong, of course, because it's a fairly well-documented effect.  Rather, if the regolith you're using as a shield generates secondary radiation, there is a simple answer: More regolith to shield from the secondary radiation.  It's also worth noting that the most common element in regolith (a plurality by mass and a majority by moles) is Oxygen, which I would consider to be pretty light.  Not Hydrogen, perhaps, but light.  Once a true colony has been established, ice-based shielding is entirely reasonable, but I would expect a couple meters of regolith to do in the meantime, especially for an initial outpost. 

I would like to read up more on the Secondary Radiation threat.  This is obviously important, but I haven't found any good resources.  Can you point me to a good overview of the matter?

I am actually of the opinion that a 5% increase in the probability of death from cancer is an acceptable risk for a one time mission followed by a life spent on planet Earth.  For longer duration missions and colonies more effort should be put into reducing radiation but I think that plain old physical shielding while on-planet is a viable solution.  I would like to add that it is in the nature of a frontier to be less safe than the homeland.  I don't consider Jamestown to be an admirable model (in any respect) but the death rate there in the first winter was 56%.  The winter two years later was even worse, with a mortality rate of 88%.  In the first 17 years of the Jamestown colony, about 6000 people immigrated to Virginia.  On the 17th year, the population was 1200, indicating that about 80% (Or more, given the tendency of humans to procreate) had died (source).  I mention these statistics not because I think that these are enviable, or even reasonable mortality rates (Though one can't help but be impressed at the chutzpah of the early modern Europeans in going off into the unknown with a near total lack of preparation or prior knowledge).  Rather, I do it to show that a frontier is not safe and it is the job of the frontiersperson to build society where none existed before.  "You live until you die" is perhaps a relevant attitude-- There is such a thing as acceptable risk and at some point you have to say that things are "safe enough".

*I contend that this constitutes a proper name and thus the acronym does not need expansion or explanation.

I think that there's something important to note about the use of artificial magnetic or electrostatic fields as radiation shielding:  These technologies can't even be considered vaporware.  As fascinating a technology as it is, M2P2 hasn't demonstrated magnetic bubble expansion beyond the size of a small test chamber.  Meanwhile electrostatic systems are power and mass intensive, and hard to set up, not to mention dangerous to crew doing EVAs and disruptive to electronics.

What we need to focus on, IMO, is better physical shielding once on Mars, and intelligent placing of mass both for in-space purposes and on-planet purposes so that the crew spends as much time as possible in well-shielded areas.  Sleeping areas are a logical place to start.  For the colony/base/hab itself, one could easily imagine a machine that packs sandbags full of regolith and piles them on top of the structure.  This will help with pressure retention in the vertical direction as well.  According to this image the pressure in Hellas (~12 mb) is enough to halve the radiation.  12 mb at 3.7 m/s^2 corresponds to a layer of water 32 cm thick.  From this I conclude that a meter or two of regolith (much denser than water) should provide enough shielding to reduce radiation while on-planet to acceptable levels.

Paraterraforming definitely has a lot of potential advantages, in the short and long run, in terms of the production of large amounts of habitable space.  This biggest question to me is what we would need to do to make the paraterraformed interior radiation-safe.

No, that's not correct.  "R" cannot be anything.  "R" refers specifically to Hydrocarbon groupings.  It wouldn't make sense to refer to any possible substituent with one representation because different substituents would have different chemistry*.  One could see how this compound would be stable with an alkyl group, because then it becomes in essence, a poly-ester.

That is not the formula for a copolymer, by the way. That is the article on Polyanhydride.  That is the general formula for polyanhydride in its pure form.

You say you have sources. I am willing to concede this point the moment you present me with a valid source that supports your claim.  I have not myself been able to find any, so if you could direct me to one I would really appreciate it.  I would be very happy if there were some stable compound made from Carbon and Oxygen in a 1:2 mole ratio (I suppose higher amounts of Oxygen wouldn't be a problem since Carbon is a solid), perhaps with other elements that are indigenous to Venus but I don't think that this polymer is it.

*Examples abound.  Take the representation of an alcohol: R-OH.  If R could, as you say, be anything, this could be the formula for Hydrogen peroxide or water, both of which are clearly not alcohols.  For that matter, it could be NaOH or NH4OH.  These are obviously not alcohols either.

Qraal, that is very interesting.  Do you have any sense of how much land area one would get from Venus if it were transformed into that kind of desert planet?

Welcome back, by the way.