Sal, considering a colony on Venus to be more feasible than one on Mars doesn't seem terribly well motivated to me. Can you please provide us some as hard as possible financial calculations on the required mission costs to back up your argument? Maybe also consider what returns you can realistically expect. Otherwise I remain unconvinced.
You seem to have me confused, Mr President, with the NASA Administrator circa 2150. No, I do not currently have full costings for colonisation of Venus. Such figures do not exist
. No, I do not have estimated rates of return, and I do not have a full and attractive business plan for the proposal. Such figures, again, do not exist. Indeed, if you've been following the conversation you'll note me saying repeatedly that there's no clear reason why anywhere
will ever be colonised. You are quite right that it would be inappropriate for you to greenlight my proposed Venus colonisation plan at this point, the Senate would never stand for it.
In the fantasy world where we are not
, actually, deciding right now whether to colonise Venus tomorrow, and where neither of us is charged with overseeing the accountancy for such a project, however...
You seem very concerned about the radiation levels on Mars. In practice, typical radiation levels on the Martian surface remain at less than 30 µSv/h1. This is noticeably higher than at sea level on Earth but still only ~150 times higher than the background radiation I measure at my home.
Well, let's take that at face value. 30 microsieverts per hour is over 250 mSv per year - which happens to be the EPA's recommended maximum radiation exposure that can be justified for life-saving emergency work. That's 1 sievert every 4 years, or 20 sieverts every 80 years. [8 sieverts in a short period is a 100% fatal dose regardless of treatment; nobody's actually tested what happens if you get the same dose over a long period, because nobody's insane enough to try it. For context, 250mSv/a is like spending a week on holiday in Chernobyl every year]. The current maximum permissable career exposure for NASA astronauts is 0.66 Sieverts. This is because 1 Sv gives approximately a 5% increased chance of a fatal cancer - in middle-aged healthy males. The cancer risk per sievert is much higher for women and for the young, and once you bring pregnant women and children into it it gets really serious. Putting women and children into a lifestyle with 20 sieverts of exposure is close to a death sentence. The document you cite sums it up: "it is not possible
for crews of younger ages, especially females, to perform long duration missions with a significant safety factor based on the current estimates of uncertainties in risk projections." And that's in the context of a mission to Mars and/or 400 days on the surface of Mars, with shielding - not a lifetime!
(annual "safe" limit for pregnant women and children is apparently around 5 mSv/a, although the dangers in pregnancy may be higher than that (we haven't really tested to see how much more vulnerable foetuses are; or if we have tested it, nobody's admitting it publically...))
[bear in mind also that long-term exposure doesn't just have a linear effect. NASA planning relies on the fact that astronauts will return to a safe environment between missions, because that period without high exposure is crucial for the body to repair the damage done in the high exposure periods. Take away that bit back on Mars and the chronic exposure gets worse and worse and worse in its consequences.]
It also says that for 40-year-old women, a mission that put them on Mars for 600 days, with 10cm of water shielding in addition to basic metal shielding, and assuming a relatively dense Martian atmosphere (and iirc the last 17 years have suggested a much less helpful atmosphere), would give a 4.5% increased risk of fatal cancer. A 4.5% increased risk of fatal cancer after two years is quite a lot, when we're talking about lifelong
colonisation, and about children and pregnant women rather than 40-year-olds.
That's before you get to things like optical damage, which can occur at much lower dose levels than fatal cancers.
However, because of the scarcity of observations and the complexity of certain types of radiation, the upside for risk is still very considerable, so in practice it could be much more than that.
What's more, your figure looks like an underestimate to me. Yes, there's a chart in that document that suggests less than 260 mSv/a. However, MARIE found levels of 400-500 mSv/a on average. The difference may be because over that baseline of radiation there are then proton storms of sometimes over a hundred times that base radiation - they're brief, but they push up the average. What's more, cancer risk and other biological damage are believed (as that document says) to be much higher from more intense exposures - 1 sievert over 10 years (the NASA model) may be less dangerous than 0.5 sieverts over two days. What's more, both MARIE and the data in your document are from a low period in Mars' multi-year radiation exposure cycle. Your document has a figure showing around 400 mSv/a as the low point (300 behind 20g/cm^3 of metal shielding), but that can spike up to 120 at the high points - still 700 behind 20g of shielding. [And 20g for every square centimetre is already a heck of a lot of metal to have to hoist up there!]
Your document suggests maximum allowable EVAs on Mars of 2-3 hours. But again, that's for people who are on a short mission to the planet, not for people who actually live there their whole lives.
The level is manageable for repeated outdoor expeditions
Not really, so far as I can see. Manageable a few times for astronauts on limited missions, sure. Manageable on a regular basis for colonists for years and years? No.
and nothing that can't be shielded to Earth-like levels by placing the living quarters below a few meters of soil.
I'm skeptical. We're not talking gamma radiation here, after all, we're talking highly energetic GCRs and proton storms. Well, maybe - apparently Martian soil is very dense. I see a reference to talcum powder, which is apparently around 1000kg per m^3. On the other hand, that means that your shelter has to be built to withstand the weight of 1000kg/m^3! I guess you're not building out of aluminium shells, then! Fine, if you build out of reinforced concrete that's no problem. But then you need the reinforced concrete. Is Martian soil good for making concrete? If you're reinforcing it, you presumably need to bring the steel with you. And the equipment to make concrete, too.
Is this impossible? No, absolutely not. I'm just pointing out that if you need to a) dig trenches into the rock, b) produce reinforced concrete (or similar) in large quantities, c) construct shelters, and d) cover those shelters with heavy soil, and end up with a dark manmade cave with no natural light and you need to put a radiation suit on to visit the greenhouse (and you're rationed in how often you can do that and you only get to see the green stuff a couple of years in your lifetime to moderate your dose)... well, I think you end up looking longingly at the colony where you just have to unfurl a light fabric balloon and you're not only safe from radiation but also surrounded by twice as much light as on Earth and bursting vegetation.
Of course, Martians would have to be good at dealing with Martian soil - because every time there was a sandstorm the entire colony would be buried in the stuff...
[at risk of damaging my own case: what you'd probably do on Mars is actually just build your shelter inside a cave system of some kind. It's still not a great place to be, but it lets you build in much more lightweight materials, which is a huge cost saver in space]
Anyway, to conclude the radiation discussion: yeah, it's only 150, or 200, or 400, or 1,000 times the radiation in your living room. Yeah, best case scenario it's only two orders of magnitude worse than we evolved for.
Likewise, when somebody suggests I go into a room that's 20,000 degrees celsius, I'll just point out "hey, it's only two orders of magnitude hotter than my living room!" (measuring in kelvin, obviously). I'm sure we'd love to build our houses at 100 atmospheric pressures... Two orders of magnitude isn't "only"! It's a lot!
In contrast, an inhabited base on Venus will in practice have to be suspended floating in the atmosphere to escape the high temperature and pressure on the planet's surface. This sounds like a logistical nightmare to me and in any case needs more expensive solutions than the problems you need to solve when colonising Mars.
This seems logistically easy enough to me. It's a balloon filled with air. We've been building balloons for a long time now, they're not particularly difficult. A century ago, we were building balloons that could carry 15,000kg - and that's much more expensive on earth than it would be on Venus. [the big problem on Earth is that the lifting gas is expensive and/or dangerous, particularly if you're going to vent it to come back down again; on Venus, the lifting gas is breathable air, and you wouldn't have to vent it]. We've sent balloons 50km into our own atmosphere (again much harder than on Venus), and had them carry thousands of kilos.
Could we put a floating city on Venus tomorrow? No. Technologically it's much harder than putting a settlement on Mars - we still need to work stuff out. We need the right fabric - superlight, corrosion-resistant, and ideally transparent, or at least translucent, if possible. We need the origami to fold and unfold the balloon - and for larger balloons we may need to piece them together in the Venerean atmosphere. We need to continue the research we're only just beginning to do with combined lighter/heavier-than-air aerodynamics, to produce the maximum stability in high wind conditions while also exploiting the shape of the envelope to produce lift. We need to work out how best to distribute weight to maximise both stability and capacity of a colony, and during the construction phase there will probably be awkward elements bringin materials in and out through an airlock (I'm assume what we'd do is inflate the balloon first, then construct a lightweight rigid structure within it).
So yeah, not happening tomorrow. But there's no part of it that seems out of reach, given modern technologies, and once you solve the technical problems the result looks much cheaper, in terms of materials and energy, than the massive construction required on Mars. Not to mention much nicer to visit.[/quote]
You'll also probably want to develop capabilities to explore the surface of Venus, which will further raise the costs that you have to cover.
There probably isn't anything interesting there. Once a colony is well established, it might want to investigate the possiblity of using local materials, which would indeed cost a lot, but that's an optional extra.
Indeed, since Venus is a paradise for plants (well, a colony would be - massive amounts of light and an infinite supply of free CO2), and since the colony would want lightweight, rigid materials that wouldn't necessarily have to bear much weight in total (we're not going to be talking about skyscrapers here), I suspect considerable use would be made of homegrown bamboo...
You also worry too much about the Martian atmospheric conditions. It's cold there, sure, but not really unearthly. On the equatorial lowlands on Mars you can get ground level temperatures above freezing while on Earth we know how to operate permanently inhabited bases in the Antarctic conditions.
Very small inhabited bases! And not a lot of people would sign up to live in them! And Mars can get a lot colder than Antarctica.
The pressure difference you'd need to maintain between the living spaces and the Martian atmosphere is also less than 1 atm. That's nothing. If we can build deep sea going submarines, that doesn't pose us with any technical problems.
Well sure, yes. But we don't try sending submarines into space. That would be expensive. And they're not very big, because that would be expensive too. And they don't tend to use their airlocks deep underwater all that much. And sometimes submarines sink. Again, there's a difference between technical problems - what it is possible to do - and feasibility problems - how expensive something is on a large scale for a long period of time, and how attractive it is for colonists. "It's no worse than spending your life on a deep-sea submarine, honestly" is just not that inviting a pitch for colonists. The Venerean sky-garden guys are going to be able to put out way
nicer brochures, and their apartments will probably be cheaper in the long term. And safer. Because again, when you have a pressure leak between the earth and (near) vacuum, that's a really serious, emergency problem. Whereas even if an entire sky-colony had to be abandoned due to leaks, the length of time it would take to sink would be leisurely for evacuation (a zeppelin riddled with holes from heavy machine gun fire flying low over London was still able to make it back to Paris, flying slowly).
We'll anyway need pressurised spacecraft to get to either of the planets and those need to deal with the nearly same 1 atm pressure differential when flying through space.
Yes, but spaceships will be expensive, and not nice to live on. It would be nice if the colony at the other end didn't have to be built to the same specifications.
Living for a long time in low gravity does have its issues, but can you provide a citation to any particular study that argues it to be fatal for permanent settlement?
Again, you mistake me for someone living 200 years from now. No, I don't have any studies to hand on what it's like to live on Mars. Because those studies haven't been done yet.
I'm sure you don't need citations for the harrowing effects of micro
gravity. Microgravity loses you about 5% of muscle mass per week, up to at least 20% total loss, and 1% of bone mass per month, probably up to 40-60% loss. That has immediate effects on the biology, as it results in massive release of calcium into the system. Microgravity doubles the blood pressure in your brain, while halving the blood pressure in your lower limbs; this causes the body to desparately destroy blood to maintain survivable cranial pressure, so within a few days you lose over 1/5th of your total blood supply. This in turn means the heart has less blood to pump, and it atrophies even quicker than the rest of your muscles. The heart pumps quicker, which in turn does other things, like pumping out more adrenaline and making us nervous. And the risk of heart failure increases.
More generally, microgravity results in high pressures in the upper body - around the lungs and the heart, and in the head. It appears to result in serious (and in at least a few cases irreversible) damage to the eyes, ears and balance organs. All the internal organs that have liquids flowing through them have big problems - kidneys, liver, even digestion. The thirst instinct fails so you become dehydrated. You sweat more, nore because of internal things but because air convection doesn't work without gravity, so it's harder to lose heat. Increased sweating and problems with the regulatory organs lead to chemical imbalances.
All told, apparently experts think the lifespan in microgravity may only be a couple of years, but we don't really know. We also don't know what happens when you gestate in space, but tests on other animals are not encouraging... likewise what happens with puberty, given that both pressures and hormone levels will be out of whack.
There are then two big questions. One is what happens with 0.4g instead of ~0g. We just don't know. It could be that everything works fine until you're down to 0.05g; it could be that it stops working when you pass 0.9g. It could be that it's not a binary thing, but a continuum, but how linear things are on the continuum we have no way of knowing. If the lifespan in space is 2-3 years, is the lifespan on Mars 10 years? 20 years? 60 years? No way to know.
However, I see no reason to be confidant. Most of the processes we're talking about aren't issues of binary response, but the result of analogue differences, so I think a considerable amount of difference could be expected at low gravity too (I suspect the eyes will probably be the first point of failure - they're very delicate things,filled with fluids, and when you change the pressures and shapes of those fluids even slightly all sorts of things can happen). Even if the body attempts to compensate for the differences, that's not something it's ever evolved to deal with, so there's no reason to think its responses will be proportionate to the threat. Indeed, it's even possible that it's worse at low gravity than at zero gravity - there may be an equivalent of an allergic reaction, where the body's mechanisms panic in response to low gravity, and do more harm than good. Just assuming that everything will be fine seems overly optimistic to me...
Then there's the other question: what we can do about it. At the moment, gravity sickness seems hard to treat. An absolute minimum seems to be an extremely hard physical training regime - fine for elite astronauts, but tougher when you're talking about civilian colonists. Some symptoms could be treated directly with medications, or even surgery - perhaps implants. But most of it is medical science we don't have today.
An interesting avenue is the question of gravity duration. Gravity all the time with brief bits of low-grav should have minimal long-term consequences for healthy adults. Permanent low-grav will probably be much worse. So how much time must be spent in gravity? If it's "99%", then you need to build an entire colony with artificial gravity, which will be expensive. If, on the other hand, you can keep yourself healthy by spending an hour a week in the centrifuge, that makes a colony far more viable.
This appears, so far as I can see, to be a genuine variable for SF speculation. The optimist can believe that gravity sickness doesn't kick in until really, really low gravity, or at least that it can be kept at bay with medications, exercise regimes, and perhaps periodic centrifuge usage. That opens up Mars at least, and maybe even the Moon, for relatively easy mass colonisation. The pessimist can believe that gravity sickness kicks in almost as soon as you're noticeably below Earth gravity, or at least that the effects are big enough to seriously militate against pregnancy and childhood in low-g environments. That focuses any colonisation efforts squarely at Venus, with any other colonial efforts probably being much later and much smaller in scale, dependant upon the construction of artificial gravity habitats.
Personally, my SF setting is further toward the "pessmistic" side of the scale, both because I think it's more interesting narratively and because I think it's intuitively much more realistic. But I recognise that this is an area where we're not going to find out the answer for quite a long time to come.
Venus, on the other hand, has a strong magnetosphere
Lastly, I want to correct this statement. Venus, like Mars, doesn't in fact have a proper magnetosphere at all. What both of the planets have, is a weak secondary magnetosphere induced by the interaction of solar wind and the planetary ionospheres. Basically we are talking about locally enhanced magnetic field of the solar wind and radiation shielding provided by the atmospheres themselves.
True, Venus only has an induced magnetosphere. However, coupled with the thick atmosphere, the effect remains the same.