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Comment by ryao | Hacker News Reader

I would prefer it if we made human settlement of the oceans a reality first. Human settlement of space has health problems that are not yet solved such as vision damage from zero gravity environments and brain damage from cosmic radiation.

http://www.space.com/25392-manned-mars-mission-astronaut-vis... https://www.rt.com/document/57fc69bac46188c6758b4599/amp

Making underwater habitats is far more practical in the short term. Experience in making closed environments for human habitation of the ocean would be useful when the problems with space exploration are solved.

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Underwater you have gravity, access to our biosphere, food, water, you can make air and make fuel.

In space... well...

The issue though, is that people want what's out there, they want to mine asteroids and somehow that laudable goal has been conflated with colonizing another gravity well in some minds.

One thing that I've always wondered is why space colonization focuses so much on planets. It seems like orbital platforms would both fix the low-gravity health issue (spin the platform) and provide easier access to lucrative resources (you can hit asteroids without dealing with getting in/out of gravity wells).

Definitely, and there are some hefty asteroids out there we could probably bubble-form into habitats, live on the interior surface and have low and high -g sectors. Hell, even moons makes more sense than planets, until lift ceases to be an issue.

1. It is much easier to land on/get into the orbit of a planet. For example, transfer from low earth orbit to Mars requires a delta V of about 4.3 km/s. Now to get into Mars' orbit, this needs to be reduced to about 3 km/s (rough napkin-top calculation, take with a grain of salt). However if you want to "stop" at a massless orbital platform/asteroid, you would have to reduce all 4.3 km/s (without any aerobrake assist).

2. If we assume an orbital platform is like a ring (similar to Halo), and if the diameter of this thing is 2km, then it would need to spin very fast (70m/s). This is okay, until you realize, that so much speed means a lot of difference in gravity from the floor to ceiling. For example, a man who is 2m tall, would feel 1g on his feet and about 0.95g = 9.3m/s^2 on his head. The difference in g would give rise to different health issues. You could make the station bigger, but then it would be probably better to stick to a natural body that is similar size instead

I thought delta-v from LEO to Mars was over 6km/s? There are near-Earth asteroids at much lower delta-v. https://www.planetaryresources.com/2015/08/how-we-choose-our... gets into some of this.

At the 1km radius you give, a 2m human would have head at 0.2% lesser acceleration than feet. Am I miscalculating? Note that 1g is just one place in the design space, though an attractive one for a big enough station.

I am probably wrong with the 4.3 number (compiled the first result from google without double checking). And it won't be 0.2%, the head's speed would be 0.2% of the feet, but since g=v^2/r, the gravity difference would be about 3%

No, g also equals omega^2 r. The angular velocity omega is the same for head and feet, leaving only the change to r. https://en.wikipedia.org/wiki/Circular_motion#Formulas

(So what's wrong with g = v^2/r? Nothing -- both v and r change in that change to g. To first order, they cancel out in the change to v/r, leaving only a linear factor.)

You are right, I was had made a very ugly mistake I guess

No worries! It's a natural mistake.

You could spin the station at half that speed and still have half a g and mitigate those other issues.

At half the speed, it would be quarter the gravity. And 2km diameter is huge, it would be easier to make a smaller base camp on a planet where there already is gravity present

I believe you're mistaken about the gravity. Position is as Re^(iv/rt), so |acceleration| is as Rv^2/r^2 -- right? For a fixed station of floor radius r, acceleration is directly proportional to distance from the center, R, so with r=1000m, a 2m astronaut will feel 99.8% of normal gravity at their head.

Assuming 5% variation from head to toe is tolerable, a 40m radius habitat would suffice, which could be rotated at 20m/s.

There has actually been research done on how humans tolerate rotational gravity (although not long term, AFAIK.) A 30% gradient at 0.5g is reportedly "disturbing". But perhaps long term one could become acclimated, just as one does at sea.

http://www.artificial-gravity.com/Dissertation/2_2.htm

When lots of people have lots of babies on Earth, we just sprawl out.

Having lots of people with lots of babies in a floating tin can is not a problem we can easily solve with our current level of technology.

Within my lifetime, I have much more faith that we'll be able to construct habitats out of dirt on planets with an atmosphere than modules out of asteroids in the vacuum of space, and that's the appeal of planets in general, and Mars in particular.

Realistically, "Colonies" will not be colonies for a long time, just the equivalent of barracks; people will live there for a while, but their main lives will not be in space.

It is a shame that Voyage to the Bottom of the Sea did not achieve the same level of fame as Star Trek. If it had, people would find the oceans more exciting.

If people expected to find nearly limitless wealth in the oceans, that would help too; they expect to find that in asteroid mining.

New places to colonize because we are running out of livable land is not the main issue. In case of an extinction level disaster, most land/ocean based humans may be wiped out. Having a "backup" colony on a different planet is needed in this regard. And we are talking about colonizing another planet, so zero G vision problems would not be that much of an issue I guess.

What disaster are you imagining that takes out an underwater colony? It'd be completely sealed off from the water, so you could vaporize the entire ocean (unlikely) and atmosphere and it would still be okay. The only thing I could see affecting an underwater colony would be an earthquake, but I'm having trouble imagining an earthquake big enough to wipe out all surface life.

Life adapts. If we put enough people out there and give it enough time, evolution will take care of health problems. Especially given that cosmic radiation should increase mutation rates. Of course, this is not a short-term project.

Floating settlements in the atmosphere of Venus would be interesting. There is at least an argument to be made about settling Venus before Mars. Likewise, I'm not sure why Mars is the first choice, especially when the moon is so close.

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