Alright, so currently we can't even predict how bad osteoporosis becomes after a flight to Mars (will astronauts break their hips on the first step out of landing module?), what would radiation exposure outside Earth's magnetosphere do to our bodies, yet we should hurry up to Titan. Currently even human space flight to Mars is a pipe dream, our practical knowledge constructing vehicles capable of reaching Moon and sustaining human life deteriorated (still using Soviet engines from the 60s?), not mentioning reaching Mars which is way way farther than Moon (50M-400M km vs 380k km, 130-1050x farther). Overcoming this would require massive undertaking of all humanity, like with LHC, and not just PR from SpaceX to secure their funding.
Actually I think the big issue is expense and willingness to fund the expense. There are reasonably straightforward engineering solutions to most of the problems that have been tested for a while (gravity from teethered capsules was tested in the 60s as I recall; Radiation shielding is straightforward with sufficient quantities of water, power through naval submarine type nuclear reactors etc). The problem is these would require massive amounts of mass to be lifted out of our gravity well through rocketry & willingness to fund with potentially insignificant returns doesn't really exist, though I believe some significant fraction of the American military budget should be sufficient.
Don't forget that as early as 50 years ago - an era almost primitive by standards of technology available today - given enough money, a number of men visited the moon.
As attractive as American military budget seems, why would it be in interest of USA to colonize another planet? A different nation would be formed with no more sense of attachment to USA than to rest of Earth.
Rather, evolution teaches us that we have to form next stage of complex entity before these kinds of funding can be secured. Atoms -> molecules -> amino-acides -> self replicating compounds -> multicellular organisms -> conscious organisms -> packs/schools/flocks/tribes -> nations -> ...world government seems to be the next logical step. Before this step happens, planetary exploration is crippled by lack of interest in non-scientific majority of population.
Yeah, re-reading this I find I expressed myself rather clumsily.
What I meant is that currently it's not in the best interest of any individual nation to invest significant resources into space exploration & colonization because it puts it to disadvantage to other nations. So far most of resources seem to be directed at spying satellites and communication networks.
The trend in evolution is that bonds/organizations/alliances form themselves at higher and higher abstraction levels. Extrapolating this trend, I expect some sort of stable planetary entity to occur at some point, that could pull off an engineering project of this scope.
> Alright, so currently we can't even predict how bad osteoporosis becomes after a flight to Mars
On a trip to Mars, I think gravity is not the problem. We can perfectly generate gravity by e.g. sending two modules instead of one, linking them by rods or cables, and then rotating them on the central axis, while sending them forward.
Changing gravity on Titan, of course, is a different problem, although at least Titan is lighter than Earth.
I think it's because you need to perform physically demanding tasks on the Mars surface, which is a bit difficult with severely damaged bones. If you are on ISS, after 6 months you get to be pampered upon landing and the doctors try to ramp your bones back up for some period of time, limiting your physical stress and minimizing risk of e.g. a fatal broken hip injury.
I assume the idea is by the time one gets to mars, they could only restrengthen through light activity—any more would risk broken bones—and yet there's a lot of work to be done so there is little time for reconditioning.
Actually that's not true. We currently don't know the bottom of osteoporosis, all we observed was a gradual decline in bone quality directly proportional to the length of stay, some astronauts returning with bones of 80-year olds, in a few cases irreversibly so. All other declines like muscular mass, amount of circulating blood, heart shrinkage have some equilibrium beyond which no adverse trend continues. With osteoporosis we never observed this, so going to long flights, we might lose all our bones. Supplements, training etc. help a bit, yet the decline + increased Ca excretion persists despite. Not mentioning this is not friendly to kidneys as well and nobody wants to end up with stones developed during a spaceflight.
To add to your list: the moonshot cost 4% of the US GDP, and it only got a couple of men to the moon in a tiny box - far from a self-sufficient colony seed.
I think the time pressure played a significant role. Building a significant colony with tens of thousands of settlers is going to take decades. So the cost would be spread out. Reusability will also reduce cost by more than two orders of magnitude.
