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If you compare it with 19th century polar expeditions, a trip to Mars doesn't look that bad. They sometimes took multiple years, with men trapped in iced up ships, usually with no chance of rescue or even communication - at least we know how to prevent scurvy now!

Have a read of the book "Barrow's Boys: A Stirring Story of Daring, Fortitude, and Outright Lunacy":

http://www.amazon.com/Barrows-Boys-Stirring-Fortitude-Outrig...

NB Having read too much Kim Stanley Robinson and Zubrin, I'd jump at the chance to go to Mars.

An expedition to Mars would cost a lot more, with a much smaller expected ROI. I too would love the idea of going to Mars, but, in order to build a sustainable colony, you'd need to put in place a whole lot of infrastructure to make interplanetary travel cheaper. And, right now, it's not even feasible.

Insurance for humanity against disaster is a small ROI? Not trying to offend, but how do you define ROI of a colony on Mars?

...is a small ROI?

You, me, and the original poster agree: it's cheap compared to the potential downside.

Now, go try and tell guys with actual money about this, see if you walk away with the bucks for a Mars-based insurance policy.

As far as I can see, there are very, very few disasters that would render Earth less inhabitable than Mars but not also destroy Mars in the process. Even if Earth were reduced to a cold, lifeless rock with almost no atmosphere or water, high radiation levels and almost all sources of energy gone (including geothermal and wind energy and things as simple as burning wood), that would just put it in the same ballpark as Mars.

Basically, if you have the technology to support human life on Mars, you have the technology to disaster-proof Earth.

The scenario that comes to mind is a massive asteroid impact, but your final sentence sums up the objection nicely: identifying and redirecting a space rock seems at least an order of magnitude less difficult & technologically distant than building a self-sustaining colony on Mars.

Even the worst asteroid impact would not render the planet uninhabitable. It might kill lots of people, but it wouldn't kill all of them.

And yet, again, a Moon colony would be handy to counter an asteroid too. The far side could host very powerful telescopes that could map NEOs with unprecedented efficiency and clarity. On Earth, you have a couple hours of sensor exposure. On the Moon, you have two weeks to trace stuff. And most of the heavy parts could be manufactured in situ, be lighter and higher quality (made in a high grade vacuum).

And that's to say nothing about the ability to launch spacecraft from a lower gravity and/or using a magnetic rail. One could even turn the asteroid into dust (which is less dangerous than a ferrous mountain falling from the sky) with a kinetic impactor packing enough energy.

What about virulent plague? Chemical warfare? Disasters don't have to come from far away.

If you're going to survive on Mars, you already need the ability to sustainably disconnect yourself from the surrounding atmosphere (we don't know of any virus that's as lethal as lack of air), so just apply your putative Mars tech to Earth.

Air is just one of many possible infection pathways. You would also need to quarantine people, food shipments, water supplies, equipment.

Food shipments? Water supplies? We're talking about the kind of technology that would allow you to live on Mars. If you need to rely on those, then 1) Your Martian colony is not really independent and thus doesn't carry any survival benefits, and thus 2) You're wasting resources shipping them to Mars. If you don't need those for your Martian colony, then why would you need them for your Earth colony?

If Earth were in a situation of having to segment populations to prevent the spread of disease, all it takes is one little mistake to wipe out an entire intermingling group of people. I'm not saying we wouldn't have the tech to prevent that from happening, but humans are fallible creatures. Is it worth risking the entirety of humanity when we could have a remote colony that would be very well protected from those types of events?

Very well protected? The danger specifically from viruses might be somewhat less (though if we're allowing people to travel there, it doesn't seem like much less of a concern), but any other danger you can imagine would be much greater. The remote colony would be no more protected from disaster than one on Earth. On the contrary, since the surrounding environment would be irreconcilably hostile, it would be constantly at risk of one little mistake wiping it out.

The concern is not a disaster that necessarily destroys Earth itself - an extinction event for humans is enough. There are plenty of species that have gone extinct before (including some close relatives) and since it's obviously never happened to us we have little idea of its shape or likelihood.

The very distance that makes Mars so hard to reach would be good protection against such an unexpected event (whether it's unintended effects of scientific experiments, novel WMDs, grey goo etc.). There is no way to create a similarly isolated colony on Earth, even if we discount the problem that nobody would want to live in such a place. (As opposed to the many people, reared on SciFi, who would volunteer for Mars quite eagerly.)

The odds of extinction within the next 50 years are still low. A self-sufficient Moon colony would cover most of the disaster scenarios adequately while being a lot cheaper to build than a Mars colony. Besides, having a self-sufficient lunar colony would probably make building a Mars colony much cheaper.

On the Moon, solar energy is abundant (close to the Sun, no atmosphere) and so are the metals used in spacecraft construction. Without atmosphere and with a low gravity, launching cargo to Mars is easier and can be done with a magnetic rail launcher, effectively using solar power to launch a spacecraft to Mars.

I's even greener to go for the Moon first ;-)

So, I'm not that guy, and really trying not to be that guy, but wouldn't it be fair to summarize your general point as: "That's no moon. It's a space station." ? (mainly mentioning it because it could be taken for an inspirational saying in this context)

> Insurance for humanity against disaster is a small ROI?

A self-sufficient colony on the Moon would be efficient insurance against most disasters I can imagine and much easier to build. A colony on Mars offers negligible benefit over one on the Moon for the purpose you mention.

Furthermore, as technology and quality of life increases, risk tolerance decreases. I think this trend will continue. Historically, technology has increased fast and uniformly enough that we've still been able to do great things. But if health care technology improves much faster than space technology, then we may never leave orbit again.

(This trend holds at least at the societal level, and over long terms. For individuals over the short term, it can be weaker, e.g., you might buy a helmet or a safer car, and then ski or drive more dangerously.)

The Aldrin cycler requires fuel to keep it going around the sun (with periodic flybys of Earth and Mars).

In principle, each Earth flyby is used to rotate the orbit so that it goes to Mars, but the problem with the Aldrin cycler is that the required flyby distance is too close to Earth: it's smaller than Earth's radius! As a result, rocket fuel is required to give it the required extra kick.

But there are other Earth-Mars cycler trajectories! One of my projects in grad school was to investigate them, and there are some that really can keep going without spending fuel (except for minor adjustments). In particular, the so-called "Ballistic S1L1" cycler is very promising. Here's a paper about it:

McConaghy, T. Troy, Landau, Damon F., Yam, Chit Hong, and Longuski, James, M., “Notable Two-Synodic-Period Earth-Mars Cycler,” Journal of Spacecraft and Rockets, Vol. 43, No. 2, March–April 2006, pp. 456–465.

Thanks! I never did the math on the Aldrin cycler. Can you give more details for the journal-challenged?

> If someone on Mars manages to, say, contaminate the colony's water supply, all we can do is record farewell messages for loved ones and deal with the bad publicity for decades. I wouldn't like that.

The same is true for a major disaster at the South Pole in winter, though. There's a several month period in which vehicles cannot reach the pole due to the temperatures and weather involved. We still go there.

Or in an African village. It doesn't take distance to maroon someone with no means.

I hadn't heard of an Aldrin cycler. Very very cool! Here is an animation of how one could work: http://www.youtube.com/watch?v=qCVfUlFZQ4U

I agree and as a kid I always wanted to visit both the Moon and Mars. But for any of this to happen we need a breakthrough that applies Moore's law to $/kg for space travel to become economical. We need cost effective nuclear fusion to increase our energy budget. Or material science has to advance to the point that space elevators or launch loops and similar become feasible. Does anyone know the timeline on those?

The moon may have fewer natural resources than Mars, but it seems strange to not practice building habitats in the Earth's backyard. "Lunarcrete" is one way to build bunkers (using materials already on the moon) that keep out gamma rays and extreme surface temperatures.

The moon is also close enough that I could imagine a private company like Virgin Galactic building lunar resorts in a couple decades. :D

The answer Musk gave at a Q&A I was at was, "We won't go to the Moon because the Moon sucks."

His point was that the Moon can never be made habitable for humans, and the low gravity makes it hard to work.

The analogy he made was the Arctic--sure, it's a lot closer to Europe and Asia, but Columbus et al. went to the Americas instead. Farther away, but more habitable.

If you're going from Earth to Mars, you waste a lot of delta-V going to the Moon first.

We need to develop remotely operated building machines first. Test them on the moon and succeed in building a sound, sealed, safe environ for humans to enter before we try to get to mars.

If I were Elon, I would focus on the building of the delivery system to get materials and equipment to the moon - then have an X-prize for people to develop the robots to build stuff.

Get a heavy payload like that to the moon, assemble some stuff and test it. Then make money off moon tourism Parlay this to mars research, funding and experience.

If you can make a 'makerbot' that can make a makerbot I think you're 95% of the way there :)