I think what we realised is that if you want to go into outer space---and with that I already mean 'go to Mars'---you need incredible amounts of money, and accept that you will see almost nothing of it back, except in perhaps a few clever spin-off technologies, and lots of fascinating history documentaries.
Take the Bush administration's wild idea to go Mars, for example. We have learnt a lot about human physiology in zero g, and almost nothing about it is good. We are literally addicted to gravity. Now gravity can be simulated, but if you look at the feeble appearance of some of the Russian cosmonauts after just one year in Earth's orbit... And that is just the beginning. There is the problem of an open nuclear reactor with a power output of 4.0*10^26 W a scant hundred million miles off, which pumps out so much radiation that an astronaut can only make one journey to Mars and back again in his lifetime. Going beyond Mars is suicide. Then there is the problem of what to do with people living in a closed and confined area for months at a time, with no option of stepping out and taking a breath of fresh air for a while. Sex is another issue. It would be a mistake to think that astronauts can bottle up their hormones for the better part of three years (= Mars journey time). I have a strong feeling that hell will freeze over ere NASA publically admits that the capsule will be carrying a few thousand condoms, sponsored by Durex. What about washing clothes? What about the problem that due to the zero g-environment, most sense of smell is lost so that food (important booster of morale) becomes tasteless? What about medical aid 75 million miles from the nearest hospital? What about communications, which take a few minutes to reach Earth? And so on, and so on.
They are interesting problems for sure, but I think that most of them cannot be solved easily. The best option we have is either a super engine which cuts travel times to mere weeks instead of years, or some sort of suspended animation, and neither will be available in the foreseeable future.
Now suppose we try the Moon instead. We've been there before, it takes us about 4 days of hard travelling, and perhaps a bit less if a new Saturn V (the only rocket capable of getting people to the moon!) is designed. That is doable, it's practically off-the-shelf technology. Now we are at the Moon. What will we do there? Well, we build a base! Okay, so we have a base. What do we do at the base? (Remember, it costs money to get us to the Moon, and no country in the world can support a Moonbase on the power of positivism alone!) The Moon offers unprecendented means of scientific observation, because of the lack of an atmosphere. You can mine kazillion tons of helium-3, which might one day prove useful if we ever get a fusion reactor operational. It offers great sex too, since the surface gravity is only 1/6th of Earth's. Tourists will dig that. But since you need a hefty and costly space suit to go out into the harsh and unforgiving (but beautiful) barrenness of the Moon's surface, that is about all you can do. And that is the Moon.
Make no mistake, I love space, and I am heartily envious of all the guys over at JPL who get to ride little cars on the surface of another planet and get paid to do so as well. I just think that given our current state of technology, we should not endeavour anything more strenuous than a return to the Moon for purely scientific reasons. When we have a working fusion drive, I'll review my opinion, but until then, we should stay put on Earth, and send every bold 'because it's there'-statement to the trash can.
