[Joe-Z]

>almost anything a human being can do, a robotic probe can do far cheaper

... and far more inefficiently. I can't find the article right now, but a while back there was a submission on here which argued that sending robots into space instead of humans is a bit of a fallacy. Because the state of robotics and their capabilities is far from what could be achieved by sending a human. There were comparisons like the Apollo astronatus bringing back half a ton of moon rocks whereas Mars probes can only sample tiny amounts of soil. Also one of the Mars rovers (Opportunity? I can't remember the names) in its years of service only covering a few kilometers, something a human could do within a day.

EDIT: It was Opportunity and its mission lasted 15 years. Impressive nonetheless, but boy is it slow ;)

[saberdancer]

You are right but it's comparing apples to oranges. If you compared missions of comparable weight you would find that capability of robotic missions increased many times over current missions, reason is that any human mission would be much more massive than current unmanned missions. This is especially true for long range manned missions where crew needs food, water, shielding and space to survive long term in space, for a robotic mission distance is just time.

What robots cannot do well is be flexible in their mission. This is something that humans excel.

[Joe-Z]

Fair point. I guess the best solution would be to just further develop both: Manned and unmanned missions.

Also I think the psychological effects of having actual humans doing this stuff on the people staying back home should not be underestimated. Would we have an Elon Musk today[0] hadn't we landed Neil Armstrong on the moon in 1969?

[0]Or at least SpaceX, this guy's endeavours are all over the place :D

[dsfyu404ed]

I'm not sure what the net tonnage of robot missions we've sent to mars to date is but that level of knowledge we've acquired is on the same order as what we'd get from a couple humans spending a week there with a bunch of tools and scientific instruments. Humans ability to improvise lets us quickly identify what is of interest and study it saving us from having to send multiple iterations of robots.

For any given fixed distance (e.g. mars) at some point there's a crossover where sending some people up there to go kick rocks is actually cheaper than sending a series of robots that kick rocks in progressively more detail. I'm not sure if we've reached that technology point yet but as space flight gets cheaper and cheaper it will eventually happen for the moon and then for mars.