Buck Galaxy said:

"I think we will colonize Mars but not for at least another 50 years."

I think 50 years from now, we won't have the capability of going into Low Earth Orbit. It would have been much cheaper (order-of-magnitude) to have started a manned Mars program in 1970 versus now (this is because back then we still had the Saturn-V and NERVA). It probably would have cost about half as much to start a manned Mars program in 1980 because most of the old NACA and NASA talent was still alive and/or unretired. Now most of those guys are gone and they took most of their technical knowledge with them. It's remarkable how much has been forgotten. Here's a clue: The nose radius to base radius ratio of the Mk-6 reentry vehicle, Viking, Pioneer Venus, Pathfinder, Galileo Probe and MER aeroshells are all 1/2 . There was a good reason for this but no one remembers why. We keep using that ratio because of legacy, e.g. we based the MER aeroshell on the Pathfinder aeroshell which was based upon the Viking aeroshell which was .... So long as we don't deviate too much from legacy design, we can keep the whole thing going. However to do a manned Mars program we must deviate wildly from legacy design. Fortunately if a manned Mars program was started today, we probably could reassemble or rederive most of the old information (it would cost a lot of money). However in another 20 years that probably won't be possible (my generation will all be retired by then). My guess is it's now or never.

Gary