My basic knock on manned spaceflight regards the return on investment versus conventional (unmanned) space. When a rational business model for manned space emerges, it will have a reasonable chance of success. Until then, it won’t. Space tourism is the current best chance for manned space and it will take some time before that capability evolves to interplanetary travel, if it ever does.
Some people think that going to the space station’s low-earth orbit is beneficial. Beyond sustaining the space industrial base, it isn’t clear just how. The space station and manned space itself looks a lot like a jobs program existing on its previous momentum, or alternatively, a program designed to placate space fans.
If you’re China and are desirous of the prestige associated with manned space flight that’s one thing. After all, what are you going to spend all that cash on otherwise, human rights initiatives? But if you are the U.S. with previous manned spaceflight success, low return on that success, and an onerous debt problem, manned spaceflight clearly falls into the ‘would like to do’ bin and not the ‘must do.’
This link closes with the estimate that a mission to Mars would cost $500 billion (likely w-a-y low) and NASA was recently plussed-up by…$6B. Since there is no known compelling reason to have a manned mission to Mars, it will have to wait until conditions here on Earth have changed.