Just because something is important (although I'm not saying that manned space exploration is), doesn't mean it has to be done tomorrow.
e.g. It's important you save for your kids college, but you don't need to have all the money saved up by time they are 10 years old.
Rushing an important task can also cause it to fail. Being overly aggressive with college savings by putting it in high-risk investments would not be conducive to meeting goals, and NASA losing public support by getting crew killed unnecessarily would not be conducive to them getting funding for future manned missions.
e.g. It's important you save for your kids college, but you don't need to have all the money saved up by time they are 10 years old.
Rushing an important task can also cause it to fail. Being overly aggressive with college savings by putting it in high-risk investments would not be conducive to meeting goals, and NASA losing public support by getting crew killed unnecessarily would not be conducive to them getting funding for future manned missions.