Good point @ucbalumnus. People judge their world by its perceived trajectory, not on its objective qualities. Objectively, circumstances in the 50s and 60s may have been worse than now, but people had the sense that things were improving. Now, people have the sense that things are deteriorating or declining.
Also, space travel is imperialism and exploration. People are less inclined to celebrate those things unequivocally now because we have, as a society, lost confidence in our own virtue.