I didn't realise there were other threads on astronomy. I did a search and came up with nothing. There are well over 600 threads on
serious discussions alone, yet I got no hits. Perhaps I am doing something wrong in my searches...
Anyway, space travel owes a lot to the work of someone I never heard of before - Michael Minovitch and the concept of
gravity assist. See this website for details:
http://gravityassist.com. Briefly until then rockets were shot up without using the slingshot technique of building up speed by this method, often several times, for example by circling the moon en route to develop enough slingshot speed to reach the goal.
Big Bang is still a theory. I can't even see how it can be proved, but one never knows…
Enormous strides in recent years, and have mapped all the inner planets and their moons with robot probes that do the job without risking human lives by sending people up into space.