America's First Shuttle Launch Columbia Space Shuttle, STS-1

@JONNOG88 two of the Apollo 13 crew members: Fred Haise (Approach and landing tests on Enterprise) and (originally member of Apollo 13, flew to the moon on Apollo 16) Ken Mattingly both stayed around for the shuttle era. Joe Engle, Jack Lousma (CapCOM for Apollo 13, was suppose to be on 19), Vance Brand (Apollo-Soyuz) Paul Wietz (Skylab) Owen Garriott (Skylab) Bruce McCandless all sticked around for Shuttle.

@JONNOG88 Alan Bean (Apollo 12 and Skylab) was also going to get a Shuttle Command, but that never came true. John Young was going to get his 7th space flight on STS-31 to deploy Hubble, but challenger exploded and that got pushed to 1990 and John never flew in space after STS-9 and STS-1.

the closest place of interest is a 4 year trip away and that is if we could solve the problem of accelerating to the speed of light.

and then you have to consider the hazards of navigating at those speeds.

Its hard to fathom being able to communicate with earth if you were accelerating away from it at such a speed.

To send men to Mars, we had to know about how humans could withstand long-term space flight, along with all the sciences that go along with it. As such, it was COMPLETELY necessary to spend the time gaining that knowledge in low earth orbit. Not a good idea sending people into deep space without knowing how their bodies and life-support systems could handle it.