THE DETAILS: Apollo 14 Lunar Module pilot and moonwalker Edgar Mitchell is often presented as an authoritative UFO witness, but during his lifetime he made it very clear that he did not support claims that he saw direct evidence of extraterrestrial presence while he was in space or on the Moon or that NASA was involved in some kind of coverup:
The notion that there are structures on Mars or the Moon is bonkers. I can attest to the latter -- I’ve been there. We saw no structures at the landing site and none was reflected in my helmet, as has been alleged.
– UFOs: It’s a coverup, by Tom Rhodes, Ottawa Citizen, October 11, 1998.
I, nor any crew I was on (I was on three Apollo crews), received any briefing before or after flights on UFO events, saw anything in space suggesting UFOs or structures on the moon, etc. We did it just like we said in official reports. My only claim to knowledge of these events is from the individuals, mostly of yesteryear, who were in government, intelligence, or military; were there, saw what they saw, and now believe it should be made public. But I claim no first hand knowledge, nor have any.
– Ed Mitchell Most Unhappy With Greer Using His Name As Disclosure Witness, Rense.com, 2001.
On the other hand, he went on record saying that he believed that extraterrestrial spacefarers have visited Earth and that there is a government coverup on the UFO phenomenon:
I happen to be privileged to [...] be in on the fact that we have been visited on this planet and the UFO phenomenon is real, although it’s been covered up by our governments for quite a long time [...] I have been deeply involved in certain committees and certain research programs with very credible scientists and intelligence people that do know the real inside story [...] The Roswell crash was real and a number of other contacts have been real and ongoing.
– Astronaut Says Aliens Are Real, Kerrang Radio (2008).
The evidence to back up these claims is, as Mitchell himself readily acknowledged, not first-hand and is based on statements by other people that Mitchell believed to be reliable but cannot corroborate. Currently there is no publicly available hard evidence and therefore this fascinating issue remains a matter of opinion.