As it is with all Christians but sooner or later one must repent.
A person can't accept Jesus and believe that he died for their sins without repenting.
Charles Duke went to, and walked on, the moon. Years later, he became a Christian. He now gives talks about his time on the moon AND talks about Jesus, who saved him. Jesus gave Charles his testimony.
If you're saying that Charles is a liar, you are saying that you don't believe Jesus.
I am sure that there are non Christians who go to hear Charles and come away, at least challenged by, or believing in, Jesus.
If they were converted, by Jesus, through Charles' testimony but that original testimony had been false, then their conversions would not be valid.
Are you so stubborn that you would say that Charles, other Christian astronauts and anyone who heard about Jesus through them, are lying/making it up, rather than; "yes, he did walk on the moon, what he says is true and he now has a fantastic ministry for God"?
Saying that men did not walk on the moon is not a sin.
Saying that men who walked on the moon, since became Christians and now tell others about Jesus, are lying, is dishonouring God. Which is a sin.