Rebecca Rosen has an Atlantic article about the intersection of religion and space exploration. It's an interesting list of oddities, alright as a fluff piece, but I think it makes a big mistake in assuming that astronauts are all serious scientists (among whom atheism is naturally pretty common). Instead, most astronauts are military pilots and engineers, and even secular pilots are traditionally pretty superstitious. (I've seen a similar piece before - possibly this one - about the weird non-religious superstitions astronauts are known to practise, including the Soviet/Russian "pissing on the launchpad bus" ritual.)
Astronauts, being public figures, are also chosen as much for their public presentability as their technical skills, and the religiousy Americans are less likely to accept an explicitly atheist astronaut, while astronauts from places like Saudia Arabia and Israel were virtually guaranteed to be explicitly theists. It's actually pretty hard to find one who is clearly and unambiguously a self-described atheist (and, awesomely, a skeptic, in Fuglesang's case). This was exacerbated in the US, early on, by a NASA press conference where John Glenn made astronauts' private lives, including religious affiliation, a major part of their public faces (this is covered well in Tom Wolfe's The Right Stuff).
One thing I'd point out that the article forgets is that if you look at the astronauts killed on missions or in training, they're almost all identified as non-atheists (though it's always hard to be sure what someone really believes deep down). Even in the Soviet Union, there's evidence to suggest Gagarin was probably some sort of religiousy wossname. And yet, he was still among the premature dead, killed in a crash in 1968. Clearly, even if one religion or another is true (which seems unlikely), it's not much help: There's no major statistical divergence between your chance of being a religious astronaut and your chance of being a dead astronaut. I think there's even a slightly better chance of survival for atheist astronauts, though that's likely just a meaningless quirk.
Astronauts are cool, they have a cool job, I wouldn't mind being an astronaut. But they're pretty much just the eyes and hands of greater, Earth-bound minds. I exaggerate there for emphasis, and some astronauts are serious scientists in their own right, but the average astronaut has more immediate concerns, like not screwing the proverbial pooch and returning to Earth as a rain of literal ash. More qualified scientists design their vessels and the experiments they carry, and their beliefs are better informed and more likely accurate, as they actually study the universe, not just facilitate that study. If some astronauts (or PR officers, perhaps) insist on splashing pointless voodoo on these rockets, that's silly and a pity. But it doesn't mean that religion belongs in space, and it certainly doesn't stand anywhere near being proof of the validity of religion. I'm moving off this rock as soon as they'll let me, and I'll be very annoyed if my fellow colonists drag a whole lot of superstitious nonsense along.