He has an itch. Inside his suit.
Real astronauts have something called a valsalva device inside their helmet, which is intended to block their nose so they can do the Valsalva maneuver and equalize their inner ear pressure. However, it's also been used to scratch an itchy eye or face. I wished for such a thing inside my motorcycle helmet many times.
More Lego train awesomeneess:
I think Lego is missing a trick: they should sell proper, accurate licensed models like that and make a killing -
this is the nearest I've seen. I'd have loved them when I was a kid, it would have been near-enough the perfect toy for me. Instead I had most of the Micromachines trains: