Bone
If you have a mustache and you hit your forehead on the moon, you’re probably going to break a bone. Ok, so it doesn’t matter so much if you have a mustache, but if you’re travelling fast enough to make it to the moon, you’re definitely breaking a bone if you run into it.
こつ
ほね
None
Outer space is cold, and if you're traveling to the moon, you're going to need a lot of coats (こつ). All of these coats will keep you warm, even if you do end up breaking your forehead bone.