I don’t write about space very much (read: at all). But if I did, I would liberally use The Space Educator’s Handbook.
If you can get past the frankly painful web design, this is a darn useful site, provided by NASA no less, for anyone teaching space stuff…or, in our case, writing space stuff.
Can’t get past the yellow-on-space-print background? Here are some specific useful links:
Aerospace dictionary, so you can learn everything from ablations to zeniths.
Sci-fi/Space technology, complete with handy scientific laws, necessary tech, and reference manuals.
Astronomy information, about planets, cool questions about water and life elsewhere in the universe, and theoretical situations like playing sports on the moon.
There’s a ton of info on here, if you can brave the asterisk page breaks and pages of bolded text. Use it wisely.