Here are some excellent links for intermediate classes studying outer space.
Enchanted Learning- All About Astronomy-This site is a wealth of information from the planets to your weight on other worlds to jokes and worksheets about space.
Nine Planets Tour of the Solar System – This is an excellent source of information.
Star Child – This site has lots of information and some activities. There is some great information about space suits here. Try level 2 for upper intermediate classes.
Astronomy magazine kids articles– the reading level is a little bit more difficult but there is excellent information here