A tutorial on space flight.

I have just spent a few happy hours at:

http://www.jpl.nasa.gov/basics/

I have found this sort of information, and at the right level for me, quite
difficult to find. Lots of fascinating facts and engineering concepts
explained. Sometimes the info is not so "basic" but it is all explained very
well and even includes tests so you can see if you really understand what
you just learned.

Well done NASA!

Sally