Just to remind you the book competition kicks of tomorrow morning, it will be on the forum by noon, the reason it is uk only is the publishers will only post to uk address,so some of you further away may be able to strike up a deal with a forum friend to use their uk postal address and you cover the postage from them to you.The competition will run for 3 weeks and the winning members names will be sent to Andrew Vine and he will pick the 5 winner out of a hat,I am pleased I cannot enter as question 3 seems hard all about space flight and propulsion and the chemicals Nitrogen Tetroxide (N2O4); Unsymmetrical DiMethyl Hydrazine, it seems to me this is Rocket Science.