Cliff Addison, as I said, was working on dinitrogen tetroxide. It so turned out that a decade later, when the Apollo programme was being developed to put a man on the moon and return him safely to earth – in Kennedy’s phrase – one of the important things was, how do you make sure that the rockets fire when you want them to. You can’t strike a match in outer space, electric sparks aren’t necessarily reliable or desirable. What you need is what is called a hypergolic fuel. Hypergolic fuel is a fuel of two components which, when put together, immediately catch fire. And dinitrogen tetroxide is one component of such a fuel – it is actually the fuel of choice. When you see a rocket blast off from the moon, as we’ve all seen on television, what happens is, that dinitrogen tetroxide is mixed with a derivative of hydrazine which is itself a derivative of two ammonias stuck together. There are methylhydrazines and then we put dinitrogen tetroxide and our methylhydrazine together, there’s an explosion, a rocket, if you like, and it blasts off. No matches, no spark – it happens every time because that is basic chemistry. Now that was clearly far from Cliff Addison’s view – he was trying to make new compounds by using dinitrogen tetroxide. But the physical background work that he’d done was enormously useful.