I want to talk to you about how you use chemistry to actually fire a rocket into space.
There are really in a sense three considerations you need to worry about
when your making your choice about the kind of system you are going to use to power your rocket.
The first is, what is the impulse, in other words how much push does your fuel
actually deliver?
The second thing is how much does it weigh, because of course the heavier it
is, the more costly.
And then finally, the third consideration, is going to be safety.
The key idea really is that you are starting a fire and to get a fire you need a fuel and
you need an oxidiser. So normally when you light a match, that match burns because the
wood is the fuel and the oxygen in the air is the oxidiser. But of course oxygen is not
available in space so you have got to take your own.
One option is essentially to build yourself a firework and a firework consists
of a solid material that you light at one end. That material contains fuel and oxidiser together.
This was the principle behind the solid state boosters that took the space shuttle into
orbit to deliver astronauts to the ISS.
A second possibility is to use cryogenic liquids. We know that hydrogen and oxygen react pretty
fast with each other and with a huge release of heat. Well imagine that you make the hydrogen
and the oxygen liquid, you store them in tanks and then you mix them together and light the result.
That was the solution that was used in the 1970's, when I was a kid, to fire the Apollo
astronauts off towards the moon. You would see that huge rocket, with plums of condensation
coming out the side.
But the other possibility is to use two liquids, which you could mix together, and they would
spontaneously ignite. This is the most intriguing, but actually, to me, the most terrifying of the possibilities
These are what are called hypergolic mixtures. They are ones that can
really give you tremendous bang for your buck.
This is the kind of chemistry that makes me very nervous. Let's have a look.
We are going to start with our oxidiser, Nitrogen Dioxide, is a very very volatile liquid and
it boils at about 21�C. So I have it on ice here and we are going to condense it into
this test tube, and down at the bottom, you can actually see some drops of NO2 coming
out of that little pipette tip. That colourless liquid is actually Nitrogen Tetroxide linked
to another one. So we call it Dinitrogen Tetroxide. Now we come to the part where we are going
to put in the fuel. Dimethylhydrazine, which is actually one of the key components of a
mixture called Aerozine 50, which NASA have used for a very long time to power some of
their rockets. And I have got it in this very long pipette.That silly pipette is there
for a reason; I don't want my hands anywhere near this thing.
You can really see here this very fast reaction which generates loads of Nitrogen and also
Ethane. All of the products here are gaseous and you get a tremendous expansion, at the
same time because it gets very hot it glows so brightly, and produces produces a big brown
plume. My God this is impressive. What's scary about it, is how fast that reaction
happens, and I think sometimes we get maybe a little bit complacent. Here we have a reaction
which is absolutely instantaneous. This is a reaction which clearly has no activation
barrier, every single collision results in a reaction, and whats more, every reaction
results in very fast hot products. So you get this extraordinary, explosive cascade.
Which is where that sound comes from.
So to me, it is a tremendous testament, not simply to the chemists who discovered this
thing, but actually to the guys who first applied it and first realised that this may
have potential. And then ultimately, to the engineers who were able to find ways to control this.
Its a remarkable thing and its not just the chemistry, its the physics and its the engineering.
Chapeau!