Esoteric rocket fuels

Over the years various chemicals have been used as rocket fuels and oxidizers. The liquid fuels include alcohol, kerosene, variants of hydrazine, and hydrogen. The oxidizers include liquid oxygen, nitric acid, nitrogen tetroxide, hydrogen peroxide, and solid perchlorates.

Yet there are two possibilities that as far as I’ve heard have never even been tried. One is using liquid methane for fuel. You’d suppose that since it’s about twice as hydrogen-rich as kerosene, it would offer better performance than kerosene but not be nearly as hard to work with as hydrogen. The other is ozone as an oxidizer. I presume it has a higher energy content than O2, and it can’t be that much harder to work with than hydrogen peroxide. Heck, I’ve read that fluorine(!) was considered as an oxidizer- but not ozone. How come?

AFAIK, ozone is a terribly unstable compound (not to mention rather poisonous), so that may play a part in their choice not to use it.

H[sub]2[/sub]O[sub]2[/sub] is a pussycat compared to Ozone.

Alternate SSTO propellants
I’ve no idea whether they are correct, but here are some numbers on the power you could expect from Ozone.
Fluorine actually is used in some chemical lasers. They’re not quite rockets, but at least a close relative.

Chemical Lasers

This isn’t something that I myself know a great deal about, but since the research group I’m in has done some work on alternative propellants, I at least know a bit.

As I understand it, the two most important issues in propellants are:
[ul][li] stability (you need to be able to store your fuel without it breaking down)[/li][li] energy density (you need to get an energetic reaction, but since you have to cart the weight of the fuel as well, you want something that gives you a lot of bang for the buck)[/li][/ul]

I have no idea how well methane meets the latter criterion, but I suspect you’d find it’s not as effective as hydrazine variants (what you really want is nitrogen, since nitrogen molecules have very energetic triple bonds). And a good reason not to use fluorine as an oxidizer is simply that you don’t want to be dumping the stuff into the atmosphere.

The use of ozone has been considered in fiction, at least. The way around the unstable-storage problem was to convert safely storable liquid oxygen to ozone via focused solar energy.

Which work of prophetic fiction contains this idea?
“Tom Swift and His Rocket Ship” (1954)

Now ask me about a really neat way to fly to the moon.

Not direct an answer to the OP, but for certain a esotoric rocket fuel being studied are the Silanes:
familiy of SinH2n+2

The book’s cover depicts this rocket in flight high above the earth, with Tom and pal Bud Barclay clearly visible through the large window at the nose.

“Holy Cow! Those fluorine reactions are very exothermic!” exploded Tom heatedly.
RR

What are the advantages of silane, other than the silicon part being abundantly available on the moon?

Squink, if ozone is less stable than hydrogen peroxide against spontaneous decomposition (and that’s saying a lot), then I can understand that it wouldn’t be practical to use. And according to the alternate fuels comparison you linked to, apparently liquid methane is less dense than RP-1 (aviation grade kerosene), so the increase in tankage weight offsets any improvement in energy content. I consider the OP answered. Thanks!

well, the company I worked for at one time had silane, F2 and HF commercially available in cylinders. Typically the HF came in nickel cylinders that had been treated internally with fluorine to create a metal fluoride protective layer inside to inhibit corrosive activity, but the silane just came in steel cylinders that had been internally cleaned and polished. HF is, while ungodly reactive, used in the semiconductor industry (as is silane) for cleaning purposes. Fluorine is used to treat plastic gas tanks in cars to create that same protective hydrocarbon-fluoride layer so the gas tanks don’t leak. The problem with fluorine compounds is the same as their attractiveness: They are king hell oxidizers. You’d probably destroy your nozzles and tubing in your fuel transfer system before too long.

to clarify: silane is not used to clean. It’s used to deposit silicon. It also does some really cool stuff when you open the valve to atmosphere. (Poof!)

Requirements for rocket fuel are not the same as for other fuels. A unique requirement is for the exhaust to have the lighest possible molecular weight. Temperature is the measure of kinetic energy of molecules, which depends on the weight of the molecules as well as speed. For a given temperature, smaller, lighter molecules are flying faster than larger molecules. You want maximum exhaust speed from a rocket engine so you get more push from the limited amount of propellant, so you want a fuel whose exhaust is composed of small molecules. With chemical reactions you can’t get much better than H2O.

If you don’t rely on chemical reactions you can get much better efficiency. For example, if you use a nuclear reactor to heat up a gas and use it as exhaust, you can use pure hydrogen as exhaust/propellant. Another way to increase efficiency is to accelerate the exhaust with an electric field instead of heat. Those are called ion engines and are already used on some space probes.