Liquid oxygen is cheap to obtain and available, but are there better oxidizers to achieve bigger thrust with JP1?

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    $\begingroup$ I think fluorine is the most energetic oxidizer, but it is rarely used because it is more expensive to produce and both the fluorine itself and the reaction products are toxic and corrosive, making it much more difficult and hazardous to handle. The benefits typically don't outweigh all the downsides. $\endgroup$ – Anthony X Mar 5 '17 at 21:36
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    $\begingroup$ Define "better". $\endgroup$ – Russell Borogove Mar 5 '17 at 21:47
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    $\begingroup$ Related: Why are hydrogen-fluorine fuels not used for rockets more frequently? $\endgroup$ – Russell Borogove Mar 5 '17 at 21:47
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    $\begingroup$ There are better oxidizers. They're just a bit too good at oxidising things like fuel tanks, pipes and pumps. $\endgroup$ – E.P. Mar 6 '17 at 8:05
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    $\begingroup$ Well, there are better oxidizers that aren't excessively corrosive. They are incredibly explosive instead. Say, ozone. $\endgroup$ – SF. Mar 6 '17 at 8:20

This depends on what "better" is.

But let us talk about fluorine. The main point of using it is that turning your hydrogen into $HF$ gives more energy than getting $H_2O$ for pure hydrogen, that gives a small improvement of $I_{sp}$. However, for fuels containing carbon, like JP1, (or perhaps RP-1 or JP4. JP1 has some unfortunate properties for rocket engine use) the situation is made more complicated by the fact that too much fluorine causes a yield of $CF_4$. That will of course make the performance go down the drain. Also, fluorine is difficult to handle. From Ignition, an informal history of liquid rocket propellants, John D. Clark:

Not only did they get a good performance, but there were no ignition problems, liquid fluorine being hypergolic with almost anything that they tried as a fuel. Unfortunately, it was also hypergolic with just about everything else. Fluorine is not only extremely toxic; it is a super-oxidizer, and reacts, under the proper conditions with almost everything but nitrogen, the lighter of the noble gases, and things that have already been fluorinated to the limit. And the reaction is usually violent.

(chapter 6, 7, 8, 10 and 12 are highly relevant to this topic)

That oxygen has to be burned into carbon monoxide, $CO$. So a compound like oxygen difluoride is a good option. It even has an excellent density. Another approach would be to mix a little liquid fluorine in the LOX. The two compounds can perfectly mixed, in contrast to many other cryogenics.

Pro: Higher $Isp$ and better density. Con: More expensive, corrosive and toxic.

(Other compound to check out are $ClF3$, $ClF5$ and $O_2F_2$.)

Another option would be mixing some $O_3$ into the LOX, again giving slightly more energy and better density. It has the nasty property of sometimes violently decomposing for no apparent reasons.

For the other possible definition of "better", thrust, the solution is generally to use a denser oxidizer and not necessarily one with a good performance. For thrust alone, nitrogen tetroxide is an excellent choice.


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