Liquid rockets usually use a propellant pair of fuel and oxidizer. I've seen some rockets from 1960's that used LOX/UDMH as propellant pair but why they are not used any more although it is mentioned that LOX/UDMH has higher performance than N2O4/UDMH but N2O4/ UDMH is used abundantly.

If there are any rockets with LOX/UDMH kindly mention them.

  • $\begingroup$ Was LOX/UDMH ever used in a staged combustion engine? $\endgroup$ – Organic Marble Aug 2 at 1:52

N2O4/UDMH is the choice if you need a non cryogenic storable hypergolic fuel. But UDMH is toxic and carcinogenic and should be avoided if possible. LOX/UDMH is not storable and not hypergolic.

There are a lot other fuels to be combined with LOX and they are not toxic or carcinogenic and thus easier to handle. There are combinations of LOX with higher performance than LOX/UDMH.

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    $\begingroup$ LOX/UDMH combines the worst of both worlds: the cooling infrastructure of cryogenic fuels, and the hazards of the storable hypergolics. $\endgroup$ – Dohn Joe Aug 1 at 8:48
  • $\begingroup$ @DohnJoe well said, the worst of both worlds! But there are a lot of combinations of cryogenic LOX with non cryogenic storable fuels. $\endgroup$ – Uwe Aug 1 at 8:53
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    $\begingroup$ LOX is stored below the freezing point of UDMH, which complicates your design. reddit.com/r/askscience/comments/4acvz2/… $\endgroup$ – Hobbes Aug 1 at 9:05
  • $\begingroup$ The bottom line is that there's always a Very Good Reason why They stopped using this or that high-performance fuel/oxidizer combo. Always. $\endgroup$ – RonJohn Aug 1 at 20:25

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