When it comes to hydrocarbons almost all state owned space agencies use kerosene in combination with LOX in bi-propellant rockets. But many hydrocarbons (such as methane, ethane, propane, ethylene, propylene, etc.) give a higher specific impulse and are cheaper than kerosene. All of them were always readily available on the market, and largely used in industry and households. Also for many of them density impulse could be matched with Kerolox if fuels are pre-chilled. Many private space companies therefore run away from kerosene at some period of development (SpaceX is switching kerosene with methane), while others avoid it from the very beginning (Blue Origin - methane, Vector space - propylene, Orbex space - propane etc.).

Boris Katorgin, famous founder of RD-180 engine proposed in his works to switch kerosene with something better. For brief period of time USSR used syntin, but soon abandoned it. Boris even found a hydrocarbon which is cheap to produce and wouldn't require any modifications to rocket or to engine with significant improvement in performance, but without success in promoting it further.

But there is catch with kerosene, in state of emergency kerosene could power virtually all military vehicles from trucks, tanks, helicopters and of course planes. Seems to me that rockets were mandatory to be added to this list, even if they were meant for civilian use. Considering this is it possible that military interests prevailed over civilian in all state owned space agencies around the world and we have a lag in space exploration because of it?

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    $\begingroup$ Kerosene is liquid at room temperature and pressure, unlike the better-performing hydrocarbons. $\endgroup$ Commented Oct 7, 2020 at 17:22
  • $\begingroup$ I was not aware that this is the practice on this site. I have accepted many of them now. Sorry for inconvenience. $\endgroup$
    – WOW 6EQUJ5
    Commented Oct 7, 2020 at 17:52
  • $\begingroup$ Related: Was General Doolittle involved in the invention of RP-1? $\endgroup$
    – DrSheldon
    Commented Oct 7, 2020 at 20:33
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    $\begingroup$ @Russell Borogove right, but there are examples where hydrocarbons are liquid at near room temperature + self pressurized + equally dense as kerosene if pre-chilled prior lunch + cheaper + easily purified + readily available and used in chemical industry + better performing in terms of ISP with LOX. One example 1,2 butadiene but there are others. Why state owned space agencies are bounded to kerosene and private doesn't have problem to switch fuel if it brings benefits? $\endgroup$
    – WOW 6EQUJ5
    Commented Oct 7, 2020 at 21:20
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    $\begingroup$ Note everything that can run on generic kerosene - in particular, jet planes - can run on RP-1 just fine. This wouldn't necessarily be the case with other hydrocarbons, so a store of rocket fuel can be repurposed for other vehicles if necessary. RP-1 is essentially a subset of JP-4; JP-4 allows for more impurities and variance of composition but doesn't forbid anything RP-1 has in it. $\endgroup$
    – SF.
    Commented Oct 8, 2020 at 8:58

1 Answer 1


RP-1 Was Adopted By The Military Because It's Storable, Temperature-Insensitive, and Similar To Jet Fuel

According to Clarks' Ignition, the adoption of RP-1 rocket kerosene as the standard fuel for hydrocarbon rockets was very much a result of military concerns, including logistics, but it was a bit more complicated than you described.

To summarize Clark:

  • RP-1 was developed in the 1950s -- the spec was published in 1957. At that time, most of the focus was on military missiles and JATO rockets, not civil space exploration.

  • The military wanted a fuel that would be storable for long periods of time and would be OK at the full range of ambient temperatures found in theaters of war -- so cryogenics are right out, and so are a number of other fuels that freeze at inordinately high temperatures.

  • The military also wanted logistics to be reasonably simple -- to be able to supply a large amount of fuel, and in some cases wanted the fuel to be the same as their commodity hydrocarbon liquid fuel -- gasoline in the 1940s, jet fuel in the 1950s and later.

  • The oxidizer was often red fuming nitric acid (I-RFNA) which meets the same requirements laid on the fuel, or in other cases was LOX.

  • Commercial hydrocarbon fuels (which are not pure compounds but complex, rather variable mixes of hydrocarbons) don't work well in rockets.

  • These missiles were coming out of the era of alcohol or aniline fuel, and were more concerned with density impulse than overall specific impulse. It also seems that cryogenics may not have been a fully developed science as Clark (writing in the early 1970s) says that the difficulty of handling liquid methane eliminates its advantages.

  • RP-1, a more tightly-specified kerosene spec, was adopted as a less-available but better-for-rockets replacement for JP-4 jet fuel.

  • Due to the immense conservatism of the aerospace industry (and the ICBM heritage of American old-guard space launch boosters) nobody really bothered replacing it until the last 20 years and their new wave of successful space launch innovators.

At the time a number of other fuels were under consideration, including turpentine, various pure substances, and the like.

  • $\begingroup$ There were years of experience with cryogenic oxygen as oxidator but none with cryogenic fuels. $\endgroup$
    – Uwe
    Commented Oct 8, 2020 at 8:36

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