# Modern ambient temperature rocket fuel?

This question is in regard to rocket propellants that are liquid at room temperature & pressure (not solid fuel, and not liquid hydrogen liquid oxygen, both of which would be gasses at STP).

It's well documented (by SpaceX and others) that the colder the temperature of the liquid fuel, the more thrust is potentially able to be produced, either increasing payload capability, or reducing launch weights. Are there any currently operating launch systems that do not make an attempt to chill the fuel component of the fuel/oxidizer components before liftoff? I would imagine that most do, but am curious if this is universal nowadays?

• There is no rocket fuel that is non toxic, liquid at room temperature and non explosive that delivers enough energy for space exploration. – Uwe Feb 13 '18 at 9:37
• – uhoh Feb 6 '19 at 0:05

The Russian Proton booster uses storable propellants (nitrogen tetroxide and hydrazine). Nasty stuff, but room temperature.

https://en.m.wikipedia.org/wiki/Proton_(rocket_family)

Using liquid oxygen (which is "naturally" extremely cold) is the standard for almost all professional civilian launchers. There are some odd exceptions - launchers like Lambda 4S using solid propellant. A lot of systems use RP-1 or other non-cryogenic fuels, but for oxidizer in commercial, planned, civilian launch systems that were developer as civilian since moment one, LOX is the king.

("Small" civilian rocketry - amateur, sounding rockets etc often utilize nitrous oxide $N_2 O$ for oxidizer - but it's a gas at STP too)

The situation is quite different with the military. The rockets either use solid propellant, or hypergolic fuels which aren't especially cooled. This also applies to civilian launchers that are derived from military - like Proton (as mentioned by Organic Marble) which was designed as a super-heavy ICBM launcher, or Start-1 which is a modified mobile ICBM launcher repurposed for civilian use.

The reason is fairly simple: boil-off. Rocket's LOX tanks aren't made to withstand high pressures - the liquid oxygen slowly boils off. It means the rocket needs to be fueled several hours before the launch. This takes time - which is not something the military systems can afford. The rockets need to be ready to launch at moment's notice and sit in the launch silo, fueled, for months or years. This requires propellants that don't boil in room temperature.

By the way: what SpaceX does is additional cooling way below boil-off or ambient temperature. Such propellants in fact have worse performance per mole or kilogram of propellant - but decrease of temperature decreases volume - increases density; you're getting a better performance out of liter of the propellant - essentially you can fit more propellant into the same volume of a rocket tank.

• If you call liquid oxygen extremely cold, you need to invent another word for the much colder liquid hydrogen. – Uwe Feb 13 '18 at 9:29
• @Uwe: I don't need to invent anything, LH2 is mere 60K colder. That's less of a difference than between normal (water) ice and dry ice. – SF. Feb 13 '18 at 9:41

SpaceX is unique in cooling down a room temperature fuel. Other users of RP-1 just use it at room temperature.

In addition to Proton, several Chinese and Indian launchers use storable propellants.

• Still needs LOX... – Antzi Feb 13 '18 at 7:50
• "Are there any currently operating launch systems that do not make an attempt to chill the fuel component" - the question ignores LOX, so I'll do that too. – Hobbes Feb 13 '18 at 7:54

H2O2 and RP1 was used in the British Black Arrow orbital launcher.

Beal Aerospace was working on Kerosine/Peroxide (KerOxide) engines before they went under.