Editing RP-1 (section)

==Fractions and formulation==
RP-1 is outwardly similar to other kerosene-based fuels, but is manufactured to stricter standards. These include tighter density and volatility ranges, along with significantly lower [[sulfur]], [[olefin]], and [[aromatic]] content.<ref>{{Cite web |title=Rocket Fuel Development |url=https://www.haltermannsolutions.com/tech-talk?id=249256/rocket-fuel-development |access-date=2024-12-10 |website=haltermannsolutions.com |language=en}}</ref>

Sulfur and sulfur compounds attack metals at high temperatures, and even very small amounts of sulfur [[Sulfur vulcanization|assist polymerization]] which can harden seals and tubing, therefore sulfur and sulfur compounds are [[Hydrodesulfurization|kept to a minimum]].

Unsaturated compounds ([[alkene]]s, [[alkyne]]s, and [[aromatics]]) are also held to low levels, as they tend to polymerize at high temperatures and long periods of storage. At the time, it was thought that kerosene-fueled missiles might remain in storage for years awaiting activation. This function was later transferred to [[solid-fuel rocket]]s, though the high-temperature benefits of saturated hydrocarbons remained. Because of the low levels of alkenes and aromatics, RP-1 is less toxic than various jet and diesel fuels, and far less toxic than gasoline.

The more desirable [[isomer]]s were selected or synthesized, with [[linear alkane]]s being reduced in number in favor of greater numbers of cyclic and highly branched alkanes. Just as cyclic and branched molecules improve [[octane rating]] in [[petrol]], they also significantly increase thermal stability at high temperatures. The most desirable isomers are polycyclics such as [[ladderane]]s.

In contrast, the main applications of kerosene (aviation, heating, and lighting), are much less concerned with thermal breakdown and therefore do not require stringent optimisation of their isomers.

In production, these grades are processed tightly to remove impurities and side fractions. Ashes were feared likely to block fuel lines and engine passages, and wear away valves and [[turbopump]] bearings, as these are lubricated by the fuel. Slightly too-heavy or too-light fractions affected lubrication abilities and were likely to separate during storage and under load. The remaining hydrocarbons are at or near C<sub>12</sub> mass. Because of the lack of light hydrocarbons, RP-1 has a high [[flash point]] and is less of a fire hazard than petrol.

All told, the final product is much more expensive than common kerosene. Any petroleum can produce RP-1 with enough refining, though real-world rocket-grade kerosene is sourced from a small number of oil fields with high-quality base stock, or it can be [[synthetic fuel|artificially synthesized]]. This, coupled with the relatively small demand in a niche market compared to other petroleum users, drives RP-1's high price. Military specifications of RP-1 are covered in MIL-R-25576,<ref name=":0">{{cite web |url=http://www.braeunig.us/space/propel.htm |title=Basics of Space Flight: Rocket Propellants |publisher=Braeunig.us |access-date=December 11, 2012}}</ref> and the chemical and physical properties of RP-1 are described in NISTIR 6646.<ref>{{cite web |url=http://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir6646.pdf | title=Thermophysical Properties Measurements and Models for Rocket Propellant RP-1: Phase I (NISTIR 6646)}}</ref>

In Russia and other former Soviet countries, the two main rocket kerosene formulations are T-1 and RG-1. Densities are slightly higher, {{val|0.82| to |0.85|ul=g|upl=mL}}, compared to RP-1 at {{val|0.81|u=g|up=mL}}.

The Soviets also discovered that even higher densities could be achieved by chilling the kerosene before loading it into the rocket's fuel tanks, although this partially defeated the purpose of using kerosene over other super-chilled fuels. However, operationally, facilities were already in place to manage the vehicle's cryogenic [[liquid oxygen]] and [[liquid nitrogen]], both of which are far colder than the kerosene. The launcher's central kerosene tank is surrounded on four sides and the top by liquid oxygen tanks with a liquid nitrogen tank at the bottom. The kerosene tanks of the four boosters are relatively small and compact, also located between a liquid oxygen and a liquid nitrogen tank. Thus, once the kerosene was initially chilled, it would remain cold for the brief time needed to finish launch preparations.

While the Soviets would eventually abandon chilling their kerosene, decades later SpaceX would revisit the idea for their [[Falcon 9]] rocket. All versions since the [[Falcon 9 Full Thrust]] have used sub-cooled RP-1, chilled to {{cvt|-7|C}}, giving a {{val|2.5|–|4|u=%}} density increase.<ref name="musk-20151217">{{Cite tweet |number=677666779494248449 |user=elonmusk |title=-340 F in this case. Deep cryo increases density and amplifies rocket performance. First time anyone has gone this low for O2. [RP-1 chilled] from 70F to 20 F |first=Elon |last=Musk |author-link=Elon Musk |date=17 December 2015 |access-date=19 December 2015 |archive-url=https://web.archive.org/web/20151231204559/https://twitter.com/elonmusk/status/677666779494248449 |archive-date=31 December 2015 |url-status=live}}</ref>