Short answers, pulled from the story.
RP-1 is a highly refined kerosene formulation. It is processed to stricter standards than aviation or heating kerosene, with tighter density and volatility ranges and significantly lower sulfur, olefin, and aromatic content. The remaining hydrocarbons are at or near C12 mass.
RP-1 has powered a wide range of rockets, including the Saturn V, Saturn I and IB, Atlas, Falcon, Soyuz, Zenit, Electron, Antares, Delta I through III, and Energia. The Indian Space Research Organisation is also developing an RP-1 engine designated SE-2000 for future vehicles.
Raw kerosene breaks down under the heat and pressure of rocket engines, forming gas bubbles and waxy deposits that block cooling passages and trigger thermal runaway leading to engine failure. In the mid-1950s, rocket designers turned to chemists to create a heat-resistant hydrocarbon formulation, resulting in RP-1.
Hydrogen engines achieve a specific impulse around 370 seconds in vacuum while kerosene engines reach roughly 270 seconds, meaning hydrogen is more fuel-efficient. However, RP-1's higher density delivers greater thrust relative to engine mass, making it preferred for first stages where lift performance matters most.
RG-1 and T-1 are the primary rocket kerosene formulations used in Russia and former Soviet countries. Their density is slightly higher at 0.82 grams per milliliter compared to RP-1's 0.81. Soviet engineers also developed techniques for chilling the kerosene before loading to increase density further.
All Falcon 9 versions since the Falcon 9 Full Thrust use sub-cooled RP-1, chilled to 20 degrees Fahrenheit, which delivers a 2.5 percent density increase. SpaceX revisited a technique the Soviets had developed and later abandoned, using existing cryogenic infrastructure at the launch site to keep the kerosene cold during countdown.