Thread by @JJSabatini

1/7 A bit of chemistry of the Atlas V rocket. Initial liftoff is achieved with “booster” solid composite propellant that contains ammonium perchlorate, aluminum powder, and hydroxy terminated polybutadiene (HTPB) as the binder system.

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https://twitter.com/dereklowe/status/1484700920269127681

2/7 Aluminum only makes up a small amount of the overall formulation of the booster, but is very important. It catalyzes efficient and clean combustion, and maximizes the burning rate of the solid booster propellant mixture.

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3/7 After the boosters finish their initial work, they separate from the rocket, and the first stage engine takes over. In the case of the Atlas V, it’s a common core booster propellant known as Kerolox.

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4/7 Kerolox contains liquid oxygen (LOX) for the oxidizer, and RP-1 for the fuel. RP-1 is a highly refined kerosene. It contains negligible water, sulfur, alkenes or aromatics. This is critical to prevent polymerization, and gumming up of the engine.

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5/7 After the first stage finishes burning, the second stage engine takes over. Known as Centaur, this contains LOX and liquid hydrogen (LH2) for the fuel. The specific impulse of this system is very high, operating smoothly in very cold environments.

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6/7 So when you see a fuel dump of the Atlas V, this is excess LH2/LOX. This is common practice to minimize an explosion risk, and poses zero threat to the environment. LH2 reacts with oxygen to give water and heat.

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7/7 It was cloudy in Maryland, so I couldn’t see the fuel dump’s brilliant blue light this time. But I’ve seen them in the past, and I’d recommend it for anybody that has an interest in space.

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