How does the Falcon 9 rocket work?

Falcon 9 combines simplicity and repetition: both of its stages burn the same pair of propellants, aerospace-grade kerosene (RP-1) and liquid oxygen, and use variants of the same Merlin engine. The first stage mounts nine Merlins in an "octaweb" arrangement (eight around a central one), which allows it to keep flying even if one fails. The second stage carries a single Merlin Vacuum engine, with a much larger nozzle to work outside the atmosphere. According to SpaceX, the vehicle stands 70 m tall and 3.7 m in diameter, with a liftoff mass of around 549 t.

After liftoff, the first stage burns for about two and a half minutes. It separates, and the second stage ignites its engine to carry the payload to the desired orbit; on geostationary missions it performs a second burn after a coast phase. Meanwhile, the discarded booster flips using cold-gas nitrogen thrusters, performs a boostback or re-entry burn, deploys titanium grid fins to steer itself, and ends with a final burn that slows it down to land on deployable legs, either on the ground or on an autonomous drone ship at sea.

Recovering the first stage, the most expensive part of the rocket, changed launch economics. SpaceX has reflown boosters dozens of times each and also recovers the payload fairings, which open at high altitude and descend by parachute. The current version, Falcon 9 Block 5, was designed to minimize maintenance between flights. The manufacturer's published capacity is 22,800 kg to low Earth orbit and 8,300 kg to geostationary transfer orbit, figures that drop when the booster must save fuel to land.