How do reusable launch vehicles achieve propulsive landing?

14 Eyl 14:30

Think of a reusable booster as a big, heavy drone that can “fly” itself back after the main ascent. Once the first‑stage separates, the flight computer runs a three‑step burn schedule. The **boost‑back burn** fires the main engine (or a set of smaller thrusters) for a few seconds to reverse the vehicle’s downrange velocity and aim it toward the recovery zone. Next, during the high‑speed re‑entry, a **re‑entry (or flip‑around) burn** reduces the thermal load and fine‑tunes the trajectory; the thrust vector is gimbaled to keep the vehicle’s angle of attack within safe limits. Finally, just a few seconds before touchdown, the **landing burn** throttles the engine down to a few hundred newtons and uses rapid TVC to counter any residual horizontal speed, essentially “braking” the booster right onto the pad or drone ship. All of this is coordinated by an onboard guidance loop that fuses an inertial measurement unit, GPS, and a radar altimeter. The computer continuously predicts the optimal throttle and gimbal commands, compares them with the measured state, and issues corrections at tens of hertz. This closed‑loop control is what lets the booster land within a few meters of the target. By contrast, a parachute‑recovered stage is a passive system: you open the chute, let the atmosphere slow you down, and drift to a pre‑planned splash‑down zone. It’s slower, less precise, and you can’t steer it in real time—hence the much larger recovery area and the need for sea‑based retrieval. Propulsive landing trades the simplicity of a parachute for the complexity of active thrust control, but it gives you pinpoint reuse and a turnaround time measured in weeks instead of months.