Week 17: Coming Down Safely

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Reaching apogee is only half of a successful flight — what happens next, as the rocket falls back to Earth, is just as important.

Forces

Under a parachute, a rocket stops accelerating once drag from the canopy balances gravity — at that point it falls at a constant speed called terminal velocity.

Math

vt = √(2·m·g / (ρ·A·Cd))

Worked example (metric): a 0.1 kg rocket under a parachute with area 0.2 m² and Cd = 0.8, in air of density 1.225 kg/m³: vt = √(2 × 0.1 × 9.81 / (1.225 × 0.2 × 0.8)) = √(1.962 / 0.196) ≈ 3.2 m/s — a safe, gentle landing speed.

Safety Note

NAR recovery system requirements set safe descent-rate thresholds specifically to keep landing speeds like this one within a safe range for both the rocket and anyone nearby.