SpaceTRC / Space Age / Interactive simulation
Land the Falcon 9 on the drone ship yourself.
The first stage is at 2,500 metres, falling towards the drone ship at about 250 metres per second. You have one engine, limited fuel and a single ignition. Light the engine at the right moment, throttle carefully, correct the drift and touch down slower than 6 metres per second.
Keyboard: Space = ignite · ↑ ↓ = throttle · ← → = steer. On touch screens, press and hold the buttons.
The physics behind it
Why can’t it simply hover?
Even minimum thrust is too much
A single Merlin engine produces about 845 kN at sea level and throttles down to roughly 40%. The nearly empty stage weighs only about 30 tonnes, so even at minimum throttle thrust exceeds weight and the stage cannot hang in the air. Velocity must reach zero exactly as it touches down; engineers call this a “hoverslam”.
The air brakes too
Falling through the atmosphere, air drag balances the stage’s speed at around 250 metres per second. The simulation computes drag with air density that thins with altitude.
Grid fins
With the engine off, steering comes from the grid fins at the top. As speed drops they lose authority, and in the final seconds engine gimbal decides the direction.
Model: two-dimensional, simplified physics. Dry mass 25.6 t, starting fuel 6 t, engine thrust 845 kN, specific impulse 282 s, cross-section 10.75 m², drag coefficient 0.8, scale height 8.5 km. Values are approximate public data; this is not SpaceX’s actual landing algorithm.
The real landing sequence: How does a Falcon 9 land?