Open-Loop vs Closed-Loop Descent Guidance

Descent Guidance

Disturbance

Wind gust strength 1.2

Sensor / actuator noise 0.3

Descent speed 1.0×

Telemetry

Altitude

–

Time to touchdown

–

Open-loop error

–

Closed-loop error

–

Position error vs time■ OL ■ CL

Touchdown accuracy tally

Open-loop0 / 0

Closed-loop0 / 0

How it works

Both landers start from the same true position and are told to fly the same straight-line plan to the pad. The plan itself is built from a slightly inaccurate initial position estimate, and both vehicles fly through the exact same wind-gust push and actuator jitter each run.

Open-loop commits to the velocity its plan computed at t=0 and never looks back — every gust and actuator error simply adds onto its actual path, uncorrected, for the rest of the descent.
Closed-loop re-measures its own position (through noisy sensors) every frame, compares it against where the plan says it should be right now, and adds a proportional correction thrust — so it keeps steering itself back toward the intended trajectory despite the same disturbance.

Turn up wind gust strength or sensor/actuator noise and watch the orange (open-loop) error curve climb through the descent while the green (closed-loop) curve stays clamped near zero. Run repeated randomized descents to build a touchdown-accuracy tally for each mode.

RUN #1

Landing pad Open-loop lander Closed-loop lander

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