GPS Rescue Reliability: Satellite Geometry, Fail-safe Logic & Recovery Loops

GPS Rescue is a critical safety system. During arming, the FC records the Home Point coordinates once a minimal satellite lock is established (typically 8 satellites).

1.1 Satellite Geometry (HDOP/PDOP)

The accuracy of the lock is determined by the Dilution of Precision (DOP):

• Low HDOP (< 1.5): Satellites are spread out, providing perfect triangulation.
• High HDOP (> 3.0): Satellites are clustered together, leading to coordinate drift and home point errors.

When control signal is lost (Failsafe), the FC takes control:

1. Climb Phase: The multirotor immediately climbs to a safe altitude.
2. Turn Phase: The FC calculates the home vector and turns towards home.
3. Return Phase: The drone flies home at a programmed speed, monitoring satellite locks and barometric altitude.

3.1 Satellite Loss Mid-Rescue

If satellite count drops below 4 during the flight, the FC loses triangulation. Betaflight failsafe rules command the drone to disarm immediately to prevent flyaways.

3.2 Glitchy Barometers

A faulty barometer can report false altitude spikes, forcing the FC to descend prematurely into trees or water.