Helicopter airborne laser positioning system

This paper presents the theory of operation, configuration, laboratory and ound test results obtained with an helicopter airborne laser positioning system developed by Princeton University.Unfortunately, due to time constraints, flight data could not be completed for presentation at this time. The system measures the relative position between two aircraft in three dimensions using two orthogonal fan-shaped laser beams sweeping across an array of four detectors. Specifically, the system calculates the relative range, elevation, and azimuth between an observation aircraft and a test helicopter with a high degree of accuracy. The detector array provides a wide field of view in the presence of solar interference due to compound parabolic concentrators and spectral filtering of the detector pulses. The detected pulses and their associated time delays are processed by the electronics and are sent as position errors to the helicopter pilot who repositions the aircraft as part of the closed loop system. Accuracies obtained in the laboratory at a range of 80 ft in the absence of sunlight were ±1° in elevation; +0.5° to -1.5° in azimuth; +0.5 to -1.0 ft in range; while elevation varied from 0 to +28° and the azimuth varied from 0 to ±45°. Accuracies in sunlight were approximately the same for a range of 80 ft, except that the field of view was reduced to approximately 40° (±20°) in direct sunlight.