Pulsed Laser Radar for Close Range Operation in Space

Summary

A high resolution laser diode rangefinder was developed which is part of an autonomous target acquisition and tracking system for rendezvous and docking manoeuvres in space. The laser radar system is capable of measuring distances to retroreflector targets from 2 m up to 20 km. At a single point measuring speed of 0.5 s the ranging accuracy is 2…3 cm and the short term stability and reproducibility 2…3 mm. The ranging unit is based on the time-of-flight measurement of a short laser pulse. To achieve the cm-accuracy and the mm-resolution some sophisticated signal evaluation techniques have to be used:

• A constant fraction discriminator reduces the influence of signal amplitude variations on the electronic trigger of the time evaluation circuit

• A dual-slope time stretching method has been introduced to support precise time interval measurements

• An internal optical fiber is used for the calibration of the ranging system

• The target return signals are adjusted to convenient levels by a piezoelectric attenuation unit