A HANDHELD OPTICAL RANGEFINDER FOR ORBITAL RENDEZVOUS

Robert T. Pitlak

Peer Reviewed

Abstract:	THE SYSTEM REQUIREMENTS associated with manned spaceflight missions often impose severe constraints upon system design. In particular, demands for greater accuracy, sensitivity and reliability are often met only with increases in complexity, redundancy and weight. Many have suggested that significant gains in reliability and simplicity may be achieved by increasing the use of human capabilities in control and navigation of the spacecraft. Kollsman, making use of human performance and anticipated mission spacecraft configurations, has designed and fabricated a manually operated instrument which is not only simple and reliable, but small, lightweight and accurate as well. Choosing the particular problem of ranging during orbital rendezvous, Kollsman has developed the KS-205 Diastimeter for it’s solution. Besides exhibiting the advantages generally associated with manual operation, this instrument takes advantage of particular target shapes. An analysis shows that targets, such as cones (approximated by the Apollo Command Module) or spheres always present’ the accurate baseline required by classical optical rangefinders. In the case of the cone or cylinder, this baseline appears as the apparent major axis of the base. In the case of the sphere, it is the apparent (i.e., corrected for viewing aspect) diameter. Since these baselines are generally large and remote, small size is not incompatible with high accuracy. When the target is viewed through the Diastimeter, two images are observed. One image is made to deviate until both images are tangent to each other. An analysis relates this situation to the measurement of range. The range is read directly from a drum scale, mechanically linked to the diasporameter which deviates the image. The instrument was designed with accuracy and reliability as primary objectives. The internal baseline is fixed within prisms to prevent environmental (i.e., vibration, et’c.) changes in its dimension. An optical bias technique was utilized to extend the usefulness and accuracy of the diasporameter to increase the precision with which tangency could be achieved. An error analysis indicates that the Diastimeter exhibits characteristics found in all optical rangefinders. That is, range error varies as the square of the range and inversely with the size of the target. Actual tests made with a prototype instrument show that the design has achieved a high degree of accuracy over long ranges. These test results and the error analysis have been used to extrapolate to Diastimeter performance for larger targets. Such estimates predict that such an instrument would be useful over ext,remely long ranges for future space vehicles.
Published in:	NAVIGATION: Journal of the Institute of Navigation, Volume 15, Number 3
Pages:	324 - 331
Cite this article:	Pitlak, Robert T., "A HANDHELD OPTICAL RANGEFINDER FOR ORBITAL RENDEZVOUS", NAVIGATION: Journal of The Institute of Navigation, Vol. 15, No. 3, Fall 1968, pp. 324-331.
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