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Bowen Ribbon-Frame Camera*
BY E. E. GREEN AND T. J. OBST
NAVAL ORDNANCE TEST STATION, CHINA LAKE, CALIFORNIA
Summary— A brief background is given of the Bowen ribbon-frame camera, as developed for the study of rockets and guided missiles under free-flight conditions. The main constructional features are discussed as well as the orienting system used on the rocket range. Timing and camera-phasing devices are mentioned which make the film record assessable to an accuracy of 20 microseconds on the CZR Bowen camera, a model recently developed to meet the increasingly stringent angular and timing accuracies needed in the testing of high-velocity missiles.
INTRODUCTION
WHEN THE California Institute of Technology was involved in the testing of rockets in 1941, it became apparent that a number of special cameras would be necessary for metric photography. Ira S. Bowen, the present director of the Mount Palomar Observatory, was then obtaining and developing photographic equipment for the Goldstone rocket range. One of his primary efforts was the construction of a camera which would give a record from which rocket positions, velocities, and accelerations could be accurately assessed.
The photographic assessment problem, in determining rocket velocities and accelerations, depends on three factors: (1) the accuracy with which a rocket position can be determined on film; (2) the accuracy with which the elapsed time between two frames can be determined; and (3) the length of film representing a given displacement increment over which the two readings are taken. In plotting results, rocket position on each frame plotted versus the time of each frame gives a trajectory. The difference between two points on the trajectory divided by the time increment between the points gives a velocity point, and two points on the velocity curve, divided by their temporal separation give an acceleration point. Unfortunately, the inaccuracies in the trajectory are magnified when the velocity is determined and again increased when the acceleration is desired. In other words, in taking the first and second derivatives of a trajectory obtained by film assessment, the trajectory error causes increasingly greater velocity and acceleration errors.
* Presented October 13, 1949, at the SMPE Convention in Hollywood.
NOVEMBER, 1949 JOURNAL OF THE SMPE VOLUME 53 515