Experiment #5: Photo Optical Degradation

With the appearance of high-performance aircraft and missiles during the mid-1950s, designers began to be concerned with the effects of a turbulent boundary layer on the performance of optical equipment. As early as 1956, wind-tunnel researchers determined that the effects of a narrow beam of light through a turbulent boundary layer were a function of the free-stream Mach number and the density of the stream. The effects of this "light spreading" on the accuracy of star trackers were studied by Autonetics in 1957 and again by North American in connection with the B-70 program. Researchers observed the first actual effects of aerodynamics on aerial photography in 1957 when pictures taken from a McDonnell RF-101 Voodoo at Mach 1.4, viewed stereoscopically, provided a false evaluation of the terrain. This led the Army Corps of Engineers to award a contract to Vidya (a division of Itek Corporation) during 1959-1960 to develop a theory that explained the phenomena. The Navy sponsored similar work at MIT during 1959 to determine the degrading effects of turbulent flow on the resolving power of cameras.1991

instrumented aerial cameras and multiple boundary-layer rakes.-1100!

Officially called the "induced turbulence experiment," this project sought "to determine the effects of aerodynamics associated with supersonic and hypersonic aircraft, typified by the X-15 research airplane, on the performance of (1) a high-acuity modern camera set, exemplified by the Fairchild KS-25, and (2) a cartographic camera, exemplified by the Fairchild KC-1." The cartographic aspects of the experiment were of interest to the U. S. Army Corps of Engineers, while the Air Force was interested in the possible effects on tactical and strategic aerial reconnaissance. This experiment also used data collected by the small two-camera package installed in X-15-2 as part of experiment #27.101

This program was very involved, and significantly funded under an Air Force contract to North American as part of Project 6220, Photographic Reconnaissance Technology. The Reconnaissance Division of the Air Force Avionics Laboratory under the direction of Donald I. Groening coordinated the experiments. Two principle subcontractors were also involved: Aeroflex Laboratories fabricated parts for the ART-15A stabilized mount, and Vidya provided theoretical and image analysis. Fairchild Camera and Instrument Corporation provided the KS-25 camera under a separate Air Force contract. The Hycon Manufacturing Company provided the camera lens and conducted resolution testing, and the Cornell Aeronautical Laboratory assisted in determining the final target design.-102!

Phase I

The Army Corps of Engineers and the ASD jointly sponsored Phase I. The initial requirement was for three separate flight profiles: high-speed, high-altitude, and one that mimicked the Mach 3 B-70 bomber. The exact profiles were important because the launch lakes had to be established well in advance of the flights so that the Air Force could erect 6 to 10 photo targets along the flight path. This involved removing yet more land from the public domain. The B-70 profile placed another constraint on the program because it required flying the XLR99 at 40% thrust, and the early engines were incapable of doing this reliably. There was also a desire to photograph the same targets during Phase II.103

The launch lakes were Delamar and Smith Ranch. The targets would be located along the flight path from Delamar to Edwards with single three-bar targets located near Pahrump and Indian Springs in Nevada, and two sets of three targets straddling the flight path at Pilot Knob and Cuddeback in California. The single target at Pahrump determined the performance of the camera primarily at the maximum altitude point on the high-altitude missions, while the single target at Indian Springs determined performance at the maximum speed point on the high-speed profile. Triple targets at Pilot Knob and Cuddeback allowed for accumulated navigation errors and measured performance at high-supersonic speeds. The Pilot Knob targets also measured the camera performance at the point of reentry from the high-altitude profile. Each target was a collection of white stripes of different widths on a black background (a standard Mil-Std-150A photo-calibration target pattern) with an additional large contract patch and two sharp edges normal to each other to determine the atmospheric attenuation and edge response. The Air Force called this the Delamar camera range.104

A photometric van from the Scripps Institute of Oceanography at the University of California was usually set up at the Pahrump site. This van had three photometers that measured the total sky radiance, solar radiance, and radiance of the surface of the target. Researchers located meteorological instrumentation near each target to provide compensation data for the analysis, and the Air Force launched standard radiosondes to support the experiment.105

The X-15 package for the cartographic program contained a KC-1 camera, an ART-15A stabilized mount, and photometric and environmental instrumentation to measure the conditions that prevailed during the time of the experiment. The KC-1 had been modified with a GEOCON I lens designed by Dr. J. Baker of Spica, Incorporated, to combine low distortion with relatively high acuity, and was adapted for operation at high altitude. The experiment package, minus the camera, weighed approximately 156 pounds. The KC-1 camera and lens added another 85-90 pounds depending on the film load, and occupied a space about 16 inches long by 18 inches wide by 21 inches high at the bottom of the instrument compartment. The GEOCON I low-distortion mapping lens had a focal length of 6 inches and a relative aperture of f/5.6, and could provide a resolution of 37 lines per millimeter on Super-XX film. North American modified X-15-1 to accept a KC-1 camera, including modification of the ART -15 mount and the addition of an 18- inch-diameter window that was 1.5 inches thick in the bottom of the instrument compartment. The film was nominally 9 by 9 inches, and 390 feet of it were stored in the magazine.-1106!

PHOTOGRAPHIC INSTALLATION

KC-1 CAMERA WITH GEOCON I LENS

PHOTOMETERS

(10° AND SCATTERED TIGHT)—i

PH CTO MEIER AN;’

SPECTROMETER

KS-25 CAMERA

PHOTO METERS

[10° AND SCATTERED LIGHT

PHOTOMETER AND

j^CTROMETER

The Photo Optical Degradation Experiment (#5) was used to determine the degradation of optical
imagery caused by supersonic and hypersonic shock waves, boundary layers, and rapid frictional heating of the photographic window. Several different experimental packages were employed using well-instrumented aerial cameras and multiple boundary-layer rakes. Two different camera systems were installed in the X-15 for the experiment. (NASA)

Bob Rushworth flew the first flight (1-33-54) with the KC-1 on 11 April 1963 and NASA shipped the exposed film to Westover AFB in Massachusetts for processing. The last of six flights (1-38­81) was made on 18 July 1963, again with Rushworth as the pilot. The majority of the detailed results are still classified, but a general overview is given in the Phase II discussion.-107