APPROVED TEST-BED EXPERIMENTS

The final name used by the FRC for the follow-on research program was "test-bed experiments," although the Research Airplane Committee and other sources continued to call it the "follow-on program." The effort was formally announced in a news release on 13 April 1962: "The hypersonic X-15 will become a ‘service’ airplane to carry out new experiments in aeronautical and space sciences, in a program planned to make use of its capabilities for extremely high speeds and altitudes beyond Earth’s atmosphere. The new program adds at least 35 flights… and may take two years to complete." John Stack and Hubert M. Drake announced that an ultraviolet stellar photography experiment from the Washburn Observatory at the University of Wisconsin would be the first.1841

Experiment #1: Ultraviolet Stellar Photography

The NASA Office of Space Sciences sponsored experiment #1 to investigate the ultraviolet emissions of large, hot stars, and the properties of interstellar media. Researchers had already obtained limited data using sounding rockets, but desired additional data prior to the launch of the Orbiting Astronomical Observatory (OAO). The purpose of the experiment was to obtain measurements of the stellar brightness between 1,800 and 3,200 200 ngstroms ( ). The ozone layer blocks this spectrum from observation by ground-based instruments. Dr. Arthur D. Code and Dr. Theodore E. Houck from the Washburn Observatory at the University of Wisconsin designed the experiment.-1851

During December 1960, North American conducted a few runs in the fixed-base simulator to determine whether a pilot could fly the X-15 precisely enough to allow the experiment to collect useful data; the answer appeared to be yes. The simulations, however, pointed out the need for the reaction augmentation system, and were yet another driver to develop and install the system in the first two airplanes.-861

Before the experiment began, researchers at the University of Wisconsin wanted to gather information on the ultraviolet intensity of the sky background. To accomplish this, they installed a photomultiplier in one of the upper bug-eye camera bays of X-15-1 in April 1962. The photomultiplier required power and the use of one recording channel, but little else in the way of support. The first flight of the instrument was made on 19 April 1962 (flight 1-26-46). Originally, the university planned to install the complete experiment in the skylight compartment of X-15-2 in August 1962, but scheduling priorities delayed this until December 1962. Unfortunately, Jack McKay’s accident on flight 2-31-52 would postpone all future uses of X-15-2.871

Ultimately, the experiment consisted of an ultraviolet "star tracker" and horizon scanner installed on a stabilized platform in the skylight compartment on X-15A-2 after it was modified. The star tracker first flew on flight 2-33-56 and functioned properly in the caged mode. The next X-15A – 2 flight repeated the same tests. Flight 2-35-60 was intended to check out an uncaged (i. e., free to move) stabilized platform without opening the skylight doors, but a blown fuse prevented this. The experiment was successfully checked out on the next two X-15A-2 flights.881

The experiment was carried on five additional flights (2-38-66 through 2-41-73); however, little usable star-tracking data were obtained because of problems in maintaining the precise attitudes required for the experiment. Nevertheless, data from flight 2-39-70 confirmed speculation that the sky background was somewhat brighter than originally expected. The brightness gave less contrast between the star or constellation and the sky, making acquisition and observation more difficult. After the last flight in this series, researchers temporarily discontinued the experiment because of the position of the desired stars during the winter in southern California. The position of the stars supported three additional flights (2-46-83 through 2-48-85) the following summer. All of these flights were successful and obtained good data.88

Researchers determined that the atmosphere above 45 miles did not absorb the light from stars of moderate or larger magnitude. During flight 2-47-84, the experiment successfully photographed the stars Eta Aurigae, Alpha Aurigae, and Rho Aurigae from altitudes above 246,000 feet, which were some of the first stellar ultraviolet images. In late 1966, NASA removed the experiment from X-15A-2 in preparation for its Mach 8 envelope-expansion program.88

Experiment #2: Ultraviolet Earth Background

The Air Force Geophysics Research Directorate sponsored experiment #2 to measure the total Earth background radiation (albedo) and horizon in support of designing missile-warning surveillance satellites. Researchers expected that the Earth’s atmosphere would absorb most of the ultraviolet rays and thus appear very black to an ultraviolet sensor. Any missile rising from the surface of the Earth would show as a bright point of light in the ultraviolet, and thus could be easily detected. As originally envisioned, the experiment would use an array of spectrometers installed in the lower bug-eye camera bays. Researchers wanted to obtain data during each of the four seasons and at altitudes above 132,000 feet to be above the ozone ultraviolet absorption level, but otherwise did not require special flight considerations. The experiments would obtain spectral background data in the middle ultraviolet spectrum, high-angular-resolution data relative to the solar-blind ultraviolet horizon gradient, high-angular-resolution data in the solar – blind gradient near 3,100 , and vacuum ultraviolet background data. The experiment was

scheduled to begin in late 1962, but was postponed almost a year because key Air Force personnel were busy with other projects.-91

Researchers planned to fly the experiment on X-15-2, but a meeting on 17 September 1962 between Captain Hugh D. Clark and Captain James H. Smith from the ASD, and James E. Love and Lannie D. Webb from the FRC resulted in a decision to use X-15-3 instead. This decision also affected the ultraviolet exhaust-plume characteristics (#3) and infrared-exhaust-signature (#10) experiments."

During the postponement, the Air Force briefly canceled the experiment due to a lack of funding, but ultimately reinstated it. The experiment required at least one flight in excess of 150,000 feet to calibrate the test package, and then six further flights to acquire data. The equipment consisted of a high-resolution Barnes ultraviolet scanning spectrometer and a solar-blind radiometer mounted on a stabilized platform in the tail-cone box on X-15-3. Mechanical problems with the experiment precluded any data collection through the end of 1963, and equipment and scheduling problems continued to conspire against the experiment until the Air Force finally canceled it in early 1965 without acquiring any useful data. Instead, researchers decided to concentrate their efforts on experiment #3, which used the same basic equipment aimed at a specific point behind the X-15 to measure its exhaust.-1931