Radiation Detection

The next experiment came from an unlikely source. On 3 August 1961, the Air Force Special Weapons Center at Kirtland AFB, New Mexico, delivered an ionizing radiation-detection device for use on the X-15. NASA installed the 10-pound package in the left side console of the cockpit outboard of the ejection seat. Actually, the first attempt to install the experiment failed because the space allocated in the cockpit was insufficient, but Kirtland soon repackaged it to fit.731

The experiment activated automatically when the pilot turned on the main instrumentation switch during flight. The package contained an ion chamber, two scintillators, a Geiger tube, and a self- contained multi-channel tape recorder. Different thicknesses of human-tissue-equivalent plastic encased the ion chamber and scintillators. With the Geiger tube acting as a count rate monitor, the detectors recorded radiation dose rates on the surface and at depths of 0.25 inch and 1.0 inch in the plastic between 1 millirad per hour and 100 millirads per hour.741

The first flight attempt was made on 29 September 1961, but this flight (1-A-38) aborted prior to launch due to a flight-control anomaly in the X-15. The package successfully flew on 4 October 1961 with Bob Rushworth at the controls of flight 1-23-39. The experiment subsequently flew several more times during late 1961. After each flight the taped data went to Kirtland for analysis, and the results ultimately showed that the pilots received essentially a normal background dosage of radiation (0.5 millirads per hour) during the flights. Since there seemed to be no cause for concern, the Air Force deleted the radiation detector from flights beginning in 1962.75

The program flew a different radiation experiment on X-15-2 from early 1961 until September 1963. The "Earth cosmic-ray albedo" experiment investigated the cosmic-ray environment at altitudes from 50,000 feet upward to determine the cosmic-ray environment in which future manned space vehicles would operate. The experiment consisted of placing small photographic

emulsion stacks in upper and lower structural (i. e., bug-eye) camera bays to obtain information on the cosmic-ray albedo flux and spectrum, as well as the flux and spectra of electrons and protons leaking out of the Van Allen belts. The X-15-2 carried the stacks to high altitudes on as many flights as practical and placed no restrictions on the flight path or trajectory. The NB-52 carried similar stacks during the same flights to provide lower-altitude references. Researchers at the University of Miami and the University of California at Los Angeles and Berkeley analyzed the film from the stacks.[76]

In a very similar experiment, X-15-1 and X-15-2 carried two nuclear-emulsion cosmic-radiation measurement packages from the Goddard Space Flight Center on the aft ends of their side fairings to investigate the cosmic-radiation environment at extreme altitudes. These emulsion stacks were considerably larger than the Earth cosmic-ray albedo stacks and were located external to the airplane. Several flights carried the packages to altitudes above 150,000 feet. The packages required no special maneuvers and no servicing other than installation just prior to flight, and removal after landing.-177