Experiment #3: Ultraviolet Exhaust-Plume Characteristics

The ASD sponsored experiment #3 to measure the exhaust characteristics from a liquid-oxygen – ammonia rocket engine (the XLR99). It used the same basic equipment as experiment #2, without the stabilized platform. The first flight (3-41-64) was made on 23 April 1965 with Joe Engle at the controls. By the end of 1965, the high-resolution Barnes ultraviolet scanning spectrometer and solar-blind radiometer that had proved so troublesome on experiment #2 had successfully obtained good data. As a follow-up, researchers installed a Millikan dual-channel radiometer in X-15-3 during the weather down period at the beginning of 1966, and installed a vacuum ultraviolet spectrometer later in the year. The Millikan radiometer flew on flight 3-55-82 but froze due to a failed heater, and there is no record of it flying again. Similarly, no record exists of the spectrometer ever being flown.-194!

Experiment #4: Langley Horizon Definition a 12,000-foot mountain using a simple photometer and several interference filters. The data indicated that the "stable phenomena" hypothesis appeared to be correct, but emphasized the need for observations made from outside the Earth’s atmosphere using equipment that was more sophisticated. Researchers flew variations of the experiment on sounding rockets and the X-

15.1951

Researchers installed a radiometer in the tail-cone box of X-15-3 along with a 16-mm motion – picture camera pointing out the rear. The camera provided wide-angle coverage to check for clouds or haze during the data-gathering period. The radiometer included a motor-driven scan mirror that provided a 30-degree field of view, and reflected energy into a parabolic mirror that focused the energy on the detector. The radiation passed through an optical bandpass filter to select the appropriate spectral band. The angle of the scan mirror and the output of the detector were recorded on an FM-FM magnetic tape recorder.1961

The experiment first flew on 2 May 1963 (flight 3-16-26) and made five additional flights during 1963. Three of these six flights provided meaningful data for the MIT-Apollo horizon photometer experiment (#17). Another successful flight (3-30-50) on 8 July 1964 investigated the near infrared in the 0.8-2.8-micron region. After the flight, the experiment returned to Langley for modifications, and was intended to fly at least three more times. In the end, only two additional flights were flown during 1965 (3-42-65 and 3-44-67), since the more sophisticated MIT experiment had already begun flying aboard X-15-1.

Langley was generally happy with the X-15 as an experiment platform: "Not only is the design of the experiment simplified because there are few restrictions due to size and weight limitations, but also the availability of standard X-15 attitude and position data are an important advantage… the radiometer is reusable… and good weather data is available." This was in contrast to sounding rockets that provided comparatively short flights, had minimal onboard instrumentation, and, of course, were not generally recoverable.-1971

This experiment provided the first infrared data gathered on the Earth’s limb from above 30 miles. From these data, researchers modeled the horizon profile to an accuracy of 4 kilometers for use in attitude-referencing systems carried aboard early orbiting spacecraft.1981