The summer 1954 third rockoon expedition

Meredith’s initial detection of the auroral soft radiation in 1953 led to vigorous follow­up work for a more discriminating examination of its latitude dependence, compo­sition, and directional characteristics. In addition to his early work on the balloon in­struments, as described in the preceding section, Frank McDonald joined in the effort to further define the new phenomenon. Over the winter 1953-1954, working with Mel Gottlieb and Bob Ellis, he developed two new rockoon instruments.16 I worked with them during most of May and June 1954 to build a set of flight instruments.

The first new rockoon instrument paired the same type of GM counter that had been used on the 1953 expedition (minimally shielded with 30 mg/cm2 in the counter wall, plus 160 mg/cm2 in the nose cone) with a second identical Geiger counter having additional shielding (150 mg of aluminum and lead). That instrument also included a photoelectric rocket-orientation indicator.

The second payload type was fundamentally new for the rockoons. Derived from the balloon instruments on which McDonald and Webber had been working, it employed a Na-I (thallium-doped) scintillation crystal mounted on a photomultiplier tube. That scintillation detector was mounted below a single thin-walled GM counter located in the nose of the rocket. The Geiger counter pulses gated the output of the scintillation detector. When both were triggered within a very short time, usually by a single particle traversing both of them, the amplitude of the scintillator detector pulse was

CHAPTER 2 • THE EARLY YEARS 37

telemetered. The raw Geiger counter pulse rate was also telemetered. Thus, the instrument was to provide information about particle type, energy, intensity, and direction of arrival.

The SUI 1954 field expedition contingent consisted of Frank McDonald (heading the team) and Bob Ellis. The NRL again fielded a team. They all left from Boston on 15 July on the USN icebreaker USS Atka.17

Two shakedown launch attempts on 16 July due east of Boston were spoiled by rocket ignition problems. So-called redesigned, greatly improved igniters had been shipped with the rockets, but, like the igniters on the 1953 expedition, they failed to fire the rockets at altitude. The team prepared a version of the Jones Igniter so resourcefully worked out during the 1953 expedition. That proved to be completely successful, and it was used throughout the rest of the expedition.

The third rocket in the series, with the improvised Jones Igniter, was launched three days later while they were still en route to their primary area of interest. Although the rocket ignited properly, that flight experienced a partial telemetry system failure and did not produce usable data.

The first fully successful flight (SUI flight 27) occurred off the northern tip of Labrador near 59 degree north geographic latitude, or at about 70 degrees north geomagnetic latitude. That, with 10 other launches, was clustered in and near the heart of the auroral zone during the short five-day period from 21 through 25 July 1954. Seven of those flights reached observational altitudes with operating instruments.

Ellis, Gottlieb, and Meredith reported later on the data from two of the successful flights of the paired GM counters. One of those flights, number 36, dramatically revealed the auroral soft radiation, as shown in Figure 2.7. The effect of the additional shielding of the second GM counter is clearly evident.18

The data from McDonald’s scintillation/GM detectors was, at first, puzzling.19 That question was partly resolved in 1954, and McDonald, Ellis, and Gottlieb reported that, of three successful flights of that instrument, two revealed the soft radiation.