Iowa City balloon flights in March 1956

A major balloon launching campaign was mounted in the spring of 1956, when three flights were made at Iowa City with larger skyhook balloons.49 50 Frank McDonald and Bill Webber had quickly followed their balloon flights on the second Goodfellow expedition with the development of an improved instrument. It contained a thin-lucite Cerenkov detector like the one used previously, but augmented by a Na-I scintillation counter and a GM counter telescope to provide improved measurements of lithium, beryllium, boron, and carbon in the primary cosmic ray radiation. The entire package, along with a camera to record the data, was assembled in a cylindrical aluminum gondola six feet long, 18 inches in diameter, and weighing 130 pounds, as shown in Figure 2.16.

The first two of those launches lofted a large assortment of experiment instruments. On the first flight, the new McDonald-Webber instrument led the chain of packages on the load line. The next package on the line, designed by Laurence (Larry) J. Cahill, constituted an early balloon flight test of the proton free-precession magnetometer that he had been developing for rockoon flights, as detailed in Chapter 4. Next on the line was one of Kinsey Anderson’s GM counter telescopes like the ones he had just flown at Goodfellow. Yash Pal, an Indian research associate at the Massachusetts Institute of Technology, provided a bundle of photographic nuclear emulsion plates. Additional items included a timer and cut-down device for terminating the flight after eight hours, a parachute for lowering the string of instruments after they were cut loose, a camera,

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an altitude-measuring barometer, another bundle of nuclear emulsion plates from the University of Minnesota, and a carefully calculated ballast to control the equilibrium altitude of the balloon. Those components, totaling about 250 pounds, were spaced along the balloon’s 100 foot long load line.

The largest Skyhook balloon used to date, at 244 feet in length before inflation, about 150 feet in diameter when fully inflated, and nearly 2 million cubic feet in volume, was used to loft the first of the three Iowa flights. That first launch was initially planned for about 1 March 1956 but was delayed because of weather. Another attempt was made to launch it on 12 March, but high winds and poor visibility caused further postponement. The launches required a ground wind speed of less than 11 miles per hour to avoid damage to the balloons and their loads during inflation and launch. It was also highly desired that the visibility across eastern Iowa and northern Illinois be clear to enable the chase teams to follow and recover the instruments.

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All conditions were met the next day, when it was finally possible to launch that first Super-Skyhook balloon from a runway at the Iowa City municipal airport. That occurred at 7:47 AM on 13 March 1956.51 The experimenters had made final checks and adjustments on their instruments throughout the night. The balloon-inflation crew began their preparations soon after midnight. Four foot weather balloons were tethered from a panel truck at 150 foot and 300 foot heights to monitor the wind speed and direction. Although the lower test balloon indicated a gentle enough wind for safely inflating the balloon, the higher one revealed a wind shear that could destroy the balloon soon after release. That situation persisted throughout most of the night. As dawn approached, the wind shear finally abated, and a decision to attempt the flight was made at about 5:30 AM. The fleet of vehicles made its way into position at the south end of the runway. That flotilla included a truck pulling the mobile launcher, another truck carrying helium, the panel truck with its weather balloons, the scientists and their instruments, and the beginnings of an entourage of onlookers that eventually swelled to more than 200. Just before the Sun appeared over the eastern horizon, the balloon was laid out on the runway and inflation began. As inflation progressed, the envelope was played out from between large rollers on the mobile launcher. As the helium bubble slowly formed, the flow was stopped at intervals and the platform was pushed forward by the tow truck to play out more of the plastic envelope.

There was great excitement in the local community about this launching. Batteries of newspaper photographers snapped their cameras as the crews worked through the night, and local radio station KXIC began a live broadcast at about sunrise. The growing crowd of onlookers pressed in on the workers—it was too early in the Space Age for us to have thought much about crowd control. As the free lift reached about twice the payload weight, the flow of helium was stopped. At that time, the helium was contained in a small bubble at the very top of the balloon. Although occupying only about 1 percent of the balloon’s volume at ground level, this bubble would expand as the balloon ascended through the decreasing air pressure until it completely filled the balloon’s spherical envelope at about 113,000 feet, or 21 miles. Until it was cut down by the timer, the balloon would float at about that altitude, moving up or down slightly as the gas temperature varied due to changes in solar illumination.

After everything was ready for the balloon release, a hold was called. That lasted for an hour while the pressing crowds were moved back and the launch platform was realigned to accommodate a slight shift in the wind direction. Finally, one end of the launch platform’s top roller was released, and the balloon floated free. Being at the top of the load line, Frank’s gondola was immediately lifted from the ground. Since the wind was blowing the balloon slowly northward, the other teams had to run across the ground with their equipment packages until the balloon took up the slack in the load line. Otherwise, the instruments would have been dragged across the ground and damaged. This was always an exciting (often comical) phase of a balloon

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launching operation. There is no greater motivation for an Olympian sprint than a graduate student’s need to thus protect the prized product of many months of intense laboratory preparation, and to keep alive his hopes for a timely completion of his thesis and receipt of his degree.

The chase plane departed immediately after the launch. The assembled crowd watched the balloon and its payload shrink to a small dot in the sky and eventually disappear. Cahill and an undergraduate assistant departed to chase the balloon with a truck on loan to the Physics Department from the Navy. They followed the balloon eastward, stopping about every 50 miles to record the payload signal, until they were stopped by Lake Michigan. A full discussion of that flight of Larry’s instrument is contained in the thesis for his M. S. degree, which he received in 1957.52

The other experimenters rushed back to the physics building, where Kinsey Anderson was able to monitor the radio signals from his instruments until mid­morning, when the balloon passed out of radio range. Frank McDonald’s data were being recorded by a special camera in the gondola, so he could do nothing but await the gondola’s return to see if his instruments had performed satisfactorily. The nuclear emulsion plates, of course, also needed to be returned for laboratory analysis.

High-altitude winds turned out to be much stronger than expected. Within the first 200 miles, the balloon had far outpaced the chase truck. It reached upstate New York by the time the timer cut the load line and the parachute lowered the payload to the ground. The chase plane was out of visual contact due to thick weather much of the last portion of the trip, but the pilots were able to follow the balloon’s approximate path with the plane’s radio direction finder. They believed that the balloon’s equipment had descended about 40 miles south of Rochester, and so landed at the Rochester airport. A ground search, however, was unsuccessful. It wasn’t until 48 days later, on 30 April, after a snow cover melted, that a farmer found the equipment 30 miles south of Utica, about 120 miles farther east than expected. The equipment was returned, the farmer was paid the promised reward of $150 for finding and reporting it, and Frank and the other scientists began to analyze their flight data.53

The second and third flights used somewhat smaller 120 foot diameter balloons. The primary instrument on the second flight was another of Frank McDonald’s heavy – nuclei cosmic ray instruments. It was in a gondola similar to that of the first flight, but somewhat lighter at 110 pounds. Carl McIlwain flew a single GM counter package sim­ilar to the ones he had launched on the 1955 rockoon expedition. Also attached to the load line were nuclear emulsion packages from the University of Minnesota, Washing­ton University in St. Louis, Missouri, and the Massachusetts Institute of Technology.

The second flight was launched at 6:27 AM on 20 March. Everything went more smoothly, the balloon’s speed aloft was more nearly as expected, the skies were clear,

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and the twin-engine Beech chase plane was easily able to follow it. After seeing the equipment string descend under its parachute about seven miles northwest of Mount Pleasant, Michigan, the pilots landed their plane at the nearest airport. People on the ground also saw the instruments descend, and the flight equipment was in the hands of the Michigan State Police 20 minutes after it landed. The pilots in the chase plane returned the equipment to Iowa City the following day.54

For the third flight, graduate student Raymond (Ray) Missert had prepared for a long-duration 24 hour flight to study variations in the cosmic ray intensity. Available records do not contain details of that flight, but it appears to have taken place, as Ray obtained his Ph. D. degree the following year based on a dissertation on that subject.55

Those three flights were supported once again by the ONR and the Atomic Energy Commission. The balloon operations were handled by Otto C. Winzen, chief flight engineer Edward Lewis, and their crew from Otto’s Winzen Research Company in Minneapolis. The Iowa experimenters were assisted by a battery of student aides and other assistants.

This chapter relating balloon, rocket, and rockoon work rounds out my account of University of Iowa high-altitude scientific research to the point where the International Geophysical Year provided an opportunity for a greatly expanded program, including the possibility of launching artificial Earth satellites. The balloon, rocket, androckoon work described in this chapter produced important scientific results, sharpened our technical skills, and shaped a high-altitude research laboratory that was second to none.

I received my bachelor’s degree at the winter convocation in February 1956 and was ready to begin my graduate work. My personal involvement with the Iowa balloon and rockoon programs, per se, essentially ended when I turned to developing Earth satellite instruments in March 1956.