Frank B. McDonald

Frank McDonald was born in Columbus, Georgia, on 28 May 1925. He did his undergraduate work at The Citadel and Duke University. In July 1948, just as he was completing work on his bachelor’s degree and looking forward to his graduate studies, the discovery of heavy nuclei in the primary cosmic rays that was mentioned above was announced by Phyllis Freier, Edward Lofgren, Edward (Ed) P. Ney, and Frank Oppenheimer at the University of Minnesota13 and, independently, by Bernard Peters and Helmut L. Bradt at the University of Rochester. That event sparked Frank’s interest in cosmic ray research, and he decided to join the University of Minnesota group.14

For his master’s degree, received in 1951 under the tutelage of Phyllis Freier and Ed Ney, he spent many hours peering through a microscope at cosmic ray tracks in nuclear emulsions spread on glass plates. Through that experience, he developed an uncommonly keen understanding of cosmic ray interactions as they traversed matter. For his Ph. D. degree, he developed and flew a Wilson cloud chamber. That chamber employed a particle telescope consisting of GM counters and a sodium iodide (Na-I) scintillation detector. Whenever the telescope indicated the presence of helium and heavier nuclei, it triggered the cloud chamber expansion, thus permitting the study of the composition and energies of those particles.

Frank joined the Iowa Physics Department as a research associate in September 1953, while still completing a few odds and ends dealing with his Ph. D. dissertation at Minnesota.

He received that degree in 1955 and was appointed assistant professor at Iowa in 1956.

Frank left the University of Iowa in 1959 to play a key role in establishing the space research program in the fledgling NASA. As a member of the initial complement in what became the GSFC at Greenbelt, Maryland, he established the Fields and Particles Branch and its early research program. He moved through a number of positions at Goddard during the next 23 years, ending that period with his service as chief of the High Energy Astrophysics Laboratory. From 1982 to 1987, he served as chief scientist at NASA Headquarters, while simultaneously holding a position as a part-time professor at the University of Maryland in College Park. He returned to Goddard as its associate director and chief scientist in 1987, and served for a time in 1989 as senior policy analyst in the Office of Science and Technology Policy in the Executive Office of the president.

Frank very successfully combined senior-level executive management with his own re­search. Even while serving as the NASA chief scientist, he continued with his personal research program. Having served as principal investigator on 15 NASA space missions, as of 2007, he was still actively interpreting data from the Voyager Deep Space Missions and Inter­planetary Monitoring Platform (IMP) 8 at the Institute for Physics, Science, and Technology at the University of Maryland.

Frank’s first goal upon arriving at Iowa was to continue his investigation of the higher-charged component (charge greater than two) of the primary cosmic rays. He immediately started the development of a new particle telescope for improved measurements of the charge and energy spectra of those heavier primary cosmic rays. It featured a combination of a thin-lucite Cerenkov detector and a three-GM counter array. That arrangement provided better discrimination between the nuclei of different energies and charges than had been provided by previous instruments. The detectors displayed their data on cathode ray tubes in the flight gondolas that were,

CHAPTER 2 • THE EARLY YEARS 35

in turn, photographed by special cameras that Frank designed. I assembled many of Frank’s new electronic circuits as part of my early work at Iowa during the 1953-1954 period.

Frank made his shakedown balloon flight in early 1954 at Goodfellow Air Force Base (AFB) at San Angelo, Texas, only five months after he started this new project. After that initial test, the next step was an expedition to Goodfellow AFB in January

1955 as part of a major two-week international balloon field project. Iowa instruments were carried on 4 of the 13 balloon flights made during that expedition.15 Iowa participants, in addition to McDonald, were William (Bill) R. Webber, Jason Ellis (not to be confused with Robert Ellis, mentioned earlier), Hugh R. Anderson, and Belle Fourche. Cosmic ray instruments from the universities of Chicago and Minnesota and photographic plates from several European universities were also flown on some of the flights.

The balloons, 120 foot diameter Skyhooks, carried more than 100 pounds of instruments per flight. General Mills again furnished the balloons and conducted the launch operations. After floating at altitudes of up to 18 miles, for an average of seven hours, they landed from 50 to 100 miles from the launch site. They were followed in flight by light airplanes and trucks and were assisted by visual sightings from the ground and radio signals to facilitate recovery of the instruments as soon as possible after they landed. Early recovery was not always possible, as the chase parties sometimes had to break off their pursuit because of bad weather and darkness. In most cases, however, instruments were eventually recovered, some of them after they were found by farmers or others at the landing sites.

After that field trip, Frank developed an improved instrument that added a Na-I scintillation detector in a telescope arrangement. The combination of Cerenkov and scintillation detectors provided an improved measurement of the energy and charge for nucleons in certain ranges. The first flight of his new instrument was made from Minneapolis on 7 July 1955, and additional flights followed during the next four years.

Concurrently, Bill Weber developed a Cerenkov-GM counter combination to ex­tend the information on charge composition at low latitudes. He flew it in Texas in

1956 and used those data for his Ph. D. thesis.

Frank McDonald, Bill Webber, Kinsey Anderson, Robert Johnson, and Larry Cahill spent six weeks in February and March 1957 on the island of Guam as partici­pants in an ONR – and AEC-sponsored Equatorial Expedition. The balloon experi­menters, Frank, Bill, and Kinsey, were able to loft only three of their balloon payloads because of strong local trade winds, but they still obtained some useful equatorial data.

Frank and Bill formed a close collaboration during that 1953-1959 period that was the start of an especially durable and fruitful association that has lasted until the present

OPENING SPACE RESEARCH

(2010). Their first joint paper, published in 1959, used the proton data from a number of Frank’s Cerenkov-scintillation detector flights. Ultimately, the pair launched some 22 Skyhook balloon flights. Other joint papers through the years dealt with various aspects of cosmic ray work, including some on charge composition. The instruments gave excellent energy measurements in the range 300-800 MeV per nucleon and complete charge resolution at the higher end of that energy range. The extended program yielded more precise hydrogen and helium energy spectra, their long – and short-term modulation, geomagnetic cutoffs, and the first electronic measurements of lithium (Li), beryllium (Be), boron (B), and heavier elements.

I especially treasure my long-standing and close personal relationship with Frank. His keen understanding of physics and the processes involved in observing cosmic rays was particularly outstanding and personally helpful. He was able to conceptualize and carry out experiments over the years that have added substantially to our understanding of space particle physics. His accomplishments in cosmic ray physics, combined with his outstanding management abilities, made him one of the truly outstanding contributors to the blossoming of space physics during the second half of the twentieth century.