Van Allen’s cosmic ray experiment proposals

Long before the president’s U. S. satellite commitment in 1955, many researchers had been turning over in their minds ideas for scientific investigations that might be conducted with such carriers. As related in Chapter 3, Van Allen prepared an outline for a cosmic ray experiment in an Earth satellite as early as 1 November 1954, after learning of the army’s thinking about a satellite launcher.2 His objectives, which remained substantially unchanged throughout the subsequently evolving satel­lite program, were “to measure total cosmic ray intensity above the atmosphere as a function of geomagnetic latitude, and to measure fluctuations in such intensity and their correlation with solar activity.” The general description of the basic apparatus, too, remained unchanged, i. e., a “single Geiger-counter, necessary auxiliary circuits, radio telemetering transmitter and antenna.”

Details of the envisioned technical implementation, however, changed dramatically between that earliest outline and the instrument that we began developing a little more than a year later. Van Allen based his early proposal on the use of vacuum tube circuitry, as transistors were not yet available except as purely experimental devices. His proposal did not even mention them. Furthermore, he believed that a transmitter radiating five watts would be necessary for reception at 1500 miles. Those factors combined to focus most of the rest of his discussion upon power supplies to provide the relatively high energy level needed for extended operation. He listed possibilities for the power source as (1) dry batteries, (2) lead storage batteries, (3) Yardney silver cells, (4) hydrogen and oxygen heat of combustion (now known as fuel cells), (5) red fuming nitric acid and aniline heat of combustion, (6) gasoline and oxygen heat of combustion, and (7) solar power. Van Allen narrowed his focus, in that proposal, to the use of a generator driven by a gas turbine fueled by nitric acid and aniline.

The president’s announcement added a sense of reality to the experimenters’ as­pirations, and Van Allen quickly prepared an updated and more complete version of his proposal.3 That one, titled “Proposal for Cosmic Ray Observations in Earth Satel­lites,” reflected some of the new technological developments. On 28 September 1955, less than two months after the president’s commitment, he submitted that new version to Joseph Kaplan, chairman of the U. S. National Committee for the International Geophysical Year (IGY).4

Despite Van Allen’s heavy workload in heading the university’s Physics Depart­ment, it is clear that Van Allen’s thinking and energies were sharply focused on the coming IGY satellite program.

As mentioned earlier, in late January 1956, the Upper Atmosphere Rocket Research Panel, under his chairmanship, held a meeting on the University of Michigan’s Ann Arbor campus to hear and discuss serious satellite research proposals. Among the 38

CHAPTER 5 • THE VANGUARD COSMIC RAY INSTRUMENT 127

papers presented there, Van Allen delivered two containing three specific proposals. His first paper, “Cosmic-Ray Observations in Earth Satellites,” actually contained two separate proposals, the first of which expanded upon his September 1955 proposal.5 It called for the use of a single Geiger-MUller (GM) counter or scintillation detector for a first-time study of the cosmic ray intensity above the appreciable atmosphere on a comprehensive geographical and temporal basis. Specific objectives were listed as “determination of the effective geomagnetic field; the magnetic rigidity spectrum of the primary radiation; time variations of intensity and their correlations with solar and magnetic observations and with the observed intensity of secondaries observed in ground stations; and cosmic-ray albedo of the atmosphere.” He also envisioned that those data would be especially valuable in helping to interpret the observations from the extensive array of cosmic ray ground stations that were being established.

In that proposal, Van Allen included an extended discussion of the effect of limited data recovery by various hypothetical networks of ground receiving stations. Conspic­uously, he did not mention onboard storage, although he and I had seriously discussed that possibility well before the meeting. But our thinking about onboard storage was still evolving at the time of the meeting, and we didn’t add that feature until a little later. That proposal, with the addition of the onboard data storage, was accepted in June 1956 for development.

The second part of Van Allen’s first paper was for the use of a Cerenkov detector to study the relative abundance of heavy nuclei in the primary cosmic radiation. That proposal was soon dropped from further early flight consideration because it could not be accommodated within the severe limitations on instrument weight imposed by the Vanguard launcher. Although not pursued in the initial satellite program, its scientific objectives were eventually achieved by other groups using later satellites.

Van’s second Ann Arbor paper (his third proposal), “Study of the Arrival of Auroral Radiations,” proposed a further study of the auroral soft radiation that had been discovered from the data from the Iowa rockoon flights.6 That proposal also had to be set aside for then, primarily because it required a much higher orbital inclination than was envisioned for Vanguard. Most of the objectives of that second proposal were also achieved with later spacecraft instruments.