Rockoons

The SUI rockoon program culminated in a pair of field exercises that were supported as a part of the IGY endeavor. The ambitious expeditions were undertaken in the fall of 1957 by James Van Allen, Larry Cahill, and their coworkers.

Cahill’s rockoon magnetometer While still at the Applied Physics Laboratory, Van Allen had been aware of an invention by M. Packard and R. Varian, a proton free-precession magnetometer.21 That instrument was intrinsically capable of making very precise measurements of the magnitude of a magnetic field—its precision was believed to be sufficient to make a clear distinction between the Earth’s strong main magnetic field and very weak magnetic fields hypothesized to result from electrical currents in the ionosphere. Members of Van Allen’s group at the Applied Physics Laboratory and researchers at the Naval Ordnance Laboratory conducted several searches for those ionospheric currents during the very late 1940s and the opening of the 1950s by the use of flux-gate magnetometers.22 The possibility of using the more precise proton free-precession magnetometer for that purpose, although attractive, was not pursued then.

The idea resurfaced in early 1954, when Van Allen suggested to the Upper Atmo­sphere Rocket Research Panel that the free-precession magnetometer might be used in the search for the ionospheric currents.23 At his fall 1954 meeting with his graduate students at Iowa, Van Allen outlined that basic idea and suggested that such a project might be undertaken by one of them by developing a miniaturized version that would fit within the physical envelope of a Loki rocket. If that could be done, the instrument could be carried at low cost to a sufficient height to detect the currents.

CHAPTER 4 • THE IGY PROGRAM AT IOWA

Larry Cahill, as mentioned earlier in connection with the 13 March 1956 balloon flight of his magnetometer, had joined the Iowa research group in 1954 and agreed to take on the challenging new developmental project.