Early Satellite Work

In 1956 I had made a formal proposal to the IGY directorate for a simple but globally comprehensive cosmic-ray investigation in one of the early U.S. satellites of the earth as a powerful follow-on to my previous and planned work with rockets. In addition, I proposed study of the auroral primary radiation, also on a global basis, if and when orbits of sufficiently high inclination were available.

The cosmic-ray proposal was given a favorable rating, placed in the pool of experiments to be conducted by one of the early IGY satellites and funded by the National Science Foundation. The development of the instrument was in the capable hands of George H. Ludwig, a former Air Force pilot and a graduate student at Iowa. He introduced many novel features including the use of then new transistors throughout the electronics and the design and construction of a miniature magnetic tape recorder.

Following the Soviet's successful flights of the first earth satellite Sputnik I and then Sputnik II, the Army's rocket vehicle Jupiter C was adopted as a U.S. alternative to the planned but faltering Vanguard vehicle for placing an early U.S. payload into earth orbit. By virtue of preparedness and good fortune, the Iowa cosmic-ray instrument was selected as the principal element of the payload of the first flight of a four-stage Jupiter C, launched on 31 January 1958 (1 February GMT).

Both the vehicle and our instrument worked. The data from the single Geiger-Mueller tube on Explorer I (as the payload was called) yielded the discovery of the radiation belt of the earth -- a huge region of space populated by energetic charged particles (principally electrons and protons), trapped within the external geomagnetic field. The attempted launch of Explorer II was a vehicular failure, but the launch of Explorer III on 26 March 1958, with an augmented version of the Iowa instrument, was successful. The Explorer III data provided massive confirmation of our earlier discovery and clarified many features of the earlier body of data.

Soon thereafter we were invited to provide radiation-detecting instruments for two satellites for the observation of the effects of several nuclear bombs to be detonated after delivery to high altitudes by rockets. On a time scale of less than three months Carl McIlwain, George Ludwig, and I designed and built the radiation packages for these satellites -- using much smaller and more discriminating detectors, chosen for the first time with knowledge of the existence of the natural radiation belts and the enormous intensity of charged particles therein.

Explorer IV was launched successfully on 26 July 1958. Our apparatus operated as planned and provided the principal body of observations of the artificial radiation belts that were produced by the three high altitude nuclear bursts -- called Argus II, and III. The back-up launch of our apparatus on Explorer V was a vehicular failure. Analysis of our Explorer IV data on the natural radiation belt as well as on the artificial radiation belts from the Argus bursts propelled the entire subject to a new level of understanding and broad scientific interest.

The first Soviet confirmation of the existence of natural radiation belts came from Sputnik III, launched in May 1958.

Late in 1958, the Iowa group supplied radiation detectors on two missions, Pioneer I and Pioneer III, which were intended to impact the moon. The lunar objective was not achieved but our data established the large scale structure and radial dimensions of the region containing geomagnetically trapped radiation. Another lunar flight, Pioneer IV (also unsuccessful in reaching the moon), of our apparatus in early 1959 provided a valuable body of confirmatory data.