James Van Allen, who died yesterday at 91, was largely responsible for the early days of the American space program, and discovered the radiation belts which surround the Earth and are named after him.

The Van Allen belts were discovered by instruments designed by him and carried into space by Explorer I, America’s first satellite. The success of the launch of the 31-lb. rocket gave America’s space mission a badly-needed boost after the Soviet Union’s propaganda coup with the Sputnik program, and Van Allen was featured on the cover of Time magazine in 1959. Time proclaimed that he had given America “a big lead in scientific achievement” and that he was the “key figure in the Cold War’s competition for prestige.”

But his lasting achievement was neither Explorer’s ability to escape the Earth’s pull, nor the propaganda coup which the rocket gave the United States, but the scientific insights which followed the analysis of data gathered from the tiny Geiger counters which Van Allen had devised for the rocket. An entire academic discipline, that of magnetospherical physics, owes its existence to Van Allen’s discoveries.

James Alfred Van Allen was born on September 7, 1914, in Mount Pleasant, Iowa, the son of a lawyer. He was educated locally and was valedictorian of his high school before attending Iowa Wesleyan College, where he studied Physics and Chemistry under Thomas Poulter, for whom he prepared instruments for an expedition to the Antarctic. He received a doctorate from the University of Iowa in 1939, and joined the Carnegie Institute in Washington, D.C., as a research fellow.

When America entered the war, Van Allen signed up to the Navy, where he worked for the Bureau of Ordnance, examining proximity fuses on artillery shells.At the end of the war, he became chief of the high-altitude research facility at Johns Hopkins University’s physics department.

There he devoted much of his attention to captured German V-2 rockets, and the smaller Aerobee which derived from it. In 1946 Van Allen established that the V-2 was capable of reaching a height of 114 miles — at that time the highest any man-made missile had reached — at a speed of 5,450 feet per second.

By 1951 he had become head of the physics department at Iowa State University, though he travelled extensively — to Peru, the Gulf of Alaska and the Arctic — for his research into cosmic radiation, which also involved studies of the geomagnetic North Pole and, in 1957, an expedition to Greenland and Baffin Island, where he carried out the first rocket flight through a “visible aurora.” From the beginning, Van Allen had been keen not only to ensure that rockets were successfully launched, but that they should provide information about aspects of the Earth. In 1950, he helped originate plans for an international scientific study of the planet which culminated in the International Geophysical Year (1957-58) of which the satellite program was the most visible and successful element.

Explorer I’s launch in January 1958 was followed by two further rockets in March, carrying a cigarette-sized “magnetic tape recorder” devised by Van Allen. Explorer IV followed in June, and confirmed the existence of a radiation band 250 miles above the Earth.

He then supervised the Pioneer 10 and 11 rockets, which studied the radiation belts around Jupiter in 1973 and 1974, and went on, five years later, to do the same for Saturn, work which he described in his book “First to Jupiter, Saturn and Beyond” (1981). He continued to survey the results of the Pioneer and Mariner programs over decades.

He was also a significant force in the interplanetary missions to Venus, Mars, Neptune, Saturn, Venus and Uranus, contributing to the Voyager program and the Galileo spacecraft. Much of the knowledge which we now have of the electromagnetic forces, plasmas and radio signals in the solar system derives from the instruments which Van Allen devised and supervised.

Van Allen was a fine teacher, who actively enjoyed conducting a course in the basics of Astronomy for undergraduates. He received numerous honorary degrees and academic honors, including the Crafoord Prize — awarded for scientific achievements which do not come within the scope of the Nobel prizes — in 1989, and the Iowa Broadcasters Association award for 1964.

Though he had pooh-poohed President Reagan’s enthusiasm for a manned space station, always preferring to rely on data from instruments, the president awarded him the National Medal for Science, America’s highest honor in the field, in 1987. Van Allen continued to be skeptical of human ventures into space, and two years ago was publically dismissive of George W Bush’s plans for a moon base and a manned mission to Mars, arguing that robots could provide all the information which might be obtained.

A reserved, pipe-smoking figure, Van Allen remained endlessly fascinated by his discoveries and by the new information which continued to be transmitted from the instruments he had put on satellites which had travelled further from the Earth than any other manmade object.”Certainly one of the most enthralling things about human life,” he once observed, “is the recognition that we live in what, for practical purposes, is a universe without bounds.”

James Van Allen married, in 1945, Abigail Halsey, with whom he had a son and three daughters.