But his first love was astronomy, and he often rode his bike to the Harvard College Observatory.
Misled by the leather patches on the Harvard astronomer Fred Whipple’s jacket into thinking that scientists led lives of genteel poverty, he chose to major in chemical engineering at Northeastern University, graduating in 1954 with a bachelor’s degree.
That same year he married Tamara Samoiloff, a former high school and college classmate. That marriage ended in divorce, as did a second marriage, to Susan Armstrong. Besides Ms. McGregor, an artist in Santa Fe, he is survived by three children from his first marriage, Kari Rasmason, Hillary Tolmen and Randall Smith; five grandchildren; and five great-grandchildren.
After college he joined the Army and was assigned to be the liaison to a group of astronomers led by Clyde Tombaugh, famous as the discoverer of Pluto, that was searching for satellites of the moon. Following his service, he went to work with Mr. Tombaugh at New Mexico State University, becoming director of planetary research.
In 1958 he and Mr. Tombaugh initiated the first program to photograph the brighter planets in a routine systematic way, but that was only a gateway drug to the solar system. His cameras and devices went to Mars on the Mariner 6 and Mariner 7 spacecraft, and he was the deputy leader of the imaging team on Mariner 9, which became the first spacecraft to orbit another planet when it slipped into place around Mars in 1971.
All this before he had attained a Ph.D. Advised by a NASA friend that he wouldn’t get anywhere without one, he finished a dissertation and was awarded his doctorate, New Mexico’s first in astronomy, in January 1973.
At about the same time he was named leader of the imaging team for the Voyager mission, an ambitious project to send a pair of probes to the outer solar system, taking advantage of rare planetary alignment to slingshot the probes from one planet to another, starting with Jupiter.