In the late 1960s and early 1970s, Pettengill led ground-based radar studies of the surface properties of all of the inner planets, including the Earth's (via a "triple-bounce" experiment: Moon-Earth-Moon). Pettengill also played a leading role in the first radar studies of an asteroid (Icarus, in 1968), a comet (Encke, in 1980), and moons of other planets (the Galilean satellites, starting in 1976). In all of this work, Pettengill made use of radar systems at MIT's Haystack Observatory and Cornell's Arecibo Observatory, systems whose development he had guided for astronomical applications. Also in the 1970s, he was involved in several unmanned missions to Mars (including the Viking program).