Pettengill began his career at the MIT Lincoln Laboratory in 1954. By the late 1950s, he was part of a group using the then-new Millstone Hill radar for the earliest work in radar astronomy. When it became operational in late 1957, Pettengill used this radar to "skin track" Sputnik I, the first such observation of a satellite. His earliest research, extending beyond the Earth's orbit was with this same radar in 1961; he used it to make the first ranging measurements to another planet, Venus. These first observations yielded a value for the astronomical unit in terrestrial units which has stood the test of time and has an accuracy some 3 orders of magnitude greater than had been possible with the armamentarium of classical positional astronomy. Such knowledge was critical for the successful navigation of Mariner 2 to Venus.