In conjunction with Venus [planetary radar astronomy]

Few people know that the value of the astronomical unit-the mean distance from the Earth to the Sun, and the yardstick for gauging distances within the solar system-was determined not by astronomers, but electrical engineers. They did it using military radar and thereby opened up a new field of scientific research, known as planetary radar astronomy. The paper discusses the early history of planetary radar astronomy up until the mid 1960s.