October 1995 marked the fiftieth anniversary of Arthur C. Clarke's famous article in Wireless World proposing the use of satellites placed in geosynchronous orbit for worldwide communications relay. The article proved prophetic, for it heralded the modern era of telecommunications. Beginning in the early 1960s, several series of satellites were launched into Earth's orbit; collectively they transformed the latter twentieth century, creating a global village of instantaneous communications. Previously, the ionosphere had defined the limits of radio communication; today, by going beyond the...

The past 50 years have brought forward a unique capability to research and expand scientific knowledge of the Solar System through the use of radar to conduct planetary astronomy. This technology involves the aiming of a carefully controlled radio signal at a planet (or some other Solar System target, such as a planetary satellite, an asteroid, or a ring system), detecting its echo, and analyzing the information that the echo carries. This capability has contributed to the scientific knowledge of the Solar System in two fundamental ways. Most directly, planetary radars can produce images of...