A voyage into the solar system 52 years ago

Space probes and planetary orbiters have become so commonplace, the launch of a new one, whether into our solar system or beyond, hardly causes a ripple in the public consciousness. But 52 years ago, March 11, 1960, a beach ball-sized spacecraft was launched from Florida's Cape Canaveral in one of mankind's first attempts to study the solar system from a vantage point other than firmly anchored to Earth's surface. Pioneer 5, looking like a slightly rotund version of the "Star Wars" droid R2-D2 wielding four tennis rackets -- actually solar panels to charge its on-board batteries -- entered an orbit around the sun between Earth and Venus to measure magnetic fields, cosmic radiation, electrical fields and micrometeorites. Lifted aloft in an era when space launches of any kind were avidly followed by millions, Pioneer 5 sent back data back until it reached a then-record 22 million miles from Earth (surpassed in 1962 by the Mariner 2 spacecraft sent to Venus and then on to the sun -- where it is still orbiting today, albeit silently). Pioneer V's most important contributions to our understanding of the solar system were confirmation of the existence of interplanetary magnetic fields and new, more accurate measurements of cosmic radiation. Today spacecraft of the size and mass of a small automobile are routinely lofted into space atop powerful rockets, but in 1960 it was considered a notable feat to send the 93-pound, 2-foot-diameter Pioneer into the solar system on its Thor-Able launch vehicle. With its solar panels held out like a skater's arms, Pioneer was stabilized on its long journey by having it spin slowly around its axis. Unlike modern space probes that can stream gigabytes of data back to Earth in an almost uninterrupted stream, weight limitations on Pioneer 5's solar cells prevented continuous operation of the telemetry transmitters, with just four operations of 25 minutes duration at a maximum of 64 bits per second scheduled each day -- with occasional increases during times of "special interest." In total, just slightly more than 3 megabits of data were received, considered a triumph at the time. Until the distance proved too great for the tiny spacecraft's signal to be received on Earth, it functioned for a then-record 106 days. Pioneer 5 was just one of a series of Pioneer missions accomplishing first-of-their-kind explorations of the moon, sun, Jupiter, Saturn and Venus. Early missions, Pioneer 1 through 4, were intended to simply achieve Earth's escape velocity and study the moon. Later Pioneer missions would go farther and farther into the solar system, with the most notable being Pioneer 10, launched in 1972, and Pioneer 11, launched in 1973, which explored the outer planets before leaving the solar system entirely. The year Pioneer 5 was launched, 1960, was a busy one for interplanetary missions, with seven launches attempted by the United States and the Soviet Union -- of which Pioneer 5 was the only success.