Pioneer program

• 1. Introduction

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  The Pioneer program gave the world its first probes to escape the gravitational pull of the Solar System entirely. Two separate programs shared that name: the first ran from 1958 to 1960, during the earliest, most uncertain days of the Space Age; the second ran from 1965 to 1992, reaching Jupiter, Saturn, and Venus. Together, they asked a simple and staggering question: how far can we go, and what will we find when we get there?

  Among all the craft those programs launched, two stand apart. Pioneer 10 and Pioneer 11 became the first two of only five human-made objects ever to achieve the escape velocity needed to leave the Solar System. Each one carried a golden plaque, engraved with the image of a man and a woman and information about where they came from, addressed to any extraterrestrial intelligence that might one day find them drifting through the dark.

• 2. A Name and Its Rivalry

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  Stephen A. Saliga, chief designer of Air Force exhibits assigned to the Air Force Orientation Group at Wright-Patterson AFB, gave the program its name under circumstances that had nothing to do with engineering. At a briefing, the spacecraft was described to him as a "lunar-orbiting vehicle, with an infrared scanning device." Saliga found the phrase too long, and thought it offered nothing useful for exhibit design.

  He proposed the word "Pioneer" with a pointed logic: the Army had already launched its Explorer satellite and was publicly branding itself as "Pioneers in Space." By adopting the same word, Saliga argued, the Air Force would "make a 'quantum jump' as to who, really, were the 'Pioneers' in space." A name chosen to win a PR battle between military branches would go on to label some of the most consequential missions in the history of exploration.

• 3. The Early Failures

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  Pioneer 0 exploded 77 seconds after launch on the 17th of August 1958, when the Thor rocket carrying it failed. That mission had been meant to orbit the Moon. It was the first launch ever attempted by NASA, the agency freshly formed from the old NACA. The Air Force Ballistic Missile Division, the Army, and NASA all took part in these early attempts, each trying to prove that reaching Earth's escape velocity was even possible.

  The losses kept coming. Pioneer 1, launched on the 11th of October 1958, suffered a partial third-stage failure and missed the Moon. Pioneer 2 failed on the 8th of November 1958 when its third stage gave out entirely. Pioneer P-1, Pioneer P-3, Pioneer P-30, and Pioneer P-31 were all lost to launch vehicle failures between 1959 and 1960. Of all the Able-series probes that attempted lunar orbit, not one succeeded.

  The Juno II probes fared only marginally better. Pioneer 3, launched on the 6th of December 1958, missed the Moon because of a launcher failure, though it did return data from interplanetary space. Pioneer 4 finally achieved Earth's escape velocity on the 3rd of March 1959, completing a lunar flyby. That single success, against a backdrop of repeated failure, was enough to prove the concept and keep the program alive.

• 4. A Network Around the Sun

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  Five years after the last Able-series probe was lost, NASA's Ames Research Center revived the Pioneer name for a fundamentally different kind of mission. Pioneers 6, 7, 8, and 9, launched between December 1965 and November 1968, were not aimed at any planet. They were designed to form an interplanetary space weather network, spread around the Sun at different orbital distances.

  Pioneers 6 and 9 were placed in solar orbits at 0.8 AU from the Sun, giving them orbital periods slightly shorter than Earth's. Pioneers 7 and 8 orbited at 1.1 AU, with periods slightly longer. The practical consequence of those different periods was that each probe, over time, drifted to a position on the far side of the Sun from Earth's perspective. From there, they could detect activity on a face of the Sun that ground-based observatories could not see, providing warning of solar events several days before the Sun's rotation brought that region into view from Earth. Pioneer 9 went inactive in 1983; a fifth spacecraft in this network, Pioneer E, was lost in a launcher failure in August 1969.

• 5. To Jupiter, Saturn, and Beyond

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  Pioneer 10 launched in March 1972, headed for Jupiter. Pioneer 11 followed in April 1973, targeting Jupiter first and then Saturn. Both returned images and scientific data from the outer Solar System, though the pictures they sent back were much less detailed than those the Voyager probes would capture on their own visits roughly five years later.

  What set Pioneers 10 and 11 apart was not image resolution but trajectory. Both were placed on courses that would carry them past the planets and continue accelerating outward, eventually reaching the escape velocity needed to leave the Solar System altogether. They became the first two of only five artificial objects ever to achieve that. A proposed third outer-planet mission, Pioneer H, would have used the flight spare built for Pioneers 10 and 11 on an out-of-ecliptic path in 1974, but it was never launched.

  Each of the two departing probes carried a golden plaque bearing an engraved image of a man and a woman alongside information about the origin and creators of the spacecraft. The plaque was addressed, in effect, to whoever or whatever might someday intercept the probe in the interstellar void.

• 6. Closing with Venus

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  The second Pioneer program ended where the Solar System's inner neighborhood begins. The Pioneer Venus Orbiter, also designated Pioneer Venus 1 and Pioneer 12, launched in May 1978. The Pioneer Venus Multiprobe, Pioneer Venus 2 or Pioneer 13, launched in August 1978. Unlike the flyby missions that had defined most of the program, these missions used orbital insertion and atmospheric entry to study Venus up close.

  The Multiprobe carried several distinct entry vehicles: a Large Probe weighing 300 kilograms that descended on a parachute, and three smaller impactor probes each weighing 75 kilograms, designated the North Probe, the Night Probe, and the Day Probe. The Pioneer Venus Probe Bus served as both transport vehicle and upper atmosphere probe. With these missions, a program that had begun with rockets exploding on the launchpad in 1958 concluded thirty years later with a detailed, multi-point investigation of Earth's nearest planetary neighbor.