The Spacecraft That Will Not Die
THE DARK EMPTINESS BEYOND PLUTO, THE FARTHEST planet in our solar system, defies comprehension. The sun is little more than a bright star in that void, Earth lost in its feeble glare. Yet even out there, there’s a little piece of Earth. Almost seven billion miles from home, faithfully calling back to a planet that has almost forgotten it exists, is humankind’s oldest functioning spacecraft, Pioneer 10. After trailblazing the path into the outer solar system as the first space probe to Jupiter, Pioneer 10 confounds its makers by functioning long past its expected life span, returning useful data nearly 30 years after its launch. And back on Earth, only a few people are still listening.
One is Dr. Larry Lasher, Pioneer ’s current project manager. Although NASA headquarters officially ended the project in 1997, Lasher and a small team of diehards managed to wangle the facilities to maintain Pioneer 10’s link with Earth. “No one seems to want to let it go, even if it requires coming in after hours or on weekends,” says Lasher. “Some will come in the middle of the night because that was the time commands had to be sent up.”
The people involved in space exploration tend to be very dedicated—they have to be to overcome the technical, financial, and physical obstacles that come with the work. But volunteering your weekends and late nights for a project that even your bosses think of as extinct is decidedly above and beyond the call. How does this humble spacecraft, built with 1960s technology, weighing less than 600 pounds, and smaller than a compact car, inspire such devotion? Maybe by proving that sometimes simpler really is better. The story of Pioneer 10 remains an impressive example of what can be accomplished by a team of skilled scientists and engineers working on a limited budget while opening up brand-new scientific frontiers.
Proposals for a deep-space mission to the outer planets began bouncing around NASA circles in the early 1960s, but not until early 1969, in the heyday of the Apollo moon program, was official approval for a Jupiter mission granted. The sterling performance of NASA’s Ames Research Center, in Mountain View, California, on an earlier series of Pioneer solar probes persuaded headquarters to give it the Jupiter project. Pioneer 10 would investigate the interplanetary medium, assess the dangers of the asteroid belt between Mars and Jupiter, and make the first flyby of Jupiter. An identical sister craft, Pioneer 11 , would follow a year later.
Time was crucial. The best time to send a spacecraft to Jupiter occurs about every 13 months, when the planet’s position relative to Earth permits a launch at minimal energy. Allowing for the design and construction of the spacecraft and the selection of scientific experiments, Pioneer ’s first launch window would open in late February to early March of 1972. To avoid the time-consuming process of competitive bidding for a prime contractor of the spacecraft, the project manager, Charles F. Hall, pushed for a “sole source” selection of TRW, Inc., the builder of the previous Pioneers. Hall assigned TRW to complete a design study, and NASA review committees began ruthlessly winnowing down more than 150 initial experiment proposals to the final 11 chosen for the mission. The scientists behind those experiments—the “principal investigators”—constituted a roll call of the world’s most distinguished planetary astronomers and physicists, including John Simpson of the University of Chicago and James Van Alien, discoverer of the Van Alien belt.
Despite Pioneer ’s ambitiousness, Hall insisted on simplicity and reliability in every aspect of the spacecraft and its mission. To avoid the expense and complexity of a threeaxis stabilization thruster system, with separate thrusters for pitch, yaw, and roll, the Pioneer craft would be spinstabilized. Once released on its Jupiter trajectory by its launch booster, it would be set spinning around its axis at about five revolutions per minute, like a cosmic top. As Daze Lozier, a trajectory specialist on the project, observes, “The spinning spacecraft idea sure made things simple. If we lost communication, we always knew it was going to be pointed in the same direction.” Three pairs of small thrusters, evenly spaced around the rim of the nine-foot main antenna, would control Pioneer ’s spin rate, velocity, and orientation.
Hall also made sure that wherever possible, only component designs previously tested in space flight were used. Bernard J. O’Brien, who headed the Pioneer effort at TRW, points out that the Pioneer 10 spacecraft design was essentially an evolved refinement of TRWs earlier models. “We used a lot of the same design concepts,” he says, “which in turn helped the cost and schedule. I think Charlie was smart in doing that.” Redundancy was built into vital systems such as the radio transmitters and receivers (two of each), with the craft designed to switch automatically to backup systems should a primary fail. “Charlie insisted that wherever there was an automatic system, we’d be able to bypass it,” says Jack Dyer, who was the mission analysis chief.
Such flexibility was crucial, for unlike later probes, Pioneer 10 lacked an onboard computer. “It was a real-time spacecraft,” Lozier says. “Everything you wanted to do was commanded from Earth.” Microprocessors and sophisticated integrated circuits were still only engineering pipe dreams, and a full-blown onboard computer would have been much too heavy and power-hungry. Lozier explains that Pioneer had a limited memory that could store up to five commands, used when the craft was out of direct contact or when commands had to be executed in faster sequence than could be transmitted from Earth. Otherwise, it was literally flown from the ground by remote control.
But because the spacecraft lacked a “brain” and thus wasn’t self-sufficient, dependable communications were absolutely vital. With the time lag between message transmission and reception ever increasing as Pioneer sped away from Earth, spacecraft maneuvers and possible problems would have to be anticipated well in advance. And over the immense distances to the outer solar system, Pioneer ’s eight-watt signal would become a mere whisper, lacking enough energy to power the dimmest night-light and pushing the extremely sensitive 70-meter antenna dishes of NASA’s worldwide Deep Space Network to their limits.
Designing a spacecraft is always a series of tradeoffs between what you want to do and what you can do, given your unavoidable limitations of budget, time, and technology. Electrical power is always precious and must be carefully rationed. Weight—or, more precisely, mass—is always critical, because the greater the mass, the greater the energy you need to send it someplace. The Pioneer craft had to be small and light enough for an Atlas-Centaur rocket, its specified launch vehicle, to lift it into space and put it on the proper trajectory going fast enough to reach Jupiter. But at only 570 pounds, it was a featherweight compared with the massive Voyager and Galileo probes that would follow. Pioneer ’s final form evolved in an intense back-and-forth between Charles Hall and Herb Lassen, the TRW engineer who authored TRWs initial proposal. It wasn’t an easy process. “The conceptual design was by Herb Lassen,” Hall recalled in a 1999 interview. “He started out laying out various designs and presenting them, and he knew I wasn’t liking them. So then I’d present something I’d been thinking about, and I knew he didn’t like them . I’d say, ‘Keep trying. It’ll come.’ Finally one day he calls up and says, ‘Get down here fast! I’ve got it!’ So I go down there, and he presented the Pioneer 10 and 11 that were actually built. It was obvious that it was just a breakthrough.”
Lassen had conceived an elegant and ingenious design. “He had thrown all constraints out the window,” Hall said. “And some of the constraints were artificial because people assumed something that was not necessarily true.” One assumption concerned the fundamental nature of the spin stabilization concept. “Most people in designing a spacecraft have the spin axis go through the center of the antenna so it won’t wobble,” Hall explained. A wobbling antenna dish could lead to a slight fluctuation in signal power back at Earth. “Herb threw that out and said it doesn’t matter. We’re talking about 8 centimeters out of about 60 billion kilometers.”
Some big questions still remained, including how to power the craft. All previous probes had stayed within the orbit of Mars, close enough to the sun so that solar panels could easily provide adequate electricity. But out at Jupiter, 485 million miles from the sun, light is only a twenty-seventh as bright as on Earth. Pioneer would need very large and delicate solar panels. Some previous spacecraft had used radioisotope thermoelectric generators (RTGs), devices that produce electricity using the heat emitted by small capsules of decaying plutonium 238. But early RTGs were considered too unreliable for long-term use, especially for a deep-space mission like Pioneer .
With all their limitations, solar panels seemed the only answer—until a representative of the Atomic Energy Commission informed Hall that the AEC and the Teledyne Corporation had developed a new RTG model, the SNAP-19, that through more advanced design promised a much longer service life. “He was really anxious to get a spacecraft to put a unit on, and ours was the only one at that time of an interplanetary nature,” Hall said. “He said, ‘We’ll build the prototypes free, and all you have to do is pay for the flight units.’ Well, this was a big bonus. Saving us 15 million bucks —I couldn’t turn that down.” Four SNAP-19s would provide about 155 watts of power. Their output would slowly decrease over time because of the deterioration of the thermocouple junctions, but there would still be plenty of power available at Jupiter.
Although the RTGs solved Pioneer ’s power problem, their residual radiation threatened to interfere with some of the craft’s scientific instruments, forcing other modifications. Placing the RTGs away from the craft at the end of 10-foot-long booms helped, but not enough. Hall recalled that “some of the scientists had to add more shielding,” which also meant more weight. But Hall had anticipated this. “Fortunately, I had about 50 or 60 pounds of contingency that I could dole out.” For problems like these, he said, “you had three choices: Don’t do anything, spend a lot of money, or add a little weight in the right places.” Hall’s preference was obvious.
His keep-it-simple credo led to some lively debates among Pioneer ’s designers, scientists, and project personnel. “There were massive negotiations on things like power and weight,” says James Van Alien, “hashed out in a series of group meetings in which we traded back and forth one thing for another.” Scientists and engineers presented laundry lists of problems and concerns and mutually agreed on solutions. Once decisions were made, Hall vigorously resisted pressures to continually modify and perfect them. Jack Dyer says, “Charlie viewed it as a contract: Now let’s do that and not get distracted by trying to make it better, because we’re going to do it within budget when Jupiter’s ready at the right place.”
With the spacecraft design established, experiments selected, and launch window conformed, construction of Pioneer 10 began at TRW, its subcontractors, and the principal investigators’ various institutions. “We didn’t have an awful lot of time,” O’Brien admits. But his company had quite an incentive. “There was a million-dollar penalty if we were not ready to launch in February-March 1972,” he recalls. “And I’d have lost my job.”
O’Brien kept his job. On March 2, 1972, at 8:49 P.M . Eastern time, Pioneer 10 lifted off from Cape Kennedy snugly within its launch window. Less than half an hour later, it set course for Jupiter, tarveling faster than any other previous human-made object, more than 32,000 miles per hour. Over the next few weeks, flight controllers remotely calibrated the science instruments and tweaked the spacecraft’s trajectory. The flight soon scored its first scientific triumph by proving that the zodiacal light, a faint glow of sunlight reflected from dust particles along the plane of the zodiac, was an interplanetary, not Earth-generated, phenomenon.
More discoveries would follow, but not before Pioneer 10 faced its greatest hazards. The first hurdle came after Mars: the asteroid belt, the unavoidable threshold to the outer solar system. (Flying above the belt is possible, but only at the cost of enormous launch energies, far too expensive for planetary missions.) In the vastness of the belt, the chances Pioneer would pass anywhere near a large asteroid were minuscule. But how many smaller rocks drifted among the big ones? At the craft’s great velocity, a particle the size of a grain of sand could pierce the hull with more energy than a high-powered rifle bullet and destroy vital systems. Even a rock no bigger than a baseball could completely take out the spacecraft. A failure here would be worse than at Jupiter, for there at least some valuable data would have been obtained. When Pioneer entered the danger zone, plans were already on NASA’s drawing boards for Voyager and other deep-space missions, and they all depended on Pioneer 10 ’s safe passage. The transit would last about seven months, with possible disaster looming every day.
The craft didn’t simply cruise along waiting passively for catastrophe during those seven months, however. Its scientific instruments busily probed the interplanetary environment, recording new data on cosmic rays, magnetic fields, and the solar wind. Meanwhile, its meteoroid detectors counted impacts from asteroid particles. Much to everyone’s surprise and relief, far fewer hits were registered than expected. The date with Jupiter was still on.
And so was Pioneer ’s next challenge: penetration of Jupiter’s lethal radiation belts. Jupiter is an enormously powerful source of radio signals, produced by whirling charged particles trapped in an intense magnetic field. No one knew just how strong the radiation might be or how deeply the zone could be penetrated by a spacecraft without its electronics being fried into slag. John Simpson puts it succinctly: “There was no assurance, since we were the first spacecraft in those radiation regions, that we would survive to come out.” As in the asteroid belt, Pioneer 10 would again play the brave scout sent through no man’s land to draw fire for those to follow.
In mid-November 1973, Pioneer 10 crossed Jupiter’s bow shock, the invisible zone in which the onrushing solar wind is deflected away from the planet by its magnetosphere. Now tension and excitement mounted in equal proportion as the radiation levels rose and the scientific bounty poured in. “Every hour we found something new,” says Van Alien. “It was a period of intense discovery.” Pioneer mapped Jupiter’s magnetic field, measured its mass and temperature, probed its atmosphere, analyzed its radiation, and took the first pictures of the planet from outside Earth’s atmosphere.
Because Pioneer ’s weak signal dictated a slow data rate, the images trickled in painfully at only 1,024 bits per second. But any pictures were a bonus. The craft didn’t even have an actual camera; it couldn’t have been held steady enough as Pioneer spun. Instead, an imaging photopolarimeter, a kind of light-sensitive phototube for measuring light intensity and wavelength, swept across the planet in sequential strips with a small narrow-angle telescope as Pioneer rotated. Earthbound computers constructed images in true color from the polarimeter’s scans of red and blue light. A Pioneer Image Converter System, developed by the University of Arizona, converted these into real-time video images for the press and television networks. Although hardly the gorgeously resolved marvels that Voyager would later provide, the pictures awed both the public and the scientific world and even won NASA’s Ames Research Center an Emmy award.
As periapsis, the point of Pioneer 10 ’s closest approach to Jupiter, drew near, the control center at Ames was flooded with scientists, technicians, engineers, and NASA officials. TRW personnel were also on hand. Once the spacecraft was launched, they had no further contractual responsibility, but the urge to watch their baby confront its ultimate challenge was too much to resist.
As Pioneer 10 reached its destination, sleep became a rare commodity and black coffee a staple. For those at mission control, a planetary encounter is a blur of long hours of waiting, brief flares of excitement, hurried meals, intense discussions, daily press briefings, and constant meetings. Hall was using a particularly infamous management technique called the “standup meeting.” Van Alien recalls, “He was famous for the idea that the way to have a brisk, get-to-the-point meeting was not to let anyone sit down.” Every morning, standing up, Hall, the principal investigators, and the operations staff exchanged five-minute reports on their activities, discoveries, and problems of the past 24 hours and planned the day to come.
Pioneer was fast approaching its moment of truth in Jupiter’s radiation field. “All of us were finding an enormous intensity of radiation,” says Van Alien, “and the question was whether the spacecraft was really going to survive the closest approach or not, whether some systems would be knocked down.”
Shortly before 6:30 P.M. Pacific time, on December 3, 1973, Pioneer 10 passed only 81,000 miles above the clouds of Jupiter, battered by radiation, some instruments saturated beyond their limits to register—but still alive and functioning. As Van Alien remembers, “We passed through periapsis and kept on going, and the intensity started going down. We were all cheering that the little spacecraft had made it.”
The suspense wasn’t over yet, though. Pioneer now began to swing around the far side of Jupiter, where it would be on its own, out of communication with home. Although it was speeding away from the planet, the craft was still deep within the radiation belt and so not yet out of the woods. “Everybody was scared and praying it would be alive when it emerged,” says O’Brien.
A tense hour of standing around, chewing nails and pencils, and gulping the always present coffee ensued as everyone waited for Pioneer to call home. Few gatherings are as helplessly anxious as a team of scientists, engineers, and flight controllers waiting to hear from an out-of-touch spacecraft. Some resort to gambling. O’Brien recalls, “I made a bet with one of our scientists that we would survive the radiation belt of Jupiter, and he bet we wouldn’t.”
Slowly, as the time for signal reacquisition arrived, the Image Converter System at Ames Research Center began to show a picture, pixel by pixel. The Pioneer team watched a bright line slowly become a crescent on their screens. They were seeing something no one had ever witnessed before: sunrise on Jupiter, as the polarimeter looked back toward the planet.
Hall, O’Brien, and the rest of the Pioneer team had won their bets. And Pioneer 10 now accomplished its last major objective, using Jupiter’s gravity and orbital momentum to hurl itself out of the solar system and toward interstellar space at 25,000 miles an hour, proving the feasibility of the gravity-boost technique for future missions to Saturn and beyond. O’Brien later collected his prize, an order of Beefeater stew.
As the research scientists began the years-long task of sifting through and analyzing their treasure trove of new information, controllers retargeted Pioneer 11 , which had been launched in April 1973 to follow Pioneer 10 ’s path. Now the newer craft set out on its own trajectory, to fill in the scientific blanks left by its older sister at Jupiter; they would later use Jupiter’s gravity assist to send Pioneer 11 on to the first Saturn encounter, in 1979. Everyone now considered Pioneer 10 a complete and unadulterated success—and assumed that its story was all but over.
They were only half-right. The Pioneer Jupiter mission was definitely a historic triumph of science and engineering, but the spacecraft refused to go gentle into the night of interstellar space. It still had a few more surprises to spring.
“It’s a lot of incentive to work on something that man has never done before,” Charles Hall observed in 1999. But the existence of a dedicated support team hardly explains how Pioneer 10 has defied the odds to survive two decades longer than its creators expected. Is it a matter of pure luck, or could its success be repeated today?
With Hall’s emphasis on keeping hardware simple and mission objectives sharply defined, the Pioneer project is a paragon of NASA’s “faster, better, cheaper” philosophy. Even 30 years later, it’s a superb demonstration of strong and responsive project management, constant communication among the engineers designing the spacecraft and the scientists conceiving the mission, accountability at all levels, and the conscientious dedication of the prime contractor. John Simpson points out that they all were doing “faster, better, cheaper” long before it became NASA’s mantra in the 1990s. James Van Alien agrees: “As far as I’m concerned, NASA just rediscovered the principle.”
Bernard O’Brien, of TRW, expresses skepticism about that mantra. “My personal opinion,” he says, “is that you can do any two of those and not get into too much trouble. Doing all three is a real challenge.” He adds that “to have done what we did significantly cheaper would have been almost impossible.” Yet at a total cost of about $250 million in today’s money, Pioneer was hardly the billion-dollar extravaganza of the more sophisticated missions that followed.
Pioneer ’s veterans consistently stress the probe’s straight-forward design. “It was part of the philosophy to keep the spacecraft simple, uncomplicated by a lot of electronic wizardry,” says Lozier. The spin stabilization, the use of space-flight-proven systems, the redundancy of vital components, and the navigation and communications techniques that allowed relatively easy ground-based piloting all reduced the risks of irreparable onboard breakdown or malfunction. Hall observed that aside from the RTG power system and some of the science instruments, “the rest of the spacecraft was pretty much standard-type electronics.”
Bernard O’Brien also cites the project’s exhaustive testing of parts and systems before Pioneer ever left the ground. At TRW, he says, “we spent a lot of time, money, and effort making damn sure those parts were designed, built, and tested before we ever brought them into our house from the vendors.” The principal investigators who designed and built Pioneer ’s science packages took the same approach. John Simpson’s Charged Particle Experiment was probably the first scientific instrument ever that could be repaired in space. “It could send the message I’m sick, I’ve lost this detector,’” he says, “and we had in our computer all the options to make the correction by switching amplifiers, and we could send a signal to fix it.”
But simple, reliable design is only part of the picture. No matter how impressively engineered it was, Pioneer 10 could never have done its job without exceptional project personnel under outstanding leadership. Talk to any of the Pioneer team and it won’t be long before Hall’s name is mentioned—always with fondness and with respect verging on awe. “Charlie Hall was really a star,” says Van Alien. “He was one of the most intelligent and responsive project managers I’ve ever worked with in the NASA system. He managed the whole thing with a firm hand but was very constructive and receptive to all the crazy requirements we tried to meet. He was outstanding, no doubt about it.”
The feelings were mutual. “ Pioneer was blessed by so many good people working on it, from the scientists to the lowest technician,” Hall remembered. “I used to sit there and watch the scientists and think, ‘God, what a team we’ve got.’”
Hall died in August 1999. He left behind a legion of friends and colleagues who remember his “intelligence, persistence, and leadership throughout his career,” as the NASA administrator Dan Goldin phrased it in a memorial service. And, of course, he left behind the remarkable Pioneer 10 spacecraft, a legacy that might be almost forgotten by now if not for the dogged efforts of the people Hall inspired and led.
“It has been a real struggle,” James Van Alien says. “I was one of those who gave a eulogy at NASA headquarters on the achievements of Pioneer , and, meanwhile, I was working the hallways trying to keep it going.” At first it wasn’t such a problem. With the spacecraft still functioning well after its Jupiter flyby and headed for unexplored space, NASA extended its mission to find the heliopause, the boundary marking the end of the sun’s sphere of influence. Most scientists had speculated that the heliopause ended around the orbit of Jupiter, but when Pioneer 10 became the first spacecraft to cross the orbit of Pluto, in 1990, it still hadn’t found it. Neither had Pioneer 11 by the time its problematic generators finally gave out and the craft ran out of power in 1995.
Pioneer 10 soldiered on, despite all predictions that it would soon suffer a similar fate. As other important missions demanded Deep Space Network resources, reducing the time that could be spent tracking Pioneer , NASA support and finances dwindled. Hall’s successors cast about tirelessly for ways to justify keeping the project alive. Valuable research still being done on Pioneer data by Simpson and Van Alien helped for a while, but pure science work on particles and fields lacks the public glamour and pretty pictures of spectacular planetary flybys.
NASA headquarters finally pulled the plug on Pioneer 10 in 1997. The spacecraft was still loyally transmitting its data, yet aside from the Pioneer team, no one seemed to care anymore. But if a scientific reason wasn’t enough to keep the project alive, Larry Lasher managed to find a technical one. With Ames now managing the Lunar Prospector project, searching for evidence of water on the moon, Lasher convinced NASA that tracking Pioneer 10 would be a perfect training exercise for Prospector’s controllers, buying Pioneer a couple more years of life.
After Lunar Prospector was intentionally crashed into the moon in 1999, prospects for Pioneer 10 again looked bleak. But the Pioneer diehards were used to that by now, and for once they got lucky. “A white knight came along in the form of a NASA headquarters study on weak signals,” Lasher explains. With more deep-space missions in the pipeline, NASA began developing new techniques of extracting useful telemetry from very faint signals, such as Pioneer 10 ’s distant chirp. For a few more years at least, Lasher has the blessing of headquarters to maintain Pioneer ’s link with home.
Ironically, now that its political problems have receded, mundane earthbound technology threatens to close the books on Pioneer . Technological progress long ago caught up with Pioneer and left it in the dust. Designed to operate in an age of huge mainframe computers and punch cards, Pioneer 10 can’t be controlled by today’s superfast desktop computers. The project’s remaining original Digital Equipment PDP 11-14 computer, standing like a museum piece in the Pioneer control room at Ames, must be kept running in order to transmit navigation commands. Its operations supervisor, Ric Campo, laments, “The equipment is barely keeping alive. Much of the hardware is maintained by stripping cards and interfaces from similar hardware in the Pioneer control center.” The data telemetry system was reconfigured several years ago to run on a Macintosh, but such a fix isn’t possible for the command system. Present-day engineers can still interpret the data sent by Pioneer ’s ancient systems, but Pioneer can’t understand commands not compiled by the computers of its own age.
Another problem is an impending change in the system software of the Deep Space Network (DSN). Lasher explains, “We’re an old project and we have a specific software arrangement that they use to contact our spacecraft, and they’re changing it over in 2001 or 2002. Even if we want to, we can’t then be supported, because the DSN software won’t be able to track it any longer. So we have until about 2002 for a hard cutoff.”
Most of Pioneer ’s science instruments have been turned off to conserve power. Only Van Alien’s Geiger Tube Telescope is still operating—and still looking for the helio-pause. It’s in a scientific horse race to make its final discovery and send the news back home before contact is lost.
Nearly seven billion miles from Earth, Pioneer 10 ’s voice is barely strong enough to be heard and is fast approaching the sensitivity threshold of the Deep Space Network. “It’s hanging on by a thread,” says Lasher. “The signal’s getting weaker and weaker, and I would guess it isn’t going to last that long. But I could be wrong,” he adds. “It’s happened before.”
Inevitably, Pioneer 10 will pass beyond the reach of the huge dishes of the Deep Space Network, and Earth will hear no more from the craft. But in the end, maybe it doesn’t matter. Transmitting or not, Pioneer 10 will outlive all of us and quite probably Earth itself.
One day, about five billion years from now, our sun will expand into a red giant star, consuming Earth and humanity itself, if we haven’t moved elsewhere by then. But something of Earth will survive. Pioneer bears a goldanodized aluminum plaque designed by the astronomers Carl Sagan and Frank Drake to describe the craft’s origins and its makers to any extraterrestrials who may someday intercept it. Long after its planet of origin is dust, Pioneer 10 will still be cruising through the galaxy as our eternal emissary, telling the universe that we were here.
