Chasing New Horizons

by Alan Stern

  The third reason was that it suddenly put JPL back in the driver’s seat. These were the guys who were at the helm of every past, stillborn Pluto mission, who lost the competition to us, and then seemed to try to get us killed because, we suspected, “if they can’t have it then no one can.” Apparently, now, JPL had found a new way back in. If that stage cost too much, or if it weighed too much, or if it wasn’t ready for the vehicle launch approval in time for the Jupiter launch window—anything—we would never get launched.

  The whole concept had risk written all over it for New Horizons, so Alan came up with the only plan he could think of to save the project from this new potentially fatal detour. Alan:

  On the phone with Weiler I said, “I hear you, Ed; we’re very glad to be at the top of the Decadal, and we’ll study how to add the electric propulsion for you.” Then I put the phone down and made a plan to completely circumvent adding that electric propulsion stage boat anchor to New Horizons by running out the clock on Ed, knowing that eventually NASA would have to drop the solar-electric-ion stage in order to make the only launch window of the top-ranked Decadal mission.

  Alan got the team together and, a couple of days later, made a call to NASA Headquarters. He said New Horizons wanted to start the solar-electric study, and then provided NASA with an impossibly long list of data items that they needed in order to begin. Alan:

  We more or less created a ridiculous homework assignment for them, probably months of work, but we only gave them a month to do it. When the deadline came a month later, of course the information we asked for was not complete, and we used every incomplete item as a reason to send them back with even more homework: define this better, finish that in more detail, et cetera.… We basically kept them in the mode of never being ready to design that electric stage we didn’t need. And we knew we would win by running out the clock because the Mission Confirmation Review was coming in the spring, and with the Decadal now firmly supporting us, NASA could not stop New Horizons over the lack of readiness of this unneeded add-on propulsion stage.

  And that is exactly what happened. In the spring of 2003, New Horizons had its Mission Confirmation Review. The team had, over the past two years, successfully passed each precursor technical review, scoring A’s across the board at their nonadvocate cost review, their preliminary design reviews, and their systems requirement reviews—all of them. But the MCR was “do or die”—the gate every mission must pass to begin building their spacecraft.

  The New Horizons’ MCR review was held at NASA Headquarters in Washington in March of 2003, and New Horizons passed: without the ion stage.

  Nearly fourteen long years after it all began in 1989, a mission to Pluto was now approved for construction and its funding was finally secure. Behind them now, at long last, was the seemingly endless era of studies, funding battles, and politics. Ahead was a spaceflight project—building, launching, and flying New Horizons to explore Pluto and the Kuiper Belt—the final planetary frontier of our solar system.

  ALABAMA

  After the Decadal Survey battle was won and after killing off Weiler’s cumbersome solar electric-propulsion stage, New Horizons seemed finally out of its endless political battles. But there was still one final twist ahead: now that the mission was past MCR and approved to be built, JPL raised the question with NASA of which NASA development center would manage New Horizons. And because all of NASA’s planetary missions back then were managed by JPL, JPL volunteered to be responsible to also handle New Horizons.

  When Tom Krimigis and Alan got wind of that, they saw that JPL was in effect offering NASA to put themselves in charge of the very mission that had beat them in the Pluto mission competition. Beyond the obvious conflict of interest, Alan and Tom suspected that JPL management saw New Horizons as an existential threat to JPL’s more or less monopoly on outer solar system exploration for NASA. Losing the NEAR asteroid mission to APL had been a blow to JPL back in the 1990s, but NEAR was a pretty simple, close-to-home planetary mission and JPL learned to stomach competition in the “minor leagues” of close to Earth planetary exploration. If JPL now lost their franchise on the outer solar system—the far away “big leagues” of planetary exploration, and had to sit on the sidelines while APL built NASA’s mission to the farthest world in history, then JPL would soon likely have to compete for every future planetary mission.

  Alan and Tom tried to talk NASA Headquarters out of putting their former rival in charge of the project office, explaining the conflict of interest, but to no avail. So once more they had to turn to their champion, Maryland’s powerful Senator Mikulski, who negotiated with NASA Headquarters to have the NASA New Horizons project office set up on neutral ground, at NASA’s Marshall Space Flight Center in Huntsville, Alabama. Once again, Mikulski had saved the day. Alan:

  Someday there really should be a “Mikulski Crater” or “Mount Mikulski” named on Pluto or Charon. She sure earned it.

  6

  BUILDING THE BIRD

  THE CORPS OF EXPLORATION

  The full New Horizons team that designed, built, and flew the mission involved more than twenty-five hundred men and women. Alan often referred to them as the “Corps of Exploration,” a name inspired by Lewis and Clark’s intrepid company two centuries before New Horizons.

  About half the total New Horizons force worked on its launch vehicle: a two-stage Atlas V rocket and its custom third stage. About a third more of that workforce designed and built the spacecraft and the science instruments, and planned or executed the mission operations. The remainder were employed on nuclear launch approval, on the science team, on public outreach, and other efforts.

  This workforce stretched far beyond SwRI and APL, with more than a hundred participating companies and universities, plus NASA, and other government agencies in the mix. Major subcontracts under APL, SwRI, or NASA included Ball Aerospace, which built the “Ralph” camera spectrometer instrument; JPL, which provided the Deep Space Network that would keep New Horizons in contact with Earth; Lockheed Martin, which provided the giant Atlas V rocket; Boeing, for the third-stage rocket that the mission needed to supplement the Atlas V and speed New Horizons toward its Jupiter encounter; Aerojet (now Aerojet Rocketdyne), for both the spacecraft propulsion system and Atlas V solid rocket boosters; and Honeywell, which produced the gyros that would help New Horizons stay oriented in space.

  Organizationally, the project was led from Alan’s office at SwRI in Boulder, with his staff organized under an “Office of the PI.” But most day-to-day engineering and mission operations fell to APL, which designed and built the spacecraft and operated its mission control. SwRI led the development of the seven scientific instruments and developed and staffed the mission’s science operations center.

  APL’s project boss during the proposal and early design/build stages was Tom Coughlin; when Tom retired due to health problems in late 2003, Tom Krimigis asked Alan for his pick to replace Tom Coughlin. Alan asked for Glen Fountain.

  Glen was a highly experienced project manager and veteran of many space missions at APL, and he’d forged a close and trusting relationship with Alan. Like Clyde Tombaugh, Glen grew up in a small Kansas farm town and wound up exploring the farthest reaches of the solar system.

  During the proposal phase of New Horizons, Glen was running the engineering branch of APL’s space department, and he helped orchestrate the mission’s technical development. “Basically,” Glen recalls, “Alan came and lived down the hall from me for three months while we wrote that proposal.” Later, after New Horizons was selected, Glen became the point man for “nuclear launch approval”—navigating New Horizons through the labyrinth of regulatory hurdles required to launch a spacecraft powered by plutonium.

  At SwRI, Bill Gibson was both payload and project manager, responsible for corralling all seven scientific instruments through design, development, and testing and also responsible for day-to-day budgets, schedules, and subcontract management. Gibson was SwRI’s most experienced spacecr
aft project manager and a gifted people person, whose quiet Southern accent helped calm even the most stressful decision meetings.

  At both SwRI and APL, New Horizons, the sexy “first mission to the last planet,” had been able to have the pick of the litter for both the engineering and mission operations team leads, recruiting an all-star team of talented and dedicated managers in the prime of their careers, with deep technical experience and unrelenting drive. The backbreaking, four-year design/development/test/launch schedule demanded nothing less. It also demanded intensive travel, work on nights, weekends, and holidays, and all-out commitment to perfection, since there was no tolerance in the schedule for “redo’s” and no second spacecraft or launcher if New Horizons failed.

  MAINTAINING THE LINK

  As we described before, New Horizons had the intense challenge of pulling off its mission on a lot less money than its predecessor, Voyager—five times less on an inflation-adjusted basis—and this required some tough thinking on how and where it made sense to save money, and where not to.

  Inventing a new spacecraft costs a lot of money because every part and process must be tested and proven to ensure that it will survive the rigors of the long trip on its own. Both to save money and to increase reliability, New Horizons borrowed electronics designs from previous APL planetary missions, avoiding starting from scratch whenever possible. For example, APL more or less cloned the spacecraft command-and-data-handling system from its just completed MESSENGER and CONTOUR spacecraft, and SwRI built the “Alice” ultraviolet spectrometer largely following an Alice ultraviolet spectrometer design it had used for the Rosetta comet-orbiter mission.

  One area where New Horizons made important advances was the telecommunications system, the vital radio link between Earth and the spacecraft, which manages the transfer of information in both directions—commands from Earth to the spacecraft, and data and health reports (“telemetry”) from the spacecraft back to Earth. As we described earlier, the New Horizons team made a decision to reduce the telecommunications capability at Pluto because antennas are heavy and deep-space transmitters are power hungry, and also because reducing the communications capacity saved money to help fit in NASA’s budget. But that meant that it would then take more than a year after the Pluto flyby to get all the precious data on the ground. Alan told the team: “If we don’t fit it in the cost box, we’re not flying. I know you’d rather have faster bit rates, but if you want to actually get to Pluto, we have to meet NASA’s cost target, and that means making compromises.”

  The clever design decisions used to create the frugal, lightweight telecom system for New Horizons illustrate just one example of the many decisions made, from propulsion to guidance to data storage to thermal control, to create an outer planets spacecraft that broke the mold on cost.

  CHOOSING A ROCKET

  To get to Pluto as fast as possible, the New Horizons team had to build a very light spacecraft and buy a powerful rocket. That combination (along with a Jupiter gravity assist) was the recipe for the highest possible speed to cross the solar system. At the time New Horizons was started, the United States didn’t have a powerful enough rocket that was already operational, but two powerful new rockets were in development. Lockheed Martin was building a massive new launcher called the Atlas V, and Boeing was building another new rocket called the Delta IV. Both were to be enormous: over two hundred feet tall and capable of generating millions of pounds of thrust at launch.

  Boeing and Lockheed Martin were fierce competitors, fighting to win contracts for every launch. In 2002 and 2003 when New Horizons was being designed, NASA and the New Horizons team went through a careful process to choose between the two rockets, comparing, for example, how each required different spacecraft mounting, and each had different performance specs, acceleration and vibration environments, and costs. In the end, Atlas V won the day over Delta IV, in part because the Atlas was likely to be ready earlier and had more launches planned to prove itself before 2006 arrived.

  The most powerful version of the Atlas V, called the 551, was selected to power New Horizons on its way. The first stage of this monster rocket is 107 feet high and 12.5 feet in diameter and is centered around a powerful, Russian-built engine that burns liquid oxygen and kerosene. Attached to that first stage are five gigantic solid rocket motors, which fire in tandem with the first stage. Together they would loft New Horizons (and the rocket’s upper stages) to hypersonic speeds of over ten thousand miles per hour. Atop that was a second stage, called Centaur. It’s forty-two feet high and is powered by an American-made Aerojet Rocketdyne RL-10 engine that provides 22,300 pounds of thrust. Significantly, the Centaur stage can be started and stopped multiple times, which was necessary to put New Horizons onto the right course to Jupiter.

  Encasing both the Centaur—and New Horizons atop it—is the rocket’s “fairing,” or nose cone, designed to protect the spacecraft from the fierce wind forces generated by launch. New Horizons ordered the lightest-weight Atlas 551 nose cone, which saved weight and further improved the 551’s launch performance.

  Yet even this maxed-out Atlas V 551 still wasn’t powerful enough to loft New Horizons on its way to Pluto. Centaur could put New Horizons into Earth orbit, and then take it out into an orbit that would carry it as far as the asteroid belt beyond Mars. But to achieve the performance to reach Jupiter and then Pluto, it was necessary to add a custom-built third stage atop the Atlas V. For this, the New Horizons team selected a highly reliable, well-proven solid rocket fuel third stage, called a STAR 48. That stage, which would fire for a brief eighty-two seconds, would accelerate New Horizons to almost 14 G’s and make it the fastest spacecraft ever launched, capable of reaching the orbit of the Moon ten times faster than the Apollo missions did and flying on with that speed for almost a decade to cross the 3 billion miles to Pluto.

  TAKING PLUTONIUM TO PLUTO

  How does one power a spacecraft that will be traveling for at least a decade on a journey so far from the Sun that our star shines there at less than a thousandth of its brightness at Earth? Solar arrays won’t work that far from the Sun, and no battery is powerful and light enough to do the job of powering a decade-long mission. But the radioactive decay of plutonium (an element that was discovered in 1940 and was named for Pluto) passively generates heat without fail—and that heat can be turned into electricity. For this reason, plutonium-fueled nuclear batteries have been the power supplies of choice for deep-space interplanetary missions to the most distant planets from the Sun. But carrying a plutonium-fueled nuclear battery introduced its own complexities: some technical, but others political and regulatory.

  NASA, along with the Department of Energy and the Department of Defense, perfected, tested, and flew many plutonium power batteries for just this purpose beginning in the 1960s. These devices are called Radioisotope Thermoelectric Generators, or RTGs. RTGs are cylindrical in shape and about the size of an oil drum; because the plutonium generates so much heat, RTGs are equipped with cooling fins. RTGs have two primary jobs: one is to power their spacecraft, and the other is to contain their plutonium in the event of a launch accident.

  The plutonium used in RTGs is packaged in small pellets made of plutonium dioxide. These pellets are in turn clad in iridium and bottled up inside the RTG’s black graphite casing.

  As an RTG creates heat from the radioactive decay of its plutonium, that heat gets turned into useful power through simple, completely passive devices called thermocouples. Thermocouples have two sides, one inside the RTG that’s hot, and one on the outside of the RTG, facing space, that’s cold. The temperature difference across the thermocouples generates an electrical current, which is what powers the spacecraft. The amount of heat generated by the RTG on New Horizons is about five kilowatts, and from that it produced about 250 watts of electricity to power the spacecraft when it launched.

  RTGs are extremely reliable. They produce power at a steady but slowly declining rate and can be operated for decades. Their decline in p
ower with time is due to the radioactive half-life of the plutonium. For new Horizons, the 250 watts its RTG generated at launch declined to about 200 watts a decade later at the time the spacecraft reached Pluto.

  In 2001, when NASA announced it would conduct a competition for missions to explore Pluto, the Agency owned two spare RTGs from the development of its Galileo mission to Jupiter and its Cassini mission to Saturn. NASA offered to provide the winning Pluto mission provider with either of these RTGs.

  Once selected, the spare RTG for New Horizons had to be disassembled and fully inspected (after all, it had been in storage for over ten years) and then rebuilt. Lockheed Martin served as the contractor to refurbish the RTG; the Department of Energy’s Los Alamos National Laboratory then prepared the plutonium to fuel it.

  While that work was going on, there was an elaborate, parallel effort that all RTG missions undergo to assess the risks of a launch accident, including the preparation of a comprehensive environmental impact statement, which addressed those risks and showed that they had been reduced to acceptable levels. This rigorous approval process involved forty-two state and federal agencies, up through the State Department and a sign-off by the White House.

  Glen Fountain supervised this complex process. Glen:

  We managed it knowing that we didn’t have the seven or eight years it would normally take. We had four, and that was a tough challenge.

  Using an RTG solved the problem of how to power a mission going so far from the Sun, but it also posed its engineering challenges for the designers of New Horizons.

  For example, the RTG is heavy, weighing more than 125 pounds. So during launch the structure holding it has to support its weight multiplied by the G-forces the rocket stages for New Horizons produced—up to 14 G’s at maximum acceleration, making it weigh fourteen times what it normally would on the ground. So the joint holding the RTG had to be able to withstand a force of 14 times the RTG’s normal weight. This challenge was made even tougher by the heat the RTG creates, which acts to weaken the metal in the support joint. So New Horizons engineers had to design the joint to be strong enough to support its weight against the G-forces during launch, even when the joint was hot.