Chasing New Horizons

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Chasing New Horizons Page 21

by Alan Stern

PLANNING TO SHARE THE FLYBY

  Flyby planning wasn’t restricted to just mission science and engineering. One final piece of planning involved finding ways to maximize public engagement during the flyby. This is an area that NASA has a lot of experience in, so New Horizons didn’t start from scratch. But Alan wanted to go big in this, and he created a vision for engaging the public at a level not seen since Apollo, a vision fit to commemorate the first exploration of a new, unexplored planet since Voyager went to Neptune in 1989.

  This began with a formal NASA Communications Plan, designed and written by the New Horizons project in 2012 and 2013. To aide in this, workshops with writers, educators, social media experts, filmmakers, and science communicators were held to explore engagement themes and target audiences and then plan over two hundred communication efforts of all kinds. Then the project created videos, press briefings, printed materials, and even “Plutopalooza” party kits for schools and astronomy clubs. Then Alan recruited “influencers,” like Bill Nye “the Science Guy,” illusionist David Blaine, Queen guitarist Brian May (who is also a card-carrying Ph.D. astrophysicist), and other celebrities who were genuinely interested in New Horizons and wanted to help connect it with wide public audiences. The encounter promised some uniquely exciting moments of discovery and exploration. The educators, scientists, influencers, and communicators brought aboard for the flyby wanted to fully realize the potential to share the excitement and results of the impending flyby and to bring everyone who was interested along for the ride of a lifetime.

  12

  INTO UNKNOWN DANGER

  FIVE’S A CROWD

  Even as the encounter planning was well under way, the Pluto system was revealing itself to be more complex, and more crowded, than anyone had known. After Pluto’s small moons Nix and Hydra were discovered back in 2005, the New Horizons project asked for and received more time to use the Hubble Space Telescope to undertake an intensive search for still more moons of Pluto. If there were other objects there to study, it was important to discover them far enough in advance to fit observations of them into the encounter sequences. Additionally, Pluto could possibly have rings, the New Horizons team surmised; these would also be important to know about in advance, both to plan their study during the flyby, and to avoid colliding with them.

  It took years, until June of 2011, to find anything. But eventually planetary astronomer and moon/ring hunter extraordinaire Mark Showalter used the Hubble to take the deepest ever long exposures of the space around Pluto. Showalter was looking for faint rings, but in one of his super deep exposures he found a small, faint moon which turned out to be orbiting Pluto in between Nix and Hydra, circling the planet once every thirty-two days. The quadruple Pluto system had become a quintuple! Then, almost exactly a year later, in an even more sensitive Hubble search for faint rings, Showalter found yet another small moon, orbiting between Charon and Nix. The system had now become a sextuple! Both of Showalter’s satellites were much fainter than either Nix or Hydra, and therefore likely to be much smaller, suggesting to many on the science team that still smaller moons might be there for New Horizons to discover when it got close.

  For Showalter, finding two new moons was thrilling and interesting in its own right, but it also meant a greater likelihood of finding his elusive rings. As had been learned at the giant planets, small moons can generate thin rings by casting off debris when impactors strike them. Because very small moons have very low gravity, any debris blasted off them this way escapes into orbit around the moon’s planet, getting spun into a ring.

  As the fourth and fifth moons of Pluto, the two newest ones were at first just called P4 and P5. But in time, Showalter, working with Alan and others on the New Horizons team, as well as NASA, organized an online, public crowd-sourcing of ideas for naming the new moons. With the public’s help nominating and voting on names, Styx (the goddess of the underworld river near Pluto) and Kerberos (the dog guarding Pluto’s realm), became the official names of Pluto’s fourth and fifth satellites.

  A SPIDER’S BITE

  With Showalter’s discoveries of 2011 and 2012, it was becoming clear that Pluto possessed a rich system of moons, all orbitally interacting with one another. The emerging picture of a system thick with tiny moons and, potentially, thin rings was scientifically enticing, but it was also a spacecraft team’s nightmare, implying a greater likelihood of debris laying in their chosen path through the Pluto system. After all, at the nearly ten miles per second that New Horizons would fly past Pluto, a collision with something smaller than even a rice grain could be catastrophic, striking the spacecraft with the energy of high-caliber ordnance and ending the mission immediately—even before its precious Pluto data could be transmitted home to Earth.

  Alan did some so-called back-of-the-envelope calculations of possible ring density that could be produced by some undiscovered moons. If his simple estimates were right, then the spacecraft could be in real trouble at Pluto. He showed his results to the science team, and it got their attention, generating some urgency to look at this situation more closely with careful computer modeling. The fact is, the spacecraft was flying into the unknown. This of course is what made the mission so exciting in terms of the promise of new science and discovery, but it also meant they were flying into unknown danger.

  Science collaborator Henry Throop created another model, and his calculations confirmed Alan’s results. Glen Fountain remembers the reaction: “It scared the pants off of everyone. The bottom line was that we could be fatally impacted up to thirty times while going through the system.”

  Could it be that Pluto, the planet of their fascination and all their efforts over so many years, was actually a death trap for their spacecraft? As Alan put it to the team at one point, “What if the object of all our affection is really a black widow?”

  So a concentrated effort to determine if the Pluto system might be hazardous for New Horizons began. This started with much more sophisticated computer modeling of what hazards might be there, and intensified to a long and thorough search for rings and moons or other orbiting debris as New Horizons approached Pluto.

  Science team member John Spencer was assigned to lead this “hazards campaign,” and he made it his baby. John got the job in part because of his deep expertise in both telescopic observing and spacecraft imaging techniques.

  John and Alan mapped out a multistage effort to assess and mitigate the risk. The first step was to carefully reanalyze all existing data sets that could shed light on potential hazards. John recalls:

  First, we just needed to gather whatever other information we had to constrain the risk. That meant looking even more closely at existing Hubble images to see if there was any direct evidence of distributed debris around Pluto in the region of the moons, or if not, what limits we could set on them. Then we looked at data from stellar occultations. The Pluto community has observed many stars passing behind Pluto to study Pluto’s atmosphere. Those stars would have also passed behind any narrow rings that might be in the system. And if there were rings, then as a star passes behind them, its brightness should dip. So we reexamined all those data sets to search for any evidence of faint rings.

  Around the same time, Alan gave the spacecraft team the task of analyzing how well-protected New Horizons was from debris particle hits. The spacecraft was not defenseless: its body was covered in protective aluminum faceplates. But more important, its thermal blankets that overlaid those faceplates included layers of Kevlar shielding—the same material used in bulletproof vests. This had been done to protect New Horizons from interplanetary meteorite strikes as it crossed the solar system.

  To assess how well those measures protected New Horizons, in 2012 and 2013 the spacecraft team used a special high-velocity gun to fire different kinds of particles at copies of these faceplates and blankets. The result was good news—the Kevlar shield was actually more effective in stopping impactors than design analysis had indicated. Using these findings, mechanical engineers at APL m
odeled the probabilities that particle impacts large enough to penetrate the Kevlar and spacecraft’s aluminum skin could damage each given component of the spacecraft, every instrument, each fuel line, each electronics cable bundle, and each box of electronics. From this they derived much more detailed damage and destruction probabilities as a function of impactor size and velocity. The verdict: the lethal hazard concern was real.

  BECOMING FAIL-SAFE

  Because the possibility of lethal hazards at Pluto had become real, Alan wanted the New Horizons team to have something to show for all their work if the spacecraft was lost before it could complete the flyby and send its close-approach data to Earth.

  The solution to this challenge was called the “fail-safe” data transmission. When he conceived it, Alan likened it to astronaut Neil Armstrong’s “contingency sample” collection, the first thing Armstrong did after stepping onto the Moon in 1969. Then the logic was to have something to show scientifically for the mission of Apollo 11 in case something went immediately wrong, and he and Buzz Aldrin had to suddenly abandon their moonwalk before more comprehensive lunar sampling could take place.

  Channeling the same logic, Alan asked Leslie’s PEP team to draw up a list of imaging, spectroscopy, and other data sets that could be fit into a fail-safe data transmission to be sent back to Earth just hours before the flyby’s closest approach, when the craft was still far enough from Pluto that there was no significant possibility of a lethal impact.

  The fail-safe data wouldn’t come close to substituting for the main data collection at Pluto, and it wouldn’t prevent the mission’s main objectives from being lost if a fatal debris strike occurred. But it would give them a sampling of the best data taken before closest approach to salve their wounds and learn as much as possible about Pluto and its moons if the spacecraft was soon thereafter destroyed.

  But nothing is free, and adding the fail-safe transmission came at a price. Pointing the antenna back to Earth to send the fail-safe data home meant taking four precious hours out of the approach observations late on the scientifically crucial day prior to flyby. Some complained, but as mission PI, Alan’s calculus was different:

  There just wasn’t any way I was going to face NASA and the press if we lost New Horizons without having something important to show scientifically from the flyby. And I also wasn’t going to put our team in the position of coming up completely empty if that happened, and of saying we hadn’t thought through the chance of failure and collected our own “contingency sample.”

  So the fail-safe data transmission became a part of the plan; as it later turned out, its best images were so good that they led the newspaper and web stories the day after flyby.

  PLANNING AGAINST A BLACK SABBATH

  The next part of the hazards effort was spent developing plans to use the onboard LORRI telescopic imager to look for rings or new moons as New Horizons approached Pluto. John Spencer:

  This imaging effort was planned to begin about sixty days out from Pluto, which is when LORRI became superior to Hubble for finding moons and rings. For seven weeks starting then, a series of hazard-search imaging campaigns was planned. Each campaign would make hundreds of images, which would be sent to Earth and “stacked” on the ground—combining many individual images in computers to make the most sensitive possible searches for faint moons or rings.

  As the hazard search images reached the ground, we planned to use software codes we built to look for any moons or rings. We also planned to build computer models to determine what orbits the debris would occupy and, in turn, what threat the debris on those orbits would pose to the spacecraft. From that we could determine whether any given hazard was acceptable or not.

  And what if a given hazard found on approach was not an acceptable risk? Was there an alternative to simply plowing ahead, taking chances that fail-safe data was all the mission would get out of the twenty-six-year-long effort to explore the Pluto system?

  There was. The approach, initiated by Alan, identified alternate trajectories through the Pluto system that would avoid various potential hazard zones. This meant planning several Pluto flybys—each with different paths through the system and different observation timing.

  Recall the monumental amount of work, described in the previous chapter, which went into planning the flyby. Now the team would have to do that all again for each new pathway selected to dodge potential debris. It was a huge new workload and cost to the project, but given the lethality of debris strikes at thirty-five thousand miles per hour, and the reality of having only one spacecraft and no second chances, there didn’t seem to be any other option.

  For each of these new, backup flybys, the nine-day-long Core load of thousands of spacecraft and instrument commands that would direct the bird during its most intense and crucial flyby phase had to be completely redesigned, rebuilt, and fully retested.

  Alan named these alternate trajectory plans SHBOT, for “Safe Haven Bail-Out Trajectory.” It was pronounced like “Shabbat,” the Hebrew word for the weekly Jewish day of rest. Alan isn’t particularly religious, but he loved honoring the heritage of the many Jewish members of the team, including himself, Leslie, Cathy, and Hal, and he loved the way this word injected a little note of prayerful hopefulness as they prepared to confront the unknown hazards. Later, in response to a paranoid journalist’s criticism that NASA was secretly planning to “bail out” of the flyby, Jim Green, the head of NASA’s Planetary Science Division, asked that SHBOT be changed to the less threatening “Safe Haven by Other Trajectory,” and it was.

  The other aspect of SHBOT that was also meant to help protect New Horizons was the idea of changing the entire spacecraft pointing plan during these backup flybys. The Galileo and Cassini missions had both used a technique called “antenna-to-ram” to protect their spacecraft by turning to use their big dish antennas as forward shields when they crossed near the rings of Jupiter and Saturn, respectively. Flying in this orientation, most debris strikes would have to penetrate the dish antenna before reaching the Kevlar and spacecraft walls, providing an extra layer of protection. Tests performed with the high-velocity debris gun showed that the dish antenna on New Horizons could withstand many ring-particle impacts and still work, so this looked like a good way to add insurance against lethal impacts if the craft had to fly through possible debris. The engineering team showed that the antenna-to-ram protection provided a 300 percent reduction in the risk of a fatal debris strike to New Horizons.

  Yet antenna-to-ram also introduced a major problem of its own. If New Horizons had to fly by with the antenna pinned in the direction of flight, it would cripple the spacecraft’s ability to “point and shoot” in various directions to get observations of Pluto and its moons. So, although moving to the antenna-to-ram orientation would protect the craft from destructive impact, it would severely curtail the mission’s ability to meet its science objectives. Scoring just how severely this damaged the flyby science was a task Leslie Young and her PEP team were assigned—grading the loss of observations for each SHBOT trajectory and comparing that to the flyby plan they had so intricately prepared and optimized.

  The SHBOT trade-offs were painful, and the discussions about them were sometimes tense. John Spencer recalls some of the deliberations: “Many—maybe most—of the most important scientific observations were compromised or killed off if we had to choose the antenna-to-ram SHBOT. Obviously, people were very unhappy at that prospect. So there were lots of heated discussions about whether SHBOT was really a viable thing.”

  But Alan was adamant:

  I looked at it pretty coldly. Everything we had worked for to explore Pluto since 1989 came down to the success of the flyby. If the spacecraft was destroyed close to Pluto, we would not only lose all the observations after that point, we would lose all the data stored from the previous observations. If we lost our baby at flyby, almost none of that data would be sent back, only the fail-safe. As I saw it, in that case we’d get a near-zero for a grade—learning v
ery little about Pluto and its moons. If we were really faced with potentially catastrophic hazards, I was perfectly happy to trade the high grades of the optimal flyby for the low grades of a SHBOT flyby, because a dismal grade is a lot better than a zero. It wasn’t what I wanted, but I wasn’t going to blink if that was the only choice that had to be made.

  13

  ON APPROACH

  HUNTING FOR STILL FURTHER DESTINATIONS

  As the Pluto flyby approached, the New Horizons team intensified a search it began in 2011 to find a Kuiper Belt Object that the spacecraft could intercept and study after Pluto. This opportunity to study ancient bodies beyond Pluto—particularly small ones that were the building blocks of small planets like Pluto—was a key part of the Decadal Survey’s motivation for its top endorsement of a Pluto Kuiper Belt mission back in 2003.

  By 2013, John Spencer and Marc Buie, who were leading the search for this flyby target using the world’s largest telescopes, had found numerous small KBOs but none that could be targeted within the fuel reach of New Horizons. With time running out before the 2015 Pluto flyby, the ground-based searches simply weren’t yielding what was needed. So Alan decided to take a new approach. The primary difficulty was that the turbulence of the Earth’s atmosphere blurred the myriad stars in the search images just enough to blend them with faint pinpoints of light of their potential target KBOs. The only way around this was to use the Hubble Space Telescope, which, because it orbited above Earth’s atmosphere, offered the crisper view needed to separate still fainter KBOs from the dense fields of background stars.

  John and Marc, working with Hal Weaver, calculated that a proper search with a high probability of success would require almost two hundred Hubble orbits, or about two continuous weeks of Hubble time—more than ten times a typical-size Hubble proposal. Such a large proposal would be a very tall order to win.

  Making the challenge even steeper, the ticking clock to the Pluto flyby in 2015 meant the team could not go through the normal process of applying for Hubble time in spring of 2014, because that observing time wouldn’t start until late summer 2014, too late given the positions of the Sun and the KBO search fields where the scientists had to look.

 

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