On July 4, 2015, there was no Independence Day celebration for Sol Alan Stern. Instead, he was hunkered down in his office talking to the New York Times. It was just three days before the project he'd shepherded, NASA's New Horizons spacecraft, was set to begin a daring flyby of Pluto, which would be the first time a spacecraft visited the famous dwarf planet.
He hung up; his phone buzzed again. He stared at the caller's name. It was Stern’s good friend, Glen Fountain, who was then the mission's project manager. Stern knew that — unlike himself — Fountain had taken Independence Day off. This is not good, Stern thought. He picked up. In a grave voice, Fountain intoned, "Alan, we've lost contact with the spacecraft."
"That's about as bad as it gets," Stern tells Astronomy, looking back on the episode five years later.
After receiving the stomach-sinking news, Stern hopped in his car and raced across the campus of Johns Hopkins University's Applied Physics Laboratory in Laurel, Maryland, to New Horizons mission control, where team members began gathering. "People were coming in in their bathing suits and flip flops," Stern says, who's normally based at Southwest Research Institute (SwRI) in Boulder, Colorado. "They didn't know if we were going to be there for an hour, or overnight, or for days."
It turned out to be days. While almost 3 billion miles (4.76 billion kilometers) from Earth, New Horizons had suffered a glitch that wiped out all of its flyby software commands — an intensely choreographed nine-day sequence of science observations that the craft would perform as it screamed by Pluto, coming within a mere 7,750 miles (12,500 kilometers) of the dwarf planet.
New Horizons’ glitch in 2015 set off a nonstop 76-hour scramble to upload and rebuild all the necessary flyby software. That meant not only recreating the full set of commands, but also the ephemeris files and other software libraries on which they depended. Such a task would normally take weeks, Stern says. He likens it to a chess match with a nine-hour time delay, which is how long it took for radio signals to make a round trip to the New Horizons spacecraft.
The result? Stern and his team restored the software with just four hours to spare before the flyby sequence began.
That Herculean effort saved New Horizons from being a "laughingstock," says Stern. The mission ultimately returned a treasure trove of data that scientists are still analyzing today, resulting in well over 100 peer-reviewed papers. And for the scientists and engineers who built it, watching Pluto grow ever larger as New Horizons approached was the scientific experience of a lifetime.
"Every day, it was a matter of being astounded," Cathy Olkin, a planetary scientist at SwRI, tells Astronomy.
Plotting the course for New Horizons
New Horizons’ nine-day flyby sequence culminated with its closest approach to Pluto on July 14, 2015, when it followed a trajectory carefully plotted by Yanping Guo, a mission design specialist at APL. Guo has also worked on the Parker Solar Probe, NASA's Near Earth Asteroid Rendezvous (NEAR) mission in the 1990s, and seven other mission studies or proposals. She began charting a course for New Horizons way back during its design phase in 1999 — some seven years before its launch.