One thing you don’t expect when planning a nine-year mission to the most distant planet in our solar system is the eventuality that Pluto might not be a planet once you got there.
Yet that’s exactly what went down in 2006. That January, NASA launched its unmanned New Horizons probe, a baby grand piano-sized, 1,054-pound spacecraft, on the first-ever route to Pluto. Then, in August 2006, the International Astronomical Union demoted Pluto to the diminutive status of “dwarf planet.”
The move “came out of left field” and shocked a lot of people, said Chris Hersman, the lead engineer on the New Horizons project. But as they say on Broadway, the show must go on. “I used to joke, ‘Well, we haven’t told the spacecraft.’”
Astronomers and planetary experts can debate Pluto’s status to the edge of the universe, but it doesn’t change the fact that nine years, five months, and 25 days after launching from Cape Canaveral Air Force Station in Florida, New Horizons made its much-heralded fly-by of Pluto today.
Planning a project whose culmination is nine years and more than 3 billion miles away requires rigorous risk assessment, strong leadership, and endless patience. Here’s how the team ultimately succeeded.
Way back in 2001, a team led by principal investigator Alan Stern crafted the proposal for the New Horizons mission, a mission that is now inspiring the most buzz about Pluto since the planet-not-planet was discovered in 1930.
But sending a probe to Pluto is no small task. A million things could go wrong. Well, actually just 249 things, but we’ll get to that.
That’s why Stern’s team put together what they called the Longevity document, a list of requirements for ensuring the probe’s successful 2015 “encounter” with Pluto. It started, Hersman recalled, with a plan for what to do with all the spare parts left over after building the probe.
Normally, the engineers would have had to order parts to fix a problem in one of the two New Horizons simulators. Not so in this case.
“We held [the spare parts] in stock for nine years,” Hersman said, “and sure enough, we had to use them. It makes it all worthwhile.”
The Longevity document also listed every key New Horizons team member, whether still involved in the project or not, so they could be reached if their expertise was urgently needed.
“If you ever had to call someone to ask about something no one else knew,” Hersman said, “it was a knowledge-retention system, even if [someone wasn’t] still on the project.”
Not everyone on the original team stayed on board throughout the 14 years between proposal and today, but many have. Besides Hersman and principal investigator Stern, others who are still deeply involved include Alice Bowman, the New Horizons mission operations manager, Glen Fountain, the New Horizons project manager, Mark Holdridge, the Pluto encounter mission manager, and many other team leads and sub-leads who worked on everything from propulsion to communications.
That’s impressive stability. Of course, all these people have other tasks beyond the New Horizons project, but everyone knew it was about to be show time. “People ramped down so they weren’t working much on the project,” Hersman said, “but when the time comes to fly past Pluto, a lot of other stuff gets put on hold, or they find time.”
One other essential element of preparing for the nine-year mission was compiling a spreadsheet of contingencies for when things went wrong. This was useful when ground control temporarily lost communications with the New Horizons probe on July 4 of this year.
The spreadsheet listed 249 items that might go wrong with either the spacecraft or ground-based operations. The latter included dealing with power outages or the team not being able to “get into the building because of a chemical spill.”
That meant making sure the primary and backup mission operations centers were in different buildings, as were the two simulators, and used different communications networks.
No one could predict everything that might fail, so “we just tried to come up with ideas for what could go wrong, and we tried to come up with ideas for how to fix them,” Hersman said.
Notwithstanding the July 4 “anomaly,” Hersman said there have been only eight significant issues during New Horizons’ nine years of rocketing toward Pluto. Mainly, they were along the lines of processor resets or power resets induced by radiation. In each case, the spacecraft went into an autonomous safe mode, and recoveries pretty much went according to the original contingency plans.
Perhaps he’s got rose-colored glasses given New Horizons’ successful trip, but Hersman insists there’s almost nothing he wishes had been done differently back when the probe was still Earth-bound.
He wouldn’t mind a little more power, given that the team had to choose a slower computer processor in order to save watts. Some tasks could have been easier with more power–like perhaps being able to keep both of the probe’s memory chips on at the same time instead of always having one turned off.
It also might be nice if New Horizons had a better camera or more memory, Hersman added. Then again, the team did get to take advantage of a new (at the time) solid-state recorder with flash memory that came out during the design stage, allowing four times the storage they’d originally expected.
It’s hard to argue with the mission’s success. Some may have been surprised that Congress authorized the project at all, but Hersman said those inside the National Academy of Sciences ranked New Horizons as the space agency’s top priority during an every-10-years survey of its projects thanks to the fact that in addition to the fly-by of Pluto, the probe was also meant to keep going and explore the Kuiper Belt.
As for its Pluto work, New Horizons will now fly through the dwarf planet’s shadow, taking measurements from its atmosphere and probing to learn about the temperature, pressure, and composition of its surface. “Then we exit the eclipse of the planet on our way out,” Hersman said. As NASA puts it in a document about the New Horizons mission, Pluto is “a harbinger of the mysteries on the far planetary frontier.” New Horizons’ job, in other words, is crucial for expanding humanity’s scant understanding of the outer reaches of the solar system.
Speaking a few days before the fly-by, Hersman said knowing it had gone as planned would be “a huge relief.”
Now that the probe has completed its Plutonian fly-by, New Horizons should soon send back the rest of the wealth of data about the former planet and its fellow icy bodies in the Kuiper Belt that rocket scientists like Hersman have been awaiting all these years.
Ultimately, there are a lot of people with more responsibility for the mission than him, but Hersman likened his role to that of the field-goal kicker on a football team.
“If the team wins, and you weren’t the one kicking the ball through the goal, you’re still thrilled,” Hersman said. “I don’t feel the need to be in the limelight. I’ll just sit back and watch and make sure all the components are working well. That’s thrilling to me, having everything working and being on the path to Pluto.”