CAPE CANAVERAL, Fla. — SpaceX has traced last month's loss of a flight-proven booster to an in-flight engine shutdown, according to a top company official.
The loss occurred during the company's Feb. 15 launch of 60 Starlink internet satellites. The booster, B1059, was making its sixth flight and successfully delivered its payloads to orbit, but missed touching down on the drone ship Of Course I Still Love You, which was deployed in the Atlantic Ocean to support the launch.
During a NASA news conference held on March 1 regarding the upcoming Crew-2 mission, set to launch on April 22, Benji Reed, senior director for human spaceflight at SpaceX, explained that the anomalous engine shutdown during the February launch happened because hot gas seeped through a worn-out engine cover.
Related: SpaceX's Starlink satellite megaconstellation launches in photos
The covers, known as "boots," are installed around certain parts of each Merlin 1D engine that powers the Falcon 9. According to Reed, one of the boots had a tiny hole in it that allowed hot gases produced by the engine to seep through into other engine parts.
"A little bit of hot gas got to where it's not supposed to be, and it caused that engine to shut down," he said.
Reed did not say at what point in the mission the engine shut down, but implied that it was during the rocket's ascent.
"A great thing about Falcon 9 is that we have engine out capability," Reed said, referring to the rocket's ability to deliver a payload to orbit even if it loses one of its nine engines. "The vehicle got to orbit and put the satellites where they needed to be."
SpaceX has always said that its primary objective each launch is to deliver whatever payload it's carrying to space; recovering boosters is a bonus. And while the Falcon 9 can carry out that primary mission down one engine, the same isn't true of booster landings.
The shutdown caused the booster to miss its targeted landing spot on the drone ship, Reed added. "Because of the problem with that particular engine, we didn't have enough thrust to get back to where we needed to be, and didn't land where we wanted to," he said.
The mishap ended a landing streak of two dozen consecutive booster recoveries the company established last year, following back-to-back losses of two other boosters in February and March 2020. Those anomalies were triggered by an early engine shutdown with unknown cause and by higher-than-predicted wind shear.
Reed said that the company has learned a lot about reusability, but is still trying to determine the life expectancy of its fleet and which parts are most susceptible to the wear and tear of multiple launches.
While this particular booster was on its sixth flight, which is not a record as two other boosters have more than eight flights on their record, Reed said that some of its components were so-called "life leaders." "This was the highest number of flights that this particular boot design had seen," he said.
Falcon 9 has since made three successful landings: the company's 77th recovery to date, on a March 4 Starlink launch, an additional touchdown on another Starlink mission a week later and a third on Sunday morning (March 14). All three flights flights used a booster with five or more flights under its belt.
Sunday's flight even set a new record, as booster B1051 became the first to fly nine times. SpaceX successfully recovered that booster and plans to fly it for a 10th time in the near future.
Historically, SpaceX has saved its most veteran boosters — those with more than three or four flights — for its own internal launches, like Starlink. Reed said that practice will continue as the company learns more about how Falcon 9 handles higher launch numbers, helping SpaceX track vehicle wear and tear and anticipate which parts may need replacement between flights.
"We get to fly our higher-count flight-proven vehicles to take the Starlink satellites to orbit," Reed said.
A thorough grasp on booster life expectancy is crucial for the company as it recently received the green light from both NASA and the Space Force to use previously flown boosters on their missions.
In fact, the upcoming Crew-2 mission will be the first astronaut mission to fly both a reused Falcon 9 rocket and a reused Crew Dragon spacecraft.
The rocket flew last November, ferrying the Crew-1 astronauts — NASA's Mike Hopkins, Shannon Walker and Victor Glover and Japanese astronaut Soichi Noguchi — to the space station, while the Dragon flew in May, toting NASA's Bob Behnken and Doug Hurley to the orbital outpost on a test flight. Neither craft has flown since, and the company is subjecting both to a thorough inspection and refurbishment process.
Following the February booster loss, NASA has been tracking SpaceX's internal investigation into the premature engine shutdown, NASA personnel said during the March 1 news conference.
"We will follow on with SpaceX’s investigation, and we’ll look at that, and that will be something we’ll bring to our program control board and make sure that we have separation from that, and understand that anomaly before we go fly [with astronauts]," said Steve Stich, manager of NASA's commercial crew program said during the briefing.
NASA astronaut Shane Kimbrough, one of the Crew-2 astronauts, said that the crew receives regular briefings on both the rocket and the spacecraft and don't have any concerns.
"It’s just been a few little things on a few of these rockets. They’re launching almost once a week, so when you’re launching that often everything is not going to go perfectly," Kimbrough said. "There’s nothing major or catastrophic that’s happened. It’s just a few things on the rocket that are going to get worked out before our flight."
"We're very confident they're going to figure out whatever's gone wrong," he added.
Kimbrough and his crewmembers — fellow NASA astronaut Megan McArthur, European astronaut Thomas Pesquet, and Japanese astronaut Akihiko Hoshide — will be the first to ride to orbit atop a previously flown Falcon 9.
"One of the things I really like about what’s happening is SpaceX’s Starlink flights are pretty far out there in terms of the number of times they’ve flown a booster," Stich said. "We’re about to embark on our first reuse here for a crew vehicle. So what we’re doing is we’re learning from each of those flights, and we’re feeding that back into our certification for reuse."
SpaceX has a few more Starlink missions up its sleeve before the Crew-2 flight, which is currently scheduled for no earlier than April 22. Those launches mean a few more flights for the teams to review before a veteran Falcon 9 is officially certified to fly people.
In the meantime, SpaceX is taking its time with each launch, as evident by the fact that its most recent launches were delayed due to the need for more prelaunch checkouts. The company is also working on future upgrades to the control systems on Falcon 9 that will help the vehicle land even in the event of an engine shutdown during flight like the one that occurred Feb. 15, Reed said.
Follow Amy Thompson on Twitter @astrogingersnap. Follow us on Twitter @Spacedotcom or Facebook.