Engineers joke that FOD is a four-letter word, but there’s nothing funny about foreign object debris and its potential to trigger a disaster.
The incident occurred around 10:25 am ET on Oct. 5 when a SpaceX pad crew was preparing Crew Dragon persistence for launch on a Falcon 9 rocket. With the four Crew-5 astronauts already inside the capsule and the hatch closed, a careful eye spotted a single human hair embedded in the breech seal. The hair was labeled FOD — a technical term for foreign object debris — prompting crash crews to take action.
The countdown clock had just expired at T-90 minutes, so time was of the essence. The pad crew calmly reopened persistence‘s hatch and removed the offending strand. They conducted another inspection, thoroughly cleaned the sealing area again, and closed the hatch for the second and final time. A subsequent pressure check confirmed a tight seal.
The whole affair lasted only a few minutes and the launch was not affected. The Falcon 9 launch took place as scheduled at 12:00 p.m. with the Crew 5 astronauts – Nicole Aunapu Mann, Josh Cassada, Koichi Wakata and Anna Kikina – who successfully reached the International Space Station the following day.
That the SpaceX pad crew would take the time to remove a single hair prior to a rocket launch is revealing and entirely understandable. In the aerospace industry, FOD is defined as any object that does not belong in a specific location, whether that location is a hatch seal, an engine, a cockpit, or the runway. Misplaced deposits can damage equipment, promote suboptimal system performance, and cause complete malfunctions.
It’s a problem in many industries, but for the aerospace industry, it’s a problem that comes with a $4 billion price tag every year. corresponding this Boeing. NASA operates a FOD program at Kennedy Space Center, whose purpose is “to minimize the possibility of damage to or loss of flight hardware or injury to personnel due to lost items within the flight hardware elements, resulting in the conservation of national resources”.
Tom Simon, deputy spacecraft manager at NASA Johnson Space Center, told me over a video call, “We were all trained from day one to be aware of FOD when handling flight systems. Foreign objects like pencils, paper clips, screwdrivers, hair, and Dust “might seem insignificant,” but they could result in, among other things, a “seal slowly leaking overboard,” he said. “When we build systems, we take it seriously,” he added.
As an engineer, FOD is “rooted in your system,” John Posey, NASA’s lead engineer for Crew Dragon, told me during the same call. It is “regarded as a top risk in training programs” because FOD has the potential to “crash missiles and planes,” he explained.
Simon and Posey weren’t able to speak to SpaceX’s specific policies and protocols, but they weren’t surprised by the pad crew’s actions in removing the human hair. FOD related to sealing of surfaces is a serious problem. When you’re dealing with a sealing surface and need to ensure a tight seal, “you don’t want anything pushing against it,” Posey said. “Something like hair — depending on their size and orientation — can lead to a leak path.”
Posey said that for time-sensitive situations such as the final closure of a capsule hatch, the sudden occurrence of FOD should be built into the timeline and process, in addition to a contingency plan should that scenario occur. Pad crews should “stand back, remove the item, re-inspect and even clean the seal, and then get on with whatever work you’re trying to do,” Posey said.
It’s not just hatches that are at risk of FOD. Launch operators implement processes to mitigate FOD risk, e.g. B. the use of covers or shields when work such as cutting or sawing must be performed in the vicinity of spacecraft. And of course the operators themselves must be clean. Propulsion systems, where fuels and oxidizers are pumped through high-pressure systems, can be affected by FOD, said Posey, who worked on the space shuttle in its final days and “spent thousands of hours on propulsion systems and working on the ground technicians to make sure everything was working.” is okay.”
As Simon explained, the level of cleanliness required often depends on the nature of the project or the mission itself. Posey said each system needs its own control plan, with engineers defining acceptable limits and deciding what needs to be checked.
Clean room protocols for unmanned satellite launches are typically minimal, “down to washing hands and putting on gloves,” he said. However, single-crew missions are a different story. “Crews not only have to have the avionics system working, they don’t want flying around everywhere,” says Simon. Once in orbit, microgravity can suddenly cause FOD to fly around unnoticed, including hair and dust. Posey said filtration systems are designed to deal with these types of things, “but you still want to avoid hassles” such as requiring covers over hatch seals, among other things. And “even covers need to be cleaned and checked for leaks,” he added.
Posey offered some sage advice: “Always make sure you open a system in a clean room, only do what you have to do, and conduct an inspection before you close it.” And “if you do something see that doesn’t look right, go in and examine it,” as it’s a “necessary exposure,” he said. A second pair of eyes doesn’t hurt, he added. “FOD will find a way to get into your system,” Posey said, hence the term “smart FOD.” He recounted an incident where a bootie or shoe cover was suddenly discovered in the shuttle compartment. “It just slipped off someone’s foot, and that kind of thing can be funny in hindsight,” Posey said, but booties or duct tape or anything else that doesn’t belong can be a flammability issue.
Measures against the ingress of FOD into components or complex systems start in the clean room, and each clean room has its own cleanliness requirements depending on the project. Cleanrooms “are specifically certified and monitored to a specific cleanliness level based on what’s in them,” and items typically need to be approved before they’re allowed into a cleanroom, Posey said.
Lockers are available for storing loose items; Duct tape and sticky floor pads can secure items that need to be in the room; and tethers can catch anything accidentally dropped. Coveralls, known to engineers as “bunny suits”, cover arms and legs and usually have a hood with a hair net. Beards are covered with beard nets while shoes are given boots.
“Once you’re ready and primed, step through a set of double doors,” Posey said, the first of which “closes behind you, and then you go into the clean room.” In the center chambers of some double doors, “air blows over you and sucks up dust or dirt,” he explained. Staff will collect any FOD found and investigate where it came from and whether additional controls are needed. Clean rooms “are never clean enough,” Posey added.
These measures are an additional but necessary headache. The good news is that FOD detection improves over time. Cameras are now routinely used to observe virtually every corner of a launch pad, while X-ray and CT scans can look inside objects and create 3D images of a part’s interior. With these tools, engineers can “see assembly problems” and “detect FOD that otherwise would not have been found,” Posey said. Improved FOD tracking capability is of increasing importance to the private sector, especially in the age of component reusability.
The human hair found in the hatch seal may or may not have caused a problem during the Crew-5 flight, but it doesn’t matter. What matters is safety and the elimination of anything that could endanger human life. Engineers will continue to look for FOD, regardless of the inconvenience it may cause.