Engineers joke that FOD is a four-letter word, but there’s nothing funny about foreign object debris and its potential to trigger disaster.
The incident occurred on October 5 at around 10:25 a.m. ET, when a team from the SpaceX platform was preparing Crew Dragon. Endurance for launch atop a Falcon 9 rocket. With the four Crew-5 astronauts already inside the capsule and the hatch closed, a keen eye spotted a single human hair on the latch seal. The hair was designated FOD, an engineering term for foreign object debris, which required the rig team to take action.
The countdown clock had just passed T-90 minutes, so time was of the essence. The pad team calmly reopened EnduranceThe hatch and removed the offending thread. They made another inspection, thoroughly cleaned the seal area again, and closed the hatch for the second and final time. A subsequent pressure check confirmed a tight seal.
The whole thing took only a few minutes and the launch was not affected. Liftoff of the Falcon 9 occurred at noon as scheduled, with Crew-5 astronauts: Nicole Aunapu Mann, Josh Cassada, Koichi Wakata and Anna Kikina, successfully arriving at the International Space Station the next day.
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That the SpaceX rig crew would take the time to remove a single hair before a rocket launch is telling and totally 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, engine, cockpit, or the runway. Wrong-placed debris can damage equipment, lead to suboptimal system performance, and lead to outright malfunctions.
It’s a problem in many industries, but for the aerospace industry, it’s a problem that carries a price tag of $4 billion each year. according to to Boeing. NASA runs a FOD program at the Kennedy Space Center, the purpose of which is to “minimize the possibility of damage to or loss of flight hardware or injury to personnel due to items lost within flight hardware items, resulting in the preservation of national resources.”
Speaking to me on a video call, Tom Simon, deputy manager for spacecraft at NASA’s Johnson Space Center, said, “We’ve all been trained from day one, when dealing with flight systems, to be careful about FOD.” Foreign items such as pencils, clips, screwdrivers, hair and dust “may seem minor” but could, among other things, result in a “seal slowly leaking overboard,” he said. “When we build systems, we take it seriously,” he added.
As an engineer, FOD is “burned into your system,” John Posey, NASA principal engineer for Crew Dragon, told me during the same call. It is “considered a major risk in training programs” as FOD has the potential to “shoot down rockets and planes,” he explained.
Simon and Posey weren’t able to discuss SpaceX’s specific policies and protocols, but they weren’t surprised by the rig’s team’s actions to remove human hair. FOD related to surface sealing is a serious concern. When it comes to a sealing surface, and when you have to ensure a tight seal, “you don’t want something pressing against it,” Posey said. “Something like hair, depending on its size and orientation, can result in a leak path.”
Posey said that for time-sensitive situations like the final closing of a capsule hatch, the sudden onset of FOD needs to be built into the timeline and process, along with having a contingency plan should this scenario arise. . Pad crews should “go back, remove the item, re-inspect and even clean the seal, and then get on with the job they’re trying to do,” Posey said.
It’s not just hatches that are prone to FOD risk. Launch operators implement processes to mitigate the risk of FOD, such as the use of covers or shields when it is necessary to perform work such as cutting or sawing near the spacecraft. And, of course, the operators themselves must be clean. Propulsion systems, in which fuels and oxidizers are pumped through high-pressure systems, can be affected by FOD, said Posey, who worked on the space shuttle during its final days and “spent thousands of hours in the propulsion systems, working on the floor with technicians to make sure everything is okay.”
As Simon explained, the degree of cleanup required often depends on the nature of the project or mission itself. Posey said each system needs its own monitoring plan, in which engineers define acceptable limits and decide what to test.
Clean room protocols for unmanned satellite launches tend to be minimal, “to the point of handwashing and putting on gloves,” he said. However, missions involving a crew are a different story. “With crews, not only does the avionics system have to work, you also don’t want things flying all over the place,” in addition to keeping the seals clean, Simon said. Once in orbit, microgravity can cause FOD to float imperceptibly, including hair and dust. Posey said filtration systems are designed to deal with this kind of thing, “but he still wants to avoid problems,” like requiring covers over hatch seals, among other measures. And “even the 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, do only what you need to do, and do an inspection before shutting it down.” And “if you see something that doesn’t look right, go in and investigate,” since it’s a “necessary burden,” he said. A second set of eyes won’t hurt, he added. “FOD will find a way into your system,” Posey said, hence the term “Smart FOD.” He recounted an incident in which loot, or a shoe cover, was suddenly discovered in the shuttle’s compartment. “It just slipped off someone’s foot, and these kinds of things can be fun in hindsight,” Posey said, but booties or duct tape or anything else that doesn’t belong can be a flammability issue.
Measures to prevent FOD from entering complex components or systems start in the cleanroom, and each cleanroom has its own cleanliness requirements, depending on the project. Clean rooms “are specially certified and monitored for a certain cleanliness classification depending on what’s in there,” and items generally must be approved before they’re allowed into a clean room, Posey said.
Lockers are available to store loose items; duct tape and sticky floor pads can secure items that need to be in the room; and the straps can catch anything accidentally dropped. Known to engineers as “bunny suits,” the coveralls cover arms and legs and usually have a hood with a hairnet. Beards are covered with beard nets, while shoes are covered with boots.
“Once you’re ready and all kitted out, you go through a double door,” Posey said, the first of which “closes behind you and then you go into the clean room.” In the medium chambers of some double doors, “the air blows over you, sucking up any dust or debris,” he explained. Staff will collect any FOD found and investigate where it came from and if additional checks are needed. Clean rooms “are never clean enough,” Posey added.
These measures are an added but necessary headache. The good news is that FOD detection is improving over time. Cameras are now routinely used to peer into virtually every corner of a launch pad, while CT scans and X-rays can peer inside objects and create 3D images of the inside of a part. With these tools, engineers can “see assembly issues” and “detect FODs that might not otherwise have been found,” Posey said. An increased ability to detect FOD is becoming increasingly important to the private sector, particularly in the age of component reuse.
The human hair found inside the hatch seal may or may not have caused a problem during Crew-5’s flight, but that doesn’t matter. What matters is safety and the elimination of everything that could put human lives at risk. Engineers will continue to look for FOD, regardless of the inconvenience it may cause.
Plus: remembering Business: The test shuttle that never flew into space.
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