A SpaceX Delivery Capsule May Be Contaminating the ISS
In February 2017, a SpaceX Falcon 9 rocket lifted through low clouds, pushing a Dragon capsule toward orbit. Among the spare parts and food, an important piece of scientific cargo, called SAGE III, rumbled upward. Once installed on the International Space Station, SAGE would peer back and measure ozone molecules and aerosols in Earth’s atmosphere. Its older siblings (SAGEs I and II) had revealed both the growth of the gaping ozone hole and, after humans decided to stop spraying Freon everywhere, its subsequent recovery.
This third kid, then, had a lot to live up to. Like its environmentally conscious predecessors, SAGE III is super sensitive. Because it needs unpolluted conditions to operate optimally, it includes contamination sensors that keep an eye on whether and how its environment might be messing up its measurements. Those sensors soon came in handy: When the next three Dragons docked at the Space Station, over the following months, SAGE experienced unexplained spikes in contamination. Something on these Dragons was outgassing—releasing molecules beyond the expected, and perhaps the acceptable, levels. And those molecules were sticking to SAGE.
Outgassing, in earthly terms, is what makes a new car smell like a new car. “There are volatile chemicals in those new materials that migrate through the material to the surface," says Alan Tribble, author of Fundamentals of Contamination Control. You’re smelling escaped seat ingredients, in other words.
Outgassing also builds up as a greasy film on the inside of your new car’s windows—or the outside of your space station. This grime is mostly a problem for instruments that measure light, but it can also reduce solar panels’ efficiency and can make surfaces hotter than they’re supposed to be. To avoid all that, engineers build Space Station additions and satellites in clean rooms, use only prequalified materials, bake out contaminants before launch, and set strict limits on how much proverbial new-car smell a craft can release. “It’s an intense process and considered extremely critical,” says Meg Abraham of the Aerospace Corporation, which consults on a number of space projects. “Everyone thinks about this.”
But that pre-planning doesn’t always work: When astronauts brought some early Hubble Space Telescope instruments back down to Earth, for example, they found that the $1.5 billion telescope’s body, which would have cost $2.89 billion in 2018 dollars, had sprayed enough molecules at them to severely degrade their ability to detect ultraviolet light—one of the telescope’s premier capabilities.
NASA has dealt with such dirt for decades—but the dirt has so far largely come from the agency’s own creations. Dragon, though, is different. It belongs to SpaceX. Today, the company plans to launch another Dragon capsule full of cargo, and perhaps outgassing contaminants, to the Space Station. This launch will be the company's sixteenth commercial resupply mission.
As NASA offloads operations to private companies like SpaceX, Orbital ATK (now part of Northrop Grumman), and Boeing, it’s having to react when their children misbehave. And that’s a big deal: New ISS instruments tell us about how our planet and the universe around it work, at prices in the tens of millions, with years-long development timelines. With those stakes, the last thing scientists, engineers, and citizens want is for a private company’s capsule to muck up measurements.
SAGE III went to the Space Station aboard SpaceX’s tenth resupply mission for NASA, as part of a SpaceX contract to do the agency’s local deliveries. As soon as SAGE was onboard, its contamination-catching crystals registered Dragon’s excessive outgassing.
These crystals are not of the healing variety (spoiler alert: none are) but are, instead, “thermoelectric quartz crystal microbalances.” Each of SAGE’s eight such sensors has two twin crystals, and working together they make two “contamination monitoring packages." These crystals oscillate at a certain frequency, which matches up with their mass. If a crystal gains mass—like, say, if a spacecraft sends new-car-smell its way—its frequency changes.
When the twin crystals start out on their missions, they’re precisely the same. But on the Space Station, one of the two is exposed to the outside environment, while the other stays sheltered. It’s kind of like twin studies in psychology. By measuring the difference in the twins’ frequencies, scientists can determine how much contamination was deposited onto the exposed one, although it doesn’t reveal the layers’ nature.
After the eleventh Dragon arrived, one contamination-monitoring package’s frequency steadily shifted, according to a presentation posted on September 1 to NASA’s Technical Reports Server, a database of documents created or funded by the agency. The data was noteworthy because NASA sets contamination limits for sensitive surfaces, which include some of the more delicate parts of the ISS. The crystals in this case were serving as canaries, warning of potential harm to those exquisite instruments.
The results are preliminary, but Dragon may have deposited, according to this presentation, up to 21 times the allowed amount of contamination on one sensor. The crystals also significantly changed in frequency when the next Dragon docked, and the report estimates that this mission may have left behind up to 32 times the rule-abiding amount of extra matter on one sensor.
The presentation was put together by the Space Environments team, a NASA and Boeing collaboration dedicated to understanding how the harsh realities of space mess with instruments and humans. With the troublesome data in hand, the Space Environments folks designed an experiment to figure out what was going on. Maybe, they thought, the problem was the solar array, or the materials on the outside of the capsule. To narrow down the list of suspects, during the thirteenth Dragon flight, engineers positioned the solar arrays so that their edges faced the Space Station. If the panels were outgassing, they then wouldn’t outgas at the spacecraft. Mass would build up on the crystals more slowly, keeping their frequency relatively constant.
But that’s not what happened. While the array was tilted away, the crystals' frequencies kept on ticking up. The Dragon capsule itself seemed to be the problem—a problem that got worse the more sunlight shone on it. During this thirteenth mission, one sensor may have been sprayed with up to 73 times more than what’s allowed during a sojourn. And for the month or so that Dragon was docked at the Station, two of the sensors individually detected more contamination than is allowed—total, from everything on the Station—in a whole year.
Among the space assets at risk from the capsule’s outgassing is the U.S. Laboratory Science Window, a porthole through which astronauts and instruments can gaze out on Earth. On the more scientific side, there’s CATS, an instrument that measures smoke, pollution, dust, and other particles in the planet’s atmosphere. In total, seven sensitive areas or instruments on the ISS, including SAGE, could be contaminated beyond the limit.
"NASA has communicated with the Station payload community its findings, and payload developers have responded either that their instruments have experienced no impact or they have taken precautions to mitigate impacts to their science," says Space Environments in a statement. The SAGE III team closes the instrument's "contamination door," as a standard operating procedure, when any spacecraft visit to protect its optical instrument, although the resulting measurements aren’t as sensitive .
And at least SAGE III, whose optics are “susceptible to molecular contamination degradation,” knows when it needs to watch out. The SAGE III team only knows those precise levels because it is carrying contamination monitors that didn’t exist on the Station before.
SpaceX, meanwhile, is looking at its ingredients. “SpaceX has scrutinized all external material selections on Dragon and is working with suppliers to custom-develop low outgassing variants of qualified materials to help improve the molecular deposition rate,” says the company, adding that NASA pre-approved all the materials used in the first Dragon design.
Antonius de Rooij, author of the Space Materials Database, believes the capsule’s paint is the likely problem. For one, he says, “the white painted surface is very large, meaning that even low outgassing products can have a large contamination effect.”
He’s curious, too, why the Space Environments team took solar heating and radiation into account, but didn’t consider the human or earthly factors. “Is the paint applied correctly? Is it cured correctly?” he says. “I was a little bit amazed that those points were not mentioned.” Paint won’t behave as advertised if the surface it’s slapped onto isn’t ultraclean, or if the humidity while it dries isn’t Goldilocks-correct. Maybe the paint stews weren’t precisely the same. “This batch variation can be the cause of different outgassing and different optical properties between batches,” he says.
Or the surface could have been tainted after the paint cured. That contamination could beget more contamination. While the precise paint for these three Dragon missions isn’t public information, at least one earlier mission used one called Alion Z-93c55, a variant of Alion Z-93. If Alion Z-93 gets contaminated after curing, it’s prone to degradation when UV rays hit it, a phenomenon documented way back in 1971. It then absorbs more sunlight, gets hotter than anticipated, and outgasses more. “I wonder why they didn’t mention this in their report,” says de Rooij.
Part of the problem here, though, is NASA's reluctance to talk about both the problem and the plans to fix it. The presentation, shared during the Payload Operations Integration Working Group meeting back in April, was approved for unclassified and unlimited public release and placed on the NASA Technical Reports Server in early September. I asked for an interview about it on September 25. The next day, the presentation was gone. “The record details page you tried to access cannot be found on this server,” the page now says. I inquired about the dead link, and more than three weeks later, I received a response: “The document is under review,” wrote Meagan Storey, of the NASA Scientific and Technical Information Program, “and we advise that you make a FOIA request for the item.”
Statistically, that's probably a losing prospect. If we use FOIA requests as a proxy for transparency, NASA is one of the government's most obscured agencies. It denied more FOIA requests by percentage in 2017 than the Department of Defense, the Securities and Exchange Commission, the Department of Energy, the Environmental Protection Agency, the Nuclear Regulatory Commission, and the Office of the Director of National Intelligence, organizations that largely have more to protect than the nation’s space agency. To be fair to NASA, which denied 71 percent of requests, the CIA denied 78 percent.
Last month, before I’d seen this report, I knew something was up. I'd seen a previous document that said, “The Dragon Trunk particulate background has not been characterized, but releases have been observed." And so I had asked NASA’s SAGE III team—knowing that outgassing could affect their instrument—if they had changed any of their plans because of concerns about Dragon. “No negative contamination effects or concerns on SAGE III science,” they responded, by email. “Nothing to add beyond that.”
As I would learn from the case of the disappearing presentation, and three missions’ worth of measurements that very team had taken, there was a lot to add beyond that.
In being cagey about contamination issues, the agency is protecting not just itself but also its private, profit-making partner, SpaceX, whose capsule in turn has an effect on the ISS instruments that are supported by federal funds.
That lack of transparency will become more pertinent soon, when private companies start shuttling not just astronaut ice cream and atmospheric instruments but also human beings back and forth from space, as part of the agency's commercial crew program. Another iteration of Dragon will take some of those future astronauts up. "SpaceX is using the data to improve its Dragon 2 crew and cargo vehicles," says the Space Environments team's statement.
Today's contamination issues might not be causing major problems, but if there were a big problem with tomorrow's Dragon, or with another company’s carrier, this case study suggests it might get worked out behind closed bay doors—or hazy windows.
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