Nithin Abraham works at the Smithsonian’s Museum Support Center in Suitland, Maryland. Credit: NASA/Chris Gunn
Every day, we’re surrounded by billions of tiny, unseen objects. Molecules of all kinds float like invisible motes of dust, impossible to detect with the naked eye but sometimes discernable through smell.
“Think about when you buy a home — you may have new furniture, such as sofas, mattresses, or memory foam pillows, and freshly painted rooms,” says Nithin Abraham, a thermal coatings engineer at NASA’s Goddard Space Flight Center. “These common household items often have a new smell associated with them, and it’s a result of volatile organic compounds being released into the air.”
As part of her job, Abraham has to think on the tiniest of scales. At NASA, she works on coatings technology research efforts. Specifically, she tries to address molecular contamination, finding ways to keep molecules from interfering with delicate instruments bound for space. Even the smallest deposition of chemical species on a sensitive telescope mirror can keep it from working properly.
Abraham is the subject matter expert on the Molecular Adsorber Coating (MAC), a NASA technology with broad applications for the aerospace industry. For nine years, Abraham has studied MAC and evaluated its use in protecting spacecraft and instruments from contamination via potentially harmful molecules.
MAC is flying in space aboard the Ionospheric Connection Explorer (ICON) mission, a space weather satellite launched on Oct. 10. MAC is also flying on the International Space Station on-board a NASA lidar mission called the Global Ecosystem Dynamics Investigation (GEDI), which launched last December. As a technology developed for space, MAC could make a valuable addition to the aerospace industry. An ongoing partnership with the Smithsonian Institution shows how MAC might have applications in other industries, as well.
Lighter, Faster, Simpler
Abraham started working with MAC during her first year at Goddard in 2010, when she was tasked with converting an old technology into a lighter, more efficient system.
“The old technology was called the adsorber puck system – they flew it on Goddard missions, but there were some disadvantages to using it,” she says.
Just like new household items can release or “offgas” molecules into the air, other materials can “outgas” in vacuum. Outgassing can occur from items that often are used within the spacecraft itself, such as epoxies, tapes, and lubricants. In the past, Goddard had used adsorber pucks made of a material called cordierite and shaped in a honeycomb pattern. The cordierite was layered with a zeolite slurry to “adsorb” or hold molecules within the surface area of the puck. Zeolite is a mineral with open pores or cavities that can capture molecules passively.
This mitigated contaminants from settling on the surfaces of sensitive instruments, where they could interfere with performance. Both the Hubble Space Telescope mission and the Tropical Rainfall Measurement Mission successfully incorporated adsorber pucks.
While the pucks did the job, they were heavy and bulky, and engineers had concerns associated with its durability. In space flight, where engineers carefully calculate mass to the milligram, extra weight can create problems or prevent a mission from adding hardware. Integration of the puck system was also fairly complex, requiring additional hardware for installation, which added time to the project schedule.
Similar to the adsorber pucks, MAC contains zeolite. With its large surface-area-to-mass ratio, zeolite works incredibly well at efficiently trapping molecular contaminants.
While the adsorber pucks are heavy objects that require installation, engineers can spray MAC directly on to a surface, such as the interior of the spacecraft itself or on panels that can be easily installed within instrument cavities and vacuum chambers. It forms a thin, lightweight coating and displays adsorbing capabilities similar to the pucks.
“Our testing has successfully shown that MAC adsorbs a wide range of molecular contaminants, such as hydrocarbons, plasticizers and silicones, in relevant space environments,” Abraham says. “The coating’s adsorptive properties are impressive and can be tailored for optimal performance per the application.”
NASA’s Ionospheric Connection Explorer (ICON) is shown attached to the Northrop Grumman Pegasus XL rocket inside Building 1555 at Vandenberg Air Force Base in California on Sept. 10, 2019.
Credits: NASA/Randy Beaudoin
MAC in Space
So far, MAC has demonstrated its effectiveness a number of times, but Abraham points to three examples in particular.
The ICON mission, which launched this year, incorporated small discs spray-coated with MAC and placed inside the instrument to adsorb contaminants and protect the far ultraviolet instrument from outgassed molecules during its mission lifetime.
“The instrument needs to meet its molecular contamination requirements – if they exceed a specific threshold, it can start to degrade the instrument’s performance,” Abraham explains. “The project has implemented MAC discs to mitigate the risks associated with on-orbit material outgassing within the highly sensitive instrument cavity.”
For the James Webb Space Telescope (JWST) mission, currently scheduled to launch in 2021, engineers used MAC during testing of the optical ground support equipment, thermal pathfinder model, and optical components in a vacuum chamber at NASA’s Johnson Space Center in Houston, Texas. NASA uses vacuum chambers to mimic the environment of space and test spacecraft before they launch.
Johnson has a vacuum chamber test facility called Chamber A, and as part of preparing JWST for space flight, engineers performed tests of the telescope’s components in vacuum. Engineers placed custom fabricated MAC samples within the test chamber, and the coating worked to entrap outgassed compounds, such as hydrocarbons and silicone-based pump oil. Testing carried on successfully, and JWST’s delicate components were not impacted by molecular contamination.
NASA also used MAC for the Global-scale Observations of the Limb and Disk (GOLD) mission, which launched in early 2018. NASA partnered with the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado-Boulder to develop and test the instrumentation for GOLD. The instrument completed vacuum environmental testing in Airbus, France. The project implemented the use of MAC as a mitigation technique to protect the instrument components from outgassed species during testing.
Abraham says that after she received the samples that were used during the test, her team analyzed them to determine the chemical species that were collected during its exposure in the vacuum chamber.
“Vacuum chambers are a great application for MAC because it will help capture those possibly harmful contaminants when testing spaceflight hardware,” Abraham says.
MAC and Partnerships
Through a Space Act Agreement between NASA and the Smithsonian Institution’s National Museum of Natural History, Abraham and a team of researchers are testing MAC’s versatility outside the aerospace industry, as well. Museum conservators wanted to know if MAC, with its ability to adsorb potentially harmful chemicals, could collect mercury vapor and other off-gassed species from some of the museum’s specimens.
“They want to protect their artifacts, just like we want to protect our instruments and satellites,” Abraham observes. “Contamination is an issue that reaches beyond space applications.”
Two years into the collaboration, the study has yielded some interesting results, and as the partnership continues, Abraham and her fellow researchers will be able to determine if MAC is a good fit for artifact conservation.
“The preliminary data seems promising,” she says.
Looking forward, Abraham says she’s open to exploring other partnerships and applications for MAC.
“I’ve been working on MAC for a long time, but it’s still exciting to me because I’m constantly learning new things about it,” she adds.