Like new cars, new telescopes come with their own unique smell. Unlike cars, telescopes are delicate enough that this smell can damage the high-precision instruments, killing them with their own outgassing. Here’s how NASA protects fragile space telescopes from themselves.
New materials outgas, releasing volatile organic chemicals that quickly disperse into the surrounding environment. The mix of residual solvents outgassing from new vehicles makes a distinctive, occasionally-enjoyable new car smell that may not be particularly healthy but aren’t critical damaging. With telescopes, that outgassing can be far more damaging.
The mix of outgassing solvents, epoxies, lubricants and other materials involved in the manufacture of telescopes and other delicate spacecraft create gasses that can easily damage the high-precision machines. NASA engineers determined to protect telescope mirrors, thermal control units, electronics boxes, detectors, solar arrays, and cryogenic instruments are always looking for new ways to protect their charges from contamination. The latest efforts led by Sharon Straka and Mark Hasegawa at NASA Goddard resulted in a low-cost, easy-to-apply sprayable paint. The paint absorbs outgassed molecules, preventing them from latching on to fragile instruments and their components.
The Molecular Adsorber Coating (MAC) is a sprayable paint made from zeolite paired with a colloidal silica binder to glue the coating together.
Zeolite is a common mineral that is highly permeable and porous to trap outgassing contaminants (and explains its industrial use in water purification), and lacks in any volatile organics that would add their own outgassing to the problem. The paint can be applied directly to surfaces without additional mounting equipment, and can be used to coat strips of tape that can be strategically tucked around the instrument.
The large pores and cavities of zeolite crystals are ideal for trapping outgassing contaminants. Image credit: NASA
The permeable, porous surface of zeolite paint is perfect for trapping volatile chemicals outgassed by new telescopes. Image credit: NASA
The paint is currently undergoing qualifications tests at NASA facilities, and is ready to be used during future flight or ground vacuum systems projects.
Several custom-designed test panels spray-coated with the paint were recently installed as a contamination mitigation tool for the Chamber A. Chamber A is NASA’s thermal-vaccuum space simulator, and the largest test facility of its type in the world. The 16.8 meter (55 foot) diameter, 27.4 meter (90 foot) tall chamber is where the space capsules for NASA’s Apollo missions were tested, both with and without crew, and has been upgraded for testing the James Webb Space Telescope. The matte interior walls look perpetually grubby, with an occasional burnished marks from where tools rubbed up against the walls, an ironic situation given the obsession with cleanliness.
Chamber A at NASA’s Johnson Space Center in Houston, Texas. Image credit: NASA
The panels were installed in Chamber A in advance of upcoming tests of the James Webb Space Telescope’s first Optical Ground Support Equipment (OGSE-1). The paint will capture any outgassed contaminants from outside the test chamber, protecting the telescope. NASA engineer Nithin Abraham explains:
Although we cannot stop contaminants within the vacuum chamber from outgassing, we can try to capture them with MAC before it tries and reaches the expensive hardware, which are housed inside the test chamber.
While NASA obviously does its best to ensure its test chambers are sparkling clean and clear of anything that may cause damage to the instruments being tested, some silicone-based contaminants are near-impossible to prevent.
The MAC panels were installed in very strategic locations within Chamber A to capture vacuum chamber contamination originating from persistent sources, such as silicone pump oil residue and hydrocarbons.
Now, even if the components outgas, the volatiles will hopefully be trapped by the MAC panels instead of migrating and depositing onto the Webb telescope’s optical surfaces.
Engineer Nithin Abraham taping a panel coated in outgas-adsorbing paint along the bottom of Chamber A in advance of James Webb Space Telescope space simulation tests. Image credit: NASA
The paint is an improvement over existing technology, which uses the same zeolite mineral but coated over cordierite, a mineral used to manufacture ceramic, to create puck-like devices. The pucks act like water-absorbing silica packets in shoeboxes, with each puck adsorbing a limited capacity of outgassed volatiles. Yet as Hasegawa complains, “These devices are big, heavy and chunky, and take up a lot of real estate,” making them less than ideal compared to the more flexible form-factor and lower-mass alternative of zeolite paint. The paint sticks to aluminum, stainless steal, and any other metal with a silicate-based coating, the most common structural materials for telescopes and spacecraft. The new paint even has about five times the adsorbtive capacity of other experiments with coating slurries, making it more useful for space applications where every gram adds launch costs. The paint is also cheaper than the other current alternative, electronic box bake-outs.
In future iterations, Straka is hoping to tweak the paint’s composition to enhance volatile adsorption even further, and possibly to tint it black so it can also suck up stray light. This would add another feature, protecting telescope sensors from being overwhelmed by noisy surplus photons during observations. The team is also experimenting with mixing the paint with high surface area systems like velvets and fibre mats are being conducted to try increasing adsorbtive capacity even further while simultaneously prohibiting electrostatic discharge.
In the future, this paint could move beyond terrestrial test chambers and be incorporated onto telescope structures directly to provide continuous protection. They could even help make living in space a bit more livable, with a quick paint job on the International Space Station trapping pollutants and odors in crew quarters. In an enclosed space with no laundry facilities, anything that reduces the stench of space habitats has to be a good idea.
Top image: Engineer Nithin Abraham performing testing on a new zeolite paint to provide low-cost, low-mass, flexible protection from outgassing contaminants. Credit: NASA/Pat Izzo