May 8, 2020
NASA to demonstrate first in-space manufacturing for space mirrors
Large telescopes that could be used for detecting and analyzing Earth-like planets in orbit around other stars or for peering back in time to observe the very early universe may not necessarily have to be built and assembled on the ground. In the future, NASA could construct them in space.
A NASA engineer was selected for a flight opportunity to show that an advanced thin-film manufacturing technique called atomic layer deposition, or ALD, could apply wavelength-specific reflective coatings onto a sample in space—one of the first steps in ultimately realizing the vision of constructing and assembling large telescopes in microgravity.
"We technologists think next-generation telescopes larger than 20 meters in diameter will be built and assembled in orbit," said Vivek Dwivedi, an engineer at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and an expert in ALD technology. "Instead of manufacturing the mirrors on the ground, why not print them in space? But you don't have a telescope mirror unless you coat it with a highly reflective material. Our idea is to show that we could coat an optic in space using this technique, which we've used on the ground and understand the processes," Dwivedi said.
He and his collaborator, University of Maryland professor Raymond Adomaitis, will now have a chance to demonstrate the concept in space for the first time.
Blue Origin Suborbital Flight Test
Recently, NASA's Space Technology Mission Directorate's Flight Opportunities program selected Dwivedi and Adomaitis to fly a football-sized ALD chamber aboard a Blue Origin New Shepard rocket. The launch will provide three minutes of microgravity, long enough for the automated payload to apply a thin film of a well-known ALD material, alumina, onto a two-inch silicon wafer. "Alumina is a bread-and-butter material in ALD applications," Dwivedi said. "It's been extensively researched."
Commonly used by industry, ALD involves placing a substrate or sample inside an oven-like reactor chamber and pulsing different types of gases to create a smooth, highly uniform film whose layers are no thicker than a single atom.
ALD-coated Samples in Space
ALD may also have applications for dust mitigation, another challenge NASA is working to solve. Currently, ALD-coated samples are being exposed to plasma from an experiment pallet aboard the International Space Station. Dwivedi and Goddard technologist Mark Hasegawa created these samples to test whether indium tin oxide—an effective compound for dissipating electrical charges—might be applied to paints and other materials to prevent lunar dust from adhering to rovers, instruments, and spacesuits.
Mitigating the dust problem is considered one of NASA's thorniest challenges as the agency plans to establish a sustainable presence on the Moon under the Artemis program.
For in-space manufacturing, ALD offers a distinct advantage, Dwivedi said. ALD chambers scale to any size and can consistently apply smooth layers over very large areas. "If we scaled a silicon wafer to the size of the Washington metropolitan area and placed it inside an ALD chamber, for example, we could deposit a layer of material that varied no more than 60 microns in thickness," Dwivedi said, illustrating the technique's precision, which would be essential for developing sensitive optics.
Although Dwivedi and Adomaitis have built several ALD chambers using Goddard Internal Research and Development program funding, they've decided to fly a chamber made of commercial off-the-shelf parts during the suborbital test flight.
Dwivedi said he and Adomaitis conceived the idea about two years ago. A Goddard colleague, Franklin Robinson, secured a test via Flight Opportunities also on a Blue Origin New Shepard rocket and proved a groundbreaking technology for effectively cooling tightly packed instrument electronics.
"We worked very hard to get this opportunity," Dwivedi said. We can't wait to get the payload launched to see how well this technique works in space."