Space telescopes are a pretty amazing thing. By deploying an observatory to orbit, astronomers are able to take pictures of the Universe unencumbered by atmospheric disturbance. At the same time, they are very expensive to build, maintain, and launch into space. As the case of Hubble’s flawed mirror demonstrated, a space telescope also has to go through rigorous checks because of how difficult it becomes to service them after launch.
To address this, NASA is investigating the possibility of constructing future space telescopes in space. A key aspect of this involves a manufacturing technique known as Atomic Layer Deposition (ALD), a process where layers of material no thicker than an atom is deposited on a surface and then hardened in place. Now, a team of NASA-supported researchers has been given the chance to test ALD in a microgravity environment (i.e. space!)
The researcher team includes Vivek Dwivedi (an engineer at NASA’s Goddard Space Flight Center and an expert in ALD technology) and Raymond Adomaitis – a professor of chemical and biomolecular engineering at the University of Maryland’s Institute for Systems Research (ISR). Together, they were selected through NASA’s Space Technology Mission Directorate’s (STMD) Flight Opportunities program.
The ALD process is commonly used in industry and involves placing a layer of material (aka. a substrate) inside an oven-like reactor chamber and then treating it with pulses of different types of gas. This end result is a smooth, highly uniform film with layers that are only a single atom in thickness. In the case of space telescopes, the method could be used to apply wavelength-specific reflective coatings onto a telescope’s mirror.
As Dwivedi explained in a recent NASA press statement:
“We technologists think next-generation telescopes larger than 20 meters in diameter will be built and assembled in orbit. 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.”
As part of their flight opportunity, Dwivedi and Adomaitis will see one of an ALD chambers they built using commercial off-the-shelf (COTS) components flown to space aboard a Blue Origin New Shepard reusable rocket. During the flight, the payload will experience three minutes of microgravity, just long enough for the ALD chamber to deposit a layer of aluminum oxide (aka. alumina) onto a two-inch (5 cm) silicon wafer.
Dwivedi and Adomaitis conceived the idea about two years ago after a fellow NASA Goddard colleague (Franklin Robinson) secured a test via Flight Opportunities to validate a groundbreaking cooling technology for tightly-packed electronics. This test also involved sending a technology demonstrator aboard a New Shepard rocket to see how it faired in a microgravity environment.
Beyond providing a means for augmenting telescope mirrors, ALD may also have other applications that will aid in future space exploration. For instance, dust mitigation is a major necessity when it comes to lunar exploration because of the way the statically-charged regolith sticks to everything.
The possibility of using ALD to combat this problem is currently being investigated aboard the ISS, where ALD-coated samples are being exposed to plasma from an experiment pallet. Dwivedi created these samples alongside Mark Hasegawa (a technologist with NASA Goddard) to test whether indium tin oxide could be used in paints and other materials to prevent lunar dust from sticking to spacesuits, rovers, and equipment.
Beyond building telescopes in space, ALD offers a distinct advantage to all kinds of in-space manufacturing, says Dwivedi. ALD chambers are scalable to any size and are capable of consistently applying smooth layers over very large areas. This level of precision would be essential for the development of sensitive optics and other applications.
“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,” he said. Aside from optics and dust mitigation, this process could be used in orbit to apply ablative shielding to spacecraft destined for other planets or even other star systems!
Between manufacturing in space, mining asteroids, and deep-space exploration, so much of humanity’s future involves setting up shop in Earth orbit and beyond!
Further Reading: NASA