3D-Printed Plasma Sensors for Satellites

Figure courtesy of the researchers and edited by MIT News 3D printing Plasma sensors.jpg
MIT researchers have demonstrated a 3D-printed plasma sensor for orbiting spacecraft that works just as well as much more expensive, semiconductor sensors. These durable, precise sensors could be used effectively on inexpensive, lightweight satellites known as CubeSats, which are commonly utilized for environmental monitoring or weather prediction.
The devices, the first of their kind to be completely digitally manufactured, can be used to measure atmospheric conditions.

Scientists have developed the first completely digitally manufactured plasma sensors, fabricating for a much lower cost devices that can be used by orbiting spacecraft to determine atmospheric conditions, they said. Researchers from MIT developed the sensors, also known as retarding potential analyzers (RPAs), which are well-suited for use with CubeSats, they said. CubeSats are the low-power and lightweight satellites currently being deployed for communications and environmental monitoring in Earth’s upper atmosphere.

Plasma sensors are used by satellites to determine the chemical composition and ion energy distribution of the atmosphere. They are typically developed in a cleanroom, which require pristine conditions and thus are associated with high costs as well as weeks of fabrication.

The 3D-printed and laser-cut sensor developed by the MIT team, on the other hand, can be produced for tens of dollars in a matter of days, with a performance on par with state-of-the-art semiconductor plasma sensors, researchers said.

RPA History and Composition

The first use of an RPA was on a space mission in 1959 to detect the energy in ions, or charged particles, that are floating in plasma—a superheated mix of molecules present in the Earth’s upper atmosphere.

When used onboard an orbiting spacecraft like a CubeSat, the instruments measure energy and conduct chemical analyses that can help scientists predict the weather or monitor climate change, researchers said.

Structurally, the sensors are comprised of a series of electrically charged meshes dotted with tiny holes. As plasma passes through the holes, it strips away electrons and other particles until only ions remain, which create an electric current that the sensor measures and analyzes.

A housing structure that aligns the meshes is integral to the function of RPAs; it must be both electrically insulating and able to withstand sudden, drastic swings in temperature, researchers noted. To create this structure, the MIT team used a printable, glass-ceramic material known as Vitrolite that’s demonstrated both of these properties.

Novel Fabrication Method Using 3D Printing

The MIT team developed the RPAs using a glass-ceramic material that is more durable than traditional sensor materials such as silicon and thin-film coatings, researchers said. They used the material in a 3D-printing process typically used with polymers to fabricate sensors with complex shapes that can withstand the wide range of extreme temperatures that a spacecraft encounters in lower Earth orbit, they said.

The research shows the difference that additive manufacturing can make in the future of space hardware, noted Luis Fernando Velásquez-García, a principal scientist in MIT’s Microsystems Technology Laboratories (MTL), who led the research. “Some people think that when you 3D-print something, you have to concede less performance,” he said in a story posted to MIT News. “But we’ve shown that is not always the case. Sometimes there is nothing to trade off.”

The 3D printing process for ceramics typically involves blasting ceramic powder with a laser to fuse it into shapes. However, this process often leaves the material coarse and creates weak points in it due to the high heat, researchers said.

To correct these issues, researchers used a process called vat polymerization that’s been used for decades with polymers or resins, they said. This process builds a 3D structure one layer at a time by submerging it repeatedly into a vat of liquid material, which in this case was Vitrolite. Ultraviolet light cures the material after each layer is added, and then the platform is submerged in the vat again. The resulting structure is composed of layers that are each 100 microns thick, making it smooth and free of pores, researchers said.

Researchers published a paper on their work in the journal Additive Manufacturing. The team developed four prototype designs using the rapid development platform.

One was effective at capturing and measuring a wide range of plasmas, for example, while another was well-suited for sensing extremely dense and cold plasmas.

Future Innovations

Researchers said the high precision of this type of design not only can be useful for typical RPAs, but also 3D-printed for applications in fusion energy research or supersonic flight. It also could spur even more innovation in satellite and spacecraft design, Velásquez-García said. “Additive manufacturing is a very different way to make space hardware,” he explained in MIT News.  “I can make space hardware and if it fails, it doesn’t matter because I can make a new version very quickly and inexpensively, and really iterate on the design.”

The team aims to continue its work to enhance the fabrication process even further by reducing the thickness of layers or pixel size in glass-ceramic vat polymerization, Velásquez-García said. This could create complex hardware that is even more precise, he said.

Other innovations researchers aim to explore are the ability to print the sensors in space as well as the use of artificial intelligence to optimize sensor design for specific use cases, such as greatly reducing their mass while ensuring they remain structurally sound, Velásquez-García added.

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