Researchers at the Massachusetts Institute of Technology (MIT) have used 3D printing to create unique plasma sensors that could help scientists better understand the impact of climate change.
Compared to traditional weather monitoring sensors, the team’s laser-cut and 3D-printed alternative can be produced outside of cleanroom conditions, reducing its delivery time from weeks to just days. This, coupled with their relatively low manufacturing cost, could make the devices ideal for installation on CubeSats, where they can monitor temperature fluctuations in low Earth orbit (LEO).
“Additive manufacturing can make a big difference to the future of space hardware,” says MIT senior scientist Luis Fernando Velásquez-García. “Some people think that when you 3D print something, you have to give up less performance. “But we’ve shown that’s not always the case. Sometimes there is nothing to exchange.
Make monitoring more accessible
When it comes to monitoring changing weather conditions in LEO, Retarding Potential Analyzers (RPA) are essential equipment. First deployed on a space mission in 1959, these multi-electrode instruments essentially detect the energy of ions floating in plasma molecules in Earth’s upper atmosphere. Also used as orbiting mass spectrometers, the general-purpose sensors are capable of measuring energy and analyzing chemicals to inform weather forecasts.
RPAs themselves work by using a series of electrically charged meshes with tiny holes to pull electrons and other particles away from the ions, which in turn create a current that can be measured and analyzed. According to the MIT team, the effectiveness of these devices depends on the alignment of their casing structure and mesh, as well as their insularity and their ability to withstand drastic temperature variations.
However, the scientists also point out that today’s plasma sensors tend to be made from silicon under cleanroom conditions, through a process that requires weeks of complex manufacturing. As such, RPAs can be very expensive, limiting their potential for adaptation to CubeSats that are making LEO-based R&D increasingly accessible. With that in mind, the MIT team has developed a way to 3D print them from glass-ceramic, which could help advance in situ ionospheric studies.
“If you want to innovate, you have to be able to fail and take the risk. Additive manufacturing is a very different way of making space hardware,” says Velásquez-García. “I can build space hardware and if it fails it doesn’t matter because I can build a new version very quickly and inexpensively and really iterate on the design. It is an ideal sandbox for researchers.
“When you make this sensor in the cleanroom, you don’t have the same degree of freedom to define the materials and structures and how they interact with each other. What has made this possible are the latest developments in additive manufacturing.
Presentation of a 3D printed ‘RPA’ sensor
At the heart of the team’s redesigned sensor is a stack of five laser-cut electrodes, inside a 3D-printed glass-ceramic electrode housing and CNC-machined shroud. In practice, the housing is designed to spatially distribute the electrodes using a set of grooves which cooperate with a set of deflection springs. That said, the researchers actually explored two different stacking designs, one in which all the openings were the same size, and another where the clusters were paired to a single opening in a “floating grid” formation. “.
Both were made using a Tethon 3D Bison 1000 system and Vitrolite, a durable pigmented glass capable of withstanding temperatures up to 800°C, and designed with hexagonal openings, to maximize the number can be installed. For each RPA design, the size of the aperture was also optimized via finite element analyses, with the goal of achieving optimum ion transmission through the device grid.
Once ready, the team put their prototypes through ion energy delivery simulations and hands-on testing via an electron impact ionizer and helicon plasma tests. In the first case, both designs proved capable of accurately estimating the average ion energy, but in practical evaluations the devices showed potential in different application areas.
In practice, the uniform grid design was particularly effective in measuring a wide range of plasmas, similar to those a satellite would normally encounter in orbit. However, the other, featuring floating gate alignment, proved better suited for detecting dense, cold plasmas, with an accuracy of only 50 µm, the likes of which are usually only measurable at using ultra-precise semiconductor devices.
Since the tests revealed that their devices could “perform at state-of-the-art heights”, the researchers concluded that they had significant potential as a way to facilitate accessible weather monitoring. In the future, the team even thinks that binder jetting 3D printing could be used to produce even more parts of the RPA, in a way that could reduce its mass and improve its performance.
Enter the era of 3D printed CubeSats
Additive manufacturing continues to find widespread satellite applications, not only in the creation of accessories, but the cases of the devices themselves. ROBOZE, for example, has partnered with the University of Colorado at Boulder to 3D print a weather monitoring CubeSat designed to analyze electromagnetic waves caused by lightning.
Alongside Alba Orbital and Mini-Cubes, CRP Technology has also continuously used its Windform XT 2.0 material to 3D print pocket satellites and deployers. Working with the former, the company has previously deployed the technology and its carbon fiber composite to reduce the weight of the PocketQube “Alba 2” deployers by 60%.
On a more commercial level, the Franco-Italian aerospace manufacturer Thales Alenia Space continues to use 3D printing in the mass production of satellites. In fact, just last month, the company announced plans to work with start-up MIPRONS to develop a new 3D-printed water-powered satellite thruster with improved maneuverability.
The researchers’ findings are detailed in their paper titled “Compact glass-ceramic polymerization-enabled retardant potential analyzers for CubeSat and laboratory plasma diagnostics”, which was co-written by Javier Izquierdo-Reyes, Zoey Bigelow, Nicholas K. Lubinsky and Luis Fernando Velásquez-García.
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The featured image shows the researchers’ 3D-printed plasma sensor. Photos via MIT.