In the continued effort to make space more effective for the warfighter, Jonathan Allison is making strides.
An engineer and lead for the Integrated Structural Systems Tech team in the Air Force Research Laboratory’s Space Vehicles Directorate at New Mexico’s Kirtland Air Force Base, Allison was recently awarded a patent for a Ground Testable Spacecraft Heat Pipe (GTSHP).
“This invention was motivated by the difficulty of ground testing typical spacecraft heat pipes, and that drives costs and risks,” Allison said. “As we do R&D (research and development), it's really important that we're thinking not just about making cool new things, but that we’re making things that integrate into existing systems, offering economic solutions that solve the bigger needs of the Space Force.”
For a spacecraft orbiting Earth, maintaining a stable temperature is a challenge. Sensitive electronics generate heat, and without effective cooling, they can overheat and fail. Heating and cooling from the sun and deep space also creates thermal challenges. Heat pipes manage this thermal load by transferring heat away from sensitive components to radiators that release it into space. Testing these systems on the ground is tough because typical spacecraft heat pipes are optimized to work well in space and gravity can prevent them from functioning, making it difficult to accurately test how they will work in orbit.
“Ground testing is always an important factor, but we often have to make compromises in the design that make the ground test more difficult in order to make the spacecraft function better in space,” Allison said. “Ground testability can drive issues relating to how long it takes to do a test, how well you're able to do the test, how well you understand what's going on.”
Allison’s invention aims to alleviate the testing problem by lifting heat against gravity without resorting to existing solutions such as tight porosity wicks, small flow paths or mediocre pumps, which lead to higher costs and lower thermal conductance.
The engineer found his pipe inspiration from a bubble pump invented by Wilfred Sorensen over 40 years ago. The tiny, built-in pump uses bubbles to lift the liquid coolant against gravity. This allows the heat pipe to function effectively during testing without relying on the aforementioned expensive and restrictive internal structures. This concept has significant implications for the future of spacecraft design, possibly adding up to cheaper spacecraft and improved reliability in orbit.
“I realized that if that (bubble pump) was combined with another kind of heat pipe, we could get a function that doesn't just carry heat up or doesn't just carry heat down but can do a combination of those,” Allison said. “That was the invention.
“The GTSHP offers a breakthrough in providing affordable ground testing capability of heat pipe thermal control systems which can enable the avoidance of pumped fluid loops. Pumped fluid loops are exceedingly expensive and have a failure rate of one failure for every six pumped fluid loops.”
Next to space, Allison sees a purpose for the GTSHP down here on Earth, as well.
“I think this one's probably going to find applications in the petrochemical industry,” he said. “In the petrochemical world, they typically just pump their fluids around when they need to move heat. But they don't necessarily have to. This ground testable spacecraft heat pipe would allow them to do that.
"Any kind of industry or sector where you're needing to isothermalize (i.e. make its temperature consistent) something or move heat from one place to another, especially when you're trying to go from up to down or some combination of up and down.”
Along with the heat pipe, Allison has a stable of space-related patents he has authored for AFRL. The others – a Deployable Radiator Panel System, Asynchronous Autogenously Pressurized In-Space Propulsion and Spacecraft Dual Use Deployable Element – tackle thermal management, propulsion and maneuverability. Much like the GTSHP there’s also a concentration on delivering value to the space warfighter.
United States Patent Office Patent: #12, 359, 876
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The Air Force Research Laboratory, or AFRL, is the primary scientific research and development center for the Department of the Air Force. AFRL plays an integral role in leading the discovery, development, and integration of affordable warfighting technologies for our air, space, and cyberspace forces. With a workforce spanning across nine technology areas and 40 other operations around the globe, AFRL provides a diverse portfolio of science and technology ranging from fundamental to advanced research and technology development. For more information, visit www.afresearchlab.com.