Air pipes

AFRL Oscillating Heat Pipes Are Even Cooler in Space > ONE AFRL / TWO SERVICES > Article Display

The Air Force Research Laboratory, or AFRL, has released the results of its Advanced Structurally Embedded Thermal Spreader Two, or ASETS-II. The AFRL experiment has been 100% efficient in testing the most recent version of the revolutionary Oscillating Heat Pipes, or OHPs, and the results of over 6,600 hours of in-orbit testing are available to the public.

“We now have a treasure trove of data,” said Jon Allison, thermal boost manager, for the Spacecraft Components Technology branch of the AFRL’s Space Vehicle Directorate. “Our results include 2.2 million data points that will increase confidence in the use of overhead projectors and facilitate continued advancements in technology. In particular, this dataset will be of great value to academics, as it offers high quality and spatial OHP performance, nothing less.

OHPs are revolutionizing the thermal control of spacecraft. ASETS-II paved the way for this next generation of spacecraft thermal control and this new data release portends further advances as the academic community uses it to increase our knowledge of OHP thermophysics.

“Quality spacecraft thermal control is important to ensure the functionality, reliability and cost-effectiveness of space systems,” Allison said. “The importance of reliable space systems cannot be underestimated as an integral part of our lives; from national defense, to commerce, to weather, and much more.

ASETS-II demonstrated that the thermal issues that plague spacecraft are not the case with well-made OHPs. Experimental space testing has proven effective in weeding out new technologies, including new thermal technologies that are prone to problems in the space environment.

“There’s a long history of testing new heat pipes and many don’t pass this type of test, but OHPs can and have,” Allison said. “We’re excited to add OHPs to this pantheon of space-suitable heat pipes – that’s something to get a heat pipe nerd excited!”

“These problems are often compounded, or at least different, in the weightless environment of space; many promising heat pipes have encountered problems in flight experiments,” he said. “In this case, we have shown that overhead projectors can overcome these problems.”

ASETS-II was flown on the Space Force X-37B, also known as the Orbital Test Vehicle, a reusable robotic spacecraft. This fifth flight of the X-37B, OTV-5, launched on September 7, 2017 and landed on October 27, 2019.

The success of this experiment builds on many years of effort by AFRL to develop overhead projectors, particularly designs that characterize their performance and under what conditions they fail.

“We are confident that OHPs can be designed to provide reliable operation in critical spacecraft applications, and ASETS-II played an important role in that conclusion,” said Colonel Jeremy Raley, Director of the AFRL Space Vehicles Directorate. “The overhead projectors worked as expected by our team, who have been working on this type of technology for many years.”

For years to come, the data collected on ASETS-II will be used to develop and test new theories about the complex thermophysics of OHPs, and will have a positive impact on future US space missions.

The data is available on the NASA Physical Sciences Informatics (PSI) website:

About the AFRL

The Air Force Research Laboratory (AFRL) is the principal scientific research and development center of the Department of the Air Force. The AFRL plays a critical role in the discovery, development and integration of affordable combat technologies for our air, space and cyberspace force. With a staff of over 11,500 people in nine technology areas and 40 other operations around the world, AFRL offers a diverse portfolio of science and technology ranging from basic research to advanced research and technology development. For more information visit: