On 7 September 2017, the U.S. Air Force Research Laboratory launched the second Advanced Structurally Embedded Thermal Spreader (ASETS-II) flight experiment on the fifth flight [Orbital Test Vehicle 5 (OTV-5)] of the Air Force’s X-37B spaceplane. OTV-5 landed on 27 October 2019 after 780 days on orbit. The ASETS-II flight experiment accomplished its mission to demonstrate functionality, characterize behavior, and explore the predicted limits of operation of oscillating heat pipes (OHPs) in a long-term microgravity environment. The three science objectives were to measure initial on-orbit thermal performance, long-duration thermal performance, and any lifetime degradation. The three OHPs on ASETS-II have varying configuration (center heating with large and small heaters and with single- and double-ended cooling) and heat pipe fluids (butane and R-134a) to isolate performance parameters of interest. Data collected during on-orbit operation are presented and favorably compared to predicted OHP limits of operation. Each OHP performed as expected with no notable differences between horizontal and microgravity flight data. All three OHPs started easily, had similar performance on ground and on orbit, showed no hysteresis effects or degradation on orbit, and performed well in several six-week-duration continuous operation tests both on the ground and in orbit.

2017年9月7日，美国空军研究实验室在空军X-37B航天飞机的第五次飞行[轨道试验飞行器5（OTV-5）]上进行了第二次先进结构嵌入式热扩散器（ASETS-II）飞行实验。OTV-5 在轨道上飞行 780 天后于 2019 年 10 月 27 日着陆。ASETS-II 飞行实验完成了其在长期微重力环境中展示功能、表征行为和探索振荡热管 (OHP) 运行的预测极限的任务。三个科学目标是测量初始在轨热性能、长期热性能和任何寿命退化。ASETS-II 上的三个 OHP 具有不同的配置（使用大型和小型加热器以及单端和双端冷却的中心加热）和热管流体（丁烷和 R-134a）以隔离感兴趣的性能参数。呈现在轨运行期间收集的数据，并与预测的 OHP 运行限制进行比较。每个 OHP 都按预期执行，水平和微重力飞行数据之间没有显着差异。所有三架 OHP 启动都很容易，在地面和在轨的性能相似，在轨上没有出现滞后效应或退化，并且在地面和在轨的几个为期六周的连续运行测试中表现良好。呈现在轨运行期间收集的数据，并与预测的 OHP 运行限制进行比较。每个 OHP 都按预期执行，水平和微重力飞行数据之间没有显着差异。所有三架 OHP 启动都很容易，在地面和在轨的性能相似，在轨上没有出现滞后效应或退化，并且在地面和在轨的几个为期六周的连续运行测试中表现良好。呈现在轨运行期间收集的数据，并与预测的 OHP 运行限制进行比较。每个 OHP 都按预期执行，水平和微重力飞行数据之间没有显着差异。所有三架 OHP 启动都很容易，在地面和在轨的性能相似，在轨上没有出现滞后效应或退化，并且在地面和在轨的几个为期六周的连续运行测试中表现良好。