Gilpin Matthew R, McGehee Will A, Arnold N Ivan, Natisin Michael R, Holley Zachary A
Jacobs Technology, Inc., 10 E. Saturn Blvd., Edwards AFB, California 93524, USA.
Rev Sci Instrum. 2022 Jun 1;93(6):065102. doi: 10.1063/5.0087716.
A dual-axis torsional thrust stand was successfully demonstrated at the Air Force Research Laboratory, enabling direct simultaneous thrust and mass loss measurement for the Air Force Electrospray Thruster Series 2 passively fed electrospray thruster. The dual-axis system is effectively two nulled torsional thrust stands sharing a single dual-axis gimbal with a thrust and mass resolution of ±0.2 µN and ±0.04 mg, respectively. The development of this system was inspired by a need for direct efficiency characterization of electrosprays via in situ mass measurements, and performance was compared to thruster masses measured pre- and post-testing using an analytical balance. Mass consumption data captured via the dual-axis stand, which is calibrated to a traceable uncertainty of 1.6%, varied between -5% and 18% as compared to analytical balance measurements throughout a multi-month testing effort highlighting the limitations in pre/post-weighing as a method for capturing propellant consumption due to absorption of atmospheric moisture when thrusters are removed from vacuum. Thrust stand tests were limited to short term operation with a daily available testing window of ∼5 h due to thrust stand drift following the 24 h cyclic temperature variations of the testing facility. A thorough investigation into the root cause of ambient thermal drift suggests that the thermal response of commercial flex-pivot bearings is directly producing spurious torques on the order of 10 μN m/°C. Additionally, unresolved charging effects on thrust stand hardware currently limit thrust stand operation to tests operating with a positive thruster polarity. Further development and long duration test stability require both a targeted investigation into flex-pivot thermal response and minimization of facility effects.
一种双轴扭转推力台在空军研究实验室成功展示，可对空军电喷雾推进器系列2被动式馈电电喷雾推进器进行直接同步推力和质量损失测量。该双轴系统实际上是两个调零扭转推力台，共用一个双轴万向节，推力分辨率和质量分辨率分别为±0.2微牛和±0.04毫克。该系统的开发灵感源于通过原位质量测量直接表征电喷雾效率的需求，并将其性能与使用分析天平在测试前后测量的推进器质量进行了比较。通过双轴台捕获的质量消耗数据，其校准后的可追溯不确定度为1.6%，在为期数月的测试过程中，与分析天平测量结果相比，变化范围在-5%至18%之间，这突出了在推进器从真空中取出时，由于大气水分吸收，预先/事后称重作为捕获推进剂消耗方法的局限性。由于测试设施的24小时循环温度变化导致推力台漂移，推力台测试仅限于短期运行，每日可用测试窗口约为5小时。对环境热漂移根本原因的深入调查表明，商用挠性枢轴轴承的热响应直接产生了约10微牛·米/°C的寄生扭矩。此外，推力台硬件上未解决的充电效应目前将推力台操作限制在推进器极性为正的测试中。进一步的开发和长期测试稳定性需要对挠性枢轴热响应进行有针对性的研究，并尽量减少设施影响。
