JPL Small Satellite Dynamics Testbed Planar Air Bearing Propulsion System Characterization

The Small Satellite Dynamics Testbed (SSDT) at JPL offers infrastructure that supports SmallSat guidance and control algorithm testing in a relevant dynamics environment while constrained by Earth’s gravitational effects. One of the SSDT’s testing environments is its planar air-bearing platform, which has two lateral and one rotational degree of freedom. This paper details the planar air-bearing test platform’s new position-control system, which uses an array of compressed-gas thrusters, and it characterizes the pertinent design and performance parameters related to the platform and propulsion system. The addition of this capability required a hardware and software redesign from the previous uncontrolled platform. A detailed description of the changes in the platform’s hardware and software systems is provided, including interface circuit and thruster control software architecture. Testing shows the reconfigured system has a maximum float time of 13.5 minutes, an average maximum thrust per thruster of 0.51 N, a tank pressure drop of 6.85 PSI/sec, and minimum impulse bit of 40 ms. The paper further presents results necessary for designing position controllers for use on this system, such as the relationship between number of thrusters firing and output force, and the timing latency in the thruster firing control system. We describe the effect of firing multiple thrusters simultaneously on the per-thruster force, and show that the embedded computer used in this platform exhibits timing delays of approximately 34 ms. The implications of these results on control system design are discussed in the conclusions.

美国喷气推进实验室（JPL）的小型卫星动力学测试平台（Small Satellite Dynamics Testbed，SSDT）提供了一套基础设施，可在受地球引力效应约束的相关动力学环境中支持小卫星（SmallSat）制导与控制算法的测试。SSDT的测试环境之一是平面气浮平台，该平台具有两个横向自由度和一个旋转自由度。本文详细介绍了平面气浮测试平台的新型位置控制系统——该系统采用压缩气体推力器阵列，并对平台及推进系统相关的关键设计与性能参数进行了表征。为新增此功能，需对原有无控平台进行软硬件重新设计。文中详细描述了平台软硬件系统的变更，包括接口电路与推力器控制软件架构。测试结果表明，重新配置后的系统最大浮起时间为13.5分钟，单推力器平均最大推力为0.51牛（N），储箱压力下降速率为6.85磅/平方英寸每秒（PSI/sec），最小脉冲宽度为40毫秒（ms）。本文还给出了用于该系统位置控制器设计所需的关键结果，例如同时点火的推力器数量与输出力之间的关系，以及推力器点火控制系统中的时间延迟。我们描述了多推力器同时点火对单推力器出力的影响，并表明该平台所用嵌入式计算机的时间延迟约为34毫秒（ms）。结论部分讨论了这些结果对控制系统设计的启示。