Single-Axis Air Bearing Testbed for Spacecraft Attitude Control Studies

Air bearings are a type of low-friction bearings which use a cushion of pressurized gas to interface between surfaces, effectively separating them while allowing the system to still hold together mechanically. Air bearings (and equivalent bushings) are generally made of a porous material through which a gas (usually air, but argon and CO₂ are also common) is sent to press against a very flat and smooth surface to create the offset. Other configurations are also possible, such as grooves and holes to carry the compressed gas, but the porous media is the most common. Due to their ability to reduce vibrations and friction throughout a mechanical system, they are ideal for use on experimental testbeds for sensitive and delicate hardware. Consequently, they have become a widely used tool in testbeds made for spacecraft attitude control studies. Previous development of testbeds utilizing air bearings for attitude control studies has focused on multiaxial motion of the system. However, a dedicated testbed for examining the motion of such a system in a single axis would be particularly useful. A single-axis testbed allows focused study and easier comparison of the observed motion with system models. This allows more accurate and useful model verification, so the generated system models can be more reliably used for design automation and to perform verification, validation, and accreditation (VV&A) procedures. The work presented in this study is a qualitative analysis of the design and development of a one-dimensional ground-based testing platform for the study of pointing accuracy and yaw for small spacecraft such as Strain Actuated Solar Arrays (SASA), Multifunctional Structures for Attitude Control (MSAC), and other dynamics and control analysis systems. This platform provides a simple, mechanically robust means for studying the pointing accuracy by removing the significant friction encountered in roller bearing systems, the instability seen in multi-axis air bearings, and additional constraints posed throughout the use of air spindles in similar testbed systems. The testbed utilizes two cylindrical air bearings that provide constraints for the vertical positioning of the shaft, while one linear air bearing provides an air cushion at the base that lifts the testbed. Initially, the design requirements and overall system robustness of the testbed are presented. Further, there is a discussion of potential experiments that can be done with the testbed, followed by verification and validation methods. There is also a discussion of the tradeoffs between different implementations of the system - specifically, the major differences between a supervised, simple system or permanent system with backup power and air supplies. Conceptual and practical approaches for each is briefly presented, with a focus on reducing damage risk, cost, and needed expertise for operation.