⚡ electrical engineering

Ground-based Air-bearing Equivalent Verification for Active Vibration Isolation for Space Microgravity Utilization

This paper establishes and validates a ground-based air-bearing platform as a faithful and stable equivalent to space microgravity for verifying the performance of active vibration isolation systems across multiple degrees of freedom.

Original authors: Tongzhe Zhang, Song Wang, Mengxi Yu, Wenbo Dong

Published 2026-08-28

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CC BY 4.0

Original authors: Tongzhe Zhang, Song Wang, Mengxi Yu, Wenbo Dong

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Space is a place of profound silence, but it is not a place of perfect stillness. For the most delicate instruments humanity has ever built, such as the optical clocks and precision telescopes intended for future missions, even the tiniest tremor is a disaster. In the vacuum of orbit, these devices require an environment of near-perfect stillness, where vibrations are suppressed to a level so faint it is measured in billionths of the force of Earth's gravity. To ensure these instruments work when they finally reach space, engineers must test them on the ground. However, this presents a paradox: how do you test a machine designed to float in weightlessness while it is firmly stuck to the floor of a laboratory? The Earth's gravity pulls everything down, creating a mechanical coupling that distorts the very behavior scientists are trying to study. Traditional methods of lifting heavy objects with cables or magnetic fields often introduce their own unwanted stiffness or friction, failing to recreate the true, free-floating state of space.

To solve this, researchers at the Technology and Engineering Center for Space Utilization have developed a new way to simulate the silence of space using a simple yet powerful principle: air. By floating a heavy platform on a thin cushion of air, much like a hovercraft, they can create a surface that moves with almost no friction. This allows the platform to drift freely in horizontal directions, mimicking the weightless environment of orbit. The team set out to prove that this ground-based air-floating system is not just a clever trick, but a faithful equivalent to the real thing. They built a sophisticated testbed to verify whether a system designed to isolate vibrations in space could be accurately tested on Earth, and whether the air cushion itself introduces any hidden problems that could mislead engineers.

The researchers constructed a test system where a heavy "floater" sits on an air-bearing platform, separated from the ground by a microscopic layer of compressed air. This floater represents the sensitive payload, while the ground beneath it represents the noisy environment of a spacecraft or the Earth itself. To keep the floater stable and isolated from vibrations, the team used a dual-loop control system. One part of the system watches the position of the floater, while the other part monitors its acceleration. By combining these two streams of information, the system can apply precise electromagnetic forces to counteract any movement, keeping the payload perfectly still even when the ground beneath it is shaking. The team first had to answer a fundamental question: does testing just the horizontal movements of this floating platform tell the whole story? In space, an object can move and rotate in six different directions, but the air-bearing platform only floats freely in three. Through detailed mathematical modeling, the researchers demonstrated that the forces connecting these different directions are so weak that they can be ignored. This means that by testing the platform in its three floating directions, engineers can confidently predict how the system will behave in the full six-directional environment of space.

With the theory confirmed, the team moved to the laboratory to put the system through its paces. They subjected the platform to a series of rigorous tests, starting with a check of its ability to hold still. They compared a simple control method that only looked at position against their advanced dual-loop system. The results were clear: the simple method struggled with the low-frequency vibrations caused by the air supply and the connecting cables, but the dual-loop system successfully suppressed these disturbances, reducing the vibration levels to a mere 2e-7g. This is the specific performance target required for the space optical clock the system is designed to protect. To test the system's strength, they then shook the platform with white noise, a chaotic mix of vibrations spanning a wide range of frequencies. Even when the ground was vibrating intensely, the floating payload remained remarkably stable. The system reduced the vibrations by a factor of one hundred in the critical low-to-mid frequency range, and in the most sensitive mid-frequency band, it suppressed the noise by a factor of one hundred thousand, effectively silencing the chaos beneath it.

Perhaps the most critical test was one of endurance. Space missions can last for years, and a vibration isolation system must remain reliable over long periods. The researchers ran their system continuously for 55 hours, monitoring its performance day and night. The data revealed a clear pattern: the system worked best at night, when the building was quiet and human activity had ceased. During the day, the vibrations from the surrounding environment were slightly higher, and the air supply system itself introduced small, periodic ripples every 40 minutes as the air pumps cycled on and off. Despite these external factors, the system maintained its stability throughout the entire test, proving that it could operate reliably over extended durations. The study concludes that the air-bearing simulation method is a viable and accurate way to verify active vibration isolation systems for space. It offers a practical path for engineers to test their designs on the ground with the confidence that the results will hold true once the hardware is floating in the microgravity of space.

Technical Summary: Ground-based Air-bearing Equivalent Verification for Active Vibration Isolation for Space Microgravity Utilization

Problem Statement
Ground-based verification of active vibration isolation systems for space microgravity applications faces a fundamental challenge: the 1g terrestrial environment differs significantly from the space microgravity environment in terms of mechanical behavior. Traditional gravity compensation methods—such as suspension systems, quasi-zero stiffness (QZS) mechanisms, and magnetic levitation—struggle to simultaneously achieve an ideal microgravity state across multiple degrees of freedom (DOFs) due to mechanical coupling, parameter sensitivity, or the need for sustained static forces that introduce noise and thermal drift. While drop towers and parabolic flights offer true microgravity, their brief duration makes them unsuitable for validating active systems requiring long-duration or ultra-low-frequency operation. Consequently, there is a need to determine if horizontal air-bearing systems, which offer nearly frictionless support in three DOFs, can serve as a faithful equivalent to true space microgravity for the verification of six-DOF active isolation systems.

Methodology
The authors developed a low-disturbance ground simulation testbed based on an air-bearing platform to verify an active vibration isolation system designed for a space optical clock (targeting a combined six-DOF performance of 2e-7g). The methodology comprised three main components:

System Design: A testbed was constructed comprising an air-bearing microgravity simulation platform, a stator/floater assembly, an electromagnetic actuation system (eight voice coil motors), and a high-precision measurement and control system. The electronics architecture, including control logic and sensor suites (PSDs and triaxial accelerometers), was kept identical to the on-orbit flight system to ensure engineering fidelity. The system utilizes a dual-loop control architecture combining pulse-averaged acceleration feedback and displacement feedback.
Theoretical Modeling and Equivalence Analysis: A six-DOF dynamic model of the air-bearing platform was established to analyze the equivalence between the ground-based three-DOF (horizontal) test and the actual six-DOF space configuration. The authors mathematically demonstrated that under specific conditions—negligible off-diagonal coupling terms in stiffness and damping matrices, small stator angular velocities (negligible Coriolis and centrifugal forces), and the use of counterweights to match mass-inertia properties—the dynamic performance of a 3-DOF air-bearing test is virtually identical to that of a 6-DOF space system. This validates a "direction-wise" testing approach where the platform is reoriented to test different axes independently.
Experimental Verification: Three categories of experiments were conducted:
- Static Control Tests: To evaluate the isolation performance in different orientations ( $[x, y, z, \theta_z]$ , $[z, x, y, \theta_x]$ , and $[x, y, z, \theta_y]$ ) using both single-loop displacement control and the proposed dual-loop strategy.
- Disturbance Rejection Tests: White-noise excitation (0.1–250 Hz) was applied to the stator to measure the system's broadband suppression capabilities.
- Long-Term Stability Tests: A 55-hour endurance test was performed to assess system reliability and characterize environmental disturbances over time.

Key Results

Control Performance: The dual-loop control strategy (combining acceleration and displacement feedback) significantly outperformed single-loop displacement control. In the 0.1–1 Hz band, the dual-loop scheme reduced floater vibrations to approximately $2 \times 10^{-7} \, m/s^2/\sqrt{Hz}$ , achieving the target precision of 2e-7g. It effectively mitigated low-frequency disturbances caused by the umbilical cable, which degraded the performance of displacement-only control.
Disturbance Suppression: Under white-noise excitation, the system demonstrated excellent full-spectrum isolation. The suppression ratio remained below -20 dB across the entire frequency range, reaching as high as -50 dB in the 5–20 Hz mid-frequency region. The system maintained stability even when stator vibration levels exceeded $1 \times 10^{-4} \, m/s^2/\sqrt{Hz}$ .
Long-Term Stability: The 55-hour endurance test confirmed the system's reliability. The results revealed distinct environmental influences, including a 40-minute periodic fluctuation linked to the air pump's intermittent replenishment and a day-night performance variation (better isolation at night due to reduced human activity and ambient vibration). Despite these factors, the isolator consistently attenuated low- and mid-frequency ambient disturbances.
Equivalence Validation: Theoretical analysis and experimental data confirmed that the 3-DOF air-bearing simulation, when reoriented to test different axes, adequately emulates the dynamics and control performance of the full six-DOF system in space, provided the system operates in a static-base, high-precision pointing scenario with negligible angular rates.

Significance and Claims
The paper claims to provide a viable technical pathway for the ground-based performance testing of active vibration isolation systems intended for space microgravity applications. By establishing a dynamic model and conducting rigorous experimental verification, the authors demonstrate that air-bearing systems can effectively substitute for the space microgravity environment. The work furnishes both a theoretical foundation and experimental support for validating these systems, addressing the critical gap between 1g ground conditions and space requirements. The study confirms that the proposed direction-wise testing method is sufficient for verifying the dynamic characteristics of six-DOF active isolators, thereby supporting the development of high-precision payloads for future space missions.

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