Low-frequency vibration and high-resolution performance in micro thrust measurement system utilizing high temperature superconducting composite bearing

High-precision space missions like drag free control demand electric thrusters to achieve highly precise thrust output, which presents challenges for ground micro-thrust measurement. Especially, the gravitational wave detection specifies a requirement for low-frequency noise to be below 0.1 μN/Hz 1/2 within 0.1 mHz ∼ 1 Hz frequency range. Coupling of low-frequency vibration noise is a primary obstacle to achieving extremely high measurement precision. Characterized by self-stabilized levitation, a high temperature superconducting (HTS) composite bearing is adopted in micro-Newton thrust measurement system to achieve non-contact vibration isolation, low measurement noise and high resolution. The bearing provides a stable measurement environment with vibration noise below 10 −6 m/Hz 1/2 in the frequency range of 10 mHz–5 Hz based on 10 000 s axial vibration performance test. Additionally, the low frequency rotation loss and oscillation damping of HTS composite bearing are experimentally investigated under different air gap and temperature. The result indicates that the HTS composite bearing achieves low friction coefficient of 6 × 10 −7 and oscillation damping coefficient of 6.09 × 10 −7 Nm/(rad/s) under 4.8 K temperature and 29 mm total gap. Electromagnetic calibration method is adopted to confirm a resolution of 0.108 μN with 16.33% error. The performance of an electrospray thruster was evaluated using the oscillation mode. The ignition test results revealed that the lateral circumferential noise remains below 0.1 μN/Hz 1/2 within the 1 mHz to 1 Hz frequency, increasing to 1 μN/Hz 1/2 within10 mHz ∼ 1 Hz frequency during thrust ignition. The low-frequency vibration isolation capability and high-resolution performance ensure the significant application value of the HTS composite bearing in micro-thrust measurement and ground simulation of micro-propulsion satellite attitude control.