Design and characterization of a nano-Newton resolution thrust stand

Abstract

The paper describes the design, calibration, and characterization of a thrust stand capable of nano-Newton resolution. A low uncertainty calibration method is proposed and demonstrated. A passive eddy current based damper, which is non-contact and vacuum compatible, is employed. Signal analysis techniques are used to perform noise characterization, and potential sources are identified. Calibrated system noise floor suggests thrust measurement resolution of the order of 10 nN is feasible under laboratory conditions. Force measurement from this balance for a standard macroscale dielectric barrier discharge (DBD) plasma actuator is benchmarked with a commercial precision balance of 9.8 μN resolution and is found to be in good agreement. Published results of a microscale DBD plasma actuator force measurement and low pressure characterization of conventional plasma actuators are presented for completeness.

Comparison of Submillinewton Thrust Measurements Between a Laser Interferometer and a Load Cell on a Pendulum Balance

“…One of the most typical techniques used for thrust measurement involves the concept of the pendulum. In its simplest form, a pendulum thrust balance can be based on a hanging pendulum (Charles et al, 2016;Wong et al, 2012), an inverted pendulum (Haag, 1991;Kokal and Celik, 2017;Asakawa et al, 2020), or be a torsional balance (Ziemer, 2001;Zhou et al, 2013;Soni and Roy, 2013;Little and Jugroot, 2019;Tang et al, 2011;Zhang et al, 2017). There are also more complicated implementations of this, such as the stand for vertically oriented thrust measurement system described in Moeller and Polzin (2010).…”

Spiral coning manoeuvre for in-orbit low thrust characterisation in CubeSats

“…In some cases, higher vacuum level requirements as well as propellant reactivity concerns add to the complexity of the characterisation [5]. For propulsion systems in the order of µN, the characterisation can be particularly difficult because factors such as the weight of the thruster, stiffness of the feed and supply elements, ambient noise, thermal deformation, electrostatic and electromagnetic forces, and vacuum pump vibrations, are generally of higher magnitude than the thrust level itself overwhelming its action [5,17,42]. Another relevant aspect of these sort of laboratory tests is that in the absence of a dominant damping medium, primarily air, the start-up transient responses are long lasting.…”

A 10 nN resolution thrust-stand for micro-propulsion devices

“…[14][15][16][17][18][19][20][21][22][23][24] Most of these thrust-stands operate by mounting the microthruster and a counter-mass on a pivoted torsion arm and measuring deflection under applied thrust with a displacement sensor, such as a capacitive sensor, 18 a laser displacement sensor (LDS), 19 a linear voltage differential transformer (LVDT), 20 or an optical interferrometer. 21 The natural frequencies of the reported thrust-stands are typically in the subHz ranges and an additional damping mechanism, such as viscous damping, 20,22 damping coil, 17 electrostatic damping, 19 or Eddy current damping, 23 is used to reach steady deflection of the arms more quickly, and to minimize coupling to lowfrequency facility vibrations, which is a major source of noise for thrust-stands with low natural frequencies. Different types of calibration sources are used for accuracy and resolution estimation and several of the thrust-stands have reported sub-100 nN resolution, 16,18,[20][21][22] and as low as 10 nN.…”

“…Different types of calibration sources are used for accuracy and resolution estimation and several of the thrust-stands have reported sub-100 nN resolution, 16,18,[20][21][22] and as low as 10 nN. 19,23 The main a) Email: herbert.shea@epfl.ch challenges for such thrust-stands are facility vibrations, drift, effects of electrical and fluidic connectors to the thrusters, and the difficulty in operating with microthrusters with different thrust to mass ratios.…”

“…Accordingly, the natural frequency of the device is designed to be >50 Hz, compared with the few Hz or less typical of both existing impingement based stands 27 and direct-thrust torsional balances. 19,23 By suppressing all external influences outside a narrow bandwidth near the excitation frequency, this approach enables high resolution and low noise measurements; although frequency dependent thruster characterizations are inherently limited to slow variations, see Section III. This dynamic detection method also obviates the need for extensive design and characterization of a damping mechanism often necessary for a steady state low thrust measurement by either (direct 19,23 or impingement 27 based) approach.…”