| The increasing interests in space science missions and fundamental experiments re-quire the miscellaneous thrusters to provide extremely accurate thrust down to theμN-level for the attitude and position control, drag compensation, and de-orbit maneuver of the space-crafts. Recently, different types of the micro thrusters are being developed to meet the re-quirements of the space missions. In order to evaluate the performance of the thrusters in the ground test, the thrust stand is a universal and direct solution to measure the impulse bit per pulse and the thrust with the required precision, which plays a significant role in the development of the thrusters.In order to satisfy the requirements of further space science missions in our country, we develop a torsion-type thrust stand suitable for studies of micro-Newton thrusters, which is combined with the rich experience within the torsion-type tools in our laboratory. By virtue of specially suspending design and precise assembly of torsion balance configuration, the thrust stand not only has a load capacity up to several kilograms, but also is able to mea-sure the impulse bit in open loop mode and the average thrust in both open and close loop mode with a sub-micro-Newton accuracy. The inherent resolution of the thrust stand tested by gravitational source method is better than 6.3nN, and the sensitivity of static for-noise measurement is better than 0.1μN/(?) from 10-4 to 0.1Hz. We consider many possible systematic error sources to correct the parameters of the thrust stand to make sure our mea-surement results are convincing, such as the fluctuation of the vacuum temperature and the pressure, the propellant decrease, and the external torque provided by the thruster wires. The final thrust stand is capable of measuring the impulse bit up to 1350μNs with a resolu-tion of 0.47μNs, and the average thrust up to 264μN with a resolution of 0.09μN, which is limited by the accuracy of angular measurement.A pulsed plasma thruster, the preliminary prototype developed by Center for Space Science and Applied Research, Chinese Academy of Sciences, is tested by the thrust stand, and the results reveal that the average impulse bit per pulse is measured to be (58.4±2.9)μNs with a repeatability of about 5%, the average thrusts were (36.0±2.1)μN with a stability of 6% at 0.5Hz, (62.6±2.3)μN with a stability of 4% at 1Hz, and (95.3±1.3)μN with a stability of 1% at 2Hz, respectively. The accuracy of the measured results is about one order worse than the systematic uncertainty of the thrust stand, which is shows that the repeatability of the continual pulses is not well and dominant in the total error of the results, Besides, after checking the continual pulses frequencies of the thruster, we find the relation between the pulse frequency and the average thrust is not linearity at higher frequency, which indicates the discharge voltage is inadequate while the PPT working at the frequency of 2Hz. According to the analysis of the test results, we propose some improvement scheme for further thruster research.This work is supported by the National High Technology Research and Development Program of China under Grant No.2008AA12A215. |
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