Impact Factors on Leakage Rate Calibration of Spacecraft in Accumulation Leak Detection with Helium Mass Spectrometer at Atmospheric Pressure

The influence of the three variables, including the quantity of filled helium, collection chamber volume and leakage-rate of realistic spacecraft, on the precision of leakage-rate calibration was theoretically and experimentally investigated in accumulation leak detection with helium mass spectrometer at normal pressure. The analyzed and calibrated results show that the three variables all have a major impact. To be specific, the calibrated leakage-rate increases linearly with an increasing amount of helium and decreases with an increased chamber volume;in a practical chamber volume of 30~100 m³, the calibrated leakage-rate steadily varies below 10^-9 order. With a realistic spacecraft leakage-rate below 1×10^-4 Pa·m³/s being calibrated within 1 h, the discrepancy between them was estimated to be less than 30%. We suggest that the calibration precision may be considerablly improved by shorting calibration time and with more uniform helium distribution.