Abstract
An air data sensor (ADS) system is one of the key components in space transports. It can provide precious information on the pressure and the Mach number data that cannot be obtained from internal motion sensors. When a spaceship or a reentry vehicle is cruising at a very high altitude, the ADS will suffer problem of the time-delay in its pressure signals that propagates through a thin pressure tube. In this study, the time delay of the pressure propagation inside a thin tube under a low-pressure environment is evaluated based on the direct-simulation Monte-Carlo (DSMC) method. A CFD analysis based on axisymmetric Navier-Stokes equations is also conducted to evaluate the contribution of rarefied gas effects to the pressure propagation speed. These results are compared with experimental results. Based on the DSMC and CFD analyses, the time constant for the pressure change is determined to be around 0.013 seconds whereas the experimental results yielded 0.12 seconds when the pressure at the exit of the tube increases for about 20 to 40 Pa starting from 30 Pa. These results suggest that the propagation delay observed in the flight test of the atmospheric-entry capsule descending at an altitude of 79 km with Mach-4.5 flight velocity was partly caused by the rarefied gas effect.
