Numerical Study of Behavior of Outgas from Heat Shield of Solar Probe

摘要

When a solar probe penetrates into the solar corona for in-situ observation of the solar wind, the graphitic heat shield temperature is expected to increase to over 2000 K and surface sublimation will occur. The sublimation gas is numerically studied by using the direct simulation Monte Carlo method. The length scale and the Knudsen number are evaluated with respect to the interaction phenomena between the solar wind and the outgas from the heat shield. When the total sublimation rate and the number density of the solar wind are large, the velocity distribution function of the solar wind around the probe is expected to become quite different from that of the undisturbed freestream due to molecular collisions. Numerical results indicate that the total sublimation rate must be 10~(-6) kg/s or lower to avoid serious errors in the solar wind measurements. Thermal analyses show that the inclined graphitic disk heat shield can satisfy this requirement. Detailed rarefied flow simulation is also made around the spacecraft consisting of the heat shield and the main body. Favorable location for the sensor is discussed from a viewpoint of the solar wind observation.