Microwave and Electrostatic Probe Measurements on a Blunt Re-Entry Vehicle
The electron density profile on a blunt nosed body has been measured by microwave antennas and electrostatic probes during re-entry and compared with flowfield predictions. The flowfield models assumed a completely viscous layer behind the shock in the stagnation region. In one model the vibrational levels of the molecular species were assumed to be in equilibrium at the gas temperature. This condition was relaxed for the second model. The probes were operated at a high bias to collect the full random current at the sheath edge. The bias was varied in order to measure the electron density at several distances normal to the vehicle surface. The microwave measurements determined signal attenuation, reflection coefficient, and mutual coupling as a function of altitude. At altitudes between 200,000 and 250,000 ft, the viscous flowfield model which assumes vibrational nonequilibrium of the molecular species predicts the electron density over the hemispherical nosecap within an altitude error of less than two thousand feet. This variation is within the limits imposed by the expected diurnal and seasonal changes in the atmosphere.