Atmospheric density measurements with a satellite-borne microphone gage

Abstract

A sensitive instrument that determines atmospheric density from ram pressure has been flown in a satellite. The sensing element of the instrument, a ribbon microphone, is rotated through the forward direction of motion to obtain the maximum ram pressure. This pressure is given by p = KpV2, where p is the atmospheric gas density, V the known vehicle velocity, and K a proportionality constant whose value (1≤K≤1.33) depends on the accommodation coefficient. The sensitivity of the instrument is monitored in flight with the aid of a calibration pressure source. Atmospheric density measurements were made at 500-km altitude during the daytime and at 550 km at nighttime. The measurements agree well with satellite orbit decay data. The day-night density variation was measured to be approximately a factor of 4 at 550 km.