This experiment was designed to measure the kinetic temperature of the neutral atmosphere by
determining the instantaneous density of molecular nitrogen in a spherical chamber coupled to the
atmosphere through a knife-edged orifice. Analysis of the measured molecular nitrogen density variation
over a spin cycle with a knowledge of the satellite's motion and orientation led to a determination
of the ambient temperature, independent of scale height. Measurements of the ambient neutral composition
were obtained when the instrument was commanded into the appropriate mode. Approximate values for the
meridional wind were obtained from the measurement of the "stream" position relative to the satellite
velocity. An alternate measurement of neutral temperature was also undertaken, using a baffle inserted
in front of the orifice to intercept a portion of the gas particle stream entering the chamber. When the
satellite was in the despun mode, the baffle was made to oscillate in a stepwise fashion in order to
interrupt the particle stream seen by the orificed chamber. These chamber density variations were
interpreted to yield the neutral gas kinetic temperature too. A dual-filament ion source sampled the
thermalized molecular nitrogen in the chamber and produced an ion beam density proportional to the
nitrogen chamber density. From the source, this ionized nitrogen beam was directed into a quadrupole
analyzer, tuned to pass those particles with a mass-to-charge ratio of 28. The beam then struck an
electron multiplier, and the output pulses were amplified and counted. The sensor was vacuum-sealed prior
to launch and opened to the atmosphere after the spacecraft was in orbit. More experiment details can
be found in N. W. Spencer et al., Radio Sci., v. 8, n. 4, p. 287, 1973.