The Miniature Electrostatic Analyzer (MESA) obtained data on the neutral density
of the atmosphere in the altitude range of 120 to 400 km by the measurements of satellite
deceleration due to aerodynamic drag. The instrument consisted of three single-axis
accelerometers, mounted mutually at right angles, two in the spacecraft X-Y plane and the other
in the Z-axis. The instrument determined the applied acceleration from the electrostatic force
required to recenter a proof mass. The output of the device was a digital pulse rate proportional
to the applied acceleration. The sample time of each measurement was 0.25 s. The measurements
allowed determination of the density of the neutral atmosphere, monitored the thrust of the
orbit-adjust propulsion system (OAPS), determined the satellite minimum altitude, measured
spacecraft roll, and provided some attitude-sensing information. Spacecraft nutations of less
than 0.01 deg were monitored. The instrument had three sensitivity ranges: 8.E-3 earth's
gravity (G) in OAPS monitor mode; 4.E-4 G between 120 km (plus or minus 2%) and 280 km
(plus or minus 10%); and 2.E-5 G between 180 km (plus or minus 2%) and 400 km (plus or
minus 10%). Numbers in parentheses represent errors. A systematic error of up to plus or
minus 5% due to drag coefficient uncertainty was also possible. The highest measurement
altitude was determined assuming the instrument could sense to 0.2% of full scale. More
details can be found in K. S. W. Champion et al., Radio Sci., v. 8, n. 4, p. 297, 1973.
NSSDC has all the data that exist from this investigation.