The miniature electrostatic analyzer (MESA) obtained data on the neutral density of the
atmosphere in the altitude range of 120 to 400 km from 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 along 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 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 (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; in addition, there may be a
systematic error of up to plus or minus 5% due to drag coefficient uncertainty. 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 useful
data that exist from this investigation.