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Instrument: ADA : Atmospheric Density Accelerometer
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Investigation Name- Atmospheric Density Accelerometer (MESA)
NSSDC ID- 75-107A-02


Brief Description
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, which is directly proportional to
atmospheric density. 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 sample time of each instrument
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.
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.

[Summary provided by NASA]