This onboard instrumentation system measures and records selected pressure, temperature, strain, vibration and event data to support payloads and experiments and to determine orbiter environments during flight. It supplements existing orbiter operational instrumentation by conditioning, digitizing and storing data from selected sensors and experiments.

The MADS collects detailed data during ascent, orbit and entry to define vehicle response to flight environments. It permits correlation of data from one flight to another and enables comparison of flight data from one orbiter to another orbiter.

All MADS equipment installed in the orbiter is structurally mounted and environmentally compatible with the orbiter and mission requirements. Because of its location, the MADS does not intrude into the payload envelope. Equipment consists of a pulse code modulation multiplexer, a frequency division multiplexer, a power distribution assembly and appropriate signal conditioners mounted on shelf 8 beneath the payload bay liner of the midfuselage.

In OV-102 Columbia), MADS inputs its information to the system control module and records it on the OEX recorder located below the crew compartment middeck floor. In OV-103 Discovery) and OV-104 Atlantis), a MADS control module and recorder are mounted below the crew compartment middeck floor.

MADS records approximately 246 measurements from the orbiter airframe, skin and orbital maneuvering system/reaction control system left-hand pod.

The MADS interfaces with the orbiter through the orbiter's electrical distribution system and operational instrumentation inputs for status monitoring. Coaxial cables and wire harnesses from the sensors are routed through the orbiter payload bay harness bundles to the signal conditioners, PCM multiplexer and FDM, attached to the midfuselage shelf. After the signal conditioners and the multiplexers have processed the data, four outputs of the FDM and one output of the PCM multiplexer are routed forward to the SCM in OV-102 for recording on the OEX recorders. In OV-103 and OV-104, the four outputs of the FDM and one output of the PCM multiplexer are routed forward to the MCM for recording on five tracks of the MADS recorder. In addition, the MADS recorder is used during ascent to record additional space shuttle data consisting of solid rocket booster wide band and external tank signals.

The MADS is not considered mandatory for launch, and its loss during flight does not cause a mission abort. It measures and records data for predetermined events established by test and mission requirements.

For a typical mission, approximately five hours before launch, the MADS is powered on from the preset switch configuration to supply a prelaunch manual calibration. (Power is supplied from the orbiter's main buses A and B.) After calibration, all switches are returned to the preset configuration, leaving the MADS in the standby position and only the MCM receiving power. This mode continues until nine minutes before launch, at which time the MADS attains the full-system mode through uplink commands and all its components are powered on. In this mode, the MADS recorder is operating at a continuous tape speed of 15 inches per second, recording aerodynamic coefficient identification package, flight acceleration safety cutoff, ET, SRB, wide-band and PCM data. The MADS PCM bit rate is 64 kbps.

The wide-band-only mode is used during the prelaunch automatic and manual calibrations. This mode records the ac and dc calibration levels provided by the FDM. Each manual calibration level is recorded for 10 seconds at a tape speed of 15 inches per second in the continuous mode.

Approximately 12 minutes after launch, the MADS is commanded into the PCM-snapshot-with-strain-gauge-signal-conditioner mode. In this mode, the recorder is in the sample mode, conserving power and recorder tape by recording data for 10 seconds every 10 minutes at a PCM bit rate of 32 kbps and a tape speed of 3.75 inches per second. Two minutes before the second orbital maneuvering system thrusting period, the MADS is commanded into the full-system mode until the thrusting period is completed. Then it is commanded into the PCM-only mode, which continues during the orbit until a quiescent period is reached. In OV-102 only, one minute of ACIP calibration is required during this period, after which the MADS continues in the PCM-only mode. The system is switched to the full-system mode for the OMS separation thrusting periods and can be returned to the PCM-only mode for the majority of the on-orbit mission.

The PCM-with-SGSC mode is similar to the PCM-only mode, but strain measurements are also recorded during this period. The SGSC operation is cycled along with the other MADS equipment and signal conditioners by uplink commands to maintain the required operational temperatures. This mode occurs between two full-system modes to minimize flight crew participation and conserve power and recorder tape. It can be initiated from the full-system mode or returned to the full-system mode by one uplink command. To shift this mode to the PCM-only mode, the SGSC must be commanded off manually by the flight crew. This mode is used on orbit.

Two minutes before the deorbit thrusting period, the MADS is put into the full-system mode for one hour to record descent (entry) data. At the conclusion of the one-hour period, it is placed in the PCM-only mode for approximately four hours to measure postlanding thermal data and is then powered down for the entire postlanding period.

With the use of the MADS switches located in the crew compartment, control can be initiated by the flight crew. To reduce the flight crew's participation, all commands are uplinked from the Mission Control Center in Houston and transmitted to the onboard payload forward 1 multiplexer/demultiplexer. The MDM then routes the commands to the SCM for processing in OV-102 and to the MCM in OV-103 and OV-104. Power for the MADS will be supplied by the orbiter's 28-volt dc main buses A and B.

The flight acceleration safety cutoff system interfaces 12 orbiter main engine vibration measurements with the MADS. The variety of MADS measurements is collected by thermocouples, resistance thermometers, radiometers, vibration sensors, strain gauges or pressure transducers.

The MADS shelf 8 components are protected from overheating by shelf temperature monitoring and control of MADS operation by ground commands. The MADS is thermally isolated from the orbiter structure by 0.049-inch thin-wall titanium struts. It is also protected from the orbiter environment by a 1.5-inch bulk-insulation enclosure.

The MADS recorders in OV-103 and OV-104 are Data Tape/Kodak 28-track, wide-band, modular, airborne recording systems similar to the OV-102 orbiter experiments recorder. The recorders are capable of simultaneously recording, and subsequently reproducing, 28 tracks of digital biphase L data or any combination of wide-band analog and digital biphase L data up to 28 tracks.

After OV-103 and OV-104 return from a mission, the recorder tape is played back to record the data on a ground recording system. The tape is not removed from the flight recorder. The total MADS weight is 641 pounds.