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HARDWARE INFORMATION

Gas Analyzer System for Metabolic Analysis Physiology (GASMAP)
Hardware Type
Measurement Devices, Physiologic

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Description
The Gas Analyzer System for Metabolic Analysis Physiology (GASMAP) device is used to monitor and analyze inhaled and exhaled breath streams to determine their gas concentrations. The primary gases of interest are nitrogen (N2), oxygen (O2), carbon dioxide (CO2), water (H2O), nitrous oxide (N2O), argon (Ar), acetylene (C2H2), sulfur hexafluoride (SF6), helium (He), and carbon monoxide (C18O).

The GASMAP flight hardware consists of two components: an analyzer module and a calibration module, both of which are housed in drawers inside Spacelab. The analyzer module contains all the sensor and electronic hardware of the GASMAP. The major sub-assemblies of the analyzer module are the Random Access Mass Spectrometer (RAMS), the Roughing system, the Gas Delivery System (GDS), the Interface Shell (IS) computer and the power connection. The module is controlled via the keypad and liquid crystal display (LCD) of the front panel, or via a laptop computer.

The Random Access Mass Spectrometer (RAMS) is the largest assembly of the analyzer module. Through software control, the RAMS can measure molecular mass-to-charge ratio in the range of 1 to 250 AMU (atomic mass unit) with a resolution of 1 AMU and sensitivity down to 250 ppm (parts per million). A Single Board Computer resides in the RAMS and is dedicated to performing housekeeping functions and calculating gas concentrations. The gas data are sent out on ten analog outputs, reading gas and range. In addition, data transfer through two computer ports is available. The analog RAMS readings are displayed on the front panel of the GASMAP device and a second signal is prepared for data down link by the Interface Shell computer.

The functional components of the RAMS include a gas inlet valve, an ionizer, a mass filter, a collector, an ion pump, a roughing system and a gas delivery system. The gas inlet valve controls the inlet of small amounts of gas into the ionization chamber (in the range of micro liters), independent from the outside pressure. In the ionization chamber the gas molecules are ionized by electron bombardment and released to the mass filter system, which consists of electrically charged rods. The electrons are neutralized when brought into contact with the rods. This allows the calculation of (gas) concentrations. The process must be repeated separately for each analyzed gas.

The Roughing system provides the necessary hardware and vacuum interfaces to pump down the analyzer in the event of a loss of vacuum, which is necessary for nominal operations.

The GDS provides constant gas sample flow rates in the range of 10 to 150 cc per minute to the RAMS for analysis. The system contains a micron screen to protect the analyzer from debris and liquid and a flow meter to provide the desired target flow. To eliminate any pulsation effects, a surge chamber is added just before the gas enters the RAMS through the inlet valve.

The IS computer also controls the GASMAP subcomponents, acquires data, and transfers data to display devices, to the rack controller, and to analog outputs. The calibration module is compatible with the analyzer module and is used to calibrate the RAMS readings on a regular schedule. Three cylinders, filled with known gas mixtures, are installed in the calibration device. Knowing the mixture enables the operator to compare the readings of the GASMAP system and adjust them if necessary.

Versions of this Hardware
+ Version Used During Space Shuttle Missions
+ Version Used During the NASA-Mir Missions
+ Version Used During the International Space Station (ISS) Experiments