The National Aeronautics and Space Administration (NASA) Kennedy Space Center requires accurate gas mixtures containing argon, helium, hydrogen, and oxygen in a balance of nitrogen to calibrate mass spectrometer-based sensors used around the space shuttle launch area and inside the shuttle cabin. NASA was in need of these gas mixtures to assure the safety of the shuttle launch system and shuttle cabin. In 2006, NIST certified three new sets of gas standards. These standards were compared to new primary standard mixtures (PSMs) and historic standards developed for NASA in 1993 that NIST had retained. Results between the suites of primary standards and the historic mixtures agreed, verifying the stability of the mixtures. NIST certified each component in these three new mixture suites to uncertainties better than 2 % relative.
Additional Technical Details:
A new suite of 22 primary standards bracketing the three concentration levels required were prepared gravimetrically. The standards used for the Level 1 and 2 NASA samples were compared to previously made standards (1993) to verify both stability and accuracy and to ensure the continuity of this program. No previously prepared standards existed for the Level 3 concentration standards (lowest concentration) and verification of stability will need to be confirmed for this mixture in the future.
NIST uses gas chromatography with thermal conductivity detectors (TCDs) to measure He, H2, O2, and Ar. TCDs provide precise measurements resulting in much low uncertainties in the final certified values. Measurement of the combination of He, H2, Ar, and O2 in a balance of N2 is a complex problem. The thermal conductivity is measured as the difference between the component of interest and the GC carrier gas. Because the thermal conductivity of the components of interest are different, two GC methods employing different carrier gases, He for Ar and O2, and N2 for He and H2, had to be developed for these analyses.
Start Date:October 1, 2005
End Date:October 2008
Lead Organizational Unit:mml
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