Gas standards development in support of NASA's sensor calibration program around the space shuttle

Area of Science:

• Metrology and Analytical Chemistry
• Aerospace Engineering and Safety

Background:

• NASA's Kennedy Space Center requires precise gas mixtures (argon, helium, hydrogen, oxygen in nitrogen) for calibrating mass spectrometer sensors on space vehicles.
• Accurate calibration is essential for monitoring launch areas, shuttle cabins, and ensuring the safety of manned and unmanned space missions.

Purpose of the Study:

• To develop and certify primary standard mixtures (PSMs) for critical gas components used by NASA.
• To provide NIST-traceable standards for calibrating NASA's mass spectrometers, ensuring measurement accuracy and reliability.

Main Methods:

• NIST developed gravimetric primary standard mixtures (PSMs) using precise weighing techniques with uncertainties below 0.1%.
• NIST certified commercially prepared gas mixtures (Scott Specialty Gases, AIRGAS) by comparing them against the developed PSMs.
• Concentration values and expanded uncertainties (95% confidence interval) were assigned to the certified mixtures.

Main Results:

• NIST successfully prepared and validated two suites of PSMs in 1993 and 2006, confirming stability and accuracy over time.
• Commercial gas mixtures prepared by Scott Specialty Gases and AIRGAS were certified by NIST with relative expanded uncertainties ranging from 0.8-10% and 0.5-2.2%, respectively.
• A total of 12 NIST-traceable standards were supplied to NASA in 1993, with additional sets provided in 2006 to meet evolving needs, including lower concentration levels.

Conclusions:

• NIST's primary standard mixtures provide a reliable basis for certifying gas mixtures critical for NASA's space exploration and safety monitoring.
• The long-term stability and accuracy of these standards ensure consistent calibration of mass spectrometers, supporting mission integrity.
• The development and certification process highlights the crucial role of metrology in advancing aerospace technology and safety protocols.