Computer models that predict the rate at which molecular contamination will deposit on
optical surfaces typically use outgassing source terms, measured with quartz crystal
microbalances, as a basis for the prediction. The American Society of Testing and
Materials, Standard Test Method for Contamination Outgassing Characteristics of
Spacecraft Materials (Method E-1559), is probably the best know technique used by the
aerospace community to measure the outgassing rates or source terms of materials.
A simple method for the insitu calibration of quartz crystal microbalances, based on the
heat of enthalphy of Adipic Acid, has been developed and demonstrated by the Marshall
Space Flight Center, Environmental Effects Branch. The calibration has been
demonstrated over a sample temperature range of 25 to 66 degrees Celsius and deposition
rates of 2 x 10-11 grams/cm2-s and greater, for several measurement system
configurations. This calibration technique is fully compatible with the American
Society for Testing and Materials, Method E-1559, as well as other methodology. The
calibration requires no modification of outgassing facilities employing an effusion cell
and does not degrade the performance or function of typical vacuum systems.