A software program analyzes data measured by the Vehicle Cabin Atmosphere Monitor (VCAM) and quantifies the concentrations of trace chemicals detected by VCAM. The software contains a unique way to quantify the signal measured by VCAM, to establish the concentration curve, and to decide which gain mode data to use for concentration estimation. It solves the problem of quantifying the concentration of trace chemicals in the International Space Station (ISS) internal air using the VCAM miniature gas-chromatograph/mass spectrometer instrument.
The developed process involves the design of a measured signal quantification scheme, the construction of concentration curves, the decision rule of applying high- or low-gain concentration curves, and the detection of saturation, low-signals, and outliers. This means that a signal must be captured, then quantified, and the relationship between the signals and concentration of the desired trace gasses is examined, within a certain margin of error.
VCAM divides the trace gas species to be quantified into three priorities. Priority 1 has the requirement of one hundred percent of successful detection and identification. Priority 2 and Priority 3 require 80 and 70 percent of detection and identification, respectively. For all three priorities, the error budget for quantification is 40 percent. When the developed quantification process is applied, the average errors of concentration for most of the trace chemicals are found to be between 14 and 66 percent.
In order to reduce the error to below 40 percent, several approaches are considered for future work. One approach is to tune the instrument hardware gain parameters in order to increase the reliability and sensitivity of the ion count to the change of concentration. Another approach is to individually fine-tune the high-low gain switch decision rule in the quantification method for each chemical.