Mass spectrometers on atmospheric entry probes require a method for introducing gas from high-pressure ambient regions to the vacuum of the mass spectrometer interior.
A microfabricated silicon mass spectrometer inlet leak has been designed, fabricated, and tested at NASA Goddard Space Flight Center. This leak achieves a much lower conductance in a smaller volume than is possible with commonly available metal or glass capillary tubing. It will also be possible to integrate additional functionality, such as inlet heaters and valves, into a silicon micro-leak with very little additional mass. The fabricated leak is compatible with high-temperature (up to 500 °C) and high-pressure (up to 100 bars) conditions, as would be encountered on a Venus atmospheric probe. These leaks behave in reasonable agreement with their theoretically calculated conductance, although this differs between devices and from the predicted value by as much as a factor of 2. This variation is believed to be the result of nonuniformity in the silicon etching process, which is characterized in this work. Future versions of this device can compensate for characterized process variations in order to produce devices in closer agreement with designed conductance values. The integration of an inlet heater into the leak device has also been demonstrated in this work.
The inlet leak has numerous benefits. Multiple flow channels are produced in parallel so that the risk of clogging with particles or droplets is reduced, and the materials used are non-reactive with most atmospheric gases to be sampled and thus will not distort the sample. The calibrated flow rates are many orders of magnitude lower than devices currently available for environmental sampling, which enables gas sampling with much smaller sample volumes. Also, a batch fabrication process means that the devices can be manufactured inexpensively.
This technology could be used in environmental gas sampling, and in small, field-deployable mass spectrometers for homeland security and point-of-care medical diagnostics.