The Space Shuttle Orbiter Atmospheric Revitalization Pressure Control System (ARPCS) and the Fuel Cell System (FCS) use a hot wire anemometer type of gas mass flow sensor for flow measurement. In the ARPCS oxygen and nitrogen mass flows are measured and in the FCS oxygen and hydrogen mass flows are measured. The existing flow sensors suffer from certain accuracy limitations and potential failure modes. A new type of commercially developed solid state micro-machined silicon gas mass flow sensor developed by Honeywell was adapted to allow the technology to be assessed for the application.
A demonstration test program has been conducted to evaluate the performance characteristics of the new sensor for space system applications and environments. The testing was sponsored by the National Aeronautics and Space Administration (NASA) at the Johnson Space Center (JSC). The primary testing was conducted at Carleton Technologies Inc. using nitrogen, oxygen and helium (as a surrogate for hydrogen). Hydrogen testing will be conducted at JSC. The objective of the tests was to determine if the new flow sensing technology would benefit the Shuttle and Space Station programs.
The new “smart” sensor has many advantages over the existing technology. These include low power consumption, very low drift rate, measurement capability over a 15000:1 flow range (compared to less than 1000:1 for the existing technology), high accuracy and the ability to be used with different gas types without modification or recalibration. The sensor has built in temperature and gas composition compensation, based upon heat transfer measurements.
The paper discusses the sensor operating principle, the test methodology, the sensor operational requirements and the test results.