This innovation is a tungsten-rhenium gauge that can be placed into an aft exit cone of a rocket motor. It will measure heat flux with time for the full duration of the RSRM (reusable solid rocket motor) nozzle environment with equal response time.

Existing gauges are made of Type T, J, or K thermocouple alloys, with Type T the most common alloy, and have a copper heat sink. All of these gauges will melt or vaporize below the temperatures found in the RSRM nozzle. The measurement of heat flux in the RSRM nozzle requires that the gauge be made from the highest operating temperature alloys available. The tungsten-rhenium thermocouple alloy is calibrated to 4,200 °F (≈2,315 °C). This is the only known material that will work in this application. The temperature and high velocities within the nozzle require the gauge wall thickness to be increased in order to survive. Existing gauges are made from thin foil and are too fragile for the nozzle environment.

The differences in the nozzle heat flux gauge design include thermocouple alloy selection (tungsten-rhenium Type C alloy), heavy wall thickness for durability, and custom mounting design compatible with nozzle instrumentation practices. The gauge also allows for the probe surface temperatures to be above the slag melt temperature to avoid slag solidification on and erosion of the gauge surface. The gauge also does not need to be water-cooled.

Data from existing heat flux gauges is of short duration — only for a few seconds until the gauge is destroyed. The gauge described here will survive for the full or nearly full duration of a RSRM motor firing and provide accurate data. Aluminum oxide slag will not coat or significantly erode the surface of the gauge. Minor thermal and mechanical erosion will occur on the gauge, but the design is robust, allowing minor erosion while still providing accurate data. The gauge installation design is compatible with standard practices and existing data acquisition equipment.

This work was done by Paul Bauer, Kenneth Rimington, and Edward Mathias of ATK for Marshall Space Flight Center. For more information, contact Ronald C. Darty, Licensing Executive in the MSFC Technology Transfer Office, at This email address is being protected from spambots. You need JavaScript enabled to view it.. Refer to MFS-33139-1.


NASA Tech Briefs Magazine

This article first appeared in the March, 2015 issue of NASA Tech Briefs Magazine.

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