Embedded Sensors for Measuring Surface Regression

The rungs are designed so that as each successive rung is eroded away, the resistance changes by an amount that yields a readily measurable signal larger than the background noise. (In addition, signal conditioning techniques are used in processing the resistance readings to mitigate the effect of noise.) Hence, each discrete change of resistance serves to indicate the arrival of the regressing host material front at the known depth of the affected resistor rung. The average rate of regression between two adjacent resistors can be calculated simply as the distance between the resistors divided by the time interval between their resistance jumps. Advanced data reduction techniques have also been developed to establish the instantaneous surface position and regression rate when the regressing front is between rungs.

A continuous MSRS is so named because instead of discrete rungs, there is one continuous strip of resistive material across the legs. Assuming that this strip has spatially uniform thickness and resistivity and that the electrical resistance of the legs is much less than that of the strip, the electrical resistance of this MSRS is inversely proportional to the remaining length of the sensor and, hence, to the remaining thickness of the host material in which it is embedded.

A ground-based sensor package has been developed (see Figure 2). Due to its small size and low mass potential, future generations of the MSRS technology could be applied to flight applications. One eventual goal is to provide the capability to record and transmit real-time regression data from a vehicle in flight. In this capacity, the sensor could serve a dual-use role by providing engineering data under actual operating conditions, as well as health monitoring of the host material.

This work was done by Daniel J. Gramer, Thomas J. Taagen, and Anton G. Vermaak of Orbital Technologies Corp. for Stennis Space Center.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to: Orbital Technologies Corp. (ORBITEC) 1212 Fourier Dr. Madison, WI 53717 Phone No.: (608) 827-5000 Refer to SSC-00140, volume and number of this NASA Tech Briefs issue, and the page number.