An array of three thermistor flow probes deployed next to a plaster model.
These pencil-shaped flow probes were used in several contexts during the mission to measure flow speeds. Each probe has a tiny thermistor bead at its tip. The bead is heated, and support circuitry varies the amount of electrical current flowing through the bead in such a way that the bead's temperature is maintained constant.
If more water flows past the bead (higher flow speed or greater turbulence), then the bead loses heat more quickly; hence more electrical current is needed to maintain its temperature. By recording the amount of electrical current put through the bead, we indirectly measure the flow speed past the bead's tip.
These probes, although home-build, proved surprisingly robust and reliable.