Ultrasonic sensors for lunar and Earth resource processing and manufacturing

The economic feasibility of a sustained human presence on the Moon (and later Mars) requires the use of resources in a manner that is minimally or not dependent on material or energy support from Earth, To that end, a prototype processing plant is being built to demonstrate the capability of extracting silicon, iron, titanium and aluminum metals and oxides to be used as feedstocks in lunar manufacturing facilities for the production of materials for structural and photovoltaic applications and non specular reflecting powders. The use of leaching and reduction vats requires liquid level sensors to provide state information for automatic process control. A multitransducer ultrasonic level sensor system has been constructed to measure liquid levels in several vats. Measurement is through the external bottom wall of each vat, with a urethane rubber gasket between the transducer and container to improve coupling. Levels are determined by conversion of time-of-flight measurement using a pulser-receiver and a GPIB-based universal counter communicating with a personal computer. Multiplexing of the electronics is accomplished with a single-pole, multithrow RF switch controllable from the computer via a digital I/O interface. The liquid level measurement accuracy requirement of 5% is easily met, and resolution better than 0.2% is routine