High-Temperature Microwave Dielectric Properties and Processing of JS']JSC-1AC Lunar Simulant

Successful development of extraterrestrial microwave heating technologies depends on the study of the dielectric properties that control the microwave heating behavior of simulants and regoliths. Microwave heating may serve many lunar applications including heating the regolith for lunar surface dust stabilization, oxygen production, building materials, and mineral refinement. The dielectric properties (dielectric constant, epsilon, and loss factor, epsilon) of the lunar simulant, JSC-1AC, were measured at 2.45 GHz microwave frequency from room temperature to 1,100 degrees C. The dielectric loss tangent and half-power depth were calculated from the measured properties. The loss tangent increased from a low value of 0.02 at room temperature to a high value of 0.31 at 1,100 degrees C, indicating increased efficiency of microwave absorption at higher temperatures. The low temperature loss tangent indicated that relatively slow, low efficiency heating would be expected at room temperature. The microwave heating experiments confirmed weak heating related to absorption below 250 degrees C, and increasingly strong absorption above 250 degrees C, leading to rapid heating and melting or the so-called thermal runaway of JSC-1AC. Heating with microwaves as the only energy source produced a thermal runaway with wide variations in the JSC-1AC, such as fully molten glass, with unsintered loose particulate located millimeters away. The addition of a supplemental radiant heat source to the microwave mitigated the thermal runaway effect and produced uniform solid materials from the JSC-1A lunar simulant. The room temperature dielectric properties of JSC-1AC were measured and found to be comparable with the range of published lunar regolith properties, making JSC-1AC a reasonable starting point for microwave heating and computational modeling studies.