The Lunar Exploration Gas Spectrometer (LEGS) is an instrument for studying the gas composition of lunar regolith. In the LEGS a 2.5 GHz solid state microwave transmitter positioned on a downward pointing horn is deployed by a lunar lander or rover using a long boom (e.g. 1-2 m) to set it down on the lunar surface, and then beams power into the regolith using its microwave transmitter. The microwaves directed down onto and into the ground contained under the horn, heating regolith to depths of several tens of centimeters. As a result, gases will be evolved from the cold subsurface regolith into the horn, where their composition will be analyzed by a near-infrared ~1 to 2.4-micron spectrometer mounted horn, and looking through a sapphire window into the interior of the horn illuminated by a tungsten lamp, enabling transmission spectra of evolved gases to be obtained. These instruments will provide qualitative and quantitative data on volatiles, potentially including water, hydrogen, helium, CO2, CO, ammonia hydrocarbons, and other species as they evolve from the subsurface over time. Since gases released by upper layers of regolith will reach the horn first, this procedure will also provide composition as a function of depth. Once gas emission ceases, the horn is lifted by the rod and placed on a new location, where the process is repeated. The LEGS deployment will involve very little disturbance to lunar soils prior to analysis, thereby preventing the accidental release of lightly-bound volatiles that is thought to be significant even following gentle handling. In the proposed program, a full scale working model of the LEGS, including horn, microwave transmitter, and spectrometer, will be built and tested in Pioneer Astronautics
The LEGS program will provide NASA with a key technology finding volatiles on the Moon, which represent a tremendous resource for human exploration. The data produced by the LEGS would be invaluable for lunar science itself, providing essential information for understanding the origin and history of the Moon and similar bodies no doubt present in orbit around numerous planets in other solar systems. LEGS could also be used on Mars, Phobos, Deimos, asteroids, moons of the outer planets, Mercury, Pluto and even comets.
The LEGS be used on Earth without major modification employing its IR spectrometer to determine amounts of volatiles, including trade contaminants, in the soil. It thus represents an instrument with broad potential utility for geology, resource exploration, and environmental remediation.