In-Situ resource assessment and process control with laser Raman spectroscopy

For in-situ resource utilization certain tasks must be accomplished, including prospecting for available resources and process monitoring and control. During prospecting, surface materials are identified as to whether they contain mineral or molecular components needed for the anticipated process; then ores are found in which these materials are most concentrated. Following size reduction and/or pulverization [1], raw materials are transported and introduced into the processor unit, where intermediate and final products are analyzed to ascertain that the production process is proceeding as desired. With continual monitoring of intermediate products, feedback may be employed as part of the control strategy. For in-situ application, laser Raman spectroscopy is the ideal resource assessment technique for all these tasks. It has the capability to (1) characterize resource minerals in rocks, soils, or ices; (2) prospect for ores by identifying high concentrations of desired resource material; and (3) monitor a production process by characterizing intermediate and final products (solids or liquids). Moreover, the technique has been implemented in a compact instrument suitable for spacecraft use, e.g. on the surfaces of Mars, the Moon, asteroids, etc. Two years ago, we proposed consideration of laser Raman spectroscopy for incorporation into lander spacecraft [2], having recognized that technological developments had progressed in a number of areas to the point where miniaturization of the typical laboratory configuration became feasible. In particular, these included (1) miniaturized lasers to provide the exciting radiation; (2) fiber-optic wave guides to allow convenient transmission of the exciting and scattered radiation, including over long distances; (3) holographic notch filters, permitting exclusion of the intense, exciting radiation from the collection fiber, and hence the detector; and (4) CCD detector arrays, which permit miniaturization of the detection system, and hence the entire spectrometer. With support from NASA’s Planetary Instrument Definition and Development Program (PIDDP), we have recently completed a (Mark Ia) laser (785 nm) Raman spectrometer measurement system that is adapted, by virtue of its small size, mass, and power requirements, for in-situ use on planetary surfaces. A more sensitive Mark II instrument is under construction. A typical measurement with this instrument requires seconds or less. To make a measurement, the Raman probe component is placed near (~1–10 mm) the target material. Being comparable in size and shape to a cigarette, the probe can easily be positioned for resource assessment by a manipulator arm attached to a rover or other mobile platform. It can also be incorporated into a production facility for continual process monitoring. With fiber access to multiple Raman probes, and appropriate switching among fibers, all of these functions could be accomplished with a single spectrometer, e.g. used to monitor various stages in the production process.