LPI Technical Report 92-06 33 3-17253 TABLE 2. Selected X-ray escape depths ( A). ASSESSMENT OF THE LUNAR SURFACE LAYER AND IN SITU MATERIALS TO SUSTAIN CONSTRUCTION- Energies (eV) RELATED APPLICATIONS. Stewart W. Johnson1 and Koon Material 30.5 72.4 91.5 151.1 Meng Chua2, 'BDM International, Inc., 1801 Randolph Road SE, 10084 glass 190 430 530 670 Albuquerque NM 87106, USA, Department of Civil Engineering, 67701 glass 180 470 510 630 University of New Mexico, Albuquerque NM 87131, USA. ZnS 380 420 660 In this paper we focus on present and future technologies to facilitate lunar composition and resource assessment with appli- It is also useful to know how thick a region of the lunar surface cations to lunar surface construction. We are particularly inter- will be sampled by these soft X-rays. We have estimated mean ested in the construction activity associated with lunar-based escape depths for several energies and compositions corresponding astronomy. We address, as an example, the use of ground-probing to a mare glass, a highland glass, and ZnS using the mass attenuation radar to help assess subsurface conditions at sites for observatories coefficients of Henke et al. [4], and present them in Table 2. and other facilities. High spatial resolution combined with the thin surface layer We feel that a multidisciplinary effort is desirable to identify from which these soft X-rays arise suggests the exciting possibility what engineering data on the lunar environment and on the lunar that X-ray telescopes could map lunar volcanic volatiles from orbit. soil and rock should be collected and how it should be obtained. The most characteristic feature of known lunar volcanic volatile Johnson and Burns [1] have urged action to acquire the following deposits is a conspicuous enrichment in sulfur and zinc on grain information and resolve issues indicated: (1) topographic maps of surfaces [5,6]. These Zn,S-rich surface films can be seen in SEM potential observatory sites (e.g., 10-cm contours over an area 1 km images. In XPS studies [7) we have found surface Zn concentrations in radius); (2) detailed boulder sizes and counts over the same higher than 5 atomic percent and have estimated a depth of at area; (3) surveys (e.g., by radar, microwave, or other means) for least 100 A. Thus Apollo 17 orange glass appears to have enough subsurface boulders over critical areas where foundations and Zn and S to be seen from orbit, and it would be very surprising excavation are desired; (4) surveys of depth-to-bedrock (with if there are not other lunar regions much richer in volcanic suitable definition and characterization of bedrock); (5) trenching volatiles. and bulldozing experiments to establish energy requirements and In our XPS studies of lunar regolith fines |8) we found that depth limitations of these operations; (6) drilling and coring exper- a significant fraction of the iron in the outer few hundred ang- iments (with energy consumption and depth limitations clarified); stroms of grain surfaces was reduced to the metallic form, pre- (7) force-vs. -depth cone penetrometer measurements to be used sumably as a result of micrometeorite vaporization and solar wind for siting settlement-sensitive telescope structures; (8) trafficability effects. Because of the strong possibility of substantial reoxidation measurements including establishing energy consumption, slope- of lunar material during storage, sample preparation, and analysis, climbing capabilities, and formation of ruts or depressed surfaces we cannot know what the reduced fraction was on the lunar by repeated traverses of unprepared surfaces; and (9) electrostatic surface, but it may have been large. The M2j XPS lines and M>}VV charge measurements. Auger lines of Fe++ and Fe° have different shapes and energies, This listing has grown out of discussions with Dr. W. David allowing them to be easily distinguished. It seems likely that the Carrier III of the Lunar Geotechnical Institute and others. The Mi)V X-ray line will also, so the oxidation state of Fe in the regolith list will vary somewhat depending on requirements for lunar-based might be mapped with properly chosen telescopes. facilities and operations. Johnson et al. [2] have noted that it is We thus suggest that, in addition to major-element mapping, necessary to start now to develop the concepts and technologies consideration be given to volcanic volatile mapping and regolith for the next generation of space-based telescopes. A successor for oxidation state mapping. the Hubble Space Telescope could be either -in high Earth orbit This work was supported by the Rockwell Independent Research (HEO) or on the Moon. To properly assess the merits of these and Development Program. suggested future telescopes, technology development for lunar as References: 111 Schmitt J. H. M. M. et al. (1991) Nature, 349, well as HEO telescopes should now be pursued so that properly 583-587. [2) Edwards B: C. et al. (1991) GRL, 18, 2161-2164. informed decisions may be made. Part of the technology devel- [3] Housley R. M. and Grant R. W. (1976) Proc. ISC 7th, 881- opment requires improved understanding of engineering properties 889. |4) Henke B. L. et al. (1982) Atomic Data and Nuclear Data of lunar surface and subsurface materials and dust behavior. John- Tables, 27, 1. [5] Butler P. Jr. and Meyer C. Jr. (1976) Proc son and Wetzel [3) note that the success of a large lunar-based Apof/o Jl LSC, 1561-1581. [6] Cirlin E. H. (1978) Proc. LPSC telescope will depend on an appropriately engineered structure, 9th, 2049-2063. [71 More complete analysis of data in reference a suitable interface (foundation) with the lunar regolith, and a [6]. [8] Housley R. M. and Grant R. W. (1977) Proc. LPSC 8th, carefully thought-out construction process. Johnson and Burns 1 1 ] 3885-3899. have discussed the technology development required for large lunar telescopes and lunar optical/UV/lR synthesis arrays. They encourage the community to plan early lunar-bound payloads and surface operations to advance the knowledge and understanding required for building large telescopes on the Moon after the year 2000. Examples of key technologies for large lunar observatories that we feel deserve attention early in the program to return to the Moon are 34 Neu> Technologies for Lunar Resource Assessment 1. Geotechnical (e.g., soils, excavation, foundations, and use AN IN SITU TECHNIQUE FOR ELEMENTAL ANALYSIS of in situ materials for shielding). OF LUNAR SURFACES. K. Y. Kane and D. A. Cremers, CLS- 2. Mitigation of detrimental effects of the environment (e.g., 4, Mail Stop J567, Los Alamos National Laboratory, Los Alamos dust, thermal, primary and secondary impacts of micrometeoroids, NM 87545, USA. radiation, and vacuum). This area includes obtaining a better understanding of the dust and debris environments above and on An in situ analytical technique that can remotely determine the surface of the Moon. the elemental constituents of solids has been demonstrated. Laser- 3. Approaches to use in construction on the Moon (e.g., ex- Induced Breakdown Spectroscopy (LIBS) is a form of atomic travehicular activity, robotics, telepresence, assembly aids, con- emission spectroscopy in which a powerful laser pulse is focused nectors). The appropriate choices can be made only with adequate on a solid to generate a laser spark, or microplasma. Material in knowledge of the surface conditions and variability. the plasma is vaporized, and the resulting atoms are excited to 4. Contamination/interference control and restoration pro- emit light. The light is spectrally resolved to identify the emitting cesses. May vary with chemistry and mineralogy. species. 5. Performance of optical and related systems and charge- LIBS is a simple technique that can be automated for inclusion coupled devices (CCDs) on the Moon. CCDs deserve particular aboard a remotely operated vehicle. Since only optical access to attention with respect to shielding requirements against cosmic a sample is required, areas inaccessible to a rover can be analyzed and solar flare radiation. Shielding will probably be with in situ remotely. A single laser spark both vaporizes and excites rhe sample materials requiring excavation and placement at desired densities. so that near real-time analysis (a few minutes) is possible. This 6. Test and evaluation techniques for lunar observatory systems technique provides simultaneous multielement detection and has and construction approaches to validate approaches before return- good sensitivity for many elements. LIBS also eliminates the need' ing to the Moon. Depends on devising appropriate simulation of for sample retrieval and preparation preventing possible sample lunar conditions. contamination. These qualities make the LIBS technique uniquely We anticipate that the initial telescopes on the Moon will be suited for use in the lunar environment. small automated instruments that have already been shown to LIBS has been demonstrated using several different types of be feasible by existing Earth-based robotic telescopes. These early samples at distances between 4 and 18 m. Analyzed samples include telescopes will not only establish the viability of telescopes on the simulants of Apollo mission Moon rocks, Mauna Loa basalt sam- lunar surface, but will also perform excellent extended observa- ples, and rock powder reference standards. An example of the tions during the long lunar nighr to test models of active stars spectra obtained with this technique using an Apollo Moon rock and galaxies, and do all-sky CCD surveys in the ultraviolet and simulant is presented in Fig. 1. The presence of several elements infrared using a Schmidt wide-field telescope to complement the such as aluminum, calcium, iron, magnesium, silicon, and titanium important sky survey done at Mount Palomar. We conclude that is clearly evident. attention must be given to instrumenting these small telescopes A portable LIBS instrument has been field tested with good in innovative ways to obtain information that will help find preliminary results. An exposed tuff face was interrogated by the answers to unknowns in the areas listed above. We suggest that laser spark at a distance of approximately 18 m in bright sunlight. there are excellent opportunities to use the early landers to Spectra obtained at this distance displayed very strong emission investigate the behavior of the soil under load, determine the extent of dust movement (e.g., levitation) associated with the passage of the lunar terminator, and place bounds on disturbances associated with vehicle operations on the Moon. Creative uses of information obtained from many innovative approaches may Mg(II) be used to help make lunar-based telescopes a reality. For example, ground-probing radar has many terrestrial appli- i cations (e.g., in-assessing pavement layer thicknesses in highway 2800 2900 3000 3100 3200 3300 engineering applications, in determining the location of fissures Ti(II) Mg(l) / in the dry lake bed at the Edwards Air Force Base shuttle landing site, and at Meteor Crater, Arizona, in investigations of the ejecta I I I blanket). We propose to use this technology on che'Moon in 3400 3500 3600 3700 3800 3900 conjunction with other techniques such as penetrometers, borings, and core recovery to ascertain needed subsurface soil and rock properties. The goal is to minimize the use of labor-intensive subsurface sampling required during site investigations on the Moon and to improve approaches to assessing in situ lunar con- struction materials. References: [1] Johnson S. W. and Burns J. O. (1991) Pro- ceedings of the Common Lunar Lander Workshop, NASA, Houston. [2] Johnson S. W. (1992) Proceedings of Space 92, American Society 3900 4000 4100 4200 4300 4400 of Civil Engineers, New York. [3] Johnson S. W. and Wetzel J. P. Angstroms (1992)j. Aerosp. Eng.. 5. Fig. 1. Laser spark spectra of an Apollo Moon rock simulant in a vacuum chamber at a distance of approximately 10 m.