Spectral Library for OPRA (Optical Probe for Regolith Analysis) ‏

1. Spectral Library for OPRA (Optical Probe for Regolith Analysis)‏ Saroj Adhikari1, Robert Pilgrim2, Rick Ulrich2 1University of Central Arkansas, Conway, AR. Email: adh.saroj@gmail.com 2Arkansas Center for Space & Planetary Sciences The NASA funded OPRA project aims to design a simple probe which can be inserted into the ground to take spectra of the various underlying layers. Such spectra taken by OPRA will enable the analysis of subsurface mineralogy with a minimum of perturbations. The spectral library needed to validate the proper functioning of OPRA is mentioned as Task 3 in the OPRA proposal. • OPRA Introduction • Simple spike-like structure with windows (fig 1)‏ • Uses fiber optics for light transmission • Inexpensive instrument with small cross-sectional area and hence easily adaptable to different missions • Deployable in any surface having regolith or icy properties Task 3: Spectral Demonstration and Creation of Spectral Library Work In Progress • Preliminary spectra collection and analysis using Fourier Transform Infrared (FTIR) spectrometer • Comparing the measured spectra with published spectra—mainly from the United States Geological Survey (USGS) Library • Initial results show good match between the OPRA and USGS spectra (fig 2) • Objectives • To validate the design from Task 1 • To test the probe experimentally with a wide variety of regolith analog materials • To create a library of spectra obtained with OPRA • Some Material Analogs to be used • Pyroxene, Olivine, Clays (Nontronite, Kaolinite, Montmorrillonite), Water Ice, Icy Soils, Sand, Metals, Metal Sulphates, Hydrated materials etc. Fig 1: Initial OPRA Design from OPRA proposal Research under Task 1 has enabled improvements in this design, including possibility of smaller cross section area, through the use of prisms. Fig 3: The fiberport extension to the FTIR is being used to take spectra. The fiber attached to the fiberport is the fiber optic cable which will be assembled into the final OPRA probe. • Work to be done • Obtain more spectra of minerals, icy soils and their mixtures • Create a complete and usable spectra library with extensive documentation Fig 2: The above plot shows a comparison between the spectra of Kaolinite sample (<63 microns) taken using the OPRA probe (green) and the published spectra downloaded from the USGS website (blue).The reflectance scale (y-axis) has been offset for clarity. A working spectra library in OMNIC software has been set up for some USGS spectra which shows 91% correlation match in the above case. This indicates that we are getting good spectra out of the fiber optics cable that will be used in OPRA. • OPRA Tasks • Task 1: Design of the Optical Train • Task 2: Mechanical Issues (penetration forces and window scratching) • Acknowledgements • NASA Planetary Instrumentation Development grant, for funding the OPRA project • Reference • OPRA Proposal, University of Arkansas Center for Space & Planetary Sciences