Neil Pearson, University of Arizona; Benjamin Sharkey, University of Arizona; Tanner Campbell, University of Arizona; Adam Battle, University of Arizona; Craig Jacobson, University of Arizona; Vishnu Reddy, University of Arizona; Roberto Furfaro, University of Arizona
Keywords: Reflectance Spectroscopy, Spectral Library, Phase Angle, Space Analog, Laboratory Measurement
Abstract:
Reflectance spectroscopy has been used in the past to remotely identify materials on Earth (Clark et al. 1990) and other planetary bodies (Gaffey et al. 1989). In recent years, reflectance spectroscopy has been successfully applied to characterize Resident Space Objects (RSOs) (Battle et al. 2021). But these efforts are limited to silicon detector-based spectrometers (0.4-1.0μm). With more InGaAs and InSb-based spectrometers coupled with fast tracking telescopes coming online, there is an increased need for longer wavelength (out to ~5.0μm) laboratory spectral measurements of spacecraft materials to identify absorption bands and determine the optical properties of these materials. This longer wavelength range allows for better characterization of materials making up specific RSOs.
Telescopic spectral characterization of RSOs requires a strong laboratory component that studies material properties over a wide wavelength range in space-like (temperature, pressure, and phase angle) conditions to help interpret the data. To this end our spectroscopy laboratory is constructing a high vacuum chamber that will take reflectance measurements from 0.2-5.2 um at phase angles ranging from 140o to 10o, and be able to cool samples to 77 K and heat them to 800 K. We are also creating a curated collection of materials both used on actual spacecraft, such as paint samples and analogs of such materials such as metal alloy pieces that conform to appropriate engineering standards.
Our vacuum chamber’s wide spectral range (0.2-5.2μm) will be achieved using a combination of three spectrometers external to the chamber and three different types of fiber optic cables that are fed into the chamber. The fibers are attached to rotating arms that are controlled via servo motors to control phase angle. The main measurement chamber will be kept at a pressure below 10-6 torr. Samples used in this setup can be solids or powders and ideally have diameter of 2.5 cm and less than 1 cm thick of both artificial and natural materials. Reflectance measurements will be taken relative to two standards, SpectralonTM for 0.2-2.5 microns and diffuse gold for 1.5-5.0 microns. These will be mounted on a stage connected to a push pull rod and will move into the sample position when it is not there. There will also be a piece of Acktar Metal VelvetTM to provide a dark background and characerize any scattered light in the system at time of observation. In addition to light spectrometers we have incorporated a Residual Gas Analyzer for determining any outgassing components from samples. Such a device is useful in determining any chemical reactions that might occur during sample heating. This range of parameters largely replicates ground-based telescopes’ viewing geometries and goes beyond the potential wavelength range of ground-based observations.
The University of Arizona Space Materials Curation Facility has been created to collect and archive samples of surplus spacecraft parts and analog materials. These include solar cells, thermal protection materials such as mylar, paints, metals, and alloys. We have already collected spectra of 70+ such samples in ambient conditions and plan to add vacuum spectral measurements with our new vacuum chamber.
Date of Conference: September 19-22, 2023
Track: Satellite Characterization