Eric Pearce, University of Arizona Steward Observatory; Benjamin Weiner, MMT Observatory; Adam Block, University of Arizona Steward Observatory; Harrison Krantz, University of Arizona Steward Observatory; Kris Rockowitz, University of Arizona Steward Observatory; Brad Sease, Computational Physics, Inc; Greg Hennessy, U.S. Naval Observatory; Michelle Wilson, SAIC;
Keywords: satellite reflectance spectra, SL-12 rocket bodies, optical, debris, aging
Abstract:
The characterization of deep space debris has posed a significant challenge in SSA. To be most operationally effective, characterization must be performed quickly and under non-ideal operational conditions, generally using non-resolved techniques. The use of multi-color photometry and the resultant color indices offer the potential to rapidly discriminate between debris and intact space objects such as rocket bodies and satellites. However, these studies are not well informed by high resolution spectra of these same objects due to the lack of prior measurements with large astronomical telescopes. High resolution spectroscopy is not routinely collected by our SSA network. Nonetheless, several researchers have collected satellite spectra for research purposes and noted the progressive reddening of spacecraft surfaces with age. Jorgensen measured reflectance spectra over a range of years on orbit (YOO) of 10-13 years of foreign discarded rocket bodies and noted significant increase in relative reflectance above 750 nm.
In this study, we re-analyze the previous UKIRT near-IR five-color photometric measurements of SL-12 fourth stage rocket bodies with the additional context of high-resolution spectra on the same objects. The SL-12 fourth stage rocket bodies (henceforth referred to as SL-12 RB) offer a convenient ensemble of objects for which photometric techniques can be developed and tested. The five SL-12s measured have a range of years-on-orbit (YOO) from 23-35 years, allowing a comparative study of the evolution of the spectra over a 12-year difference in age. The spectra were collected with the Blue Channel Spectrograph on the 6.5 m MMT telescope at Mt. Hopkins. Using the 300-line grating, blazed for the red. The spectra cover a 5200 Å range at a dispersion of 1.96 Å/pixel. The large collecting aperture of the MMT allowed the rapid collection of multiple high signal-to-noise spectra with short 2-minute exposures. This short exposure allowed us to have confidence the solar phase angle was near constant during each collection, but that the spectra were averaged over the rotation of the rocket body. These spectra allow analysis of both the variation in albedo over a large wavelength range, and detection of discrete absorption features. The SL-12 (also called the Proton K) was a mainstay Russian four-stage to GEO launch vehicle that was used from 1974 to 2012. In addition to the UKIRT measurements, we supplement the analysis data with Sloan r, i, and z high speed photometric data with the Chimera High-Speed photometer on the Kuiper 61 telescope at Mt. Lemmon. The spectra are analyzed for evidence of the effects of on-orbit reddening and other changes over time.
Date of Conference: September 17-20, 2019
Track: Non-Resolved Object Characterization