Hiroshi Oda, Japan Aerospace Exploration Agency (JAXA); Manuel Cegarra Polo, Japan Aerospace Exploration Agency (JAXA); Hirohisa Kurosaki, Japan Aerospace Exploration Agency (JAXA)
https://doi.org/10.64861/GGBZ8428
Keywords: spectroscopy, LEO, object type identification, small‑aperture, precision autoguiding
Abstract:
In congested orbital regimes, orbit information alone can be insufficient to characterize unknown‑origin objects or closely spaced neighbors. Spectral signatures add complementary cues about surface materials and state, supporting object type identification at the level of category and material tendencies. This work presents a ground‑based effort focused on low‑Earth‑orbit (LEO) objects and examines how differences in surface composition appear in measured spectra, with the goal of extracting features that enable type‑level identification across observing systems.
A distinctive aspect of the effort is its emphasis on small‑aperture practicality: with a compact system, we pursue useful spectral signal quality through careful acquisition and processing design. This choice naturally focuses the scope on relatively bright LEO targets; under comparable constraints, the photon budget at geosynchronous range makes the same approach not intended for GEO observations. Within this scope, we employ a slit spectrograph with precision autoguiding to stabilize targets during short exposures — an approach required by the fast apparent angular rates of LEO objects. When appropriate, multiple short frames are stacked to enhance usable contrast for feature extraction.
To anchor wavelength mapping, we observe line‑rich reference stars in the same configuration as the targets and use two prominent line positions as anchors for a simple two‑point linear interpolation from pixel to wavelength. The same stellar observations are used to verify effective spectral resolution and throughput under on‑sky conditions.
Beyond on‑sky data, we acquire bench‑top reference spectra — using the same instrument chain without the telescope — of representative materials including solar cells, gold, silver, and copper. These in‑lab references are used comparatively against LEO spectra to highlight distinguishing spectral tendencies and to guide feature selection for type‑level identification.
Results (type‑level examples). Within the stated scope, our results indicate that type‑level identification is feasible without reliance on narrow emission/absorption features. For example, spectra of LEO objects known to carry solar‑array‑like surfaces show qualitative consistency with our solar‑cell references, and spectra of LEO objects known to include gold‑coated components are consistent with our gold references. Although the available spectral resolution makes identification by isolated lines challenging, continuum slope and relative feature contrast provide discriminative power sufficient for type‑level identification under the stated constraints. These examples are illustrative rather than exhaustive and are intended to convey what classes of objects are likely to be separable with the presented setup.
Contributions (1) A practical acquisition approach that enables spectroscopy of fast LEO targets with a compact, small‑aperture system using a slit spectrograph and precision autoguiding tailored to high apparent rates; (2) a type‑level identification methodology that couples feature extraction with comparative analysis against bench‑top material references acquired through the same instrument chain; and (3) on‑sky evidence — expressed through continuum slopes and relative feature contrasts — that supports type‑level identification for classes such as objects with solar‑array‑like surfaces or gold‑coated components.
Future Work We plan to deploy the spectrograph on larger‑aperture telescopes with higher‑sensitivity cameras to expand the observable target set, improve signal quality and spectral leverage, and broaden the catalog of type‑level identification examples.
Date of Conference: September 15-18, 2026
Track: SDA Systems & Instrumentation