Lord of the (sub-)Rings : Mapping the surface reflectance and spin-axis of Ajisai

TL;DR

This paper demonstrates that streak photometry from ground-based observations can effectively determine the spin-axis and rotation period of fast-spinning objects like Ajisai, aiding debris removal efforts.

Contribution

Develops an MCMC-driven method to map surface reflectance and spin-axis of Ajisai using streak photometry, advancing techniques for characterizing space debris.

Findings

Good agreement with empirical models for Ajisai's spin state

Streak photometry can recover spin-axis and rotation period of fast objects

Method is scalable to other targets and ground-based observatories

Abstract

Active debris removal techniques are posed to become an important tool in maintaining the safety of the near-Earth space environment. These techniques rely on a clear understanding of the rotational motion of the debris targets, which is challenging to constrain from unresolved imaging. The Ajisai satellite provides an ideal test case for developing and demonstrating these techniques due to its simple geometry and well constrained spin behaviour. We present four observations of the Ajisai satellite taken with SuperWASP in August of 2019, where high cadence photometry was extracted from streaked images as a part of a larger survey of Low Earth Orbit. We develop an MCMC-driven method to determine the spin-state of Ajisai by comparing the alignment between a map of modelled mirror positions and a novel derived map of surface reflectivity. We generally find good agreement within the expectation and uncertainties set by empirical models and our determined spin-state solutions align the surface reflectivity map and modelled mirror location well. Our results show that streak photometry can be used to recover the spin-axis and rotation period of fast-spinning objects such as Ajisai using modest ground-based instrumentation, making it readily scalable to a wider range of targets and observatories.