Photometric Analysis of Rotating Rocket Bodies through Ground-Based Optical Observations
Abstract
This paper presents the preliminary results of an ongoing optical survey of space debris using ground-based sensors undertaken with the primary goal of performing generalised space debris characterisation. The focus of this section of the research is on the rotational dynamics of the observed objects, primarily rocket bodies, through analysis of their light curves. The light curve of an object is a temporal history of its apparent magnitude over time and it can be used to determine information about the object's characteristics including size, shape, orientation and material properties. This investigation is being undertaken in conjunction with Australian based company Electro Optic Systems (EOS), who operate six optical sensors around Australia and have collected all the optical data presented in this research.
Object classification and characterisation is a significant goal in Space Situational Awareness (SSA) due to the coupling between an object's characteristics and the external forces acting on it. These external forces such as solar radiation pressure and atmospheric drag result in orbital perturbations and increase the risk of on-orbit conjunctions. Improved knowledge of the rotational dynamics of an object, as well as its other characteristics, lead to refinements in orbital predictions and help to mitigate the risk to operational satellites. Additionally, this information can be critical in identifying objects that are at risk of break up as well as providing data for future active debris removal missions. Since June 2019, EOS sensors have been collecting light curves on a range of space debris with a primary focus on rocket bodies. Rocket bodies are of particular interest in SSA as they are often left in highly elliptical orbits where they are subject to both atmospheric drag and solar radiation pressure as well as posing a higher risk of break-up due to the instability of surplus fuel. Initial analysis determined that there was a regular pattern in the light curves of more than 70% of the objects observed indicating that they were rotating. The Lomb-Scargle Periodogram was then applied to the light curves to enable the determination of the dominant period. Comparison with a high fidelity blender based simulation environment determined that rocket bodies generally experience two bright peaks per rotation due to their symmetrical nature, so the dominant period was doubled to provide the spin period of the object. The majority of rotating rocket bodies were found to have spin periods between 50 and 150 seconds. Further observations of these objects in the following months allowed for an analysis into the stability of these rotations and an examination of the changes in spin period over time. A significant portion of the observed objects have remained in relatively stable rotations over the current 8 month observation period. However, two of the observed rocket bodies experienced considerable changes in spin period with some evidence of cyclical nature to the change in spin period over time. Additionally, one of the observed rocket bodies was found to have a complex rotation, with precession around a secondary spin axis. Future work will involve observations of decommissioned satellites of a range of different shapes and sizes in order to develop a database of light curves for generalised object classification.- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E2194A