Light curves sequential comparison strategy for improved understanding of LEO uncontrolled objects

Abstract

In the framework of Space Situational Awareness activities, space debris light curve analyses have been used as a tool to study the tumbling motion of uncontrolled orbiting objects using only optical data and often without any assumptions about their geometry. Through this strategy, frequency analysis can be performed to extract the objects' rotation periods, which are necessary to predict variations in attitude for both monitoring and management purposes. In the context of international tasks and activities, the Sapienza Space System and Space Surveillance Laboratory research group at Sapienza University of Rome, on behalf of the Italian Space Agency delegation to the Inter-Agency Space Debris Coordination Committee, has created a historical record of light curve data by observing seven rocket bodies in low Earth orbit. This dataset, supplemented with further investigation over the years, has revealed the long-term evolution of the motion states, with particular attention to the recorded tumbling rates, which would be unobservable with short-term campaigns. These data allow for long-term light curve inversion and historical analyses of rotational frequency and photometric response to optical observations, which are of interest to Space Surveillance and Tracking and Space Situational Awareness services for database updates, monitoring of uncontrolled resident space objects, and future re-entry observations. In this paper, the sequential comparison strategy used to investigate the long-term evolution of space debris rotation rates is presented, with a specific focus on the SL-14 R/B (NORAD ID 18340), which has exhibited an anomalous increase in its rotation period over the years. To investigate the underlying causes of this behaviour, a dedicated attitude evolution analysis was conducted, employing various methodologies. First, attitude simulation techniques were used to explore potential root causes of this sudden acceleration, including the hypothesis of a failure in the propulsion system leading to pressurized gas leakage. Different leakage models were analysed to assess the plausibility of this scenario. Additionally, a digital twin simulation was developed to perform light curve inversion, enabling the reconstruction and validation of the object's attitude motion. The results of these analyses provide deeper insight into the dynamics of non-cooperative space objects, fostering the development of improved tracking, characterization, and predictive modelling strategies in support of Space Surveillance and Tracking activities.