Sam Kirkwood, HEO; Jack Sines, HEO; James Allworth, HEO; Karla Vincent, HEO; Hannah Dawe, HEO; Francesco Scopelliti, HEO; Hiranya Jayakody, HEO; William Crowe, HEO
Keywords: non-earth imagery, non-earth imaging, imaging, NEI, space based assets, attitude, tumble rate
Abstract:
Resident Space Object (RSO) characterisation is essential for effective space domain awareness, supporting both government and commercial operations. Understanding the attitude state and stability of RSOs is a critical component of characterisation. Traditional observation methods, such as ground-based optical and radar observations, face limitations including resolution constraints, atmospheric interference, and indirect inference of object properties. Light curve analysis, a ground-based technique that infers rotation status and periodicity from brightness variations, can be ambiguous due to object shape, reflectance properties, and viewing geometry. Additional observation methods that provide independent, spatially resolved data can help refine attitude estimates and improve confidence in characterisation.
Non-Earth Imaging (NEI), particularly through flyby imaging techniques, offers a complementary observational approach by directly capturing resolved images of RSOs. The term “flyby” refers to capturing imagery during periods when the regular precession of orbits brings a target object within the imaging range of a sensor. HEO’s approach to flyby NEI leverages a large network of on-orbit sensors, including both existing Earth Observation systems and purpose-built NEI telescopes hosted on third-party platforms. By capturing spatially resolved images during flyby windows, flyby NEI provides direct measurements of an object’s orientation and structural features. This capability enhances existing characterisation methods by offering additional data points that can support and refine attitude and tumble rate assessments.
Our approach to attitude and tumble rate estimation using flyby NEI consists of three key components: (1) estimating the orientation of an RSO from a single, short-duration flyby mission where one or few frames of the object are captured; (2) comparing instantaneous attitude measurements across multiple short-duration flybys to assess whether an object is stable or in an uncontrolled attitude state; and (3) utilising longer observation windows for objects in favourable orbits to capture multiple frames, allowing for a more detailed estimation of an object’s tumble rate and rotation axis by comparing many instantaneous attitude measurements. This tiered methodology enables both rapid classification of object stability and analysis of rotational properties when sufficient data is available.
To validate our approach, we compared derived tumble rates with those obtained from light curves or other ground-based methods for objects with available data. This cross-analysis demonstrates how spatially resolved imaging can serve as an independent verification method. Additionally, our method correctly identified stable, actively controlled satellites as non-tumbling, reinforcing its ability to differentiate between operational and uncontrolled objects. Further comparisons with independent pointing data provided additional validation for the accuracy and reliability of our approach.
Reliable attitude state characterisation has broad implications for space situational awareness and satellite operations. NEI-derived attitude and attitude state can support satellite health assessments, anomaly detection, and debris monitoring, contributing to improved space traffic management and operational decision-making. Additionally, by providing direct evidence of object behaviours, NEI enhances attribution efforts and reduces uncertainty in object classification.
This paper presents an overview of the approach used to derive attitude state and tumble rates for a number of targets, demonstrating the effectiveness of flyby NEI in providing attitude state data across multiple objects in different orbits. Through further development and implementation, flyby NEI can serve as a valuable augmentation to existing RSO characterisation techniques, improving confidence in attitude assessments and supporting the long-term sustainability of space activities.
Date of Conference: September 16-19, 2025
Track: Space-Based Assets