Di Wu, University of California San Diego; Aaron J. Rosengren, University of California San Diego
Keywords: proper elements, space situational awareness, space domain awareness, astrodynamics
Abstract:
The ability to quantify, assess, and predict the behavior of resident space objects (RSOs) is foundational to space situational and domain awareness (SSA and SDA, respectively). The trustworthy detection and characterization of orbital events (e.g., orbit maneuvers, fragmentations, etc.), in particular, are essential problems that have eluded resolution for decades. All techniques proposed to date, spanning classical filters to probabilistic inference and machine learning, require significant fine tuning of algorithm parameters, are plagued by noise statistics, and cannot holistically cope with all situations. Effective space traffic management (STM) and safe operations in the forthcoming space environment requires new methods and algorithms to maintain an expanded space object catalog (SOC) in quiescent operations, during the presence of a debris-generating event, and with the ongoing and planned deployment of satellite mega-constellations. “Debris or not debris” is the fundamental questions that has motivated much recent interest in developing a taxonomy for identifying, grouping, and discriminating RSOs. We have adapted and extended a concept from small-body taxonomists used in characterizing asteroid families known as proper orbital elements, which give a dynamical fingerprint of the object’s inherent state and provide a unique criterion that is otherwise lacking. Proper elements, used extensively in asteroid dynamics and genealogy studies but hitherto undervalued in the circumterrestrial context, offer a paradigm-shifting framework for solving several cardinal problems of SSA, SDA, and STM.
Asteroid families consist of swarms of fragments generated after energetic interasteroidal collisions in the distant past that result in the breakup of their progenitors. They are recognized by searching for clusters in the three-dimensional space of proper elements; parameters characterizing the asteroid orbits that keep a dynamical record of the initial proximity of the orbits generated by a catastrophic fragmentation event. Neither the current osculating nor mean elements, both being time-dependent quantities, keep a fingerprint of the state of the parent body at the instant of family origin. Indeed, osculating orbital elements are time-varying parameters that describe the instantaneous state (position and velocity) of an object in space. While mean elements, such as those provided by the two-line element (TLE) sets of the SOC, are constructed from their osculating counterparts by removing all high-frequency oscillations, and thus change more smoothly over longer time scales. Proper elements, on the other hand, stay nearly constant for very long times and can therefore be used as a rigorous dynamical criterion in the family identification and breakup-event estimation procedure.
These innate orbital parameters have not been adequately explored in the geocentric domain, in part, because the traditional orbits of artificial Earth satellites and space debris, and their dynamical environments, differ so markedly from the classical problems presented by nature (e.g., dominant forces, relevant time scales, etc.). This fact renders many of the time-honored methods of Solar-System dynamics inapplicable for near-Earth space. We have developed an extensive set of advanced computational tools for the simulation of the long-term orbital dynamics about Earth, accounting for gravitational and non-gravitational forces, which have been adapted for the computation of geocentric proper elements. We will show herein how these dynamical fingerprints can form an alternative path, leveraging merits directly from proper elements, for a handful of applications: the dynamical taxonomy of RSOs, the association of debris from breakup events into its “parent” satellite, and maneuver detection through induced changes in these fundamental invariants. For example, proper elements, being linked to the underlying dynamical structure of orbits, can provide a more robust metric within existing maneuver detection algorithms, through assessment of the induced changes in these quasi invariants of the motion. We will explore ensemble propagations as a way to spectrally decompose dynamical modes and obtain statistically relevant elements for this purpose.
Date of Conference: September 14-17, 2021
Track: Astrodynamics