Phillip M. Cunio, ExoAnalytic Solutions, Inc.; Jaycie Bishop, ExoAnalytic Solutions, Inc.; Christopher W. Ingram, ExoAnalytic Solutions, Inc.; Bill Therien, ExoAnalytic Solutions, Inc.; Doug Hendrix, ExoAnalytic Solutions, Inc.; Clinton Clark, ExoAnalytic Solutions, Inc.; Michael Bantel, ExoAnalytic Solutions, Inc.; MJ Jeffries, ExoAnalytic Solutions, Inc.
Keywords: Rendezvous and Proximity Operations, Geosynchronous Orbit, Docking, Remote Sensing, Space Traffic Management
Abstract:
As both announced and unannounced activities on orbit over the most recent few years have indicated, spaceborne operations that include elements of physical contact as a culminating event following extended rendezvous and proximity operations will become more increasingly common in the geosynchronous neighborhood. Physical contact between active spacecraft in the geosynchronous neighborhood may occur with mutual cooperation between two space vehicles or with passive acquiescence on the part of one of the vehicles, and often is approached with great caution due to the inherent danger of accidental debris generation, even though the contact does itself not necessarily bespeak malicious intent.
To mitigate this danger of accidental debris generation and to perform initial in situ orientation and preparation for precise maneuvers, a period of rendezvous and proximity operations (RPO) often precedes physical contact between space vehicles. Although RPO and culminatory docking are not at all historically unattested, the bulk of such operations since spaceflight began have occurred with humans in visual contact with one or both of the docking vehicles, usually from onboard one or both vehicles, as most docking has been in support of human spaceflight. Only a few operations, most notably the MEV-1 and MEV-2 servicing missions and the SJ-21/COMPASS-G2 orbit alteration, have been conducted with no humans nearby. However, the relative success of these recent missions augurs well economically and practically for further such missions in the near future, most likely principally for the purposes of servicing aging commercial spacecraft which nonetheless may still be profitable, although it is of course feasible that such technology will also shortly be deployed to address the growing problem of orbital debris as well.
From a ground telescope network, a pair of vehicles engaged in RPO may appear as one vehicle, due to the extreme physical proximity of the two; that is, on ground sensors without prohibitively high resolving power, they appear as one bright dot instead of two bright dots. This state is sometimes referred to as Closely-Space Objects, or CSO. Two objects in CSO are not easily distinguishable from one another under most conditions.
However, if two vehicles are in a CSO state while performing RPO, an algorithm projecting the path of one of those vehicles can display structured residuals, which may provide additional insight into the behavior of the two vehicles. Residuals are the mathematical mismatch between the actual apparent position of an orbiting vehicle and the predicted apparent position, and can indicate whether a vehicle appears to be exactly in the position its past behavior and orbital mechanics would predict, or whether it is in a slightly different location. High-quality data in large volumes, with high position accuracy and a substantial degree of persistence, is a precursor to generating structured residuals for two objects in CSO, along with a capable and validated orbit propagation routine.
The expected structure of residuals can vary with the precise nature of the RPO being performed, but in general there is a small noise floor of residuals driven by sensor and data quality. If two objects are in CSO, the apparent bright center of the combined signal from both objects observed optically may fluctuate in some pattern, and this pattern can potentially be analyzed to provide insight into the nature of the RPO.
Similarly, alterations in residuals or photometry, followed by a settling of residuals into a level matching the expected noise floor, may be a strong indicator that physical contact has been made and the two objects are now orbiting as a single object – that is, they have docked. The ability to extract this information from orbit residuals may provide a powerful new tool for tracking and comprehending RPO and even docking in the geosynchronous neighborhood.
In this paper, a model for observed residual structure is described, and then deployed to review several real events known or believed to have included physical contact between two vehicles in geosynchronous orbit. ExoAnalytic’s global telescope network and the data it has collected are compared to the developed model, and interpretations of the structured residuals, particularly where they may suggest details of approach methods, are offered. Finally, an assessment of the levels of data quality desirable in order to improve on residuals analysis is given, and recommendations for further future work are offered.
Date of Conference: September 27-20, 2022
Track: Conjunction/RPO