Joshua Wysack, Ball Aerospace; Kevin Ferrant, Ball Aerospace
Keywords: Cislunar, Space Domain Awareness, Space Traffic Management
Abstract:
Discussions of Space Domain Awareness (SDA) and Space Traffic Management (STM) often get muddled in terms of the objectives that they are trying to meet. Though the two missions have significant overlap in requirements, they do have significant differences that will drive different architectures to support cislunar space. Chief amongst these differences are the surveillance volume and revisit rate to search the volume.
The primary goal of STM is to detect, track, and retain custody of RSO. Revisit rates may be chosen such that reliable state vector information can be maintained and close approach encounters can be predicted several days in advance; in cislunar space this revisit time can be on the order of days. The SDA mission must account for change detection (specifically unwarned spacecraft maneuvers), which necessitates that the revisit rate be on the order of hours. This requires the mission to discover new objects that might come from outside the cislunar surveillance volume or are released from a parent object. Maneuvers from known objects that puts them on a collision trajectory must be tracked and reacted to in a timely manner.
Search volumes for STM are often defined as spherical shells extending from GEO altitude to some multiple of GEO altitude; i.e., the 4pi XGEO volume. This multiplier can extend the outer radius to near Earth-Moon L2 at 10 XGEO, with some definitions extending even further [1]. The result are volumes that range from 1000 (10 XGEO) to 2000 (~13 XGEO) times larger than the typical volume used for Earth-orbiting objects defined as a spherical shell extending from a 300 km LEO orbit out to GEO. With a focus on threat detection of GEO and below and activity around the Moon, smaller SDA volumes have been proposed with tighter requirements on search time. An example volume is composed of a 3.4 XGEO spherical shell and a corridor volume that extends to L2 [2]. This volume if roughly 50 times larger than the LEO to GEO volume.
This paper will present architectures for SDA and STM that reflect the differences in requirements space between these two missions. Various tracking technologies will be evaluated to determine their viability for deep-space tracking, and their applicability to the different mission focuses. These will include Very Long Baseline Array (VLBA), Radio Frequency (RF), visual, and infrared (IR) technologies. Surveillance volumes will be defined for both mission areas. Some weighing factors that will be evaluated for the volume definitions will be: likelihood of use for certain subvolumes, DV cost for cislunar transfers, transit time, etc.
It will be shown what role ground sensors can play in a cislunar architecture, and how they can work in collaboration with space-based sensors to form robust cislunar surveillance architectures. The primary focus will be on space-based sensors that utilize visual or IR sensors that are designed for the vast ranges of cislunar space. We will trade families of periodic cislunar orbits using metrics of orbit stability and access to the cislunar surveillance volume. Best performing architectures will be those that have high coverage using capacity analysis. Architecture design will utilize optimal scan plans that allow the observing sensors to work in collaboration [2].
1. Cislunar Technology Strategy Interagency Working Group of the National Science & Technology Council. National Cislunar Science & Technology Strategy, Nov 2022.
2. Fahrner, N., Correa, J., and Wysack, J. “Capacity-based Cislunar Space Domain Awareness Architecture Optimization”, Amos Conference 2022.
Date of Conference: September 19-22, 2023
Track: Cislunar SDA