Randa Qashoa, York University; Paul Harrison, Magellan Aerospace; Regina Lee, York University
Keywords: SSA, SDA, optical systems, RSO detection, sensor selection, WFOV imagers
Abstract:
Space-based optical systems are powerful tools for providing Space Situational Awareness (SSA) and Space Domain Awareness (SDA) as they are not limited by weather or by fixed geographic location. As part of Canada’s new microsatellite SDA mission, named Redwing, a wide field imaging capability will be employed for both proximity and co-orbital awareness around Redwing’s Low Earth Orbit. Repeated close-range observations of “co-orbiting” objects are highly valuable for accurate orbit determination, as well as assessment of collision risk for the host platform. Co-orbiting objects present a geometric challenge in observation, however, in that the look angles can vary rapidly during close approaches [1]. In addition to co-orbital objects, the increasing congestion in Low Earth Orbit is giving rise to many objects in near-coplanar orbits of different altitudes. A method to survey coplanar and co-orbital space objects is somewhat underdeveloped and observability issues are weakly addressed. As many optical space surveillance sensors’ targets are often viewed at ranges greater than ~1000 km, a technology and concept of operations gap exists when performing space surveillance on objects at ranges less than 250 km from the host sensor in space.
A variety of different imaging options are utilized for RSO detection. To have an awareness of as many RSOs near the host platform as possible, as opposed to having a more detailed view of a smaller portion of the sky, wide Field-Of-View (FOV) systems are used. These can be dedicated sensors for RSO detection, or they could be sensors developed for other purposes, such as star trackers that are used in a dual-purpose fashion. Even though wide-FOV sensors tend to have smaller apertures and therefore do not have the faint magnitude detection capability of large-aperture / narrow-FOV systems, the ability to study larger volumes of nearby sky is highly desirable for the co-orbital tracking application. There are in fact many examples of using wide FOV systems for SSA, including projects that the authors have previously participated in. For example, in [2] the Cascade, Smallsat and Ionospheric Polar Explorer’s (CASSIOPE’s) Fast Auroral Imager (FAI) has been used for RSO detection, while in [3], the PCO Panda 4.2 and the UI-3370CP-M-GL IDS were used to capture starfield images from a stratospheric balloon platform at about 40 km in altitude.
The goal of this study is to compare different small-aperture / wide-FOV sensors by assessing their RSO detection limits. This includes finding the number of detectable co-orbiting RSOs that regularly pass within 250 km of the observer, the expected brightness of detected RSOs, as well as other supporting statistics. When designing an SSA mission, choosing the correct sensor is a challenging task but one with important consequences on achieving mission goals. By comparing the performance of different sensors in RSO detection performance, we can determine which sensors would best accomplish mission objectives.
To perform this analysis, an algorithm was developed to model the orbit of the observing platform along with orbits of potential nearby RSOs in the sky around it. Then the brightness and signal-to-noise ratio (SNR) for different sensors are calculated and used, along with the FOV size, to determine the detection rate for these sensors.
For this study, a comparison between three sensors is made. The sensors chosen for the comparison are the FAI, the PCO Panda 4.2, and UI-3370CP-M-GL IDS cameras. All three of these sensors have been used for SSA purposes in previous research, and have well-established optical characteristics, which make them ideal candidates for this study. Additionally, a series of typical wide-FOV sensor parameters are generated using a Monte Carlo algorithm to determine the impact of parameters such as F-number, focal length, and integration time on a sensor’s RSO detection capability. This analysis allows us to find sensor parameter combinations that provide optimal detection performance. A crucial extension to this, which is examined at a preliminary level, is the use of repeat observations by these wide-FOV sensors during close approaches to obtain useful orbit knowledge.
This analysis is being performed with an eye to using low-cost, off-the-shelf, and dual-purposed sensors to provide SSA across multiple distributed platforms, including non-SSA missions. The authors are performing proximity analysis for the Redwing mission, so this research is being applied to dedicated SSA/SDA mission development as well as being a general sensor trade study.
References:
[1] K. Bernard, “Optical Co-Orbital Measurements in Low Earth Orbit,” Carleton University, 2019.
[2] R. Qashoa, M. Driedger, R. Clark, P. Harrison, M. Berezin, R. Lee and A. Howarth, “SPACEDUST-Optical: Wide-FOV Space Situational Awareness from Orbit,” in Advanced Maui Optical and Space Surveillance Technologies (AMOS) Conference, Hawaii, 2023.
[3] R. Qashoa, V. Suthakar, G. Chianelli, P. Kunalakantha and R. Lee, “Technology Demonstration of Space Situational Awareness (SSA) Mission on Stratospheric Balloon Platform”, Remote Sensing, 2024.
Date of Conference: September 17-20, 2024
Track: Space-Based Assets