Jeff Shaddix, Numerica Corporation; Cameron Key, Numerica Corporation; Alex Ferris, Numerica Corporation; James Herring, Numerica Corporation; Navraj Singh, Numerica Corporation; Todd Brost, Numerica Corporation; Jeff Aristoff, Numerica Corporation
Keywords: Daylight Techniques for Satellite Characterization, Imaging, Modeling, Optical Systems, Small or Autonomous Telescope Systems, Space Situational/Domain Awareness (SSA/SDA)
Abstract:
The low Earth orbit (LEO) satellite population is burgeoning. Commercial, academic, and government programs continue to see proliferated LEO constellations as a key to success, which both necessitates and complicates space domain awareness (SDA). As the LEO population grows, so do situations that pose risk to spacecraft (unmanned or manned) and the relevant missions that led them there. Some examples include rendezvous and proximity operations (RPOs), conjunction risk assessment, collision monitoring, launch/reentry monitoring, and custody of maneuverable and/or separable satellites. These situations may warrant timely SDA with high revisit rates on a subset of the LEO RSO population.
RSOs in LEO are predominantly tracked by radar systems. These systems are highly capable, but also costly to build and operate. This has limited the number of radar sites in operation, which in-turn limits maximum revisit rates. Optical systems are often used to track deep-space RSOs, but when properly equipped they can also track RSOs in LEO. Optical systems can also be orders of magnitude cheaper than radar systems, but they are typically limited to short periods of LEO monitoring during the night when RSOs are not in Earth’s shadow (an eclipse event from the vantage point of the RSO). Without sunlight reflecting off the LEO RSOs, these telescopes would have significantly less signal to form a detection, and therefore could not be used for tracking purposes. Thus, traditional LEO-focused optical systems spend much of their time idle or in-use for other applications. But what if optical systems could be used during the day? The RSO would remain sunlit as well as receive a significant amount of illumination from the upwelling radiance of earthshine.
In 2018, Numerica designed and prototyped a daytime-capable optical tracking system named Aquila. Aquila senses in the shortwave infrared regime and applies specialized algorithms to cut through the noise of the bright sky background to produce RSO observations. At first this system was limited to tracking RSOs in and near geosynchronous Earth orbit (GEO), but in 2020 the technology was successfully expanded to enable daytime tracking of LEO RSOs. In 2021, multiple mature systems were deployed worldwide. From an access perspective, a daytime-capable optical system has approximately 5 times more viewing opportunities than its nighttime-only equivalent, depending on LEO altitude and seasonal considerations. Furthermore, some sun-synchronous orbits may primarily be visible only to daytime-capable systems, as these orbits create limited night viewing opportunities at reasonable observation elevations. These increases in observability likewise increase the cost-efficiency for a network of optical systems to supplement radar with timely SDA.
In this paper, we investigate how a hypothetical network of low-cost cathemeral (active throughout day and night) optical telescope systems can supplement radar systems for enhanced custody of a subset of LEO objects. We perform sensor access and data quality simulations accounting for weather, solar exclusion, and accuracy limitations to present salient performance statistics such as time delays since last observation and positional uncertainty volumes. We will sample various orbit inclinations, altitudes, and object sizes to serve as exemplar high interest LEO RSOs. The analysis will also consider the downsides of optical tracking, including capacity limitations as the number of objects under custody grows. Finally, we will investigate the fusion of radar and cathemeral optical networks as synergistic components to create a more complete and timely LEO SDA solution.
Date of Conference: September 14-17, 2021
Track: SSA/SDA