Jeffrey Shaddix, Numerica Corporation; Jacob Brannum, Numerica Coorporation; Alex Ferris, Numerica Corporation; Austin Hariri, Numerica Corporation; Ari Larson, Numerica Corporation; Tyler Mancini, Numerica Corporation; Jeff Aristoff, Numerica Corporation;
Keywords: Space Situational Awareness, Daytime Satellite Tracking, SWIR Imaging, Small Autonomous Telescope Systems, Global Telescope Networks, Persistent Monitoring, Maneuver Detection, Characterization
Abstract:
Space-based systems are relied upon internationally for the advancement of science, communication, defense, and our modern way of life. Protection of these systems requires continuous, timely, and accurate orbital updates on all nearby resident space objects (RSOs), whether those be controlled satellites or uncontrolled debris. RSOs in geosynchronous and geostationary orbits (GEO) can be especially dim to detect given their near 36,000 km altitude. The US Space Surveillance Network, as well as current commercial telescope networks, primarily track GEO objects through ground-based optical sites. These systems are routinely limited to night operation due to the daytime sky background. This background quickly saturates these sensors and reduces their detection potential through the large increase in photon shot noise. While some exquisite ground systems have overcome these limitations, to date there are no low-cost options capable of global proliferation. Space-based sensors offer capability during daylight hours without terrestrial weather concerns, but are costly, may be limited to predictable observation patterns, and must deal with solar avoidance with limited baffle systems. Ground-based passive RF systems can detect active GEO satellites throughout the day, but only when those satellites are actively transmitting. As such, many GEO objects spend the majority of daytime hours unobserved, allowing windows for undetected and potentially nefarious activity. In light of this challenge, Numerica has developed a low-cost ground-based optical solution with demonstrated capability to produce observations on GEO objects in broad daylight. This capability can complement space-based and passive-RF solutions toward closing the daytime GEO observation gap.
The new daytime GEO satellite tracking system, codenamed Aquila, senses in shortwave infrared (SWIR) to mitigate the issues of daytime imaging. SWIR provides two complementary benefits: (i) the diffuse sky spectral radiance is approximately two orders of magnitude lower in regions of SWIR than visible, and (ii) the spectral reflectance profile of many satellites markedly increases around 1.0 micron (where visible sensors fall off). GEO objects are predominantly illuminated by direct sunlight at local night, but are also affected by earthshine reflection during the day. Even though both of these sources provide more incident light for reflection in the visible than the SWIR, daytime sensing in SWIR can provide an order of magnitude improvement in signal-to-noise ratio. Likewise, the reduced background flux in the SWIR allows for longer integration times before sensor saturation. This paper will delve into more detail describing the efficiency of daytime sensing as a function of wavelength.
The optical train for Aquila was carefully selected to maximize SWIR throughput and minimize the SWIR spot size for point-source targets. The telescope trades a small field-of-view in order to cut through the sky radiance and improve detectability. Multiple filters are employed to maintain saturation control and provide SWIR target characterization potential. Even with this carefully selected hardware, imaging techniques suitable for night observations are not sufficient during the day. Images must be acquired at high data rates and stacked effectively to reduce shot noise effects. For example, over 10GB of data is collected off the Aquila system per 1-minute observation. To address these and related challenges, Numerica has developed specialized image processing and observation reduction software.
The first Aquila prototype was assembled and tested at Numericas headquarters in Fort Collins, Colorado. The test proved daytime GEO tracking potential through successfully detecting satellites from the Anik GEO cluster from before dawn into broad daylight. Through collaboration with AFRL, Numerica is now operationalizing this capability and augmenting their global telescope network with multiple Aquila systems in 2019. These systems will integrate with the Numerica Telescope Network, leverage its existing operational software architecture, and provide real-time observational data to the Unified Data Library in late 2019.
Date of Conference: September 17-20, 2019
Track: Optical Systems & Instrumentation