Alexander Pertica, Terran Orbital; Willem Devries, Lawrence Livermore National Laboratory (LLNL); Chris Shaffer, Terran Orbital; Jeremiah Dimatteo, Terran Orbital; Emily Milne, Terran Orbital; Robert Goodloe, Terran Orbital; Bailey Cortright, Terran Orbital; Weston Pruitt, Terran Orbital; Kyle Clarke, Terran Orbital
Keywords: Space Domain Awareness, Space Situational Awareness, Space-based Assets, Guidance Navigation & Control,
Abstract:
We present the results from a flight campaign dedicated to exploring the utility of satellite tracking mode for Space Domain Awareness (SDA) metric observations from a nanosatellite in low Earth orbit (LEO). Metric observations from space-based assets are typically obtained in inertial pointing mode. In inertial pointing mode, the stars are fixed and satellites streak through the frame with a streak length dependent on the target satellites crossing velocity. There are two significant limitations to operating in this mode that apply mainly to LEO-to-LEO observations. The first limitation is sensitivity which is limited by the time it takes for the target satellite to cross a pixel on the sensors focal plane array. Increasing sensor exposure duration beyond the pixel-crossing time does not improve sensitivity it only lengthens the satellite streak. Streak length is the other significant limitation in LEO-to-LEO metric observations. To obtain a useful metric observation, the endpoints of the streak must lie within the frame. For targets with large crossing velocities, it is necessary to decrease exposure to limit the streak length, and this can result in not detecting enough stars in the scene to obtain a good astrometric solution for the frame-center coordinates.
In this effort, we explore the utility of using satellite tracking mode for SDA. In satellite tracking mode, the target satellite is fixed in the frame, but the background stars are streaking. Although exposure can be increased in this mode to get better signal to noise on dim targets, there is a limit imposed on metric observations by the requirement of obtaining good astrometric solutions on the streaking stars in the background. However, there is still potential utility for images where an astrometric solution is not possible. An example of this is detecting a dim object in rendezvous proximity orbit to a bright object.
For this study, we have upgraded the GEOStare2 6U imaging nanosatellite with a satellite tracking capability. GEOStare2 was launched in May 2021 and features dual 8.5cm aperture panchromatic imagers, one of which was optimized for SDA applications. Prior to the upgrade, GEOStare2 demonstrated the capability of providing inertial pointing mode metric observation on objects in GEO, MEO, and LEO, and it was returned over 50,000 observations since launch. As the satellite was already equipped with a rate mode capability, the upgrade added an ability to propagate TLEs using the onboard flight computer to generate pointing quaternions for target satellites.
We will present the results from a dedicated flight campaign using GEOStare2 to explore the utility of satellite tracking mode for SDA applications across the GEO, MEO, and LEO orbital domains. The study explores the sensitivity improvements obtained by increasing exposure and the practical limitations on obtaining good astrometric solutions in this mode. In addition, we will discuss the attitude determination and control system (ADCS) estimation and pointing performance impacts on imaging sensitivity. We will also look at limitations imposed by the satellites maximum slew rate on targeting opportunities in LEO and compare this to inertial mode limitations imposed by streak length.
Date of Conference: September 19-22, 2023
Track: Space-Based Assets