Zachary Leffke, Virginia Tech National Security Institute; Kevin Schroeder, Virginia Tech National Security Institute; Matthew Phelps, USSF SSC/SZGA; Justin Fletcher, USSF SSC/SZGA
Keywords: Passive RF, PRF, Radio, Interferometer, Polarimetry, Satellite Characterization
Abstract:
Passive Radio Frequency (PRF) technology for Space Domain Awareness (SDA) has been identified in US Space Force’s (USSF) Space Doctrine “Publication 3-100, Space Domain Awareness” as a technology of interest to the SDA mission. Passive RF sensors utilize the signals emitted from spacecraft to determine the vehicle’s position and motion which in turn can be used for orbit determination and custody maintenance. Passive RF techniques also include analysis of signal external characteristics, using both traditional signal processing and RF Machine Learning techniques (RFML), in order to characterize the spacecraft including identification, pose estimation, pattern of life, change detection, intent estimation, early warning, and tipping and queuing of other sensors systems including RADAR and optical sensors. Primary advantages of passive RF include persistent observations during day and night, observation during inclement weather, and rapid revisit. This work will cover efforts at the Virginia Tech National Security Institute to develop an initial proof of concept Passive RF capability utilizing assets from the Virginia Tech Ground Station and relatively low cost commercial off the shelf (COTS) Software Defined Radio (SDR) technology. Current objectives of the system include tracking geosynchronous spacecraft at S-Band satellite communications frequency allocations, exploring pose estimation via polarimetric analysis of satellite downlinks, and initial data collection for exploring multiple algorithms for tracking and satellite characterization. The specific Passive RF technique being examined for this initial proof of concept is RF Interferometry which utilizes long separation, called baselines, between multiple coherent satellite receiver systems and offers potential sub-arcsecond angular resolution for tracking observations. The technical design of the real-world interferometer will be presented, including implementation challenges such as timing and synchronization between multiple sites and system calibration. Initial results of the system, derived from on air real world measurements, will also be presented concerning both satellite tracking and characterization. The paper will conclude with discussion of refinements and future work for the system, including tracking and characterization in alternative flight regimes, expanding the frequency coverage of the system and the resulting impacts to system design, and potential signal processing and RFML techniques that can be leveraged for the SDA mission and tested with the system.
Date of Conference: September 17-20, 2024
Track: SDA Systems & Instrumentation