Radio-Frequency Pulsar Observation using Small-Aperture Antennas Ryan McKnight, Frank van Graas, Ohio University BIOGRAPHY Ryan McKnight is pursuing his Ph.D. in Electrical Engineering and Computer Science at Ohio University as part of the Avionics Engineering Center. His research interests include GNSS inter-constellation time ofset determination and radio- frequency pulsar navigation and timing. He was previously involved with development and operations of the Bobcat-1 CubeSat. He received his B.S. in Electrical Engineering from Ohio University in 2019. Frank van Graas holds an endowed Fritz J. and Dolores H. Russ Professorship in Electrical Engineering and Computer Science, and is a Principal Investigator with the Avionics Engineering Center at Ohio University. Dr. van Graas is a Past President of The Institute of Navigation (1998–1999) and served as the Institute of Navigation (ION) executive branch fellow at the Space Communications and Navigation Ofce, National Aeronautics and Space Administration, Washington, DC (2009). He is a fellow of the ION (2001) and received the ION Kepler (1996), Thurlow (2002), and Burka (2010) awards, as well as the American Institute of Aeronautics and Astronautics John Ruth Avionics Award (2010). He has been actively involved with navigation and timing research since 198». ABSTRACT Recent research on pulsar based navigation and timing by organizations such as NASA and ESA has primarily focused on X-ray measurements as opposed to previous research which instead focused primarily on radio-frequency (RF) measurements. X-ray based systems ofer the potential for greater accuracy than RF based systems and do not require the large antenna apertures historically considered to be necessary for adequate performance of an RF system. However, recent RF studies have suggested the feasibility of 1-10 microsecond timing performance using an antenna with an efective aperture on the order of 10 square meters, which is more optimistic than many previous results. This level of performance may be sufcient to prove useful for both terrestrial and space applications, particularly in deep space or even cislunar space where navigation and timing performance requirements are typically more relaxed. Such a radio-frequency based solution would not require the large, heavy, complex hardware required to receive X-ray signals and could be particularly advantageous for small spacecraft where size, weight, and cost are of higher concern. This paper serves as a literature review of radio-frequency pulsar observation, timing, and navigation systems. It examines the theoretical relationship of system parameters such as antenna size, amplifer noise fgure, observation time, and processing techniques to overall system signal-to-noise ratio (SNR) and measurement performance. It then details the design of a terrestrial experiment to observe pulsars in the radio-frequency band using two small-aperture observing stations and low-cost hardware with the goal of determining experimentally the minimum practical antenna size for radio-frequency pulsar measurements as a function of signal-to-noise ratio, measurement performance, and observation time. Additionally, experimental results of pulsar observations performed by amateur radio operators are discussed and used to provide context to the theoretical results. I. INTRODUCTION Pulsars are highly magnetized rotating neutron stars that emit high-energy beams of electromagnetic radiation [1]. As the pulsar rotates, this beam sweeps through space and can be observed at a large distance as a series of regular, short pulses. Hundreds of pulsars have been observed, each with their own unique rotational period and pulse characteristics. Typically, these rotational periods range from just a few milliseconds to several seconds. The pulses can be observed at a wide range of frequencies ranging from radio-frequency to X-ray bands, although the signal strength can be highly frequency-dependent. The pulses are highly regular and stable over long periods of time, and certain pulsars have even been known to rival the stability of atomic clocks [2]. These properties have led to the development of many useful applications for pulsars, such as their use as scientifc tools to aid the detection of gravitational waves [«]. Many studies have been performed on the use of pulsars as naturally-occurring beacons for timing and navigation purposes. For example, Fuhr [»] proposed the terrestrial use of pulsar signals as an alternative to GNSS for power grid timing purposes. For navigation purposes, most studies conclude that the attainable accuracy of a pulsar-based system would not prove very useful for terrestrial use. However, many authors have proposed the use of pulsars to navigate spacecraft in deep space or even cislunar space [5], where accuracy requirements for a useful system may be more relaxed.