International Research Journal of Engineering and Technology (IRJET) Volume: 12 Issue: 03 | Mar 2025
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e-ISSN: 2395-0056 p-ISSN: 2395-0072
Cislunar Communications Path Delays: A Comparison Between Two Idealized Relay Satellite Constellations Savan C. Becker1, Michael E. Johnson, PhD2, John Carrico Jr.3 1
2
Department of Engineering, Capitol Technology University, Laurel, MD, USA Adjunct Professor, Department of Engineering, Capitol Technology University, Laurel, MD, USA 3 Chief Technology Officer/Astrogator, Space Exploration Engineering (SEE), Laurel, MD, USA
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Abstract - Multiple National Aeronautics and Space
[11, 17, 18, 21, 22, 23, 24]. When considering cislunar space, it is well known that the average light travel time (LTT) between the Earth and the Moon is approximately 1.3 s, with a round-trip time (RTT) of 2.6 s [18]. However, future lunar exploration programs will involve more than just point-to-point communication between Earth and the lunar surface. Artemis plans include the establishment of an orbiting space station (i.e., Gateway), a possible surface outpost near the Moon’s South Pole, a constellation of relay satellites in lunar orbit (i.e., LunaNet), and the construction of additional terrestrial Lunar Exploration Ground Stations (LEGS) (see Fig – 1) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 25].
Administration (NASA) sponsored and independent studies have examined and/or proposed deployment of spacecraft in key cislunar orbits as part of LunaNet, a communications relay and navigation network to support operations on and around the Moon [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. Additional research promotes the possibility for immersive, collaborative, multi-user human and human-robotic exploration during future lunar and interplanetary space exploration initiatives, including Artemis [11, 12, 13, 14, 15, 16, 17, 18, 19, 20]. Delay (i.e., latency) due to distance and frequency/duration of access intervals are significant, fundamental factors in determining the extent and quality of dynamic communications, teleoperation of robotic systems, and immersive interaction – particularly in space operations [11, 17, 18, 21, 22, 23, 24]. This article describes how we used Systems ToolKit (STK) software to investigate the access intervals and path delays (PD) in an idealized lunar relay satellite constellation modeled on a proposed LunaNet baseline [3, 8, 9, 10, 25]. We also compare these results to a hypothetical “Lagrange-Centric” (i.e., Earth-Moon L1) alternative relay constellation. While simplified, our estimates for PD and access intervals may help bound “worstcase” scenarios and expectations when considering feasibility, quality, and frequency of collaborative cislunar exploration activities.
Fig – 1: LunaNet described in NASA LunaNet Overview. [8]
Key Words: Technology, NASA, Space, Spaceflight, Artemis, Gateway, Shackleton, LunaNet, Satellite, Satellites, Communications, Constellations, Spacecraft, Moon, Mars, Cislunar, Space Exploration, Telepresence, Exploration Telepresence, Astrodynamics, Orbits, Orbital Mechanics, Systems ToolKit, Satellite ToolKit, STK, Astrogator, CODE, Lagrange, Libration
Consequently, when performing collaborative exploration, the aggregate delay – or latency – encountered by communicants using any elements of this network will differ based upon the specific locations involved (e.g., terrestrial ground stations, orbiting spacecraft, and lunar outposts), and whether the paths used are line-of sight (LOS) and/or via relay. In a satellite communications system, one very basic parameter factored into latency estimations is the free space path delay (PD; or propagation delay) between space and ground elements in the network. The PD between two locations is equivalent to the LOS signal travel time (i.e., the LTT), and the RTT represents the overall delay between initial contact and response/acknowledgement (i.e., twice the PD) [26]. Also, the access intervals between the various elements and users of the system are often examined when designing and operating communications satellites constellations. Access intervals represent the frequencies and durations that
1. INTRODUCTION Research conducted by independent investigators and sponsored by the National Aeronautics and Space Administration (NASA) suggests the possibility for immersive, collaborative, multi-user human and humanrobotic exploration of the Moon during the planned Artemis program [1, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]. Communications delays in space operations impact the extent to which astronauts, researchers, and enthusiasts can dynamically participate in collaborative exploration
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