The core technology behind distributed time synchronization is heavily biased toward software development, with nearly all core hardware technology available commercially today. This proposal aims to use agent-based modeling and simulations to explore how centralized and decentralized PNT service network topologies evolve in a growing lunar ecosystem. Modeling network topologies representative of near-term lunar missions and large future populations of cislunar actors will predict the relative performance, “critical mass” of assets required for service, and coverage of decentralized PNT services and/or GNSS-like beacons providing PNT to lunar missions. There is an abundance of prior art describing optimal orbit configurations for such systems that can also be evaluated in this way.

The model will feature a population of agents, where each agent has a Stratum, a location and velocity, a clock with drift, and a communications system with a spectral band and radiation power. Agents belong to one of three groups based on their behavior: Transmitters, Receivers, and Peers. Transmitter agents radiate signals but do not listen for incoming signals. Receivers listen for incoming signals but do not radiate. Peers are capable of listening for and radiating signals. Agents move in space independently along orbits or surface routes around a sphere in the simulation space representing the Moon. Terrestrial communications systems are modeled as a Stratum 0 Transmitter. Every node reports measurements of each metric described in the subsequent Metrics section at every step of the simulation period.

Over the simulation period, each agent’s clock encounters simulated drift that accumulates over time. The agents record their perceived position by integrating instantaneous velocity observations over time, where the observed time is based on the local clock’s epoch. At the end of the simulation period, the observed position is compared to the true position. Agents may interact with one another over the simulation period using modeled communications links for PNT measurements and time synchronization. Links are only established between two agents if both 1) share a common spectral band; 2) have line-of-sight to each other; 3) have sufficient radiation power to transmit across the distance between them; and 4) at least one agent is a Transmitter. When a link is established, the Receiver agent’s clock is synchronized to the Transmitter’s epoch. If both agents are Peers, the agents synchronize to the epoch of the agent with a lower Stratum, or the mean epoch between them. Each time an agent synchronizes to another agent, it becomes Stratum n+1 where Stratum n belongs to the agent with the lower number. Agent A syncs to UTC and becomes Stratum 1, then Agent B syncs to A and so Agent B becomes Stratum 2, and so on.

This model framework permits rapid simulation of heterogeneous nodes acting as PNT servers, clients, or both. The proposed study seeks to evaluate decentralized networks as alternatives to GNSS-like services for cislunar PNT. The described model allows each network topology to be tested and instrumented while subject to realistic client population densities in near-term (tens of agents) and future scenarios (hundreds, thousands of agents). The described model also permits the simulation of multiple PNT services coexisting, such as Parsec, weak-GPS, and the proposed decentralized network. The model also accounts for the evolution of competing providers as the populations of servers and clients grow.

Insights obtained from models will then be applied to create an optimal mission profile for a constellation of cislunar spacecraft equipped with space-rated Time Cards that enable the proposed capability of a publicly available minimum viable PNT service. With relevant prediction of cislunar PNT users for each PNT service configuration over the next 5 to 15 years, and also computing the equivalent cost per user for terrestrial GNSS, data-driven investment decisions related to deploying new PNT fleets in cislunar space are possible.