Description: Satellite-based navigation is a promising solution to provide lunar position, navigation, and timing (PNT) services to support NASA's plans for sustained presence on the Moon. Satellites part of the network providing these services must broadcast their ephemeris as finite parameters in a navigation message to lunar users for user PNT. The proposed innovation is to create a novel framework to generate reliable navigation message parameters for lunar orbiters to broadcast with reduced dependency on lunar ground infrastructure and high Size, Weight, and Power satellite components. The first objective is to generate long-term satellite ephemeris parameters. These parameters will be obtained via stochastic constrained convex optimization, leveraging known parameterization error requirements to find a satisfactory representation of the true satellite state in lunar orbit over a long time interval. The trade- off between long-term navigation data volume, validity interval, and achievable approximation error performance will investigated. The next objective is to harness long-term ephemeris parameters to perform onboard satellite orbit determination and enable onboard generation of real-time and precise ephemeris parameters for navigation message broadcast. Onboard orbit determination will be accomplished by using inter-satellite links to exchange information across the network for collaborative state estimation and timekeeping. Over time, results from orbit determination will correct the long-term navigation parameters, enhancing the precision of the satellite state representation. The performance of this approach will be tested over different lunar constellation configurations employing small satellites to reduce Size, Weight, and Power requirements. The last objective is to determine the feasibility of the innovation from a system-level design perspective. System requirements to implement this innovation within the ever-evolving NASA lunar PNT architectures will be identified. Precise ephemeris parameterization onboard lunar satellites will help reduce orbit and ground infrastructure costs to provide lunar PNT services, alleviating substantial financial burdens of future NASA lunar exploration endeavors.