This paper describes an achievable and affordable approach for building a shared space infrastructure. This infrastructure will benefit all three space sectorscommercial, civil and national defense-by providing new and enhanced shared capabilities that will improve the safety, reliability and affordability of their robotic and human space operations.The proposed Phase 1A (2000-2017) infrastructure will be comprised of commercial Reusable Launch Vehicles; a Shuttle-derived, unmanned, heavy-lift launch system; four low Earth orbit (LEO) spaceports; spaceport-based interorbit transports capable of reaching geosynchronous orbit; and, an in-space logistics support capability. During Phase 1B (2018)(2019)(2020)(2021)(2022)(2023)(2024)(2025), the infrastructure expands the size of the LEO spaceports to accommodate specialized user needs, adds new Earth-to-orbit low cost launch systems for durable cargo, adds upgraded interorbit transports to provide support lunar and deep space exploration, and adds first-generation interplanetary spaceships to extend routine transportation to lunar orbit. This space infrastructure will also be capable of supporting a manned Mars exploration program and robotic probes to near-Earth asteroids and comets. This paper focuses on a strategy for building and financing this shared space infrastructure. Specifically, it describes an acquisition strategy for Phase 1A that effectively uses current space technology and infrastructure capabilities to reduce programmatic risk and enables achieving an initial operational capability in 2012. Further, it describes an approach for financing the fabrication and operation of the Phase 1A infrastructure and covering necessary transportation transition costs using funds already budgeted for in the present government spacelift budget.