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Stepping-Stones to the Future of Space Exploration: A Workshop Report
Four possibly transformational conceptual elements of spaceflight were presented:12
Lunar elevators would be a reusable, space-based chemical propulsion transport system for payloads from low Earth orbit (LEO) to the Moon or beyond. The elevators would refuel at their destination and never need to return to Earth. One advantage would be mass-efficient lunar exploration with a one-person vehicle.
Solar-electric-propelled freighters would integrate high-performance, efficient electric propulsion into a vehicle to propel payloads from LEO to high-energy orbit. Advantages include the potential reduction in beyond-LEO transportation costs and required launch vehicle capacity.
Cryogenic propellant depots would provide an on-orbit reserve of cryogenic chemical or electric propulsion propellant, decoupling the launch of propellant from that of hardware.
Orbital maneuvering vehicles are autonomous orbital maneuvering, rendezvous, and docking vehicles that can transfer propellant launch packages to tankers, move payloads, and safely de-orbit hardware.
The team looked at a variety of missions and architectures and concluded that human lunar return is one of the most important to study because its trade space of implementation options includes technology elements of other missions. The team also attempted to include options in its analysis that would answer questions such as, Where should in-space staging be done? Where should the primary vehicle be located? Do vehicles stay in orbit all the time, or do they return to Earth after every mission? NASA is investigating this entire trade space and also considering mass as a metric in the design. Geffre did point out that mass and cost are usually interconnected in such a trade space. One example of this interconnection was a comparison between the mass of Apollo (approximately 130 tons) and the mass of these new architectures (on the order of 150 to 200 tons). One important difference between the old and new designs is that a larger fraction of the mass in the new architectures is reusable (that is, is not a propellant).
The team also looked at payload capabilities for use by other government entities, including other NASA enterprises and DOD. The studies emphasized the cost-benefit of not having to launch propellant each time a vehicle is launched. Additional autonomous activity was also considered in the scenarios studied. Geffre said that Mars architecture studies have been ongoing for last 15 years; however, the team is using a newer set of transformational space infrastructures. The goal of this architecture is to improve performance and affordability relative to what is achievable with more traditional approaches.
Geffre ended his presentation by mentioning briefly key capabilities and technology needs that have been identified during these mission and architecture studies. They fall into five areas: (1) advanced space transportation, (2) Earth-to-orbit transportation, (3)
James Geffre, NASA Johnson Space Flight Center, “A Summary of Recent NASA Exploration Architecture Studies: Transformational Space Infrastructure Strategies,” presented to the workshop on February 23, 2004.