On-Orbit Propellant Re-supply Options for Mars Exploration Architectures

Abstract

A report detailing recommendations for a transportation architecture and a roadmap for U.S. exploration of the Moon and Mars was released by the NASA Exploration Systems Architecture Study (ESAS) in November 2005. In addition to defining launch vehicles and various aspects of a lunar exploration architecture, the report also elaborated on the extent of commercial involvement in future NASA activities, such as cargo transportation to the International Space Station. Another potential area of commercial involvement under investigation is the delivery of cryogenic propellants to low-Earth orbit (LEO) to refuel NASA assets as well as commercial assets on orbit. The ability to resupply propellant to various architecture elements on-orbit opens a host of new possibilities with respect to a Mars transportation architecture – first and foremost being the ability to conduct a Martian exploration campaign without the development of expensive propulsion systems such as nuclear thermal propulsion. In-space propellant transfer in the form of an orbiting propellant depot would affect the sizing and configuration of some currently proposed vehicles such as the Earth Departure Stage (EDS) and the Mars Transit Vehicle (MTV). In addition, it would influence the overall affordability and sustainability of a long-term Mars exploration campaign. To assess these consequences, these vehicles and their various stages are modeled to approximate the ESAS performance figures using a combination of analogous systems and physics-based simulation. Well established modeling tools -- such as POST for trajectory optimization, APAS for aerodynamics, NAFCOM for cost modeling, and Monte Carlo analysis for technology advancement uncertainty -- are used to perform these analyses. To gain a more complete view of the effects of an on-orbit propellant refueling capability, a reference Mars mission is developed and compared to an equivalent mission without refueling capability. Finally, the possibility of propellant resupply in Mars orbit is also discussed along with its implications on the sustainability of a long-term Mars exploration architecture.