The Moon-based Advanced Reusable Transportation Architecture (MARTA) Project conducted an in-depth investigation of possible Low Earth Orbit (LEO) to lunar surface transportation systems capable of sending both astronauts and large masses of cargo to the Moon and back. The goal of this project was to create a profitable venture with an Internal Rate of Return (IRR) of 25%.The architecture was quickly narrowed down to a traditional chemical rocket using liquid oxygen and liquid hydrogen.However, three additional technologies identified as potentially cost saving were: aerobraking, in-situ resource utilization (ISRU), and a mass driver on the lunar surface.The vehicle was modeled using the Simulated Probabilistic Parametric Lunar Architecture Tool (SPPLAT) that incorporated several different engineering disciplines. This tool uses ISRU propellant cost, a dry weight reduction due to improved materials technology, and vehicle engine specific impulse as inputs and provides vehicle dry weight, total propellant used per trip, and price to charge the customer in order to guarantee an IRR of 25% as outputs. Estimation error, market growth, and launch cost uncertainty were also considered.The results of the project show that the desired operation is possible using current technology. Based on the stipulation that the venture be profitable, the price to charge the customer was highly dependent on ISRU propellant cost and relatively insensitive to the other inputs.

ASPEN was a study conducted by Los Alamos National Labs in the early 1960's to examine the benefits of using a Nuclear Thermal Rocket (NTR) for Earth-to-Orbit (ETO) single-stage launch vehicle applications. Using the analysis methods and assumptions of the time, this formerly classified study showed that a significant performance potential might be derived from using NTR engines for the final acceleration phase to orbit (air-breathing engines were used to Mach 11). Given the increased NASA interest in low-cost reusable space transportation, the ASPEN concept has been revisited using contemporary design assumptions and conceptual analysis techniques.