Shown is a large orbital transfer vehicle (OTV) and lander in low lunar orbit over the crater Copernicus. Both vehicles return to the Space Station in Earth orbit after every mission for maintenance, component changeout and to be reloaded with propellants and other consumables. The lander is multi-purpose, capable of landing cargos up to 25 metric tons (one way, lander expended) or carry a crew module round trip. The crew module, shown in the illustration, can be removed and replaced with cargo. The lander is separating from the OTV, seen preparing to descend to the surface. Later it would return to low lunar orbit, single stage. It has a pressurized tunnel running down the center which tees into another tunnel shown on the bottom. The tunnels provide pressurized volume to locate equipment requiring maintenance, replacement or inspection. The tunnel also allows pressurized access to a surface rover and doubles as an airlock. The lander would require about 30 metric tons of propellant. The lander engines are the chief long term development item. Requirements for throttling ratios as high as 20:1, space basing, and reusability, place them at or beyond the state of the art. Study participants feel work on the lander should continue until the engines are defined well enough for long lead development to begin. The OTV is a large, aerobraked, specially designed vehicle, designed to place the lander and payload in low lunar orbit and then aerobrake the empty lander back into Earth orbit. The OTV does this single stage from low Earth orbit and back. The OTV and lander may be able to use common engines, but this requires more study. The illustration shows common engines. The OTV would carry roughly 120 metric tons of propellant.