MANNED SPACE CONCEPTS
Lunar Waverider Return Mission
This concept of using a spacecraft with a waveriding atmospheric return seemed initially, to be impossible to achieve, but through the use of drop tanks for propellant, the task suddenly became more viable.
The design examined the feasibility of building a small manned spaceplane and descent stage, which is delivered to Low Earth Orbit (LEO) by a conventional rocket booster, from whence it flies to the Moon, descends from Lunar orbit to the Lunar surface, then returns to Lunar orbit and from there, back to the Earth's surface, using waveriding in the Earth's atmosphere for the atmospheric decceleration and re-entry.
A flight to the Moon would obviously require some form of earth escape stage, so reducing the size of the vehicle to a minimum, and making the concept a real no-frills system, and making use of drop tanks and drop stages along the way, all helped to enable a vehicle that would be able to reach its delta vee requirements for mission success. Commonality of the propulsion systems was investigated for Earth escape, lunar descent and ascent and Earth return. The concept seemed feasible, but required a large number of drop tanks, which would make it impractical in reality.
This is one of those concepts that was investigated just to see if it was feasible rather than proposing it as an integral part of a cis-lunar transportation system. In order to make it more viable, orbital propellant depots, and even propellant depots at Earth Moon Lagrange points would realistically be required.