I am wondering if there is any work being done on a manned vehicle able to execute a 6.5 kilometer-per-second velocity change. This is the requirement for a vehicle to get from LEO to the lunar surface. It seems at times we derail transportation work by imposing Apollo-era constraints. For example, a three-stage rocket with the third stage performing both a LEO insertion burn AND the TLI burn - on a single tank load of propellant. This has to be dreadfully large and the launching vehicle much larger still.
A simpler solution may be to design a two-stage vehicle where the first stage provides only some 4 km/sec velocity change. The manned second stage then takes over and performs the remaining 6 km/sec velocity increment to achieve orbit. Both stages are reuseable.
On orbit, the now empty manned stage docks with a propellant depot and takes on a full load of propellant. This is the only 'proximity' operation in the entire flight. The vehicle then performs the TLI, lunar orbit insertion and landing maneuvers. It arrives on the lunar surface with little or no propellant in its tanks.
A good conception of what the vehicle might look like is the DC-X vehicle tested in the 1990's. Imagine that on the payload end of a Solid Rocket Booster and you get a pretty good idea of how the system would operate.