How a Starship gets built ( video )

 

Comment (lunar starship version):

This shows how the header tank fits inside of the cone section on top. Since the header tank is only used for landing, this could be removed, and a crew compartment could replace it. Make it detachable, and leave the rest on the ground when the Starship does its job and lands on the moon. The big ship wouldn't be needed anymore, and the crew just needs to get to lunar orbit to hitch a ride back to Earth.

A review of the video shows that it may require some tweaking to get this idea to work. If the header tanks can hold enough propellant for the SuperDracos, and for the ride back up, then the header tanks could stay. Instead of hooking up to the raptor engines down below, it could hook up to the SuperDracos. You may need the SuperDracos to soft land on the lunar surface because the raptors are too powerful, and may dig a hole into the lunar surface.

Anyway, it doesn't appear that it would be out of the question ( for now ) to do the lunar version this way. No information on header tank capacity seems to be easily available.

It only takes 1/2 of the spacecraft's wet mass in order to get to lunar orbit. If the detachable part wet masses out at two tons, then it needs one ton of propellant to get back to orbit.

The reason for doing it this way is to increase the payload fraction that could be taken to the surface. If more mass is left behind, then less propellant is needed to get back to orbit. The entire Starship masses out at 110 tons or more. That would entail a loss of mass for payload as opposed to propellant needed for lifting all of that mass back to orbit. A tiny fraction of Starship could be made detachable, thereby making the trip back to orbit much less fuel intensive. The mass savings could be used for payload instead.