If it's a realistic SSTO, it won't be loading its own cargo. It'll be loaded and unloaded at the pad or in the hanger, like Space Shuttle. Carrying the mass of the crane is a waste of mass, especially when you consider that this thing is not sci fi, it'll take several days or weeks to be turned around between flights in order to service the engines and check out the TPS, etc.
I bet it would be faster and cheaper to turn around than Shuttle, though.
---------- Post added at 12:28 AM ---------- Previous post was at 12:26 AM ----------
BTW, the concept of using LOX extracted from the atmosphere in a rocket is not complete nonsense, but it's difficult. Liquid air, on the other hand, has been studied for a long time, and was considered in many early Space Shuttle proposals:
http://en.wikipedia.org/wiki/Liquid_air_cycle_engine
I bet it would be faster and cheaper to turn around than Shuttle, though.
---------- Post added at 12:28 AM ---------- Previous post was at 12:26 AM ----------
BTW, the concept of using LOX extracted from the atmosphere in a rocket is not complete nonsense, but it's difficult. Liquid air, on the other hand, has been studied for a long time, and was considered in many early Space Shuttle proposals:
http://en.wikipedia.org/wiki/Liquid_air_cycle_engine