A ca. 1964 Boeing rendering of an HL-10-derived spaceplane in orbit. Numerous companies – Boeing, McDonnell, Lockheed, Northrop, etc. – contemplated the development of a logistics spaceplane based on the HL-10. The spaceplane itself would, rather like the X-20 Dyna Soar, have been minimally functional in space; most of the propulsion and power would have come from the attached adapter module. The conical adapter would have also carried the bulk of the vehicles payload to be delivered to orbit, and would be used to provide a de-orbit burn for the spaceplane. The adapter would therefore burn up on re-entry, leaving the lifting body to glide to a runway landing. The spaceplane itself would be crammed full of astronauts and the life support they’d need; there would generally be little capacity for anything else, certainly not payload going back downhill. This was fine, though, as there were few enough payloads other than humans that made sense to send *back* down the gravity well.
