Shinkansen

Designed as a pair of identical airframes, one filled with fuel (the carrier plane) that would boost the second (the spaceplane), which had crew, cargo, and fuel, which continues to Earth orbit, the Shinkansen system had numerous tight constraints. Its goal was not merely to bring crew to Earth orbit, but to transfer them back and forth from Earth orbit to Moon orbit, so it had to be refuelable in Earth orbit by SpaceX’s Starship or SLS, and was designed to be refueled in one launch of those systems. Its wings allow for an aerobraking down from high Earth orbit (after leaving lunar orbit) to low Earth orbit, saving propellant on that part of the journey.

The Shinkansen uses methane and oxygen to make it more compatible with Starship systems and also because the increased density allowed for a tighter airframe – using more efficient hydrogen fuel would have required two carrier planes instead of one, similar to the Trimese design from the 1960s – we found the propellant choice to allow little capacity for cargo without additional boosters. So, small recoverable
boosters using the same ED-8 engines were added. These were fitted with floats as well as an engine shroud to protect the engine from corrosive water on splashdown.

The Shinkansen is a highly refined system for transfer between Earth and the Moon, adding some mass of aerodynamic surfaces to save the mass of propellant to propulsively return to low Earth orbit after a journey to the Moon. Its flight characteristics leave a lot to be desired, though, as it is touchy in roll and highly sensitive to the center of mass location. It would be best left in orbit and serviced there.

Single Airframe length: 40.1 meters
wingspan: 18.9 meters
height: 8.4 meters

Mass
Full system; no boosters: 465.1 tons
Carrier plane full: 312.04 tons
Carrier plane dry: 26.04 tons
Spaceplane full: 153.06 tons
Spaceplane dry: 27.91 tons

Engines (Carrier): 5 x ED-8
1013.2 kN thrust (vac.) each
322 s ISP s.l. – 338 s ISP vac.

Engines (Spaceplane): 2 x ED-8V
1088.4 kN thrust (vac.) each
322 s ISP s.l. – 371 s ISP vac.

2 x ED-7 47.4 kN thrust (vac.) each 358 s ISP (vac.)
RCS thrust: 2.2 kN ports @ 343 s ISP (vac.)

Carrier propellant: 154562 liters liquid methane, 195358 liters liquid oxygen

Spaceplane propellant: 66832 liters liquid methane, 84468 liters liquid oxygen