Upper stage / space tug - studied by NASA Marshall in 1965. Launched by Saturn V. S-IVB structurally strengthened to handle larger payloads, otherwise unchanged

Length: 18.08 m (59.31 ft). Basic Diameter: 6.61 m (21.68 ft). Span: 6.61 m (21.68 ft). Mass: 195,000 kg (429,000 lb). Main Engine: J-2. Main Engine: 1,438 kg (3,170 lb). Main Engine Thrust: 912.000 kN (205,025 lbf). Main Engine Propellants: Lox/LH2. Main Engine Propellants: 158,700 kg (349,800 lb). Main Engine Isp: 421 sec.