On 29 December 1970 Grumman and Boeing received contract NAS9-11160 to study two-stage-to-orbit shuttle configurations using both internal and external liquid hydrogen tanks. Reviews with NASA in January and March 1971 showed there could be significant weight, risk, and cost reductions through use of a booster with a heat-sink airframe and an orbiter equipped with an external liquid hydrogen tank. In April 1971 NASA authorised the contractors to make a detailed study of the most promising configuration - a three-engine orbiter with an external liquid hydrogen tank and heat-sink booster. Staging would be at 7660 kph instead of the 11,000 kph optimum for the all-recoverable two-stage-to-orbit designs. This lower separation velocity meant a smaller booster requiring less thermal protection and using less JP-4 fuel for the return to base. The team quickly established that using 2 x 250,000 kgf engines on the 405 tonne orbiter resulted in unacceptable abort constraint. Therefore 3 x 188,000 kgf baseline Phase B engines would have to be used. Configurations used in the trade study were the H-33 three-engine orbiter with an external tank and the G-3 three-engine fully-reusable orbiter.
The H-33 orbiter used 3 x 188,000 kgf main engines and 4 x JTF22A-4 turbofans. The orbiter's 55 deg sweep delta wing provided a cross range of 2040 km and a landing speed of 333 kph. Ferry range would be 556 km using the jet engines. The orbiter weighed 89,300 kg empty and had two internal liquid oxygen tanks with a capacity of 320,044 kg below the payload bay. Two external liquid hydrogen tanks, each 31 m long and 4.5 m in diameter, held 2 x 27,000 kg of the low-density fuel. The orbiter used titanium as its basic structural material. The H-33 booster weighed 99.835 kg empty. It was equipped with 12 SSME and 12 x GE F101 or P&W JTF22A-4 turbofan engines, which gave it a 715 km ferry range. The 10 m diameter fuselage used Saturn S-IC propellant tanks, mounted in a hot structure that required no thermal protection system.
R&D was estimated at $ 2.674 billion for the orbiter, $ 32.6 million for the external tanks, $ 2.181 billion for the booster, and $ 893 million for flight test and project management, a total of $ 5.878 billion. This did not include $1.0165 billion of government furnished equipment (primarily engines). Grumman estimated that production orbiters would cost $615 million each; boosters $ 274 million; and each pair of expendable external tanks, $740,000. The marginal costs for each H-33 flight were calculated as $ 4.2 million. Given a March 1972 go-ahead, first orbital flight could be accomplished by April 1978. The team estimated 3,000 people would be needed to support a launch rate of 75 flights per year, working out to $540,000 per flight costs for manpower.
Stage Data - Shuttle H33
Status: Study 1971.
Gross mass: 1,963,916 kg (4,329,693 lb).
Height: 90.00 m (295.00 ft).
Diameter: 10.00 m (32.00 ft).
Thrust: 22,148.00 kN (4,979,068 lbf).