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Boeing also investigated several different classes of VTVL TSTO for solar power satellite
heavy-lift missions. Like the "Leo" single-stage-to-orbit rocket, the TSTO would have landed
vertically at sea or land by way of a ballistic entry through the Earth's atmosphere with
parachutes and/or retrorockets providing a soft landing. An actively cooled metallic heat
shield would be used. The smallest version (depticted above) would have had a net payload of
91,000kg. The 526-tonne (dry wt.) first stage was powered by nine LOX/kerosene engines plus
three SSMEs for landing while 7 SSMEs were used on the 217-tonne second stage. The evaluation
was discontinued in early 1978 due to operational considerations, and the studies focused on
larger VTVL TSTO versions instead. Boeing estimated that the VTVL TSTO could reduce the
cost per kilogram to orbit to $30/kg [1976 $] or only three times the cost of the propellant
required to operate the vehicle.
Heavy-lift launch vehicle booster/orbiter staging at 65km altitude. This VTVL TSTO
variant had a payload capability of 400 metric tons. Boeing envisioned a launch schedule of
3125 flights per year and 14 years of operation!
Liftoff thrust: 157,506KN (sl). Total Mass: 10,000t. Total length: 73m.
Payload capability: 400t to a 92.6km x 500km low Earth orbit.
Cost per flight: $7 million [1976 $]
Stage 1 : 6 x SSMEs & 16 x LOX/kerosene gas generator cycle engines. Liftoff thrust: 6 x 2,091KN + 16* 9,060KN. Isp: 350s. Gross Mass: 8,243.39t. Empty Mass: 787.59t. Length: 23.81m. Diameter: 33.68m. Propellants: LOX/LH2+kerosene.
Stage 2 : 8 x SSMEs. Liftoff thrust: 9 x 2,091KN . Isp: 455.2s [vac.]. Gross Mass: 1,750t including payload. Empty Mass: 258.81t. Length: 49.15m. Diameter: . Propellants: LOX/LH2.
This illustration depicts the medium-capability version of Boeing's VTVL TSTO (left) along with
the “Leo” VTVL SSTO (center) and a NASA/Johnson Space Center VTHL TSTO concept (right). All
three vehicles would have a 272-tonne payload capability and the average turn time (incl. water
recovery of the booster 300km downrange) for Boeing's TSTO vehicle would be 7-8 days.
”Overview of the Satellite Power System Transportation System” -- Hanley & Bergeron, AIAA 1978-975
”Space Transportation Systems 1980-2000” -- Salkeld,Patterson & Grey, AIAA Aerospace Assessment 1978/Vol.1