Slide 43 of 125
Boeing's giant "Leo" VTVL SSTO RLV was part of the company's NASA-funded solar powersat studies
in 1976-77. Leo utilized twenty-four 4.5MN oxygen-hydrogen main engines plus twenty-four 2.25MN
lox-kerosene booster engines to generate a thrust-to-weight (T/W) ratio at liftoff of 1.3. The
booster engines would be shut down 127.4 seconds after liftoff.
Leo would generate so much noise that it would have to be launched from an artificial lagoon
located a few kilometers from the existing Shuttle launch pads at Cape Canaveral. It would have
been towed into a water-filled lock and then lowered to the launch pad to undergo servicing,
fueling and launch. The turnaround time was estimated to be four days.
The landing site would have consisted of a 5km diameter pond adjacent to the launch area. The
dark circle in the background is a receiving antenna, to which power generated in space would
Leo's base heat shield would be water-cooled and the engine nozzles were to be protected by
steam ejection. A normal mission would last only one orbit to avoid reentry phasing problems
since the vehicle would have a relatively limited crossrange capability.
“Leo” landing. 16 of the LOX/kerosene engines are ignited during terminal descent to
decelerate the vehicle. The final low-speed, low-thrust landing maneuver is performed by four
Heavy-lift RLVs probably will have to land vertically due to the weight of the propulsion
system. Boeing's "Leo" VTVL SSTO baseline would have a mass of (841t/10306t), cost $9B to
develop  and the cost of launching a 228t payload would be $9.7M. For this vehicle, the
base heat shield and supporting thrust structure, penetrated by 48 rocket engine exit openings,
would require intensive work to provide adequate thermal protection during reentry. The ”Space
Transportation Systems 1980-2000” study claimed an advanced VTVL SSTO version might be made 50%
smaller and cheaper if tripropellant dual-expander engines and other advanced technologies were
used . However, VTVL TSTO still appeared to be more attractive since the lower propellant cost
appears more important than operational complexity for such missions.
Estimated development cost [1976 $s]: $9-12 billion. Cost per flight: $9.7 million (including
$2.7 million for propellants) nominal cost; $7 million at 500 flights/year [1976 $s]
Liftoff thrust: 160,200KN (sl). Total Mass: 10,423t.
Payload capability: 228t to a 92.6km x 500km low Earth orbit; Payload bay: 23m diameter.
Stage 1 : 24 x LOX/LH2 rocket engines & 24 x LOX/kerosene motors. Liftoff thrust: 24 x 2,225KN + 24 * 4,450KN. Isp: Gross Mass: 10,306t. Empty Mass: 841t. Length: 64-76m depending on payload fairing. Diameter: 41m. Propellants: LOX/LH2+kerosene.
”Reusable Rocket Transports” -- SPACEFLIGHT, 1977/p.172
”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