Slide 8 of 100
In 1964, Phil Bono of Douglas Aircraft Co. proposed a low-cost heavy lift VTVL SSTO RLV plus
lunar base as a logical follow-on to the Apollo project. Bono's "Reusable Orbital
Module-Booster & Utility Shuttle" (ROMBUS) concept was based on his patented plug nozzle
rocket engine design, which doubles as a heat shield during atmospheric reentry. The vehicle's
base-first reentry mode assures a stable condition during recovery since the mass of the engine
is very high, i.e. far aft center of gravity. The plug nozzle would be cooled by circulating
liquid hydrogen through the same regenerative system used for cooling the engines and base of
the vehicle while the engines are operating during ascent. Mixture ratio of liquid oxygen to
hydrogen was raised to 7:1 -- about as close as one can get to the stoichiometric value of 8:1
without running into combustion chamber cooling problem. During ascent, the plug nozzle
provides automatic altitude compensation and therefore good performance at both sea level
atmospheric pressure and in space. For final orbital insertion, 16 of the 36 engines would burn for
3 seconds to provide the required velocity. ROMBUS would typically spend 24 hours in orbit
before the ground track passes close enough to the launch site for de-orbit. Parachutes and
(beginning at 0.73km altitude-) retrorockets would be used to safely land the vehicle. The
final touchdown burn would be provided by four engines running at 25% thrust for approximately
To reduce the size and weight of the vehicle, the hydrogen fuel was to be stored in eight external
jettisonable tanks. The tanks were jettisoned and then recovered by parachute as they were
depleted during ascent to orbit. The earlier fully reusable "ROOST" concept was thus rejected
since it did not leave much margin for growth in vehicle structure mass.
The total life cycle cost would have been $10 billion [1964 $'s] over 10 years including
$4.088 billion for the development program. Bono mentioned the following SSTO RLV-specific
advantages : increased reliability since each vehicle has a history, reduced development
cost & complexity vs. multi-stage vehicles, economies of scale possible since plug nozzle
engine units & tanks could be mass produced. The estimated direct launch cost was
$22.4 million (=$28/lb. to a 568km orbit at 1964 economic conditions) and the planned vehicle
turnaround time about 76 days. Bono also mentioned a direct operations cost goal of $12/lb
(5-6 reuses) - $5/lb (>20 reuses) for a vehicle payload capability of 450t by the year 1975.
In comparison, the Saturn V was then expected to cost $150-250/lb. The vehicle would have used
the same Kennedy Space Center facilities as the Saturn boosters, although a new launch pad
would have been required (below).
Liftoff Thrust: 80.1 MN. Total Mass: 6,350.3t. Total Length: 29m.
Payload capability: 362,274kg to a 568km Earth orbit.
Development cost: $22 billion at 1999 economic conditions. Launch cost goal of $60-$330kg [1999 $s].
Stage Number 1: ROMBUS. 36 x plug-nozzle engines (3000psia pressure, 1:7 mixture ratio). Gross Mass: 6,350.3t incl. ~5,000t LOX. Empty Mass (core vehicle only): 306.175t. External fuel tank mass: (18.143t + 89.358t of LH2 fuel) * 8. Liftoff Thrust: 80.1 MN. Isp: 455s [vac.]. Length: 29m. Width: 24.4m. Propellants: LOX/LH2.
"ROMBUS concept" -- Bono, Astronautics & Aeronautics 1964/January/p.28
"All-Purpose Moon Vehicle" -- Space World 1964/December/p.16
"Reusable Booster for Logistics and Planetary Exploration" -- Bono,Woodworth & Ursini, IAF XV:th INTERNATIONAL ASTRONAUTICAL CONGRESS PROCEEDINGS 1964/p.547