Robert Truax, an engineer at Aerojet General, in 1962 designed a two-stage rocket 150 m long that would be built in a shipyard, towed out to sea and launched directly from the ocean. The vehicle, called Sea Dragon, was designed to carry up to 550 tonnes to low Earth orbit, more than the mass of the entire International Space Station, which weighs about 450 tonnes.
Sea Dragon was a design study. It was never built.
The rocket was 23 m in diameter and would have weighed about 18,000 tonnes at launch. Its payload of 550 tonnes, or 1.2 million lb, to an orbit of about 229 km would have allowed the whole space station to be launched in a single flight.
The design followed the "big dumb booster" concept. The aim was the lowest possible launch cost through low development and production costs, accepting a larger vehicle, lower-performance propulsion and heavier stage dead weight than the designs then favoured by NASA and the US Air Force.
The structure was to be made from inexpensive 8 mm maraging steel sheet, similar to that used for Aerojet's 260-inch solid motor, and assembled at a seaside shipyard. Aerojet reviewed the design with Todd Shipyards, which concluded the work was well within its capabilities and not unlike building a submarine hull.
The rocket would be fuelled with RP-1 kerosene in port and then towed horizontally to the open ocean. There, liquid oxygen and liquid hydrogen would be supplied from tankers or produced by electrolysis of sea water, using a nuclear aircraft carrier such as the USS Enterprise as the power source.
Ballast tanks attached to the bottom of the first-stage engine bell, which also served as a protective cap for the engine, would be flooded with water. The rocket would swing to vertical with the second stage and payload just above the waterline for final checks before launch.
The first stage used a single pressure-fed engine burning liquid oxygen and kerosene, with thrust of about 36 million kgf. It would burn for 81 seconds, reaching 1.8 km/s at an altitude of 40 km, and fall into the ocean about 290 km downrange. Recovery and reuse of the stage was considered as an alternative.
The second stage burned liquid oxygen and liquid hydrogen with thrust of about 6.35 million kgf. Over a burn of 260 seconds it would reach orbital velocity at about 230 km altitude, 940 km downrange. An expandable nozzle exit cone raised the engine's area ratio from 7:1 to 27:1.
The scale of the vehicle was such that a Saturn V second stage would fit inside the Sea Dragon first-stage engine and nozzle, according to NASA drawings prepared to the same scale.
Liftoff noise from the first stage was estimated at about 184 dB. Launching from the ocean avoided the cost of the acoustic infrastructure that a land pad would have required.
Aerojet had tested the sea-launch concept earlier with Sea Bee, a surplus Aerobee fired from underwater, and Sea Horse, a surplus Corporal missile. The Sea Bee tests showed a turnaround cost of about 7 per cent of a new unit.
Aerojet estimated the cost of placing payload in low Earth orbit at between $60 and $600 per kg in 1963, about one-quarter of the cost of Saturn V or less.
NASA Marshall passed the Aerojet designs to TRW's Space Technology Laboratories for evaluation. TRW fully confirmed Aerojet's cost and engineering figures, to the surprise of both TRW and NASA. The work was reported under contract NAS8-2599 as "Study of Large Sea-Launch Space Vehicle" in January 1963.
Aerojet considered buying Sudden Ranch, a stretch of coastline between Santa Barbara and Vandenberg Air Force Base, as a launch site. It was the only site in the continental United States from which a rocket could launch directly into polar orbit without overflying populated areas. The land later became part of Vandenberg.
The programme ended with the cutbacks to Apollo and the budget demands of the Vietnam War. NASA dissolved its Future Projects Branch, dropping almost all work on crewed Mars landings, and Aerojet could no longer fund Sea Dragon from its internal research and development budget.
Truax later proposed smaller successors, Excalibur and SEALAR, in the 1990s. Neither flew.