The Sea Dragon was a 1962 conceptualized design study for a two-stagesea-launched orbital super heavy-lift launch vehicle. The project was led by Robert Truax while working at Aerojet, one of a number of designs he created that were to be launched by floating the rocket in the ocean. Although there was some interest at both NASA and Todd Shipyards, the project was not implemented. At the massive dimensions of long and in diameter, Sea Dragon would have been the largest rocket ever built., among rockets that have been fully conceived, it is by far the largest ever and, in terms of payload into low Earth orbit, equaled only by the Interplanetary Transport System in the latter's expendable configuration with both designed for 550 tonnes.
Design
Truax's basic idea was to produce a low-cost heavy launcher, a concept now called "big dumb booster". To lower the cost of operation, the rocket itself was launched from the ocean, requiring little in the way of support systems. A large ballast tank system attached to the bottom of the first-stage engine bell was used to "hoist" the rocket vertical for launch. In this orientation the payload at the top of the second stage was just above the waterline, making it easy to access. Truax had already experimented with this basic system in the Sea Bee and Sea Horse. To lower the cost of the rocket, he intended it to be built of inexpensive materials, specifically 8 mm steel sheeting. The rocket would be built at a sea-side shipbuilder and towed to sea for launch. It would use wide engineering margins with strong simple materials to further enhance reliability and reduce cost of complexity. The system would be at least partially reusable with passive reentry and recovery of rocket sections for refurbishment and relaunch. The first stage was to be powered by a single enormous thrust engine burning RP-1 and LOX. The fuels were pushed into the engine by liquid nitrogen, which provided a pressure of for the RP-1 and for the LOX, providing a total pressure in the engine of at takeoff. As the vehicle climbed the pressures dropped off, eventually burning out after 81 seconds. By this point the vehicle was up and downrange, traveling at a speed of. The normal mission profile expended the stage in a high-speed splashdown some downrange. Plans for stage recovery were studied as well. The second stage was also equipped with a single very large engine, in this case a thrust engine burning liquid hydrogen and LOX. It was also pressure-fed, at a constant lower pressure of throughout the entire 260 second burn, at which point it was up and downrange. To improve performance, the engine featured an expanding engine bell, changing from 7:1 to 27:1 expansion as it climbed. The overall height of the rocket was shortened somewhat by making the "nose" of the first stage pointed, lying inside the second stage engine bell. A typical launch sequence would start with the rocket being refurbished and mated to its cargo and ballast tanks on shore. The RP-1 and nitrogen would also be loaded at this point. The rocket would then be towed to a launch site, where the LOX and LH2 would be generated on-site using electrolysis; Truax suggested using a nuclear-powered aircraft carrier as a power supply during this phase. The ballast tanks, which also served as a cap and protection for the first stage engine bell, would then be filled with water, raising the rocket to vertical. Last minute checks could then be carried out, and the rocket launched. The rocket would have been able to carry a payload of up to or into LEO. Payload costs, in 1963, were estimated to be between $59 to $600 per kg. TRW conducted a program review and validated the design and its expected costs. However, budget pressures led to the closing of the Future Projects Branch, ending work on the super-heavy launchers they had proposed for a crewed mission to Mars.
Sea Dragon in fiction
The Sea Dragon appears in the season finale of the 2019 Apple TV+ series For All Mankind. In the post-credits scene, set in 1983 in an alternate timeline in which the Soviet Union landed on the Moon before the United States, and the '60s era "space-race" did not end, a Sea Dragon is depicted launching from the Pacific Ocean to resupply the US lunar colony. An astronaut claims in a voice-over that the ocean launch is being used as a safety measure because the payload includes plutonium.
