The Sea Dragon was a 1962 conceptualized design study for a two-stage sea-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.

As of 2024[update], among rockets that have been fully conceived but not built, it is by far the largest ever and, in terms of payload into low Earth orbit (LEO), equaled only by the Interplanetary Transport System concept (the predecessor to SpaceX Starship) in the latter's expendable configuration with both designed for 550 tonnes.

A large ballast tank system attached to the bottom of the first-stage engine bell was used to "hoist" the rocket vertical for launch.

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, sinking the rocket to vertical with the second stage above the waterline.

[6] 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.

In the post-credits scene, which takes place in 1983, a Sea Dragon is depicted launching from the Pacific Ocean to resupply the US lunar colony.