History

The Sea Dragon was a massive sea-launched rocket design and, to date, the largest rocket ever designed (Figure 2). It could, in theory, carry a huge 550 metric tonne cargo into low Earth orbit but it was never built, falling foul of budget cuts and the closure NASA's Future Projects branch (Grossman 2017). The rocket was designed by Robert Truax for Aerojet on the principle of building a "big dumb booster" - it was the complexity that made rockets expensive, he claimed, not their size. The idea was to reduce manufacturing complexity and costs by accepting less efficient engines and more deadweight. Building big allows for larger error margins, using common materials such as steel means using established processes, and launching from the ocean avoids complicated ground launch facilities. Rather than specialist manufacturers, existing shipyards could be commissioned to build the craft, and then it could be towed to the sea for launch (Figure 1). While it was never built it passed various engineering reviews and costings and seemed, despite its tremendous size, feasible - bearing in mind this was 7 years before the Saturn V took Apollo 11 to the moon (Sea Dragon 2019).

Figure 1: The Sea Dragon launch process. 1) a tug tows the craft to sea 2) The base of the launcher is flooded, causing the craft to righten itself. 3) the craft now vertical can be mated with cargo and prepared for launch 4) the base detaches and the rockets fire. (Wikipedia Contributors 2022)

Big Dumb Booster

Aside from the development of amphibious rocket launching, Robert Truax was a big proponent of ultra-low-cost rocket design and recoverable launch vehicles - concepts that are gaining traction again in the modern private space race. He also worked on and advanced the concept of staged rocket combustion, which would later be used in the RS-25 - the space shuttle's main engine (Robert C. Truax Collection | Collection | SOVA 2016).

The rocket design was relatively simple - in keeping with the "big dumb booster" philosophy. It consisted of two stages. Stage 1 had one huge engine capable of generating 350 MN fueled by LOX + Kerosene. This engine was not gimbaled, so four additional auxiliary engines mounted about halfway up would provide attitude control. This main engine was powerful enough to lift the 18,000 metric tonnes of spacecraft to an altitude of 40km traveling at a speed of 1.8km/s in 81 seconds. The second stage would have been powered by a relatively small engine, generating 59MN of thrust - still substantially more than the Saturn V's first stage, which could generate 34.5MN! An alternative single-stage-to-orbit version was designed with the intention of returning to Earth and being reusable. Costs would have been brought down to about 1/4 of the Saturn V's (NASA - Saturn V 2022, Sea Dragon 2019).

Figure 2: The largest (American) rockets - SpaceX's Starship (L), Sea Dragon (C), Saturn V (R) - credit

David Willis / Twitter

USSR

Meanwhile, in the USSR, Sergei Korolev designed the N1 as the USSR's answer to the Saturn V. It would have been capable of launching 80 tonnes into orbit using thrust from 30 engines generating 44 MN of thrust. Unlike the Sea Dragon, the N1 was actually built - four in total - but every launch failed. The pressure of trying to catch up with the Saturn V development meant that corners were cut and key testing regimes were minimized or skipped completely. Unlike Truax's simplistic approach to the Sea Dragon, Korolev seemed to favour big and bold directions. For example, the N1 relied on being able to synchronize the firing of 30 engines all at once for a successful launch. The programme also, at some point, touched on all manner of complex and risky emergent technologies like aerospikes, nuclear engines, ion, and plasma engines. After these failures, and a lack of a clear way to resolve the issues, the 5th launch, and the programme as a whole, was eventually canceled in 1974 (N1 2012, N1 | Soviet launch vehicle | Britannica 2022).

References

Grossman, D. 2017, Popular Mechanics (Popular Mechanics),

https://www.popularmechanics.com/space/rockets/a25915/sea-dragon-history-curious-droid/

Sea Dragon. 2019, Astronautix.com,

http://www.astronautix.com/s/seadragon.html‌

Wikipedia Contributors. 2022, Wikipedia (Wikimedia Foundation),

https://en.wikipedia.org/wiki/Sea_Dragon_(rocket

) Robert C. Truax Collection | Collection | SOVA. 2016, Si.edu,

https://sova.si.edu/record/NASM.2016.0008

NASA - Saturn V. 2022, Nasa.gov,

https://www.nasa.gov/centers/johnson/rocketpark/saturn_v.html

N1 | Soviet launch vehicle | Britannica. 2022, Encyclopædia Britannica,

https://www.britannica.com/technology/N1

N1. 2012, Astronautix.com,

http://www.astronautix.com/n/n1.html