The closing stages of 2015 saw some major advances in the world of commercial spaceflight. Both Blue Origin and Space X demonstrated the ability to fly rockets into space and recover them. In the case of Blue Origin, their New Shepard rocket sent an uncrewed but ballasted capsule above the Kármán line (at 100km this is the internationally recognised as the boundary of space) on a test flight – the same booster has since been re-used and recovered for a second time.

Space X’s achievement was maybe more significant in that they were able to recover the first stage of a Falcon 9 booster to a controlled landing near the Cape Canaveral launch pad as part of an operational flight delivering payload to orbit. While a subsequent attempt to recover a Falcon 9 to a barge following a launch from Vandenberg AFB in California failed, there is good reason to hope recovery may soon become commonplace.

Reusability offers the promise of reduced launch costs meaning a reduction in the price of placing a pound of payload into orbit. The economics are by no means simple – the non-recurring development costs for the launch system must be amortised over a number of successful flights to make such systems economical – but the promise of reduced payload to orbit prices seems certain to drive commercial launch providers in the direction of at least partial reusability.

While we currently recognise the achievements of Elon Musk and Jeff Bezos, they are by no means the first to look towards providing a reusable rocket for commercial launch services. In the early years of the Reagan Presidency, new legislation sought to open space up to private enterprise. A number of companies sprang up to explore the possibility of providing private launch systems with the aim of competing with NASA’s Shuttle for this predicted commercial payload boom. One such company was Truax Engineering headed by a true unsung visionary of American rocketry – Bob Truax.

Early Years
Robert C. Truax, born in 1917, became interested in rocketry at an early age, fascinated by the work of early liquid-fuelled rocket pioneer Robert Goddard. By the mid 1930s while attending Naval Academy, he was already working on early rocket experiments and designing combustion chambers. While serving in the US Navy Truax worked in the Bureau of Aeronautics on rocket propulsion projects including some of the early work on hypergolic fuels and Jet Assisted Take-Off (JATO) systems for Navy flying boats and carrier-based aircraft. Following his wartime service Truax worked on the Navy’s Viking rocket and became a keen proponent of guided missile systems as a major weapon for submarines, but receiving little encouragement from his superiors he decided to look elsewhere offering his services to the United States Air Force who were building up a ballistic missile team in the mid 1950s.

A portrait of Bob Truax during his Navy years [IMG: USN]
Truax was re-assigned to the Air Force Western Development Division in California under General Bernard Schriever and was quickly put to work on the development of the Thor Intermediate Ballistic Missile (IRBM). As missile technology developed rapidly during the 1950s, thoughts turned to using this new technology to place artificial satellites in Earth orbit. The Air Force had a keen interest in such ventures and the promise they held for military reconnaissance. General Schriever gained control of the nascent spy satellite programme and soon Truax was appointed Deputy Director of what would soon become the Discoverer programme (the publicly acknowledged name for the Corona series of first generation photographic spy satellites). Truax’s original two-year transfer to the Air Force was extended, but eventually he returned to the Navy completing his active service back at the Bureau of Aeronautics where he helped shape Navy ideas on their prospective role in space.

Into Industry
Following the end of his military service, Truax moved into industry taking a position at Aerojet General where he began work on an idea that would come to characterise his subsequent career – the sea launched rocket.

During his latter years in the Air Force and Navy, Truax had come to the conclusion that the cost of a rocket was not directly related to its size beyond a certain point. He felt it would be possible to make very large launch vehicles for the same cost as a medium sized booster if certain assumptions were made. His mantra became “Make it big, make it simple, make it reusable” a concept that soon became christened the Big Dumb Booster.

Truax reasoned that by making a large rocket from heavier grade materials, construction could be made cheaper by using existing manufacturing infrastructure such as shipyards. Whereas contemporary space boosters had expensive launch facilities, he proposed launching the rocket from a semi-submerged position offshore. For propulsion he chose to eschew the technically complications of turbo-pumps, instead opting for a technically simpler pressure feed system to drive propellants to the combustion chambers. His rockets would be less efficient than their land launched cousins, but could be far bigger offering payload capacity that no other launcher then under design could come close to.

During the early 1960s Traux began to experiment with his sea launch principle with two proof of concept projects, Sea Bee (using and Aerobee rocket) and Sea Horse using a Corporal rocket. During these tests he gradually lowered the rockets closer to the water of San Francisco bay across a series of test firings. Eventually he was able to demonstrate that it was indeed possible to fire rocket motors while submerged. His next step was to design a system that could take full advantage of his sea launch concept, and not one for half measures Truax conceived a design that was staggering in it’s audacity – Sea Dragon.

A Monster rises – the Sea Dragon
It’s difficult to convey the true size of Bob Truax’s vision for Sea Dragon. No rocket then or now comes close to its gargantuan dimensions. To put it into some sort of perspective, Sea Dragon was 150m long and 23m in diameter. Consider that the Saturn V as built was only 111m tall and 10m in diameter and it’s easy to see that Sea Dragon would simply have dwarfed the von Braun’s moon rocket. While the Saturn V was designed to lift a payload of around 130 tons, Sea Dragon was intended to launch an incredible 550 tons to orbit.

A size comparison of Truax’s 1963 Sea Dragon design and the Saturn V (note the Apollo Command Module and escape Tower at the tip of the Sea Dragon) [IMG: via Wikipedia Creative Commons licence – modified]
Sea Dragon was to be constructed in shipyard dry dock using techniques more closely associated with the manufacture of submarines than aerospace projects. The majority of the structure would be constructed from heavy gauge 2014 T6 aluminium with the first stage RP-1 tanks being created from 18% Ni maraging steel (due to perceived difficulties in welding 8inch thick aluminium!). The rocket would feature two stages each with a single massive engine bell. Propellants for the first stage would be RP-1 kerosene and liquid oxygen which would be pressure fed to the combustion chamber (The RP-1 would be pressurised using methane, the LOX via the use of a heat exchanger on the first stage engine). Second stage propellants would be liquid oxygen and liquid hydrogen. Truax proposed that while some propellants could be pre-loaded onto the rocket before it set off for the launch site, an electrolysis station could be set up to create the liquid oxygen and liquid hydrogen in situ prior to launch.

Following construction, Sea Dragon would lie horizontally in the water for transport to its launch site. A system of ballast tanks would be attached to the bottom of the first stage and once the launch site had been reached these could be flooded to right the rocket in the water. At the point of ignition, the ballast tanks would be detached and Sea Dragon would launch. The first stage was predicted to burn for between 80-90 seconds at which point it would be jettisoned and fall back to the sea using an inflatable drag skirt system to lower velocity for recovery. The second stage would then continue on lofting the massive payload to orbit.

Aerojet General produced detailed studies including proposed costings for Sea Dragon in 1963 and the concept caught the attention of NASA’s Future Projects Branch as a possible means to mount an expedition to Mars. Unconvinced by the details of the proposal, NASA commissioned TRW to conduct a review of Sea Dragon. Apparently to the surprise of NASA, TRW concluded that Aerojet General’s figures were broadly correct and the concept appeared feasible, but before things went much further a contraction in NASA budgets led to the closure of the Future Projects Branch and an end to official interest in Sea Dragon.

In a way the scaling back of NASA’s budgets points to the real achilles heel of the whole Sea Dragon concept. While apparently offering extremely cheap costs to orbit (estimated at around $10-20 per pound at the time), Aerojet General were assuming the development costs of Sea Dragon could be effectively amortised over 240 flights with a proposed minimum of 12 flights per year. In reality, there wasn’t even enough demand for heavy lift boosters to keep the Saturn production line running beyond what was needed to directly support Apollo. There was simply no job big enough at the time or even now to require a reusable booster the size of Sea Dragon.

New beginnings
With Sea Dragon effectively dead in the water, Bob Truax moved on from Aerojet in 1966. He initially worked with TRW as a technical consultant on the Minuteman missile, but also set up his own company, Truax Engineering. Still convinced by the sea launch concept, Truax looked to continue studies into a smaller version of Sea Dragon, but not before one of the more interesting detours in his colourful career. In the early 1970s Truax became involved in a project to build a rocket powered vehicle for the renowned motorcycle daredevil Evel Knievel. Following an earlier model called the X-1, Truax Engineering constructed an improved ‘Skycycle’, the X-2, in which Knievel hoped to jump the Snake River Canyon in Idaho. The attempt took place on September 8th 1974 but rapidly ran into trouble as the parachute system deployed during launch. Although the Skycycle initially cleared the canyon, winds blew it back towards the launch site leading to a crash that could have cost Knievel his life.

The X-2 Skycycle created by Truax for Evel Knievel’s Snake River jump [IMG: via Wikipedia Creative Commons Licence]
The failure at Snake Canyon didn’t seem to dull the global obsession with Knievel’s stunts and at one point Truax was apparently flown to Japan to assess whether an improved Skycycle could clear Mt. Fuji. Fortunately, no such attempt was made, but Knievel remained interested in Truax’s rocket projects and put forward the initial funding for a new venture aimed at making Knievel the first private astronaut – the X-3 Volksrocket.

Built using surplus rocket parts obtained from scrapyards (including 4 Atlas vernier thrusters obtained for $25 a piece!) the X-3 was constructed by Truax in his backyard. When Knievel had to withdraw from the project, Truax hit upon the idea of advertising for a private astronaut – the only requirements being reasonable health, relatively small stature and $100,000 to contribute to development costs. A number of applicants came forward but were generally unable to provide the required finances.

The X-3 Enterprise reusable piloted sub-orbital rocket [IMG: Truax Engineering]
Truax understood that, were he able to launch a private astronaut on a suborbital flight above 100km and recover the rocket (and passenger) as planned, he may have a lucrative way to provide funds for his dream of a large sea launched rocket. At one stage he even discussed selling the live TV rights to the X-3 launch, but after various engine runs and other tests in the early 1980s, the Volksrocket (re-christened Enterprise) never got off the ground. Undeterred, Truax felt the X-3 could still provide a useful first step towards his new project, Excalibur.

Truax’s 1980’s Excalibur design (centre) compared to his revised Sea Dragon and NASA’s Shuttle [IMG: Truax Engineering]
Excalibur was essentially a small scale version of Sea Dragon with a proposed payload of 100,000 lbs. Truax proposed Excalibur as a land or sea launched reusable two stage booster. In effect it was Phase II (with Enterprise forming Phase I) of his hopes to create a commercially funded Sea Dragon to his original designs but with improved materials and electronics. Truax continued his work throughout the 1980s even conducting helicopter drop tests of his X-3 in Monterey Bay, California to prove his recovery model. Finally, as that decade neared its end it seemed his hard work may reap some long awaited rewards.

Truax had approached the Secretary of the Navy with his Excalibur concept and the initial response was favourable. Excalibur was passed to the Naval Centre for Space Technology for further analysis and this eventually led to Truax Engineering being awarded a contract for a new Sea Launch and Recovery system (SEALAR) in 1988.

SEALAR was to be a much smaller vehicle than even Excalibur, able to place around 10,000 lbs to orbit, but Bob Truax once again had official investment for his sea launched rockets. As research continued into the early 1990s a tentative first flight date of 1996 was set, but sadly as with so many of his other ventures SEALAR would never take flight.

Truax continued to work throughout the 90’s on various attempts to resurrect his sea-launch idea in the form of a smaller Excalibur S and a new design carrying the Sea Horse name he had used way back in the early 1960s, but none of these ventures ever led to flight hardware.

Bob Truax passed away on September 17th 2010 at the age of 93 after a life in rocketry. His big rockets may never have flown but his influence remains strong amongst Big Dumb Booster enthusiasts who periodically propose concepts using elements of his ideas. Many of Truax’s concepts seem way ahead of their time, but the sheer scale of his ambitions for Sea Dragon feel slightly anachronistic to a Cold War era when huge space infrastructure projects were briefly, but seriously considered.

It seems difficult to imagine that Sea Dragon could ever fly today given the undoubted environmental impacts of such a venture – in that respect it almost belongs alongside Freeman Dyson’s Project Orion, the only other proposed launch system of the era that could compete for sheer scale and lifting power. But many Sea Dragon supporters would argue that we NASA are currently creating their own Big Dumb Booster and Truax’s concepts would be no less practical, and possibly cheaper. Whatever the rights and wrongs of those arguments, Truax’s firm belief in the importance of reusability in opening up access to space still echoes strongly with today’s new breed of commercial launch pioneers.

Who knows, maybe Elon Musk’s colossal and much discussed Mars Colonial Transporter may evoke the spirit of Sea Dragon again.

Sea Dragon Concept Vol.1 – Aerojet General (January 1963)

Sea Dragon Concept Vol.3 – Aerojet General (February 1963)

Rockets from the Sea – Ad Astra (July/August 1990)

From Canyon to Cosmos – Air & Space (October/November 1990)

Truax Engineering promotional materials – various

VIDEO TMRO interview with Emory Stagmer (August 2014)

Many of these documents and other materials about Bob Truax’s work can be found at the Truax Engineering Multimedia Archive

Acknowledgement: Thanks to R7 on forum for providing advice and suggesting corrections to the original text