Robert Truax was one of the great originals of American rocketry and a major proponent and inventor of ultra-low-cost rocket engine and vehicle concepts. He became involved in rocket programs as a Naval officer during World War II. This work continued in the post-war Navy, culminating in a loan to General Schriever of the US Air Force from 1955 to 1958. During this period he was very active in studies (along with STL and other study agencies) of advanced ballistic missile and space-based weapons systems. This was in addition to his normal duties of running the Thor IRBM program. He refined some of his low cost launch concepts, but was not able to develop financial support within the Air Force. In 1959 he retired as a Captain, and came to Aerojet where he headed the Advanced Development Division until leaving in 1967. Here his low-cost booster program plan was elaborated and further studied, but he was again unable to interest NASA or the USAF in the concept of cheap access to space.
|Launch Vehicle: Sea Bee. |
Seabee was a brief proof of principle program to validate the sea-launch concept for Sea Dragon. A surplus Aerobee rocket was modified so that it could be fired underwater. The rocket worked properly the first time in restrained mode. Later tests were made with various approaches to readying the unit for repeat firings. This proved to be so simple that the cost of turn-around was found to be about 7% of the cost of a new unit.
|Launch Vehicle: Sea Horse. |
The second phase of Sea Launch was to demonstrate the concept on a larger scale, with a rocket with a complex set of guidance and control systems. Sea Horse used one of 39 surplus Corporal missiles that Truax obtained from the Army. Tests of the 9,000 kgf pressure fed, acid/aniline rocket were made from a barge in San Francisco Bay at Tiburon. The engine was first fired several metres above the water, then lowered and fired in successive steps until reaching a considerable depth. Firing from underwater posed no problems, and there was substantial noise attenuation. In actual operation, it was planned to tow the missile to its launch site, flood attached compartments so that the missile rode vertically in the water, and then fire it. In order to support such a program, tentative agreements were made with the Navy for Aerojet to take over an unused facility at Tiburon. All of this was done on a modest amount of IR&D funding.
Years later Truax Engineering proposed a different Sea Horse - an 'entry level' two-stage orbital launch vehicle that used the Sea Dragon principles - pressure-fed engines, stage recovery, amphibious launch.
|Launch Vehicle: Sea Dragon. |
Sea Dragon was a two-stage design of 1962 capable of putting 1.2 million pounds (550 tonnes) into low Earth orbit. The concept was to achieve minimum launch costs through lower development and production costs. This meant accepting a larger booster with a lower performance propulsion system and higher stage dead weight then traditional NASA and USAF designs. The first stage had a single pressure fed, thrust chamber of 36 million kgf thrust, burning LOX/Kerosene. The second stage was ‘considerably smaller’ (thrust only 6.35 million kgf!) and burned LOX/LH2. The complete vehicle was 23 m in diameter and 150 m long. The all-up weight was 18,000 tonnes. The launch vehicle would be fuelled with RP-1 kerosene in port, then towed horizontally to a launch point in the open ocean. It would then be filled with cryogenic liquid oxygen and hydrogen from tankers or produced by electrolysis of sea water by a nuclear aircraft carrier (such as the CVN Enterprise in the painting). After fuelling, the tanks at the launcher base would be flooded, and the vehicle would reach a vertical position in the open ocean. Launch would follow. The concept was proven with tests of the earlier Sea Bee and Sea Horse vehicles. Aside from the baseline two stage expendable version, a single-stage-to-orbit reusable vehicle with a plug nozzle was designed. Costs to low earth orbit were estimated to be between $60/kg and $600/kg - eg one fourth that of the Saturn V or less.
Stage one used liquid nitrogen to force the propellants into the engine. At ignition, combustion chamber pressure was 20 atmospheres, and kerosene was forced into the chamber at a pressure of 32 atmospheres and liquid oxygen at 17 atmospheres. By burnout 81 seconds later combustion chamber pressure had declined to 14 atmospheres, kerosene feed pressure to 20 atmospheres, and liquid oxygen pressure to 8.5 atmospheres. At burnout the stage had reached a velocity of 1.8 km/second at an altitude of 40 km and a range of 33 km. After separation the stage would impact the ocean 290 km downrange (one alternate was recovery and reuse of the stage). Losses due to gravity and drag were minimised by the high 2:1 thrust-to-weight ratio and low drag losses (deceleration at max q was about 0.2 G’s ) resulting from the large size of the booster.
Stage two had a burn time of 260 seconds and a low constant combustion chamber pressure of 7 atmospheres. The stage achieved a total delta V of 5.8 km/second, shutting down at orbital velocity at an altitude of 230 km and 940 km downrange from the launch point. A significant feature of the concept was the use of an expandable nozzle exit cone. This increased the area ratio of the nozzle from 7:1 to 27:1 when deployed. Initial tests showed considerable promise, but development ceased because of lack of in-house funding. This concept was later fully developed under the solid rocket Peacekeeper program.
The design was reviewed with Todd Shipyards, who concluded that it was well within their capabilities, and not too unlike making a submarine hull. 8 mm thick maraging steel was used, similar to the Aerojet 260 inch solid motor of the time. NASA Marshall gave the Aerojet designs to TRW for evaluation. TRW fully confirmed Aerojet's costs and engineering, a great surprise to both TRW and NASA. Aerojet was considering purchasing Sudden Ranch as a launch site for Sea Dragon. This property included several kilometres of coastline between Santa Barbara and Vandenberg AFB. This was the only site on the continental United States that could launch directly into a polar orbit without overflying populated areas (and was later incorporated into Vandenberg).
But this came just as Apollo was being cut back and the Viet Nam war was eating an ever greater amount of the US budget. NASA dissolved their Future Projects Branch (dropping almost all the manned Mars landing work). Prospects for Sea Dragon essentially disappeared, and Aerojet could no longer fund it on IR&D.
Many thanks to Mark C Goll for providing some of the materials on which this article was based.
|Launch Vehicle: Excalibur. |
Excalibur was a subscale version of Sea Dragon proposed by Truax Engineering in the 1990's. It featured the same attributes as Sea Dragon: low cost design (pressure fed engines), Lox/Kerosene first stage (combustion chamber pressure 24 atmospheres) and Lox/LH2 second stage (chamber pressure 5 atmospheres). Guidance would be by a combined Inertial/GPS system. An even smaller Excalibur S vehicle would prove the concept and place 500 kg in orbit.
|Launch Vehicle: SEALAR. |
SEALAR (SEA LAunched Rocket) was yet another attempt by Truax Engineering to get the amphibious-launch concept off the ground. The project received some Navy Research Laboratory funding in the early 1990's, with a planned first launch date of 1996. A production model would have been able to achieve orbit at an estimated cost of $ 10 million per launch. As with the earlier Truax projects, it did not achieve flight test status.