The unfinished X-3 Project of Robert Truax

Robert C. Truax was the former director of the Advanced Development Division of Aerojet General Corporation. Before and during World War II, he worked with the U.S. Navy rocket programme. After retiring from Aerojet General, he began in the early 1970's to study the possibilities of a small manned sub-orbital re-useable booster constructed of surplus rocket components. In 1977 was founded the "Project Private Enterprise".
Finally, his initial version X-3 Volksrocket stands 24 ft tall and is 25 in in diameter. Empty weight is 1.100 lb; fuelled it weighs 3,100 lb. The propellants (liquid oxygen and kerosene) are pressure fed to four Atlas vernier engines (Rocketdyne LR 101's) giving a total thrust of 4,000 lb (17.79 kN). A propellant utilization system insures simultaneous depletion of both propellants. Guidance is provided by HIG-4 floated gyros.
The vehicle is designed to reach an altitude in excess of 50 miles qualifying the passenger as an astronaut. Burnout will occur at 100,000 ft (30.48 km). Maximum acceleration will be 3 g's. The momentum will carry the rocket, now slowly tumbling, to peak at an altitude in excess of 50 miles (80.5 km).
When Truax began development, the major problem was with the engines. The Atlas vernier engine's fuel system was designed to feed a single engine. Truax had to design a new manifold and gimbal system for four engines. Up to late 1978, six static tests of the system have been made.  Also tested were the steering servos which gimbal the engine. Engine operation, at reduced pressure, was checked. This allowed the removal of one of the two pressurised helium spheres in the original design.
Truax worked on his Volksrocket until 2004. Then he lost a competition to be the first non-government agent to send civilians to space. In the end, Robert Truax did not manage to qualify his X-3 in such a way that a suborbital flight test could take place.

Note: The "Skycycle" X-1 and X-2 were vehicles for the stuntman "Evel" Knievel, for whom Truax had developed a steam propulsion system. The X-2 had two small nozzles. The X-2 had a larger single nozzle for higher thrust. Both attempts to overfly the Snake River Canyon have failed.



Parameter of propulsion

Engines Thrust (s.l.)
Isp (s.L.)
Thrust (vac)
Isp (vac.)
Flow rate
Burn time


4.45 1952 5.56 2442 2.28 - -

RL-101 (4)

17.79 1952 22.24 2442 9.12 907.2 100

Before static testfire from a Naval barge


Latest design