WAC-Corporal rocket

WAC = Without Attitude Control

Historical background of sounding rockets:

• The possibility of employing rocket propulsion for lifting a vehicle to great heights was realized at the beginning of the century. Robert H. Goddard first gave serious consideration to this possibility in about 1914. At first he studied the feasibility of using a constant-volume process, short-duration smokeless powder rocket propelled by successive impulses was made by Tsien and F. Maline in 1939.
  Black powder rockets were capable of reaching several thousand feet before the 20th century, and balloons in the 1930s could reach altitudes of about 100,000 feet. A successful sounding rocket, therefore, had to surpass the altitudes achieved by balloons. Furthermore, to be useful, it had to be designed to minimize costs of production and of servicing and maintenance. In the 1920s, Goddard had decided that a liquid-propellant rocket engine offered better possibilities for constructing such a sounding rocket, and he obtained limited financial support for developing one from the Smithsonian Institution. In 1936,Goddard published a very general report on the progress of his work at Roswell.
  In 1936 our group at Caltech concluded that Goddard had not succeeded in constructing a successful sounding rocket because he had underestimated the difficulties involved, the day of the isolated inventor of complex devices was over. Even so, success for anyone in the 1920s and 1930s was not likely because of the state of rocket technology, there were no high thrust, short-duration booster rocket engines, and no suitable guidance systems. Goddard's LOX-gasoline rocket engines, did not provide a high enough specific impulse for the task.
• Similar difficulties confronted experimenters in Germany and in the Soviet Union, where a group headed by M.K. Tikhonravov first launched a liquid-propellant "Rocket 09" in vertical flight on 17 August 1933. In Germany, the V-2 (A-4) ballistic missile was launched in the early 1940s in vertical flight.
• But the situation in 1944 differed radically from the one that faced Goddard ten years earlier. Solid-propellant rocket engines for boosters could be taken from wartime armament rockets and used to circumvent the necessity of a guidance system within a sounding rocket. Both solid and storable-liquid propellant rocket engines with a thrust of sufficient magnitude and duration, and with adequate specific impulse, had been developed at JPL.
• The Army Ordnance Department requested that JPL study a sounding rocket. It was quickly completed and submitted on 16 January 1945 under the title "Consideration of the Feasibility of Developing a 100,000 ft. Altitude Rocket (The WAC Corp0ral). The WAC was to be capable of carrying an instrument payload of 25 1b., that would be lowered to the ground by parachute.

History Wac-Corporal:

WAC-Corporal (without Booster) nr.5 with ORDCIT Director Frank Malina, October 11, 1945. (NASA Photograph)

WAC-Corporal being hoisted into firing position in the launch tower

P.Meeks, F. Malina and B. Terbeeck weighing WAC Round #5

• By late 1944, it was clear from progress in the Private and Corporal missile programs that ORDCIT was well situated to build a sounding rocket. Frank Malina, ORDCIT′s director, and other Caltech workers had originally entered the missile business with a sounding rocket in mind, so the sounding rocket, justified as a developmental version of the Corporal missile, was proposed to the Army. The Army approved of this „little sister„ to the Corporal, and funded the Wac Corporal (WAC either stood for Women's Army Corps. reflecting the little sister metaphor, or Without Attitude Control, reflecting the simplicity of the rocket). The vehicle was assembled by the Douglas Aircraft Co., Santa Monica, California, from components supplied by JPL's ORDCIT Project. The WAC-Corporal was an unguided rocket used for high-altitude research and to provide information and engineering experience to be used in future surface-to-surface missile programs. The WAC sounding rocket was boosted from the launcher by means of a modified ballistic solid propellant rocket engine from an armament projectile called the Tiny Tim. The rocket used a liquid propellant (the first to use hypergolic fuels) and developed a thrust of 1,500 pounds for 50 seconds.
• The Wac Corporal was to carry 25 pounds (11 kg) of meteorological and cosmic ray instruments to an altitude of 100,000 feet (30 km). An Aerojet liquid propellant engine, originally designed for the jet assisted take-off of aircraft, was selected, as its low thrust would be easy on scientific instruments. The engine used the IPL innovation of hypergolic propellants-compounds that ignited on contact. The elimination of an ignition system simplified the design. To further simplify the design, three fins stabilized the Wac, eliminating the need for the full Corporal missile guidance system. This required a high speed launch, so a solid booster and long launch tower were used.
• In addition to holding 25 pounds of meteorological instruments, the nose section contained a parachute and automatic equipment to release the parachute and the entire nose cone.
• The launcher at White Sands Proving Ground consisted of a 77 ft. triangular structural steel tower, 6 feet on a side, resting on a platform 25 ft. high with a 26 ft. base giving an overall height of 102 ft. The tower contained three launching rails set 120 degrees apart to guide the WAC and its booster. The effective length of the rails was 82 ft. A control house was constructed by the Ordnance Department 465 ft from the launcher.
• To check the flight characteristics, tests were made with 1/5 scale model, called the Baby WAC. It was launched from a scaled-down launching tower at Camp Irwin, California, beginning 4 July 1945. One of the interesting aspects of these tests was the verification of the suitability of employing three instead of the traditional four tail fins. Stewart, to save weight, proposed to use three fns. The tests of the Baby WAC settled the arguments; the model behaved very well, reaching an altitude of around 3,000 ft. This also persuaded one Army ballistics expert that three fins were enough to stabilize a rocket.
• Full scale tests began on Sept. 26, 1945, with the launch of 3 four Tiny Tim solid boosters. The Tiny Tim was a Navy air-to-surface missile, built around a standard oil drill casing. Four solid propellant grains, cruciform in cross section and designed to bum from the outside in, ran the length of the motor. Two dozen nozzles surrounded a pressure relief diaphragm on the aft face of the missile. The fins and nose of the Tiny Tim were replaced for the Wac Corporal flights.
• The next day Sept. 27, a Tiny Tim boosted Wac Corporal Round-1, a dummy vehicle made of concrete-filled steel pipe.
  Another dummy flight was followed by two „quarter-charge„ partially fueled missiles, reaching altitudes of about 5 miles (8 km). Finally, on Oct. ll, 1945, the 37-member team from GALCIT launched the first fully fueled Wac Corporal, ROUND-5.
• Ignition of the Tiny Tim booster started the Wac up its 100 foot (30 m) launch tower. The sudden acceleration of the Wac opened an inertia valve, allowing compressed air into its propellant tanks. This action in turn sent an aniline/furfuryl alcohol mixture and red fuming nitric acid into the Wac Corporal's combustion chamber. These propellants ignited on contact. After 0.6 seconds, the booster burned out and fell from the sustainer, leaving the liquid fueled stage to continue its 47-second burn. At an altitude of 15 miles (24 km), the Wac exhausted its fuel, and the ground crew lost sight of the vehicle. Radar tracked the vehicle to an altitude of 43 1/2 miles (70 km).
  When the rocket arced over to horizontal at the peak of its flight, a gyroscope was to trigger the recovery system. Pins holding the nose to the missile would be blown, and residual air pressure in the nose section was to push the nose and body apart, releasing a parachute. A cord connected the rocket body and nose cone for ease of recovery. The nose of Round 5 was filled with radar "window" (radar reflective material to aid tracking) to be ejected at nose blowoff. But, the nose failed to eject, and the first full-charge Wac Corporal crashed into the ground 7 1/2 minutes after launch, less than a mile (1.6 km) from the launcher.
• This was the first rocket or missile to be launched at White Sands.
• The GALCIT team launched five more Wacs in late 1945. The Wac Corporal proved to be a reliable rocket, although the nose cones were plagued by a series of failures. The parachute failed on Round 6, but the rocket was unstable after the nose blew off.
  The missile tumbled down slowed by high broadside drag. Wac Corporal No. 6 was found relatively intact on the desert floor, inspiring the tumble recovery of later V-2′s. Round 7′s parachute failed as well. Round 8′s nose ejected as it left the tower, but the rocket continued on an otherwise successful flight. Before the launch of Round 9, a leak in one valve had led to partial opening of the propellant valve. This led to premature combustion in the engine. The launch crew hastily fired the booster for an emergency launching. This action fully ignited the Wac Corporal sustainer which then continued on a normal ascent, followed by a failure of the nose to eject. Round 10 flew at night Its flight was marred only when its nose did not eject. By October 25, the initial development flights were complete.
• Five more Wac Corporals were built, two of which flew in May of 1946 to the Wac&primes highest and lowest altitudes. One was launched on May 10, a few hours after the demonstration launch of a captured V-2. This Wac was not as successful as the previous rounds, reaching only 10 miles (l6 km). Another, launched May 22, reached an altitude of 50 miles (80 km), and could thus be regarded as the first American rocket to enter space.
• After the supply of Wac Corporals was depleted, the Caltech team retumed to their drawing boards to develop an improved rocket, the Wac B. Through changes in materials and design, the engine was lightened from 50 to 12 pounds, the structure of the missile was modified, and a new 5~channel telemetry system was added. About a half dozen Wac B vehicles were flown in December 1946, February and March of 1947. One Wac B, launched from White Sands on Feb. l7, 1947 reached an altitude of 45 miles (72 km).
• By March 31, 1947, the Wac Corporal development testing was complete. The Wac Corporal program had seen 17 launches. In addition to various tracking aids, the payload of the Wac had been outfitted to study temperatures, pressures, and sky brightness at altitudes previously beyond the range of human measurement. Later that year, Aerojet engineering, a commercial spinoff of the Caltech team, replaced the Wac Corporal with the Aerobee.
• An inability to reach altitudes greater than 70 km limited the WAC-Corporal's usefulness, relegating the vehicle to the testing of recovery parachutes. The parachutes were designed to lower the entire rocket back to the ground with as little damage as possible.
• Key members of the WAC team were (under direction of F. Maline):
  M.M. Mills (Booster), P.J. Meeks (Sounding rocket), W.A. Sandberg and W.B. Bary (Launcher and WAC nose), S.J. Goldbert (WAC Field Tests), H.J. Stewart (External Ballistics), and G. Emerson (Photography).

Wac Corporal Specifications:

Credit: Peter Alway

Wac Sustainer   Overall lenght: 194 in Max diameter of body: 12.2 in Fins: 3 tail fins of 34 in. half span Loaded weight: 665 lb Empty weight: 296.7 lb (135 kg) Red Fuming nitric acid: 286 lb Aniline-furfuryl alcohol mixture: 114 lb Air at 1900 psi: 191 lb Motor thrust: 1,500 lb (6,700 N) Duration: 45 sec Impulse: 67,000 lb-sec (300,000 N-sec) Impulse-weight ratio: 102 sec Tiny Tim Booster   Overall length: 96 in Max diameter of body: 11.75 in Fins: 3 tail fins of 26 in. half span Loaded weight: 759.2 lb (345 kg) Propellant weight: 148.7 lb (67.6 kg) Motor thrust: 50,000 lb (220,000 N) Duration: 0.6 sec Impulse: 30,000 lb-sec (130,000 N-sec) NAR designation: Q 220,000-0

Launch list:

Note:

- The BABY-WAC-Corporal were fired at the Goldstone Range, Camp Irwin, California

- The full-scale WAC's were launched at White Sands Missile Range (LC-33)

- The Tiny-Tim, launched on 26 Sep 1945, was the first missile firing at White Sands.

- ROUND-A to D were four booster tests launched from Complex 33