Launch Vehicle: V-2 rocket and WAC Corporal
Launch Site: White Sands Missile Range, N.M., and Cape Canaveral, Fla.
NASA Center: Jet Propulsion Laboratory
Spacecraft Instruments: 1) Cosmic Radiation Detector
White Sands Missile Range, Bumper Project Fact Sheet
Prior to July 1946, Major General H. N. Toftoy, then Colonel, Chief of the Research and Development Division, Office of the Chief of Ordnance, suggested the possibility of combining the V-2 rocket and WAC Corporal. This would provide a two-stage rocket capable of reaching heretofore unattainable altitudes and would greatly increase the possibilities of upper atmosphere research.
On 20 June 1947, the Bumper Program was inaugurated. This was a co-operative program established among the agencies responsible for the various phases of the basic programs. The purpose of this program was to investigate launching techniques for a two-stage missile and separation of the two stages at high velocity, to conduct limited investigation of high-speed high-altitude phenomena, and to attain velocities and altitudes higher than ever reached.
Over-all responsibility for these missiles was given to the General Electric Company and were included in the Hermes Project. The Jet Propulsion Laboratory of the California Institute of Technology was assigned responsibility for the theoretical investigations required, the design of the second stage and the basic design of the separation system. The Douglas Aircraft Company was assigned responsibility for the fabrication of the second stage, and the detail design and fabrication of the required special V-2 parts.
Thorough study was made of the problems and difficulties to be encountered and several methods of combining the rockets were investigated. In the design finally decided upon, the powder rocket booster, normally used to launch the WAC Corporal, was dispensed with in order to limit the size of the combination missile and to allow the smaller rocket to fit as deeply as possible into the V-2, and yet retain enough space in the instrument compartment of the V-2 for housing the indispensable components of the guidance equipment. Also fitted within the instrument section were the guide-rails and expulsion cylinders used as a launcher for the WAC Corporal. These cylinders were activated by means of a compressed-air-bottle through a pressure reducer and a solenoid valve. This valve was activated by the final cut-off signal of the V-2, causing the fins of the WAC Corporal to slide out of the three slots in the upper part of this warhead launcher.
Eight of these missiles were assembled during the Bumper Program and the first six were launched at White Sands Proving Ground. The first Bumper-WAC was fired on 13 May 1948. This was the first large, two-stage rocket to be launched in the Western Hemisphere. This first combination rocket had a short duration, solid propellant motor propelling the second stage and the WAC attained only slightly more speed and altitude than the V-2. The firing was considered successful in all details. The second Bumper was fired on 19 August 1948 and, like Bumper 1, contained only a partial charge. The velocity of the V-2 was about ten percent below normal, but the steering was good. Up to 28 seconds the propulsion system was performing normally, but at 33 seconds the turbine started to overspeed. It reached a peak speed of 4,800 rpm a few tenths of a second later, then decreased in the manner typical of an overspeed trip.
This action was attributed to the premature closure of the alcohol preliminary valve in the V-2, due to a failure in the controlling circuit.
On 30 September 1948, the third missile was launched. The second stage used a liquid propellant with 32 seconds burning time. Operation of the V-2 was successful in all aspects; however, the second stage motor exploded just prior to separation. The fourth Bumper, like the third, used a liquid propellant with 32 seconds burning time for the second stage. The flight appeared normal in every respect and missile velocity was close to average. A break in the alcohol piping resulted in an explosion in the tail section at 28.5 seconds. This caused the jet to broaden, the telemetry record to fail, the beacon signal to disappear and the servo signals to increase to near maximum. The spurious signals drove the jet vanes hard over, causing the missile to execute a fast turning motion. Impact followed. The only other known tail explosions occurred in another series of modified V-2 missiles, which, like Bumper, involved major structural changes.
Bumper 5, fired on 24 February 1949, was the first Bumper to be fired with a fully tanked second stage, which allowed 45 seconds burning time. This flight was successful in every phase. Thirty seconds after take-off the V-2 attained a speed of 3,600 miles per hour and the V-2 and the WAC Corporal separated. The WAC, with its power added to that of the V-2, attained a speed of 5,150 miles per hour and an altitude of approximately 250 miles. This was the greatest velocity and the highest altitude ever reached by a man-made object. The nose cone was instrumented to measure temperatures at extreme altitudes. In addition, the WAC carried telemetry which transmitted to ground stations technical data pertaining to conditions encountered during flight. This was the first time radio equipment had ever operated at such extreme altitudes. Although the missile had been tracked by radar for most of its flight, more than a year passed before the smashed body section was located.
The sixth V-2 WAC combination missile to be fired at White Sands Proving Ground was launched on 21 April 1949. This missile also had a fully tanked second stage, and it was hoped that the performance of Bumper 5 could be surpassed. The nose cone was instrumented to record data on cosmic radiation at altitudes greater than could be reached by other missiles. Performance was normal for 47.5 seconds when the cut-off relay was operated by some malfunction in the control system. It was considered that excessive vibrations, due to structural changes made to accommodate the WAC Corporal, could have caused this failure as well as the failure of missiles 2 and 4.
Bumper missiles 7 and 8 were shipped from White Sands Proving Ground to Florida by standard Army tractor and flatbed for firing at the Joint Long-Range Proving Ground. Since the V-2 missiles previously shipped to Norfolk, Virginia, had been damaged in transit, modifications were made in the shipping cradle in that the rigid tail support was replaced by a partially inflated truck tire, which provided a non-rigid support for the tail. The Army vehicle was driven with extreme care and the missiles arrived in excellent condition.
In general, the conventional V-2 ground equipment was used. The one major change was in the type of working platform used to service the upper levels of the missiles. The platforms were made up of standard commercial iron pipe scaffolding of the type commonly used by painters. These assemblies were mounted on casters. The scaffolds, extending to about 55 feet above the concrete pad had sufficient strength and rigidity for the purpose.
The first attempt to launch Bumper 7 was unsuccessful due to moisture collected within the missile. It was necessary to return it to the hanger where it was dried and rechecked.
Two steps were taken to reduce the probability of further condensation troubles: (1) silicone grease was applied at vulnerable points and (2) the loading sequence was reversed to load liquid oxygen after loading hydrogen peroxide. These measures proved adequate in two subsequent launchings.
Bumper 7 was successfully fired on 29 July 1950. Bumper 8 had been fired on 24 July 1950. The experiments to be carried out on these missiles called for a relatively low trajectory, with a separation angle of approximately 20 degrees from horizontal. The General Electric Report on these firings stated:
"This trajectory required a relatively rapid turn during the powered flight of the V-2. Both missiles made the turn successfully and the general performance appeared good. A closer examination of the trajectory data showed, however, that the program had been greater than desired. Trajectory data showed the separation angle for Bumper 7 to be approximately 10 degrees and that for Bumper 8 to be about 13 degrees. The fact that the two trajectories showed the same type of discrepancy indicated a systematic rather than a random fault. Since it seemed highly improbable that the pitch device itself would fail in such a fashion as to increase the program, precession of the pitch gyro circuits had been modified to obtain a much larger than normal program, these circuits were among the first investigated. This investigation turned up a "sneak-circuit" which caused the erecting motors of the pitch gyro to be energized after take-off. This in turn caused a procession which operated to increase the program angle. This fault appeared to answer fully the observed discrepancy."
Notwithstanding the error in trajectory, Bumper 7 attained a speed of Mach 9, the highest sustained speed that had ever been reached in the Earth's atmosphere. Results of these launchings were discussed in the Patrick Air Force Base, Long-Range Proving Ground Division, Technical Report No. 1, "Bumper Missiles 7 and 8," 29 September 1950.
Through Bumper firings, it was learned that the speed of a rocket or missile could be increased with each successive stage. Step-rockets, fired when the assisting rocket was at maximum velocity, gave the final rocket a speed equal to all stages. Innumerable problems connected with rockets' motor ignition at high altitude and attachment and separation of successive stages were solved satisfactorily, providing a basis for later missile designs requiring similar experiments. The program was officially concluded in July 1950.