The Bumper Project
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 the 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.
In October of that year, the BUMPER Program was inaugurated. This was a cooperative 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 previously reached.
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 discarded 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 guiderails 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-of 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 WAC. 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 of 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. In the first 28 seconds, the propulsion system was performing normally, but at 33 seconds the turbine started to overspeed. It reached a peak speed of 4,800rpm a few tenths of a second later, then decreased in the manner typical of an overspeed trip. This action was attributed to the premature dosing 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 this 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 dose 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 shortly after. 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, allowing 45 seconds burning time. This flight was successful in every phase. Thirty seconds after take-off, the V-2 had 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 cosmic radiation at altitudes greater than could be reached by other missiles. Performance was normal for 47.5 seconds before the cut-off relay was tripped by a malfunction in the control system. It was determined that excessive vibration 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 trailer 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 so that the rigid tail support was replaced by a partially inflated truck tire which provided a non-rigid support of the tail. The Army vehicle was driven with extreme care and the missile arrived in excellent condition.
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. It was successfully fired on 29 July 1950. BUMPER 8 had been fired five days earlier 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 tum successfully and the general performance appeared good. However, closer examination of the trajectory data showed 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 showed a “sneak-circuit” which caused the erecting motors of the pitch gyro to become energized after take-off. This in turn caused a precession 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.
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 related to rocket 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.
Participation by the General Electric Company in the V-2 project terminated by agreement on 30 June 1951. All V-2 material was transferred to the Army Ordnance Corps, which assumed responsibility for completing the V-2 Program. Nine static firings tested the propulsion units while five upper-air research vehicles had been fired by the latter part of September 1952. These flights were termed “training flights”. TF-3 was the first V-2 to be completely assembled, serviced, checked out and fired by military personnel. One TF missile attained an altitude of 132 miles, the highest to be recorded by any V-2 fired during the program.
Much had been learned about the upper atmosphere through the V-2 firings. But the V-2 was a massive structure that severely limited the maximum altitude attainable. Consequently, it was considered unwise to contract for American manufacture of additional rockets of the same design. Utilizing the experience and knowledge gained during the V-2 program, new rockets were designed specifically for upper atmosphere research.