V-2 sounding rocket

A V-2 sounding rocket at White Sands Missile Range in 1946.

German V-2 rockets captured by the United States Army at the end of World War II were used as sounding rockets to carry scientific instruments into the earth's upper atmosphere at White Sands Missile Range (WSMR) for a program of atmospheric and solar investigation through the late 1940s. Rocket trajectory was intended to carry the rocket about 100 miles (160 km) high and 30 miles (48 km) horizontally from WSMR Launch Complex 33. Impact velocity of returning rockets was reduced by inducing structural failure of the rocket airframe upon atmospheric re-entry. More durable recordings and instruments might be recovered from the rockets after ground impact, but telemetry was developed to transmit and record instrument readings during flight.

History

The first of 300 railroad cars of V-2 rocket components began to arrive at Las Cruces, New Mexico in July 1945 for transfer to WSMR. In November General Electric (GE) employees began to identify, sort, and reassemble V-2 rocket components in WSMR Building 1538, designated as WSMR Assembly Building 1. The Army completed a blockhouse in WSMR Launch Area 1 in September 1945. WSMR Launch Complex 33 for the captured V-2s was built around this blockhouse.

Initial V-2 assembly efforts produced 25 rockets available for launch. The Army assembled an Upper Atmosphere Research Panel of representative from the Air Material Command, Naval Research Laboratory (NRL), Army Signal Corps, Ballistic Research Laboratory, Applied Physics Laboratory, University of Michigan, Harvard University, Princeton University, and General Electric Company. German rocket scientists of Operation Paperclip arrived at Fort Bliss in January 1946 to assist the V-2 rocket testing program. After a static test firing of a V-2 engine on 15 March 1946, the first V-2 rocket launch from Launch Complex 33 was on 16 April 1946. As the possibilities of the program were realized, GE personnel built new control components to replace deteriorated parts and used replacement parts with salvaged materials to make more than 75 V-2 sounding rockets available for atmospheric and solar investigation at WSMR. Approximately two V-2 launches per month were scheduled from Launch Complex 33 until the supply of V-2 sounding rockets was exhausted. A reduced frequency of V-2 sounding rocket investigations from Launch Complex 33 continued until 1952.

Sounding rocket modifications

The 2,200 pounds (1,000 kg) explosive warhead in the 17 cubic feet (0.48 m³) nose cone was replaced by a package of instrumentation averaging 1,200 pounds (540 kg). Instrumentation was sometimes added to the control compartment, in the rear motor section, between the fuel tanks, or on the fins or skin of the rocket. Nose cone instrumentation was typically assembled at participating laboratories and flown to WSMR to be joined to the rocket in Assembly Building 1.

Rockets returning to earth intact created an impact crater about 80 feet (24 m) wide and of similar depth which filled with debris to a depth of about 35 feet (11 m). In an effort to preserve instruments, dynamite was strategically placed within the airframe to be detonated at an elevation of 50 kilometres (31 mi) during downward flight at end of the high-altitude scientific observation interval. These explosives weakened the rocket structure so it would be torn apart by aerodynamic forces as it re-entered the denser lower atmosphere. Terminal velocity of tumbling fragments was reduced by an order of magnitude.

Sounding rocket performance

V-2 sounding rockets were 47 feet (14 m) long and 5 feet 5 inches (1.65 m) in diameter and weighed 28,000 pounds (13,000 kg) with a full load of liquid fuel contributing two-thirds of that weight. The fuel was consumed in the first minute of flight producing a thrust of 56,000 pounds-force (250 kN). Maximum acceleration of 6 Gs was reached at minimum fuel weight just before burnout, and vibrational accelerations were of similar magnitude during powered flight. Velocity at burnout was approximately 5,000 feet (1,500 m) per second. The rocket would typically have a small, unpredictable angular momentum at burnout causing unpredictable roll with pitch or yaw as it coasted upward approximately 75 miles (121 km). A typical flight provided an observation window of 5 minutes at altitudes above 35 miles (56 km).

Instrumentation

Servomechanisms were devised to compensate for rocket aspect changes as it tumbled after burnout. These allowed sun-tracking devices to measure the solar electromagnetic spectrum. Limited success was achieved with parachute recovery of instrumentation, but some of the more durable instruments or recordings within the rocket airframe could withstand impact with the earth at subsonic velocities.

NRL developed a telemetry system using a 23-channel pulse-time modulation. Voltage presented to the input terminals of a given channel determined spacing between two adjacent pulses. Space between first and second pulses was determined by channel 1, between second and third pulses by channel 2, and so forth. The system made 200 samplings per second of 24 pulses. Information was transmitted via high-power frequency modulation. Ground receiving stations translated pulse spacings back into voltages which were applied to a bank of string galvanometers to make an approximately continuous record of each channel on a moving roll of film. Accuracy was within approximately 5 percent.