MERCURY REDSTONE VEHICLE

The Mercury-Redstone vehicle, a proven modification of one of the most reliable large rockets developed in the United States, will serve as the launch vehicle for the coming experiment in the Nation's Mercury manned space flight program.

Personnel of NASA's George C. Marshall Space Flight Center at Huntsville, Ala., who originally developed the Redstone, first altered the rocket for use in scientific space exploration and more recently for the Mercury project. A Mercury-Redstone will soon launch an astronaut on a suborbital flight down the Atlantic Missile Range from Cape Canaveral, Fla., in a prelude to future U.S. manned orbital flights.

In an earlier modified version, the Redstone was used as the first stage of the Jupiter C vehicle, which orbited the free world's first satellite - Explorer I. The greatest achievement of Explorer I was the discovery of the inner Van Allen radiation belt encircling the earth. A special long range version of the rocket had previously boosted the first nose cone to successful reenter the atmosphere from space.

As the initial launch vehicle to be used in the manned phases of the Mercury program, the Mercury-Redstone is a further departure from the original design. Some 800 changes were required to transform the "old" Redstone into a modern, man-carrying power plant. The MR-3 mission Redstone was built by the Chrysler Corporation.

In its redesign, the rocket's 70 inch diameter tank section was lengthened about 6 feet, adding more than 20 seconds of burning time. This increased the vehicle's length to 83 feet -- including spacecraft and escape tower, and its lift-off weight is 66,000 pounds. Major changes in the engine, which increased its reliability, were also necessitated. For example, provisions were built into the engine to allow for the extra burning time, and major improvements were made in the peroxide system which drives the fuel and liquid oxygen pumps and provides thrust control. Other modifications improved the engine's stability, and added and anti-fire hazard system. The Mercury-Redstone engine, developed and built by the Rocketdyne Division of North American Aviation, generates a thrust of 78,000 pounds. In addition, a new instrument compartment, a completely automatic emergency sensing system, and a spacecraft adapter were added.

The instrument compartment, produced by the Marshall Space Flight Center, houses the sensitive control system. It is located between the fuel tanks and the spacecraft. Unlike the ordinary Redstone, this compartment does not separate from the booster after burnout, rather it descends to the earth attached to the propulsion unit. The sensing or "about" system, also developed by MSFC engineers, gives an electric signal warning of possible trouble. If this signal is given, it causes (1) termination of launch vehicle thrust, (2) separation of the spacecraft from the booster and (3) activates the spacecraft's escape rocket which propels the craft to a safe distance within a fraction of a second.

The abort system senses and is activated by such conditions as unacceptable deviations in the programmed attitude of the rocket, excessive turning rates, loss of thrust, critical irregularities of thrust or loss of electrical power. In a manned mission, the escape system could be activated by the pilot in the spacecraft, and manually in the launching blockhouse and at the NASA Mercury Control Center.

The control system of the Mercury-Redstone is less complex than the earlier ballistic model. This system, simpler and more reliable than before, uses an autopilot which minimizes drift during powered flight. Carbon vanes located in the jet exhaust of the propulsion unit coupled with air vanes used as control surfaces to maintain proper attitude. The major portion of this system was provided by the Ford University Company.

Instruments are installed in the booster to provide and telemeter some 65 measurements surveying all aspects of booster behavior during flight, such as attitude, vibration, acceleration, temperature, pressure, and thrust level. These measurements are in addition to the many channels of information which will be telemeter from the spacecraft itself during its journey. Several tracking signals are also telemetered by the booster.

Three Mercury-Redstones have been flown. The first fired on December 19, 1959, launched a heavily-instrumented production Mercury spacecraft on a successful sub-orbital flight. The test verified the operation of the Mercury system in the space environment.

A second vehicle, launched on January 21, 1961, carried a chimpanzee on a similar flight. The passenger, named Ham, was recovered unharmed in a test that proved the Mercury life support system in flight. The test did, however, reveal several trouble areas. Systems vibration, resulting from the greater length and altered mass distribution of the Mercury-modified Redstone, fed into the vehicle's automatic pilot and disturbed its control system. In addition, the Redstone engine ran with its throttle wide open, increasing the vehicle's speed from 4,900 to 5,300 mph. Consequently, liquid oxygen was consumed at a higher rate than usual, causing the engine to cut off prematurely. The rocket's short sensing system reacted properly, activating the spacecraft's emergency escape device which pulled the craft away from the vehicle. Firing of the escape rocket added further to the already greater range in altitude of the craft's flight.

As a result of this flight, steps were taken to correct the problems and a test of the effectiveness of these modifications was conducted on March 24, 1961, when a Mercury-Redstone carrying a dummy spacecraft was fired from Cape Canaveral.

Project officials at the Marshall Center termed the test an unqualified success. The rocket, with its spacecraft remaining attached throughout the flight, followed its prescribed trajectory, reaching an altitude of about 100 miles and a distance of some 400 miles.

During the flight, the power plant functioned normally, the vehicle was well controlled along the planned trajectory, and all networks and ground equipment operated as programmed.

The MR-3 rocket, assembled at MSFC, will be launched by the Center's Launch Operations Directorate.