NASA's Flight Research Center at Edwards Air Force Base (renamed the Dryden Flight Research Center), generally thought of as an aeronautical flight-test facility in the 1960s, made a number of contributions to the NASA space program during that era as well.For example, researchers explored the concept of paraglider landings for a space vehicle and the use of wingless spacecraft that could glide to precise landings, but it was the X-15 hypersonic research program and the Lunar Landing Research Vehicle that had the most direct impact on the Apollo missions to the Moon.
The North American Aviation X-15 rocket planes--designed to explore the problems of atmospheric and space flight at supersonic and hypersonic speeds--served as flying laboratories, carrying scientific experiments above the reaches of the atmosphere. Many research results from the X-15 program at Dryden Flight Research Center contributed directly to the success of the Apollo lunar missions, now being celebrated on the 40th anniversary of the first moon landing on July 20, 1969. North American – later North American Rockwell, then Rockwell International – served as prime contractor for both the X-15 and Apollo Command/Service Module spacecraft.
Designers of the Apollo CSM drew upon experience from the X-15 program, and even used the X-15 as a test bed for new materials. Advanced titanium and nickel-steel alloys developed for the X-15 were used in the Apollo and later spacecraft designs. The discovery of localized hot spots on the X-15, for example, led to development of a bi-metallic 'floating retainer' concept to dissipate stresses in the X-15's windshield. This technology was subsequently applied to the Apollo and space shuttle orbiter windshields.
The X-15's performance allowed researchers to accurately simulate the aerodynamic heating conditions that the Apollo Saturn rocket would face, and allowed full recovery of test equipment, calibration of results, and repeated testing where necessary. In 1967, technicians applied samples of cryogenic insulation--designed for use on the Apollo Saturn V second stage--to the X-15's speed brakes to test the material's adhesive characteristics and response to high temperatures.
X-15 re-entry experience and heat-transfer data were also valuable, and led to design of a computerized mathematical model for aerodynamic heating that was used in the initial Apollo design study. Lessons learned from X-15 turbulent heat-transfer studies contributed to the design of the Apollo CSM because designers found that they could build lighter-weight vehicles using less thermal protection than was previously thought possible.
Following the challenge by president John F. Kennedy in 1962 to land on the moon, two groups began working on a way to prepare astronauts for the critical descent and landing on the moon. The problems facing them were considerable: how to build a free-flying simulator that could negate 5/6ths of the Earth's gravity while entirely eliminating the effects of the atmosphere, since the moon had no atmosphere and only 1/6th of Earth's gravity.
Ideas for this unique type of flying machine had begun circulating at Dryden Flight Research Center, a year earlier. Center engineers initially didn't know that Bell Aircraft Company, later Bell Aerosystems, was also working on the task, but by the end of the year, the center had awarded a study contract to Bell. Bell was the only firm in the United States that had significant experience developing vertical takeoff aircraft using jet lift for takeoff and landing. After winning a contract from the center to design and build the machines in 1963, Bell delivered two Lunar Landing Research Vehicles or LLRVs--often called 'flying bedsteads' due to their ungainly appearance--to the Flight Research Center in 1964 for flight testing and development.
The LLRV had a jet engine hung vertically in the middle of the frame, fixed inside two gimbals, allowing the vehicle itself to rotate as much as 40 degrees in any direction while the jet remained vertically aligned. A series of hydrogen peroxide thrusters, eight around the frame's center and four at each corner, provided lunar simulation thrust that the pilot controlled.
Three analog computers took data on side forces and vehicle weight and produced just enough jet thrust so that, in lunar simulation, the LLRV descended as though in lunar gravity. Any gusts of wind were cancelled when the computers sensed them and fired thrusters to automatically cancel the wind. There were no mechanical links between the pilot and the engine or thrusters: everything was sent to the computers that, in turn, commanded the thrust desired.
During flight tests, a pilot directed the LLRV to climb about 300 feet, initiated lunar simulation mode, and then had less than eight minutes to complete a safe descent. Research flying over the next two-and-half years yielded a configuration suitable for astronaut training, and Bell subsequently built three similar craft--Lunar Landing Training Vehicles--that were sent to the Manned Spaceflight Center in Houston, now the Johnson Space Center. One of the LLRVs at the Flight Research Center was also sent to Houston for the training.
Apollo 11 commander Neil Armstrong recalled later that his landing on the moon on July 20, 1969 was a familiar job because of the LLTV’s authenticity.
As a side note, today's aircraft with fly-by-wire digital electronic control systems trace their lineage to the LLRV and its analog computers, and to the engineers who worked on that project. They cut their teeth on computer-controlled flight systems with the LLRV, allowing them the confidence to modify an F-8 jet fighter into the first aircraft with pure digital fly-by-wire electronic controls.
Partially restored by a movie company in the late 1990s, one of the two original Lunar Landing Research Vehicles remains on sheltered display today at NASA Dryden.
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