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INTRODUCTION
Before a new type of aircraft takes off, a space vehicle is launched or a satellite is placed into orbit, the critical systems of each have been put through an extensive series of Earth-bound tests to ensure safe and proper performance.
The value of testing flight systems on the ground becomes even greater when the vehicle contains a crew and valuable cargo such as unique satellites and scientific payloads. Ground testing is an essential element in the development of liquid propellant engines because the same item can be static tested and then flown. Confidence in successful flight is increased because the static test closely simulates the flight environment. The more realistic the test conditions and the test item, the more confidence can be placed in the test results since reliability is demonstrated in the testing process. Analysis and theory, even the most detailed, can never adequately replace ground testing. History indicates that a good, thorough mix of both analysis and testing is required for success.
In order to make sure that all elements work according to plan, NASA, through several of its field centers around the country, conducts an extensive and ongoing ground test program in which everything from small models to actual aircraft and space vehicles are put through their paces to achieve maximum performance.
Each of the centers has developed highly specialized testing capabilities, equipment and other resources to carry out their precise work.
Three centers—Ames Research Center, Lewis Research Center and Langley Research Center—have wind tunnels for testing models and aircraft. At the Johnson Space Center, astronauts train in simulators designed to give the experience of functioning in zero gravity. Kennedy Space Center and Goddard Space Flight Center test spacecraft components in various laboratories during launch preparations. Unmanned spacecraft are tested at the Jet Propulsion Laboratory in a facility which simulates the harsh environment of space. As a test and evaluation center for both large and small hardware, the Marshall Space Flight Center has developed unique facilities for simulating the space environment. The Stennis Center has three massive test stands for static firing Space Shuttle main engines to certify their flight worthiness and a capability to static fire the proposed Advanced Launch System propulsion test vehicles and engines.
All of the centers have individual missions, but they share a common goal of ensuring the safe, reliable performance of new and complex flight systems.
AMES RESEARCH CENTER
NASA’s Ames Research Center in California specializes in scientific research, exploration and applications aimed at creating new technology. With its major program responsibilities being in the areas of flight simulation and research, the center employs advanced equipment, including aircraft, supercomputing systems, wind tunnels and flight simulators to achieve its goals.
At Ames-Dryden, which has unique capabilities for conducting flight research programs, the primary tools are research aircraft. Ground-based facilities include a high
temperature loads calibration lab for testing complete spacecraft and a flow visualization facility for testing models. Also, aircraft systems are routinely hooked up to a computer for tests prior to research aircraft flights.
At Ames-Moffett, the National Full-Scale Aerodynamics Complex contains the world’s two largest wind tunnels measuring 40 X 80 feet and 80 X 120 feet. Most of the major aircraft classes have been tested in this facility. In addition, advanced aircraft simulation facilities create authentic air-craft environments by generating the appropriate physical cues that provide sensations of flight.
Ames-Moffett’s test capabilities also include the Outdoor Aerodynamic Research Facility where Vertical Takeoff and Landing aircraft are tied down and whole systems can be run prior to flight. This facility can be used for instrumentation checkout and to require baseline data for unobstructed hover tests.
In other activities, Ames develops and ground tests flight hardware for future animal and plant payloads on the Space Shuttle and Space Station.
GODDARD SPACE FLIGHT CENTER
The Goddard Space Flight Center, NASA’s first major scientific laboratory, has evolved into the only national facility that can develop, design, fabricate, test, launch and analyze space science missions using all of its own resources. Since its 1959 inception, Goddard has built and tested more than 40 spacecraft at its Maryland facility. The unique tests performed at Goddard prior to launch assure that all spacecraft will withstand the rigors of space.
Spacecraft undergo a variety of environmental tests at Goddard including: vibration, acoustics, shock, acceleration, thermal and solar vacuum, temperature and humidity, radio frequency interference, and magnetic fields.
Goddard’s specialized test facilities cover a wide range of capabilities. Included among those facilities is the Vibration Facility, which performs shock and vibration tests on spacecraft and subsystems, reduces test data and calibrates transducers. In the Battery Test Facility, tests of aerospace batteries and cells are performed under simulated space environmental temperatures, and in the Large Area Pulsed Solar Simulator, solar cells and panels are irradiated with simulated solar radiation. All standard tests on electrical insulations for space use are tested in the High Voltage Testing Facility. Also, a Magnetic Field Component Test Facility is used to calibrate and align magnetometers, while the Spacecraft Magnetic Test Facility checks out spacecraft, sounding rockets, attitude control systems, magnetometers and subsystems.
In other areas, the High Capacity Centrifuge simulates launch and landing loads on spacecraft hardware, and a Space Simulation Test Facility contains thermal vacuum test chambers with different dimensions and environmental capabilities. Also, various sized scientific satellites, subsystems and components are tested in an Acoustic Facility containing a reverberation chamber, acoustic horns, noise generators, control console and a data handling system. In addition, two electromagnetic interference test facilities are available for proving spacecraft and scientific instruments worthy for flight.