NASA-STD-7001 Shaker Testing

Engineers conduct multiple validation tests throughout the process of designing and building a spacecraft. Validation determines whether the test item can withstand the environmental conditions of the task and identifies potential defects. This standard is specifically designed for acoustic and random vibration environments and test levels, primarily for the vibration-acoustic verification of aerospace payload hardware. It provides test factors for the verification of payload hardware for prototypes, prototype flights, and flight acceptance procedures. Topics such as test duration, test control tolerances, data analysis, test tailoring, payload filling effects, and analysis methods are covered.

Test requirement

NASA-STD-7001 specifies the acoustic and random shaker testing levels associated with the maximum expected flight altitude (MEFL), which determines the severity of the test, the standard also includes test duration and control tolerance, and the following is a summary of the test requirements.

Test control tolerances.

For prototype program validation and acceptance tests, test control tolerances shall be such that the acceptance test level does not exceed the validation test level. The use of limiting tolerances is particularly critical when minimum process random vibrations or acoustic specifications control any part of the envelope spectrum. In this case, acceptable tolerances are as follows:

Acoustic experiment

Acoustic testing is typically required at the entire spacecraft assembly level, and in addition, aerospace hardware that requires acoustic testing for vibrational acoustic validation is typically large area weight ratio structures such as skin panels, reflectors, dish antennas, and solar panels that respond significantly to the direct impact of the 8nasa-std-7001 acoustic environment.
Two types of parts require vibration and acoustic testing :(1) parts fitted with a vibration isolator, and (2) parts consisting of important parts with a first resonance frequency greater than 2000 Hz. The isolator attenuates the high frequency mechanical vibration caused by direct acoustic impact. Therefore, these components should be reviewed on a case-by-case basis, and a test program that meets minimum process standards should be implemented. In addition, the microstructural components of many electronic black boxes and glass components have resonant frequencies above 2000hz, which is usually the limit of most large electric shakers. Acoustic tests should be performed by controlling the sound pressure level (dB re 20 μPa) in a 1/3 octave frequency band within the specified frequency range. All payload structures and components that require acoustic testing shall be tested in a wideband reverberation field. The amplitude of a random noise source should be approximately normally distributed.

Random shaker testing

Virtually all electrical, electronic and electromechanical components and mechanisms require random vibration testing. Exceptions are structures with larger area than weight that can be acoustically tested in place of random vibration, and hardware that does not actually vibrate at the component level, such as structures, cables, pipes, blankets, etc., that can be deferred to system-level vibration or acoustic testing. Compact payloads weighing less than 450 kg (1000 lb) should be tested for system-level random vibration, unless the analysis shows that the payload response is significantly dominated by the immediate acoustic environment.
The test specimen shall be subjected to random vibration with a Gaussian amplitude distribution in each of three orthogonal axes. Random vibration testing shall be performed by controlling the acceleration spectral density (g2/Hz) in the frequency range from 20 to 2000 Hz. The spectrum shall be within the test tolerance specified in 4.3.4.
If multiple control accelerometers are used, the test level can be controlled using an average or extreme control scheme: but the controller must be derived in accordance with the test requirements. The test fixture should be measured at a bare resonance of up to 2000hz before the test begins. If feasible, the fixture should have no resonance in the test frequency range. The test specimen shall be mounted to the fixture by its flight or flight equivalent mounting attachment.

Test duration

Prototype
The test time of vibration acoustic identification was 2 minutes for acoustic test and 2 minutes for vibration test on three orthogonal axes. If the flight hardware needs to be repaired N times, the corresponding qualifying test time is 2+0.5N minutes.
Protoflight
The protoflight vibroacoustic qualification test durations shall be 1 minute for an acoustic test and 1 minute in each of the three orthogonal axes for a vibration test.

Acceptance test duration

Prototype program.
The vibration acoustic acceptance test time of the flight unit developed according to the prototype concept should be 1 minute for the acoustic test and 1 minute for each of the three orthogonal axes of the vibration test
Protoflight program.
For subsequent spacecraft hardware and spare parts, the acceptance test time for acoustic testing should be 1 minute and vibration testing 1 minute on each of the three orthogonal axes. In other cases (e.g., retesting of flight hardware), the test conditions will be determined by applying test clipping.
The random test curve is arranged in a breakpoint table, which includes the frequency (Hz) and amplitude (G^2/Hz) values and the cross slope (dB). Power spectral density (PSD) diagram shows the value; The change of PSD level is measured in dB.



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