Acoustic and Random Vibration Test Tailoring

Abstract

When developing a qualification test program for spacecraft, it is necessary to determine whether there should be an acoustic or random vibration test for each instrument, component, etc. The decision (key) factor is the area/mass ratio of an instrument, component, etc., which is very helpful to make a choice to perform either a random vibration on a shaker table or an acoustic test in a acoustic reverberant chamber. The calculation of the decision factor is completely based on random response analyses applying Miles’ equation.

Problems

6.1

A scientific instrument has a measured weight of 60 kg. The surplus of heat is radiated into outer space with the aid of an external radiator with total area of 0.75 m. The minimum required natural frequency of the instrument fixed at the spacecraft is $f_n=100$ Hz. The random vibration specification is provided in Table 6.5.

Table 6.5 Spectral density of vibro-accelerations, DNEPR (logarithmic distribution)

• Calculate the $3\sigma$ design quasi-static acceleration with the aid of Miles’ equation ($\mathrm{{Q}}=10$).

• Evaluate if a random vibration test or acoustic test is needed to verify design specifications.

• The acoustic loads of the DNEPR launch vehicle are specified in Table 6.6. Verify if the key factor $A/m=0.251$ is still applicable for $f_n=100,200,300$ Hz.

Table 6.6 DNEPR acoustic loads