Preparations for Acoustic Testing of Herschel Structural Model
6 March 2006The Herschel Structural Model spacecraft is being prepared for a series of qualification tests in the acoustic test chamber, LEAF, in ESTEC.
The Large European Acoustic Facility (LEAF) is a test chamber aimed to replicate the vibration environment experienced by a satellite inside the fairing on top of the launcher during the first 30 seconds after ignition. The main source of these vibrations is the acoustic pressure exercised by the air surrounding the satellite. The air is excited by the huge solid rocket booster fumes and shock waves bouncing against the ground and the rocket.
For this purpose the LEAF test facility is equipped with giant loudspeakers which excite the air in the facility chamber in the frequencies between 30 to 3000 Hz. The acoustic levels can reach up to 145 dB representing a very harsh environment for any object and completely lethal to human beings.
A LEAF test is complementary to the vibration test carried out on a electromechanical shaker (Sine test) in the frequency range of 2 - 100 Hz. This latter test replicates the vibration environment experienced by the satellite due to its mechanical mounting on top of a rocket with trembling rocket engines and quivering global structure.
By means of these tests the structural and thermal model of the complete Herschel satellite has been exposed to slightly stronger vibrations than the equivalent Ariane5 environment. This is in order to confirm the structural design with positive margin and to mitigate the risk of damage during test of the real flight model and its actual launch.