Design News for Mechanical and Design Engineers

Vibroacoustical measurements require a unique test system, a verification Test Article (VETA), mounted on the launch pad at the level of the Shuttle's main engines. The VETA simultaneously measures acoustic and vibration data.

A data recorder on the launch pad is connected to a host PC control system in a safe-room 100 ft below the pad through a 16-bit, RS-232C data transfer system from Sony Precision Control (Lake Forest, CA). The system runs a special version of Sony's PCscanII recorder control and data acquisition software. A second computer system resides in a laboratory 10 miles away. The set-up facilitates accurate monitoring of vibration data from the VETA and remote control of the data acquisition process.

Accurately accessing the Space Shuttle's vibroacoustics required a data acquisition system that samples data at a rate of 12 ksamples/sec for each of the 16 data channels. The system also required a high 84 dB range, an amplitude sensitivity of 16-bit A/D and D/A, and a phase shift between channels of fewer than 2°. Sony's PC216Ax DAT recorder with SVB-10, digital video interface card records up to 32 hours of digital video and analog and digital data that are stored in a single cartridge.

NASA found that acoustic loads are significantly affected by the vehicle trajectory away from the pad in order to reach the required orbital angle to the equator.