NASA measures Shuttle shake, rattle & roll

Cape Canaveral -Launching a Space Shuttle exposes ground support equipment and other nearby structures to intense acoustical vibration from rocket exhaust. Vibroacoustics also degrade structures over time, so monitoring them is important for NASA's safety and operational needs.

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 degrees . 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.