In NASA’s ongoing efforts to reduce potential debris sources of impact to the space shuttle during take-off, the elimination of the Protuberance Air Load (PAL) ramps on the external tank was investigated. Part of this investigation included testing scaled models of the external tank in NASA Glenn Research Center’s 8x6 foot Supersonic Wind Tunnel (8x6 SWT). To complete this test effort, Glenn worked with Johnson Space Center, Langley Research Center and Boeing.

The PAL ramp was made of layers of foam that were shaped to protect external tank hardware from excessive amounts of force and vibration during flight. The hardware that was tested included the cable tray, the pressurization lines (used to pressurize the liquid oxygen and liquid hydrogen in the external tank) and the liquid oxygen feed line.

 

Liquid hydrogen PAL ramp location on external tank (Credit: NASA).

Inside Glenn’s 8 x 6 foot SWT, a team from Glenn’s Research Testing Division tested a simulated portion of the external tank’s surface along with scaled versions of the cable tray, pressurization lines and liquid oxygen feed line. During testing, the simulated external tank and hardware was subjected to wind speeds between Mach 0.5 and 1.6. (Mach 1.6 is equal to 1.6 times the speed of sound or 1055 mph.) As a result of the testing performed in spring 2006, the two sections of the PAL ramp have been removed from the shuttle’s external tank.

Previous testing in the 8x6 SWT in 2003/2004 documented the steady state pressure environment of the external tank hardware. This project documented the dynamic pressure environment of the external tank hardware where pressures change at rates of up to thousands of times per second. The data resulting from the wind tunnel tests validated computer simulation models that were generated prior to wind tunnel testing.