Arnold AFB linked to space shuttle return-to-flight program

  • Published
  • By Janae’ Daniels
  • Arnold Engineering Development Center Public Affairs
The Arnold Engineering Development Center here played an important role in supporting NASA’s space shuttle return-to-flight program that will culminate with the July 13 scheduled launch of Space Shuttle Discovery.

Following the February 2003 breakup of Space Shuttle Columbia during re-entry into the Earth’s atmosphere, AEDC people were called upon to conduct tests to assist NASA in its return to manned space flight.

Testing, conducted in five of AEDC’s 58 testing facilities, consisted of wind tunnel, foam impact and “full stack” testing.

The first of three series of wind tunnel tests occurred in June 2003 to demonstrate the aerodynamic capabilities of some of the space shuttle redesign initiatives and provided valuable data on the aerodynamic heating caused by the new design during ascent.

Using an AEDC-designed and fabricated scale model of the bipod ramp that connects the space shuttle to the main external fuel tank near the shuttle’s nose, test people generated an environment in the tunnel similar to that encountered during various launches to orbit to observe aerodynamic flow conditions.

The second series of tests began August 2003 to measure the air pressure on models of the same bipod, ramp and a redesigned bipod area by placing pressure sensors in the models.

Embedded heaters on the insulation foam models prevented ice formation on the exposed metal components during tests and allowed an accurate simulation of how it would perform in space.

Another series of tests was conducted in the center’s hypersonic tunnel. During this series, an AEDC-designed and fabricated 30-percent scale redesigned bipod model was used to collect the heating rates and pressure measurements from locations distributed around the redesigned bipod attachment fitting and surrounding insulation foam.

During foam impact testing, engineers and test operators at AEDC’s ballistic impact range launched hundreds of block-shaped projectiles made of the insulating foam material used on the shuttle’s external tank. These “shots” simulated pieces of external tank foam breaking away from the tank during flight, as happened to Columbia, and striking various parts of the space shuttle such as the solid rocket booster.

Test operators launched the blocks at various velocities and angles to simulate the different ways in which foam might strike the solid rocket booster. These tests helped determine the effects of foam impact and provided information on the rocket booster’s ability to withstand those impacts.

During each shot, high-pressure helium gas launched the foam projectiles at speeds from 150 to 2,255 feet per second down an 86-foot-long rectangular barrel. The targets included the struts connecting the solid rocket booster and external fuel tank and core panels. The core panels were representative of the thermal protection system materials and cover material for the range safety system antennae that would be used to abort a mission if sufficient damage occurred to the shuttle.

High-speed video cameras operating at speeds up to 20,000 frames per second documented the impacts and provided a means for measuring the velocity of the projectiles. Instrumentation on the target’s panels acquired data at 50,000 samples per second to provide information on the stresses the targets sustained during the impact.

AEDC officials completed a week of testing on a 3-percent scale “full stack” model in the center’s 16-foot transonic wind tunnel in October. The “full stack” model represents a space shuttle configuration similar to the vehicle at launch, with the external fuel tanks attached.

The objective of the test was to perform detailed pressure and force measurements, and flow visualization on the shuttle model, particularly in the bipod area. The model was subjected to speeds ranging from those encountered just after takeoff to Mach 1.5.

Pressure-sensitive paint flow visualization was used to determine pressure data over the entire surface of the shuttle model as it was tested. This specialized paint fluoresces, or glows, under certain lighting, with brighter areas indicating lower pressure and dimmer areas indicating higher pressure.

The paint is applied to the model, which is then imaged with digital cameras while the wind tunnel is operating. The images are processed through a program in a supercomputer to show the varying pressures in different colors. The team acquired pressure data on the two versions of external tanks, including the newer superlightweight tank and the older standard weight tank that dates to the late 1970s, to compare aerodynamic performance.

The people of AEDC have a long history of supporting the nation’s manned space programs. The center played a key role in the development of space projects Mercury, Gemini and Apollo. It also provided critical testing to the development of the space shuttle.

The $7.8-billion center is the nation's largest complex of flight simulation test facilities. It was dedicated in June 1951 by President Harry Truman and named after Gen. Henry H. Arnold, visionary leader of the Army Air Forces in World War II and the only Airman to hold a five-star rank.

Every high-performance flight system in use by the Department of Defense, and all NASA manned spacecraft, has been tested in AEDC's facilities. Today the center is testing the next generation of aircraft and space systems.