The current phase of testing at the U.S. Air Force's Arnold Engineering Development Center (AEDC) has concluded on the X-37 NASA demonstrator spacecraft for future flights in Earth's orbit and for reentry from space missions.

A six-percent scale model of NASA's X-37 underwent testing in three high speed wind tunnels at the Arnold Engineering Development Center to establish how redesigns to the demonstrator spacecraft's control jets and body flap affected its aerodynamics during re-entry into and through the Earth's atmosphere. Credit: AEDC

The scale model of the X-37 has made the rounds in the center's von Karman gas dynamics facility's three wind tunnels during May and June with testing concluding July 1, according to John Hopf, an AEDC project engineer.

"The testing in Tunnels A, B and C for the X-37 was a retest entry to establish the incremental effects of a redesign of the nozzles and body flap (external contour of the demonstrator which joins the spacecraft to the Delta IV rocket or other launch vehicle carrying it into space)," he explained. "The purpose was to look at these changes and effects to determine if significant adjustments to the previous database would be required."

The X-37 is an unmanned, autonomous reusable orbital and re-entry vehicle which will serve to test a number of new technologies in the area of advanced airframes, propulsion and operations of a range of different launch, orbital and reentry vehicle and spacecraft designs. Built by the Boeing Company, the major focus for the demonstrator model will be to find improvements of current space craft's thermal protection systems.

The X-37 was originally intended to either be carried aloft in the shuttle cargo bay or via an expendable launch vehicle. Due to the Columbia Shuttle accident and subsequent delays in NASA's shuttle Return-to-Flight program, the shuttle is not an option.

The X-37's body flap was made longer and narrower to better fit onto one of the (alternate) launch vehicles like the Delta IV rocket.

According to Hopf, the X-37's new Primary Reaction Control System (PRCS) jets were incorporated because the old ones were not as effective as desired and the X-37 program was not impacted by repositioning and resizing the control jets and by using more robust propellant due to overall program delays.

Hopf expressed satisfaction with the data obtained from the recently completed X-37 testing, adding, "The new nozzles produced the desired result of larger jet interactions (JI) on the vehicle's aerodynamic characteristics. Combined with the effects of the extended body flap, the flight control system will be adjusted to fit the new wind tunnel JI test database for the X-37 vehicle."

Wayne Hawkins, flight dynamics business development manager with AEDC's support contractor, added, "During this second round of wind tunnel tests, engineers acquired data in tunnels A, B and C to determine aerodynamic jet interaction effects from plumes of small reactor control system jets located near the aft (rear) end of a six-percent scale vehicle model."

Testing on the spacecraft model began at Langley, Va., and subsequently at AEDC during the summer. Hawkins further put the recent testing into perspective, saying, "The original testing on the X-37 model took place in 2000. This second round of testing we just completed was much more conclusive than just covering the propulsion system ­ it documented the overall aerodynamic performance of the X-37."

The earlier X-37 testing was followed by additional testing in 2001. Subsequent changes in the propellant, PRCS jets and the body flap drove the need to update the database from previous computational fluid dynamics (CFD) analysis studies and wind tunnel testing accomplished at AEDC in those earlier years.

The testing, which took 29 days to complete and 76 air-on-hours, was of particular importance in demonstrating the need to update the existing database due to the variation in nozzle plume interaction and aerodynamic performance of the X-37 throughout the lower range of Mach speeds. According to NASA officials, the X-37 Orbital Vehicle is being designed so that it is capable of orbital operations for periods of up to nine months.

The orbital flight test for the X-37 is scheduled for the summer of 2006.

Arnold Engineering Development Center is the nation's largest complex of flight simulation test facilities. The center was dedicated in June 1951 by President Harry Truman and named after 5-star General of the Air Force Henry 'Hap' Arnold, visionary leader of the Army Air Forces in World War II and the only airman to hold 5-Star rank. Today, this $7.6 billion complex has some 58 aerospace test facilities located at Arnold Air Force Base, Tenn., and the center's remote operating location Hypervelocity Tunnel 9 in White Oak, Md. The test facilities simulate flight from subsonic to hypersonic speeds at altitudes from sea level to space. Virtually every high performance flight system in use by the Department of Defense today and all NASA manned spacecraft have been tested in AEDC's facilities. Today the center is testing the next generation of aircraft and space systems.