Hot, high Mach test builds confidence in missile seeker window

  • Published
  • By Philip Lorenz III
A team at the Arnold Engineering Development Center's (AEDC) Hypervelocity Wind Tunnel 9 in Silver Spring, Md., turned up the heat recently on a key component of the Terminal High Altitude Area Defense (THAAD) defensive missile system.

They subjected a full-scale model of a THAAD missile nosecone with a new infra-red (IR) seeker window to hypervelocity airflow conditions exceeding what a missile would experience in the final stage of flight.

"This was a thermal structural test of seeker windows for the THAAD missile system that uses a new material," explained Ladd Henneman, an engineer from Lockheed Martin, the primary contractor for THAAD. "We evaluated the survivability and performance of this new material under hypersonic conditions that produced high heating and stress. These conditions were in excess of what the window assembly would experience toward the end of its flight."

Although the IR seeker window is protected by a shroud during early flight, the window still experiences moderate convective heating after shroud removal for low altitude, short range intercepts, he said. 

The tests conducted at Tunnel 9 provided reliable, high-value data, according to Mr. Henneman.

"This test has provided us with high confidence in the performance of our advanced window," he said. "AEDC's Mach 7 thermal structural facility provided the ideal seeker window test environment."

Tunnel 9 is comprised of two tunnels or legs. The primary leg is used for aerodynamic testing, while the center leg was developed to support high enthalpy flight duplication Mach 7 testing for several programs, including the THAAD system's window design, and other entries requiring duplication of Mach 7 aerothermal loads. Significant missile aerodynamic testing as well as shroud deployment on the THAAD system has been conducted in Tunnel 9 primary leg at Mach 8 and 10.

Ten years ago, a team at Tunnel 9 ran a test similar to the recent IR seeker window series in the Mach 7 leg. Some of the original hardware from that project was also used during the recent tests.

All seven of the flight-quality full-scale IR seeker windows survived the most current testing. The information these runs provided will be used to validate or enhance flight performance models.

"The pressures, temperatures and deflections measured in these tests will improve the fidelity of the complex analytical computational models used to predict window response," said John Lafferty, Tunnel 9's senior projects engineer for the facility and test engineer for this test series. "These tests are a testimony to the caliber of this facility. Tunnel 9 provides a unique combination of pressure, temperature, test time and a size which is unmatched by any other hypersonic wind tunnel in the world.

"Additionally, the airflow is sufficiently free of particles which make the testing of optical windows possible. The bottom line is we provide an affordable approach to obtaining critical hypersonic flight data for ballistic missile defense interceptors and associated technologies on the ground."

THAAD is the first weapon system with both endo-atmospheric (inside the atmosphere) and exo-atmospheric (outside the atmosphere) capability developed specifically to defend against short, medium and intermediate range ballistic missiles.
The THAAD system will provide high-altitude missile defense over a larger area than the complementary Patriot system, and, like the Patriot, intercepts a ballistic missile target in the "terminal" phase of flight--the final minute or so when the hostile missile falls toward the earth at the end of its flight. THAAD uses "hit-to-kill" technology, using only the force of a direct impact with the target to destroy it.

The THAAD Program is managed by the Missile Defense Agency in Washington, DC, and executed by the THAAD Project Office in Huntsville, Ala.