Which of the following statements about the THAAD window is true?

• A. The interceptor uses a cooled sapphire window.
• B. The window is uncooled glass.
• C. The window is made of plastic.
• D. The system has no window.

Answer: (A)

Protecting the infrared seeker while keeping optical performance in the extreme conditions of flight is what the THAAD window is about. The window must shield the seeker from aerodynamic heating, debris, and contamination, yet still let the infrared signals reach the detector clearly. Sapphire is chosen because it’s incredibly hard and resistant to scratches, can handle the high accelerations and temperatures of launch and flight, and transmits infrared light well in the wavelengths used by the seeker. Cooling the window further reduces self-emission and stabilizes its temperature, which helps keep the detector sensitive and prevents image blur during the high-speed intercept. An uncooled glass window would heat up and distort the optical path; plastic wouldn’t withstand the harsh environment and would degrade optically; and having no window would leave the sensor unprotected and unusable. So, the statement that the THAAD window is a cooled sapphire window is the accurate description.