The US Department of Defense (DOD; www.defenselink.mil) has hired Boeing (Chicago, IL, USA; www.boeing.com) to build a weapon system to intercept incoming ballistic missiles. To test the system, a ballistic missile launched from Reagan Test Range at Kwajalein Atoll in the Pacific Ocean targets a mock interceptor vehicle launched from Vandenberg Air Force Base (Vandenberg, CA, USA; www.vandenberg.af.mil). Under contract to Boeing, Lawrence Livermore National Laboratory (Livermore, CA, USA; www.llnl.gov) has developed several sensors whose data help the DOD determine the effectiveness of the interceptor.
To monitor the event, Livermore’s sensors and cameras are installed in a jet, flying at an altitude of 14 km, that takes off from Reagan Test Range one hour before the interceptor is fired from Vandenberg. Once in the air, the jet remains within 650 to 900 km of the interceptor, until the interception with the incoming missile occurs.
“While on-board spectrometers examine the chemical makeup of debris from the mid-air intercept, radiometers measure impact temperature and intensity,” says physicist Alex Pertica, who leads the Livermore Remote Optical Characterization Sensor Suite (ROCSS) project. “At the same time, high-speed cameras document the intercept.”
A SpecterView camera from Southern Vision Systems (SVSi; Madison, AL, USA; www.southernvisionsystems.com) performs a key role in the ROCSS design. Says Andy Whitehead, president of SVSi, “The numerous instruments on-board the jet need to be triggered moments before the intercept.” To accomplish this, SVSi delivered a modified version of its SpecterView camera with custom firmware. This allows a dynamic region of interest (ROI) within the 1280 × 1024 imager to achieve 15,000 frames/s. Whenever an event is observed anywhere within this dynamic ROI, the camera generates a trigger signal.
To properly trigger the other instruments, the SpecterView is pointed at a tracking mirror that is guided by ground-based radar. After the camera tracks the interception, it triggers a bank of additional sensors and cameras 64 μs after the detection of the interception. “Because the position of the missile is tracked by radar, the tracking mirror can position the image on a small quadrant of the imager that can run at 15,000 frames/s rates,” says Whitehead.
Pertica describes the SpecterView camera’s role in ROCSS as a master trigger to start data acquisition on several sensors. “The camera allows us to detect a small flash in the midst of a daylight sky and issues a trigger with low latency, typically about 100 μs. Images captured from the camera also provide a radiometric profile of the flash intensity over time,” Pertica adds. In operation, images are downloaded directly to a host computer over the camera’s USB 2.0 interface. This interface also can select frame size and location and the external trigger source and can allow the user to define whether a single image or sequence of images is stored.
Many on-board sensors, including several from Livermore, collect IR data. Five Livermore instruments on-board the jet collect data on the interceptor rocket and the collision. An IR echelle-grating spectrometer (EGS) detects the presence of gaseous chemical species in the effluent cloud. If the intercept had involved an enemy missile, this chemical and temperature data could determine the type of incoming rocket. Another spectrometer operating in the visible wavelength determines rocket temperature and identifies materials produced by the interceptor and by the collision of the interceptor with the target missile. This reveals the spectral signatures of the colliding metals.
Radiometers operating in the visible, short-wavelength IR, and mid-wavelength IR spectral bands collect data on the temperature and intensity of the impact. A high-speed camera captures 16,000 frames in 4 s to record the evolution of the debris cloud created by the collision. Slower-speed video recorders and analog video systems also record the collision. Boeing has successfully demonstrated the system, and the deployment phase of the project is planned to continue until 2008. Pertica and his colleagues plan to upgrade the EGS to include the full mid-wavelength IR range, almost doubling its spectral coverage.