Thermal, mechanical, and optical properties of Cleartran® multispectral zinc sulfide were measured. Heat capacity, thermal conductivity, and thermal expansion were measured over the temperature range 213 to 643 K. Young's modulus and shear modulus were measured at 289 to 473 K. The characteristic four-point flexure strength for a 1-cm2 area was 75.4±0.5 MPa at 289 K and 89.5±0.4 MPa at 473 K, with Weibull moduli of 11.0±0.7 and 19.3±1.5, respectively. All 24 specimens tested at 289 K conformed to the Weibull curve. However, 2 of 23 specimens tested at 473 K had low, outlying strengths. The fracture origins of the outliers were surface flaws that were not detected by microscopic examination prior to mechanical testing. The only reliable means that we are aware of to identify weak material is a mechanical proof test. Infrared transmittance and reflectance at 297, 373, and 473 K were measured with an integrating sphere. The transmittance of s- and p-polarized infrared light was measured at angles of incidence of 0 to 60 deg. By fitting the transmittance with the Fresnel equations, the absorption coefficient was computed for wavelengths of 8 to 14 µm. Bidirectional transmittance and reflectance distribution functions (optical scatter) were measured at 3.39 and 10.6 µm.
Researchers engaged in the development of infrared detector technologies may well benefit from a broader understanding of their products from the perspective of the end-user. An appreciation of how this technology is to be used by system designers, many of whom possess only a rudimentary understanding of quantum physics, is highly germane. Answers to questions like: "What device technology will be employed," "How will the device be used?" and "What are the impacts on signal-to-noise?" are of critical importance. In this paper, some of the fundamentals of hit-to-kill missile defense technology are examined in a largely non-mathematical context. From its "Star Wars" inception during the Reagan administration, to today’s Missile Defense Agency, the core requirement of missile defense has not changed - find the threat and destroy it before it reaches its destination. This fundamental requirement, while conceptually straightforward, is extraordinarily difficult to satisfy, and is almost exclusively dependent on our ability to detect and designate a relatively small, very fast-moving, room-temperature object, at great distances, and usually in a severe environment of shock and vibration further clouded by error and uncertainty. With an obvious bias toward passive IR detection and associated focal plane array characteristics, the flight of a fictitious interceptor is followed from launch to impact. At various points along the interceptor’s trajectory, a "peel the onion" approach is utilized to expose increasingly detailed layers of behavior, including the eventual release of the kinetic kill vehicle, and its autonomous flight to a body-to-body impact with its target. Various sources of error and their impact on the success of the mission are examined, and an overall understanding of the key features of the infrared seeker and its critical role in missile defense are ultimately developed.
The Lockheed Sensor Test Facility, located in Sunnyvale, California, is a state-of-the-art LWIR
sensor calibration resource designed to calibrate strategic seekers against a simulated
exoatmospheric optical background. Increasingly accurate and sophisticated seeker technology has
created a demand for improved performance in test equipment, particularly in the area of
cryogenic optical systems. Diffraction-limited optics and sub-arcsecond pointing have become the
norm rather than the exception in these systems.
This paper chronicles the two-year development of several precision mechanisms for use in
cryogenic environments to 20 K at pressures below 1 microtorr. The Lockheed mechanism
development is highlighted by the successful adaptation of traditional mechanism design principles
to the cryogenic environment through the judicious selection of materials, lubricants and electromechanical
devices, and the appropriate use of both open- and closed-loop controls.
All of the mechanisms developed are associated with the 500-inch effective focal length, eccentric
pupil Ritchey-Chretien collimator which forms the basis of the Lockheed seeker calibration
approach. Although fundamentally athermal in design, this collimator has traditionally exhibited
unacceptable warm-to-cold alignment variations. This phenomenon has been precluded through
the use of a precision, six-degree-of-freedom refocusing mechanism which allows the in situ
positioning of the collimator's secondary mirror. Together with two precision scan mirrors and
their associated positioning mechanisms, the optical performance of the system at operating
temperatures and pressures is assured. A source select mirror and its associated drive mechanism
has been completely redesigned to provide the accurate positioning of several LWIR radiometric
sources at the collimator prime focus.
The Low-background Scanning Point Source (LSPS), a field-portable low-background target generator designed to allow vehicle-level ground test and checkout of infrared seekers, is discussed. The LSPS can be used to simulate a room-temperature point source moving at a constant rate against an exoatmospheric background or as a point-source calibration change. It incorporates a cryogenically cooled off-axis Gregorian collimator and a dual-axis scan mirror viewed through a zinc selenide window. An analysis is presented of its optical and radiometric performance, and its integration to the vehicle is discussed.
Since it was first introduced to the public in the early 1980's, the Lockheed Sensor Test Facility (STF) in Sunnyvale, California, has undergone a dramatic transformation from a highly labor intensive experiment to a fully automated, state-ofthe-art production LWIR sensor calibration laboratory. Radiometric traceability is assured with the first blackbody calibration by the National Institute of Standards and Technology (NIST-formerly NBS), and the optical system has been thoroughly revamped to provide diffraction-limited performance in the infrared at wavelengths above 6 μm for LWIR sensors with input apertures to 15 cm. New, modern refrigeration equipment has been added, and the vacuum system has been thoroughly overhauled to provide a simulated exoatmospheric environment as low as 20 K absolute temperature and 10<sup>-8</sup> torr absolute pressure.
This report traces the evolution of the STF during the last two years, and details the many enhancements and capabilities introduced in that period. The results of a two-year characterization and calibration activity are summarized, and a full description of capabilities and services available to the LWIR sensor community is included.