Heard S. Lowry

Test and Evaluation of Sensor Platforms in the AEDC Space Sensor Test Chambers

The space simulation test chambers at the Arnold Engineering Development Center (AEDC) offer a means of performing high-quality, economical, and timely state-of-the-art test and evaluation (T&E) to satisfy a variety of space system testing requirements. These requirements include sensor and focal plane array level characterization (including radiometric calibration and characterization and goniometric evaluation) and mission simulation. Such a ground test capability is crucial for reducing system development risk by testing the latest technologies developed for space-based, interceptor, and airborne sensor platforms. In response to the evolving requirements for testing sensor platforms, AEDC continues to develop new methodologies and techniques to maintain a suite of facilities capable of testing sensor systems at any level of development. This involves the integration of high-fidelity, complex, and dynamic scene projection systems in conjunction with comprehensive analysis and measurement of the properties of the optical systems. This paper describes the AEDC methodology for space sensor T&E, including uncertainty methodology and enhancements that are currently planned for the space sensor test facility.

Ground Testing of Space-Based Imaging Sensors in AEDC's Space Chambers *

Arnold Engineering Development Center (AEDC) space chamber facilities offer a means of satisfying a variety of space system testing requirements, including sensor and focal plane array level characterization and mission simulation, radiation effects simulation, spacecraft contamination effects, spacecraft propulsion testing, and thermal/vacuum environment simulation. Such a ground test capability is very important in testing the latest technologies developed for spacecraft components. AEDC has developed a suite of chambers and a methodology that addresses the complex, high-fidelity issues of the test and evaluation (T&E) community. This methodology encompasses the testing of sensor systems at any level of development, from characterization of the imaging chip to full-scale testing of the sensor. This paper discusses the AEDC space chamber facilities and some of the tests performed there recently.

Cryogenic optical system development for AEDC's 10V chamber

The 10V Chamber Test Facility at the Arnold Engineering Development Center (AEDC) is being upgraded to provide a closed-loop capability to assess multi-band electro-optical sensor performance under realistic operational scenarios against evolving threats. This test facility will leverage existing facilities and expertise from several Government agencies including AEDC, Army/AMCOM, and USAF/KHILS to investigate performance issues during ground testing at cryogenic conditions. Radiometrically accurate simulated scenes will be presented to the test article using dual-band infrared point sources, a dual-band infrared emitter array projector, and a visible array projector. Various optical assemblies will be required to project the images from these radiometric source systems onto the sensor aperture. The infrared point sources will be positioned in the XY plane using two-stage linear translators, which must meet stringent spatial coverage and position accuracy requirements to create realistic closed-loop target motion. A large two-axis steering mirror will simulate sensor line of sight movements for the blackbody sources. A high-speed jitter mirror will simulate high frequency image motion for the emitter arrays. These mirror systems must be vibrationally isolated to minimize the jitter induced in other optical elements. Narcissus and ghost image effects will be minimized using appropriate fabrication, shielding, and calibration techniques. A multi-spectral calibration and alignment system will be integrated into the facility to ensure proper radiometric and goniometric operation of the various target sources. The target and optical systems must all meet performance specifications at cryo-vacuum conditions. Code V will be the primary tool used to evaluate wave front error and distortion coating performance for ghosting/polarization/transmission effects, optical manufacturing errors, and energy-on-detector (EOD). Finite element models of the facility will be used to analyze the structural rigidity and dynamics of the components due to the cryogenic environment.

Completion of the scene generation test capability (SGTC) at AEDC

The scene generation test capability (SGTC) has achieved an initial operating capability (IOC) at the Arnold Engineering Development Center (AEDC) using direct write scene generation (DWSG). This test tool will be able to present realistic mission scenarios directly to sensor focal plane arrays (FPAs) for developmental and operational test and evaluation (DT&E and OT&E), and will be integrated with the full-up sensor test capabilities at AEDC. The concept validation phase of this program is an operational system that is currently involved in sensor testing. The final phase provides scene projection at three infrared wavelengths and one visible wavelength. The facility is ready for FPA testing. This paper presents an overview of the current SGTC program, including a report of the hardware testing performed as part of the validation process.

Integrated approach to space sensor testing

The Arnold Engineering Development Center (AEDC) has developed new test technologies and methodologies for realistic mission simulation testing of infrared space-based sensors. These technologies and methodologies have been combined into an integrated approach for space sensor testing. This approach integrates component, subsystem, and system level tests. Computational models are used to address both sensor optic and chamber optics effects. Simulations and real-world phenomenology are used to generate scenarios tailored for each specific orbit, mission, threat, etc. The synergism of test technology and sensor design characteristics is evaluated and integrated into the test process in order that issues ranging from radiometric calibration to overall mission performance may be properly addressed. A case study based on AEDCs Direct Write Scene Generation (DWSG) test technology is used to illustrate this integrated approach.

Applying Test and Evaluation Technologies, Techniques, and Methodologies to Enhance the Space Sensor Test Infrastructure at AEDC *

The Arnold Engineering Development Center (AEDC) continues to apply emerging test and evaluation (T&E) technologies, techniques, and methodologies to enhance the significant T&E infrastructure that has been developed for the characterization and calibration of space-based, airborne, and interceptor sensor systems. The 7V and 10V Chambers both provide a suite of radiometric target systems that operate in a simulated space background (~ 20K) and allow complete evaluation of sensor performance within a single test installation. These space simulation test chambers offer a means of performing high-quality, economical, and timely state-of-the-art T&E to satisfy a variety of space system testing requirements. Such ground-test capabilities are crucial for reducing the system development risk of the latest technologies developed for sensor platforms. Complex target systems that provide the ability to evaluate system performance against representative mission scenarios are included in both test chambers. The 7V Chamber emphasizes calibration and characterization of infrared seekers and sensors against a low-infrared background, but is also capable of mission simulation testing. The 10V Chamber hardwarein-the-loop (HWIL) chamber is dedicated to real-time interceptor testing. Upgrades to each chamber are being pursued to keep pace with evolving sensor technologies, as well as the development of methodologies to test wide-field-of-view (WFOV), polarimetric, space situational awareness (SSA) and multispectral/hyperspectral imaging systems. This paper reports the current status of these chambers and planned modifications for their continued development to meet test customer requirements.

Further results in measuring water ice buildup on optical components in cryogenic vacuum chambers

Experiments presented in a previous paper established proof-of-principle that water, the most prevalent contaminant in high-vacuum cryogenic systems, initially collects on the surfaces of optical components as a thin film of ice, and thus can be detected and its thickness measured via multiple-beam thin-film interference phenomena. In those earlier experiments, a molecular sieve zeolite in a canister external to a vacuum chamber served as a water source, while the buildup of ice was measured using a HeNe laser beam reflected off the surface of a mirror with a quartz crystal microbalance (QCM) used for verification of the mass accumulation. Additional experiments have improved upon the techniques used earlier and provided further insight into the ice accumulation process. Use of a shorter wavelength (450 nm) laser in conjunction with a first-surface gold mirror produced greater depth of modulation and thus increased signal-to- noise ratio in the light interference. Data reduction using cross-correlation analysis over single-period interference records provided more accuracy and precision in the ice thickness measurements. Ice buildup under varying pressure and temperature ranges established baseline conditions for transparent thin-film deposition, and the transition to ice fracture and specular reflection. These recent experiments have demonstrated that the optical monitoring of ice accumulation via multiple-beam interference is applicable over a wider range of mass and thicknesses than the conventionally-used QCM method.

Continued development and integration of scene projection technologies in the AEDC space simulation chambers

The process of integrating high-fidelity, complex dynamic scene projection systems into space simulation test chambers is a continual challenge which requires comprehensive analysis and measurement of the properties of the optical components involved. This includes the multiple-band source subsystems and the spectral tailoring methods invoked to represent target temperatures. Techniques currently employed in the AEDC space sensor test facilities will be discussed in this paper.

Development and integration of scene projection technologies for the AEDC 10V upgrade and other space sensor test programs

The continuing effort to provide a complex, broad-based (low-background, complex dynamic scene projection) sensor test capability at Arnold Engineering Development Center involves the development of scene projection technologies and their integration into existing space chambers. New radiometric source concepts are being investigated that will allow greater flexibility in simulating multiple target scenarios for space sensor testing. Alternate sources, filtering techniques, beam combining methods, and optical power delivery systems are being investigated for possible use in meeting the ultimate objectives of current and anticipated testing programs.

Test and Evaluation of Space and Airborne Imaging Sensor Platforms

The space simulation test chambers at the Arnold Engineering Development Center offer a means of performing high-quality, economical, and timely state-of-the-art tests and evaluations to satisfy a variety of space system testing requirements. These requirements include sensor and focal plane array level characterization (including radiometric calibration and characterization and goniometric evaluation) and mission simulation. Such a groundtest capability is crucial for reducing system development risk by testing the latest technologies developed for spacebased, interceptor, and airborne sensor platforms. In response to the evolving requirements for testing sensor platforms, new methodologies and techniques are being developed to maintain a suite of facilities capable of testing sensor systems at any level of development. A roadmap has been created that integrates high-fidelity, complex, and dynamic scene projection systems in conjunction with comprehensive analysis andmeasurement of the properties of the optical systems to meet imaging sensor test needs.