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.
Standard vacuum practices mitigate the presence of water vapor and contamination inside cryogenic vacuum chambers. However, anomalies can occur in the facility that can cause the accumulation of amorphous water ice on optics and test articles. Under certain conditions, the amorphous ice on optical components shatters, which leads to a reduction in signal or failure of the component. An experiment was performed to study and measure the deposition of water (H2O) ice on optical surfaces under high-vacuum cryogenic conditions. Water was introduced into a cryogenic vacuum chamber, via a hydrated molecular sieve zeolite, through an effusion cell and impinged upon a quartz-crystal microbalance (QCM) and first-surface gold-plated mirror. A laser and photodiode setup, external to the vacuum chamber, monitored the multiple-beam interference reflectance of the ice-mirror configuration while the QCM measured the mass deposition. Data indicates that water ice, under these conditions, accumulates as a thin film on optical surfaces to thicknesses over 45 microns and can be detected and measured by nonintrusive optical methods which are based upon multiple-beam interference phenomena. The QCM validated the interference measurements. This experiment established proof-of-concept for a miniature system for monitoring ice accumulation within the chamber.
An experiment was performed to study and measure the deposition of water (H2O) ice on optical component surfaces
under high-vacuum cryogenic conditions. Water was introduced into a cryogenic vacuum chamber via a hydrated
molecular sieve zeolite housed in a valved external chamber, through an effusion cell, and impinged upon a quartz-crystal
microbalance (QCM) and first-surface gold-plated mirror. A laser and photodiode setup external to the vacuum
chamber monitored the multiple-beam interference reflectance of the ice-mirror configuration while the QCM measured
the mass deposition. Data acquired and analyzed from this experiment indicate that water ice under these conditions
accumulates on optical component surfaces as a thin film up to thicknesses over 45 microns and can be detected and
measured by nonintrusive optical methods based upon multiple-beam interference phenomena. The QCM, a well-established
measurement technique, was used to validate the interferometer.
Arnold Engineering Development Center (AEDC) is tasked with visible-to-LWIR imaging sensor calibration and
characterization, as well as hardware-in-the-loop (HWIL) testing with high-fidelity complex scene projection to validate
sensor mission performance. They are thus involved in the development of technologies and methodologies that are
used in space simulation chambers for such testing. These activities support a variety of program needs such as space
situational awareness (SSA). This paper provides an overview of pertinent technologies being investigated and
implemented at AEDC.
Arnold Engineering Development Center (AEDC) is involved in the development of technologies that enable hardwarein-
the-loop (HWIL) testing with high-fidelity complex scene projection to validate sensor mission performance.
Radiometric calibration with National Institute of Science and Technology (NIST) radiometers has improved radiometric
and temporal fidelity testing in this cold background environment. This paper provides an overview of pertinent
technologies being investigated and implemented at AEDC to support a variety of program needs such as HWIIL testing
and space situational awareness (SSA).
KEYWORDS: Calibration, Data modeling, Sensors, Data acquisition, Mirrors, Projection systems, Light emitting diodes, Systems modeling, Black bodies, Cryogenics
The characterization, calibration, and mission simulation testing of imaging sensors require continual involvement in the
development and evaluation of radiometric projection technologies. Arnold Engineering Development Center (AEDC)
uses these technologies to perform hardware-in-the-loop (HWIL) testing with high-fidelity complex scene projection
technologies that involve sophisticated radiometric source calibration systems to validate sensor mission performance.
Testing with the National Institute of Standards and Technology (NIST) Ballistic Missile Defense Organization
(BMDO) transfer radiometer (BXR) and Missile Defense Agency (MDA) transfer radiometer (MDXR) offers improved
radiometric and temporal fidelity in this cold-background environment. The development of hardware and test
methodologies to accommodate wide field of view (WFOV), polarimetric, and multi/hyperspectral imaging systems is
being pursued to support a variety of program needs such as space situational awareness (SSA). Test techniques for the
acquisition of data needed for scene generation models (solar/lunar exclusion, radiation effects, etc.) are also needed and
are being sought. The extension of HWIL testing to the 7V Chamber requires the upgrade of the current satellite
emulation scene generation system. This paper provides an overview of pertinent technologies being investigated and
implemented at AEDC.
KEYWORDS: Data modeling, Sensors, Calibration, Light emitting diodes, Black bodies, Optical components, Data conversion, Mirrors, Projection systems, Data acquisition
The characterization, calibration, and mission simulation testing of space-based, interceptor, and air-borne sensors
require a continual involvement in the development and evaluation of radiometric projection technologies. Activities at
Arnold Engineering Development Center (AEDC) include Hardware in the Loop (HWIL) testing with high-fidelity
complex scene-projection technologies as well as improvements in the radiometric source-calibration systems. These
technologies are integrated into a low cryo-vacuum (~20 K) environment. The latest scene simulation and HWIL
projection technologies are being investigated that can produce desired target temperatures and target-to-sensor ranges
such that sensor mission performance can be evaluated. These technologies include multiple-band source subsystems
and special spectral-tailoring methods, as well as comprehensive analysis and optical properties measurements of the
components involved. Emphasis areas include the development of methodologies to test wide field of view (WFOV),
polarimetric, and multi/hyperspectral radiometric imaging systems.
The characterization, calibration, and mission simulation testing of space-based, interceptor, and airborne sensors require a continual involvement in the development and evaluation of radiometric projection technologies. Recent efforts at the Arnold Engineering Development Center (AEDC) include hardware-in-the-loop (HWIL) testing with high-fidelity, complex scene projection technologies integrated into a low-cryovacuum (~20 K) environment as well as improvements in the radiometric source calibration systems. The latest scene simulation and projection technologies are being investigated, technologies that can produce desired target temperatures and target-to-sensor ranges that will make it possible to evaluate sensor mission performance. These technologies include multiple-band source subsystems and special spectral tailoring methods, as well as comprehensive analysis and optical properties measurements of the components involved. This paper discusses the implementation of such techniques at AEDC.
KEYWORDS: Black bodies, Calibration, Sensors, Temperature metrology, Infrared radiation, Resistors, Temperature sensors, Infrared sensors, Control systems, Target acquisition
The Space Systems Test Facility (SSTF) at the Arnold Engineering Development Center (AEDC) has tested interceptor, airborne, and space-based infrared sensors for over 30 years. In that time, the 7V Chamber has been the primary calibration facility at AEDC. It is used to perform sensor characterization, calibration, and mission simulation testing. The 10V Chamber has been developed to perform hardware-in-the-loop sensor testing. A crucial aspect of this testing is the accurate simulation of point-source targets. The sources used must be able to simulate the range and temperature of the simulated target for realistic testing. A detailed characterization and analysis program is conducted to ensure their radiometric fidelity. The 7V Chamber has a total of six blackbody sources. Four are used as point targets, one is a flood source, and one is a standard reference source. For every chamber pumpdown, source calibrations are performed and radiometric data are taken. The data are then used to perform uncertainty analyses. A total of four blackbody sources are used in the 10V Chamber. Two of these blackbodies are used for point targets, one is a standard reference source, and the final blackbody is a spare. All four blackbodies have been tested and compared with NIST-traceable blackbodies at AEDC. The design and testing of these sources is discussed.
The space simulation chambers at the Arnold Engineering Development Center (AEDC) have performed space sensor
characterization, calibration, and mission simulation testing on space-based, interceptor, and air-borne sensors for more
than three decades. A continual effort to implement the latest scene simulation and projection technologies into these
ground-based space sensor test chambers is necessary to properly manage the development of space defense systems.
This requires the integration of high-fidelity, complex, dynamic scene projection systems that can provide the simulation
of the desired target temperatures and ranges. The technologies to accomplish this include multiple-band source
subsystems and special spectral tailoring methods, as well as comprehensive analysis and optical properties
measurements of the components involved. Implementation of such techniques in the AEDC space sensor test facilities
is discussed in this paper.
The ground testing of a sensor system under flight conditions is fundamental to characterizing its performance. It should be accomplished early and often in order to manage operational uncertainty and reduce system life-cycle cost. As a DoD Major Range Test Facility Base (MRTFB), the Arnold Engineering Development Center (AEDC) provides a comprehensive capability that strives to ensure system performance evaluations that are not limited by test infrastructure. For over 30 years, the space chambers at AEDC have performed space-sensor characterization, calibration, and mission
simulation testing on space-based, interceptor, and airborne sensors. In partnership with Missile Defense Agency (MDA), capability upgrades are continuously pursued to keep pace with evolving sensor technologies. A critical aspect of these chambers is the quality of the mirror coatings used to project simulated target scenes to the unit under test in low-background cryogenic conditions. This paper discusses the recent effort at AEDC to refurbish and/or replace the
mirror collimating systems in their 7V and 10V Aerospace Chambers and the coating choices that have been considered.
Testing system performance early and often under flight conditions is fundamental to managing uncertainty in system performance predictions and reducing system life-cycle cost. As a Department of Defense (DoD) Major Range Test Facility Base (MRTFB), Arnold Engineering Development Center (AEDC) strives to ensure that DoD system performance tests are not limited by test and evaluation capabilities. For over 30 years, the space chambers at AEDC have performed space sensor characterization, calibration, and mission simulation testing on space-based, interceptor, and air-borne sensors. In partnership with the Missile Defense Agency (MDA), AEDC continuously pursues capability upgrades in order to keep pace with evolving sensor technologies. Upgrades to sensor test facilities require rigorous facility characterization and calibration efforts, all of which are routinely included in AEDC's annual activities to ensure quality test data. This paper discusses the status of such upgrades especially with regard to scene projection.
For over 30 years, the Space Systems Test Facility and space chambers at the Arnold Engineering Development Center (AEDC) have been used to perform space sensor characterization, calibration, and mission simulation testing of space-based, interceptor, and airborne sensors. In partnership with the Missile Defense Agency (MDA), capability upgrades are continuously pursued to keep pace with evolving sensor technologies. Upgrades to sensor test facilities require rigorous facility characterization and calibration activities that are part of AEDC's annual activities to comply with Major Range Test Facility Base processes to ensure quality metrology and test data. This paper discusses the ongoing effort to characterize and quantify Aerospace Chamber 7V measurement uncertainties. The 7V Chamber is a state-of-the-art cryogenic/vacuum facility providing calibration and high-fidelity mission simulation for infrared seekers and sensors against a low-infrared background. One of its key features is the high fidelity of the radiometric calibration process. Calibration of the radiometric sources used is traceable to the National Institute of Standards and Technology and provides relative uncertainties on the order of two to three percent, based on measurement data acquired during many test periods. Three types of sources of measurement error and top-level uncertainties have been analyzed; these include radiometric calibration, target position, and spectral output. The approach used and presented is to quantify uncertainties of each component in the optical system and then build uncertainty diagrams and easily updated databases to detail the uncertainty for each optical system. The formalism, equations, and corresponding analyses are provided to help describe how the specific quantities are derived and currently used. This paper presents the uncertainty methodology used and current results.
A continual effort to develop the latest scene simulation technologies into actual space simulation test chambers is necessary to ensure that the U.S. has the proper ground test capabilities to test space defense systems. This involves the integration of high-fidelity, complex, and dynamic scene projection systems, including multiple-band source subsystems and the spectral tailoring methods used to simulate the desired target temperatures. Comprehensive analysis and measurement of the properties of the optical components involved are also required. This paper discusses implementation of these techniques in the space sensor test facilities of the Arnold Engineering Development Center (AEDC).
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.
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