The key responsibility of the quality assurance organization is to assess and eliminate the potential sources of error which are an ever-present threat to quality and reliability. A guiding principle in this process is that human error is a constant, and that controlling it requires a systematic approach. It is essential to control work operations and manufacturing processes as well as inspections and tests. Work operations include design, materials procurement, vendor liaison, configuration control and packaging. This is the distinction between quality assurance and quality control. Q.C. is a check of the product. Q.A. is a check of the entire system that produces quality, from design to fabrication to shipping and installation. Q.C. is measurement quantification. Q.A. is conceptual, organizational. But the planners who saw the need for formalized Q.A. systems had more on their minds than the complexity of modern weapons systems. They were worried about human nature too.
The Advanced X-ray Astrophysics Facility (AXAF) will be a space-based observatory consisting of special mirrors to form images in x rays. The mirrors are composed by nested conical shaped thin walled ZERODUR cylinders. ZERODUR is the ideal material for grazing incidence optics. The production steps of these ZERODUR blanks are briefly described. Different QA techniques, detection of tiny inclusions in the glass ceramic via infrared light, precise dilatometer measurements of the coefficient of thermal expansion and specific optical metrology, had to be applied. Results of the metrology are discussed.
Properly planned and executed metrology crosschecks at low to mid system test levels can provide up to the same degree of end item performance insurance protection that a top-level end-to-end test can, at a small fraction of the cost, and in a much more timely manner in terms of identifying and correcting problems. This philosophy has been put into rigorous practice on the optics fabrication activity being performed by Hughes Danbury Optical Systems, under contract to TRW, on the Advanced X-ray Astrophysics Facility (AXAF) program being managed by NASA's Marshall Space Flight Center. The process to date, while for the most part having provided confidence that the primary calibrations and tests are correct, has also identified several significant but subtle errors that were corrected. The focus of the paper is on the process itself as an optical quality insurance tool, with examples from AXAF described.
The development of the Space Shuttle Orbiter in the early 1970s marked the first time that a fracture mechanics approach was taken to the design of the window systems of a manned space craft. Earlier vehicles were never subjected to repeated launch and re-entry and therefore fatigue or slow crack growth were not major concerns. The design and proof test methodology evolved at that time continues to be applied in the development of the window systems for the Space Station Freedom. A combination of fixed abrasive grinding, lapping, and chemical machining is employed on the fused silica window panes to insure that sub- surface damage is carefully controlled and minimized. All panes are proof tested under controlled atmospheric conditions which preclude crack growth during the test. This paper also covers some of the history of space craft window design, the rationale for the material choices as well as a review of the finishing and test methods employed.
In this paper, we give a little background into the work of ISO/TC172/SC1/WG1, the ISO subcommittee that is writing standards for the environmental testing of optics and optical instruments. By environmental test standards, we mean standards that outline what sort of climatic variations and conditions of use optical instruments must survive and still operate within given performance specifications. The scope of the standards this subcommittee is writing is then described followed by a thorough description of the general content of the 2 standards that are nearing completion. Finally, we discuss the applicability of these standards and how they may affect optics and optical systems that are intended for sale in international markets. We also discuss briefly the relationship of these ISO standards to MIL-STD-810E, Environmental Test Methods and Engineering Guidelines, the U.S. Military standard.
In response to the current need for physical standards for the calibration of bidirectional reflectance distribution function (BRDF) instruments, NIST has initiated a program to develop such calibration standards. Black glass was selected as a candidate material. An assortment of black glass samples were prepared using optical finishing techniques. BRDF profiles of these samples were measured and showed promising results for use in calibration. Some BRDF profiles are presented in this paper as well as the status of the program and future work that will be performed.
This paper describes and illustrates simple expressions for evaluating the effects of conventional and fractal surface errors on image quality, and conversely, of specifying finish parameters in terms of system performance requirements.
We report on the design and fabrication of an all-silicon test pattern that is very useful for assessing the performance of all types of profiling instruments. We present examples of results obtained from applying this method to various kinds of profiling instruments, including a WYKO TOPO 3D system, Micromap Promap 512 profilers, a ZYGO Maxim 3-D system, and scanning probe AFM systems. We also present the results from a measurement of the BRDF of the step with a TMA CASI scatterometer to show the utility of the step as a potential calibration standard for scattered light measuring instruments.
As optical components become larger and more complex, it becomes more difficult to use traditional techniques for the measurement of figure accuracy. The Large Optics Diamond Turning Machine (LODTM) located at Lawrence Livermore National Laboratory and the Off Axis Generating Machine (OAGM 2500) located at Eastman Kodak Company are examples of surface generating machines capable of manufacturing optics for which there are no independent means of figure measurement. Consequently, the LODTM and the OAGM are provided with metrology capabilities to perform their own quality control. This situation violates the conventional quality control practice of independent part inspection. Independent part inspection can be achieved on the M60 Universal Coordinate Measuring Machine located at Martin Marietta Energy Systems Corporation. The M60 is capable of inspecting an anamorphic optic measuring two meters on the diagonal to an accuracy approaching one half of a wavelength RMS in the visible spectrum. The M60 represents the first in a class of large coordinate measuring machines providing greater accuracy and precision. This paper provides an overview of the design and accuracy achieved in the LODTM, OAGM, and M60. Applications and future potential are discussed.
An optical test has been devised to test and qualify null correctors that are used for measuring highly aspheric primary mirrors. The technique employs a rotationally symmetric computer- generated hologram (CGH) that tests the null corrector directly by synthesizing a wavefront that would be returned by a perfect primary mirror. A description of the test and summary of the error analysis are given. The error analysis includes hologram errors from pattern distortion, substrate flatness, and etch depth variations. It also includes the effects of errors in the wavelength and data analysis errors. This resulting analysis shows +/- 78 ppm accuracy for measuring the conic constant of null correctors built for measuring 3.5 -m f/1.75 primary mirrors.
The second generation Wide-Field/Planetary Camera (WF/PC-II) for the Hubble Space Telescope (HST) was modeled to access the impact of manufacturing, alignment, and environmental tolerances on performance. This analysis showed that the lateral registration of the image of the Optical Telescope Assembly (OTA) pupil to the surface providing the spherical correction must be aligned and maintained through launch to 50 microns; WF/PC-I was an order of magnitude less sensitive. Inherited WF/PC-I hardware was subjected to new WF/PC-II environmental tests. As a result WF/PC-II was reconfigured to ensure on-orbit performance: the focus mechanism was removed to increase stability through launch and on- orbit, and four formerly fixed mirrors were actuated, to provide capability for on-orbit pupil alignment. This paper traces the evolution of the WF/PC-II error budget from its WF/PC-I beginnings to the current configuration.
High performance requirements for the Imaging Science Subsystem/Narrow Angle Camera (NAC) instrument on the NASA/Jet Propulsion Laboratory (JPL) Cassini spacecraft impose very stringent demands for dimensional stability of metering rods in the camera's athermalizing system. Invar 36 was chosen as a baseline material because it possibly could meet these requirements through high purity control and appropriate thermomechanical processes. A powder metallurgy process appears to be the manufacturing method to ensure high purity and cleanliness of this material. Therefore, a powder metallurgy manufacturer was contacted and high purity (HP) Invar 36 was produced per JPL engineering requirements. Several heat treatments were established and heat treated HP Invar 36 samples were evaluated. Coefficient of thermal expansion (CTE), thermal hysteresis and temporal stability test results are reported here. The test results indicate that JPL has succeeded in obtaining possibly the most dimensionally stable (lowest CTE plus lowest temporal change) Invar 36 material ever produced. CTE < 1 ppm/ degree(s)C are reported here along with temporal stability < 1 ppm/year. These dimensional stability properties will meet the requirements for metering rods on the NAC.
Many future space optical systems are dependent on large apertures to achieve the collecting power or resolution necessary to meet mission goals. Traditional mirror materials such as glasses and metals result in optics which are heavy and costly to both fabricate and deploy. In recent years, an approach for fabricating large, lightweight, precision optics from fiber reinforced organic matrix composite materials has been developed and demonstrated. These mirror panels consist of composite facesheets bonded to an open cell core. A key element of this technology is the durability of the composite construction materials. Extensive testing has been performed on a number of composite materials based on carbon fiber and organic resins. Ultimately, a high modulus graphite fiber/cyanate ester composite system was chosen for the panel facesheets due to its superior mechanical properties, processability, thermal stability, radiation resistance, very low water absorption, and temporal stability. This program has successfully demonstrated the feasibility of fabricating space durable mirrors using composite materials technology.
Design of experiment (DOE) methods were employed to optimally develop thin films with respect to optical absorption and mechanical stress performance. The goal of the experiment was to identify key deposition characteristics which would yield very low optical absorption and minimized film stress characteristics. A fractional factorial matrix was utilized for the preliminary portion of the experiment. Key deposition parameters with respect to low absorption and low film stress were identified as a result of the DOE effort. In addition, the interaction effects of each key deposition parameter with other key deposition parameters as a function of performance were identified. Details of the DOE setup, analysis, and evaluation are presented. Subsequent application of statistical process control methods to control these optimized critical parameters during production to ensure consistent, high quality production yields are discussed.