1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-04-04a71 Center Point of Contact: MSFCa71 Submitted by: Wil HarkinsSubject: Integrated Optical Performance Modeling of X-Ray Systems Practice: To ensure that high resolution mirror assemblies for grazing incidence x-ray optic
2、al systems meet their requirements, image quality must be predicted during design and verified during fabrication by modeling the system for in-orbit and x-ray test configurations. Computer based modeling programs should be used to verify that both the initial design and the as-built configurations
3、will reliably produce the required image quality.Programs that Certify Usage: N/ACenter to Contact for Information: MSFCImplementation Method: This Lesson Learned is based on Reliability Practice No. PD-ED-1264; from NASA Technical Memorandum 4322A, NASA Reliability Preferred Practices for Design an
4、d Test.Benefit:The use of computer-based models for integrated x-ray optical performance modeling will provide an independent check of optical systems design and will ensure high quality optical systems by providing in-process verification of the fabrication process. These models can save time and m
5、oney in optical systems design and development, and should result in highly reliable x-ray imaging.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Implementation Method:Software has been developed and is being refined to model the images produced by
6、the grazing incidence optics of the Advanced X-ray Astrophysics Facility (AXAF-I) based on a number of optical system and mirror parameters. Commercial optical design and analysis programs are not tailored for grazing incidence mirror systems with their highly annular entrance apertures and cylindri
7、cally shaped mirrors. Analytical modeling is required to verify the design and to check fabrication in real time based on in-process mirror inspection metrology. A computer model has been developed that includes the effects of x-ray source position, x-ray source size, mirror figure errors, mirror su
8、rface roughness, mirror reflectivity, mirror alignment, and detector shape. Links are provided in the program to mirror surface metrology data and the mirror distortion predictions of standard structural analyses programs. Mirror figure errors are incorporated into a ray trace model by interpolating
9、 metrology data and structural model results onto a finely spaced grid. Individual surface parameters such as curvature and slope errors can also be applied to influence model results. The ray trace results can be convolved with the x-ray scattering predicted from the roughness of the mirror surface
10、s, and with the detector aperture shape and x-ray source size.An integrated, interactive program has been developed which will produce various two and three-dimensional image plots as well as parameters such as x-ray collecting area, root mean square image size, and image encircled energy distributi
11、on. This model is being developed as part of the AXAF-I project, but it is applicable to other grazing incidence x-ray optical systems. Figure 1 is an illustration of the Wolter I combined paraboloid/hyperboloid mirror system used for x-ray telescopes.refer to D descriptionD Provided by IHSNot for R
12、esaleNo reproduction or networking permitted without license from IHS-,-,-Figure 1. Combined Paraboloid/Hyperboloid Mirror Systems Used in X-ray Telescopes Where:r = radius z = coordinate along the optical axis (z = 0 at midpoint between the mirrors, z 0 at system focus) ro= radius at z = 0 S = subn
13、ormal k = conic constant = 1 - e22 = eccentricity |R| = |vertex radius of curvature| = refer to D descriptionD The mirrors are bodies of revolution around the longitudinal or z- axis.A flow diagram of the integrated optical performance computer model is shown on Figure 2. The model will produce a th
14、ree-dimensional picture of the image intensity distribution as well as an X/Y plane contour map of this intensity distribution at preselected intensity intervals. These outputs can be compared with the ideal output configurations by running test cases from a collection of stored parameters and by co
15、mparison with the results of ground tests and the analyses of independent investigators. Contamination and gravity (weight) effects are not included in the models parameters and must be considered separately. Gravity structural and thermal effects for the ground test can be analyzed by exercising th
16、e structural/thermal distortion program inputs.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refer to D descriptionD Figure 2. Flow Diagram of Integrated Optical Performance Technical Rationale:Due to the expense of ground x-ray tests of precision
17、grazing incidence x-ray mirrors for aerospace applications and the extensive time required for fabrication, it is imperative to have performance predictions ahead of time and to evaluate actual configurations in near real time as they reach completion during the manufacturing process. Optical perfor
18、mance modeling is necessary to ensure accurate and reliable performance before the mirror is put into service.References:1. Final Report: “Software to Model AXAF Image Quality,“ Center for Applied Optics, University of Alabama in Huntsville, Huntsville, AL, June 1993.2. Zissa, D. E.: “AXAF-I Perform
19、ance Analysis Software Development,“ (a presentation), Marshall Space Flight Center, AL, February 1, 1994.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-3. “Software for AXAF-I Performance Analysis,“ (a presentation), Center for Applied Optics, Univ
20、ersity of Alabama in Huntsville, February 1, 1994.4. D. E. Zissa: “Comparison of Ring-Focus Image Profile with Predictions for the AXAF VETA-I Teat,“ Proc. SPIE, Vol. 1742, pp. 91-103, 1992.5. P. Glenn, P. Reid, A. Slomba, and L. Van Speybroeck: “Performance Prediction of the AXAF Technology Mirror
21、Assembly using Measured Mirror Surface Errors,“ Proc. SPIE, Vol. 830, pp. 278-282, 1987.6. M. Freeman: “Interim Report, Transfit, Finite Element Analysis Data Fitting Software,“ Smithsonian Astrophysical Observatory Memorandum SAO-AXAF-DR-93-052, September 1993.Impact of Non-Practice: Failure to emp
22、loy optical performance modeling, coupled with inadequate testing and comparison with modeling results, could result in blurred x-ray images, inaccurate energy level results, and loss of scientific data. Repeat flights to regain lost data could be enormously expensive.Related Practices: N/AAdditional Info: Approval Info: a71 Approval Date: 2000-04-04a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
