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At least 307 records · Page 17

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NASA NTRS1992

Method and apparatus for phasing segmented mirror arrays

A method and an apparatus are disclosed for edge phasing an array of segments in a segmented primary telescope mirror using white light from a far field source and starting with the inner edge of each segment in the first ring of segments. The segments are individually phased for zero piston and tilt error with respect to the edge of a reference surface in the open center position of the telescope mirror. After edge phasing of all segments in the telescope mirror array is completed, full surface phasing can be achieved by using a conventional Shack-Hartmann technique followed by finding the RMS best fit for each segment of the mirror array.

Manhart, Paul K.↗

NASA NTRS1990

Cryogenic surface distortion and hysteresis of a 50 cm diameter fused silica mirror cooled to 77 K

A 50 cm diameter, lightweight, Amersil TO8E, fused-natural-quartz mirror with a single arch cross section was tested at the NASA/Ames Research Center Cryogenic Optics Test Facility to measure cryogenic distortion and hysteresis. The mirror was cooled to 77 K in four serial tests and the mirror figure was measured with a phase-measuring interferometer. On the basis of the repeatability of room temperature and cryogenic optical measurements, it was determined that the Single Arch Mirror had no measurable hysteresis and displayed repeatable cryogenic distortion. The Cryogenic Optics Test Facility, optical and thermal test methods, test results, and measurement accuracy are described.

Young, Jeffrey A.↗

NASA NTRS1992

General analysis of two-mirror relay systems

The general two-mirror system used at finite conjugates is examined here. Relations for first-order geometric properties and third-order aberrations are given in terms of five design parameters: object distance, image distance, exit pupil size, and the two mirror magnifications. The conditions for aplanatic solutions are derived for conic mirrors. The curvatures of the astigmatic image surfaces are given, and the condition for anastigmatic solutions is derived. The relations are applied to infinite conjugate systems and spherical mirror systems as special cases.

Hannan, Paul G.↗

NASA NTRS1993

Multilayer mirrors and filters for imaging the earth's inner magnetosphere

The requirements for imaging the inner magnetosphere in the light of 304-A He(+) emission are examined. The expected EUV emission spectrum of the inner magnetosphere is used to establish guidelines for the performance of the imager's multilayer mirrors and filters. The design of multilayer mirrors and the results of a computer search that determines the best multilayer mirror design for this application are discussed. B4C, Be, Si, and SiC are identified as promising top-layer materials for a multilayer 304-A mirror, while Al, Mg, and Mg2Si are recommended for other layers. Si-passivated Te and a combination of Al or Si with B or C are promising filter materials for this application.

Schulze, Dean W.↗

NASA NTRS1992

The effects of thermal gradients on the Mars Observer Camera primary mirror

The paper discusses the effect of thermal gradients on the optical performance of the primary mirror of Mars Observer Camera (MOC), which will be launched on the Mars Observer spacecraft in September 1992. It was found that mild temperature gradients can have a large effect on the mirror surface figure, even for relatively low coefficient-of-thermal-expansion materials. However, in the case of the MOC primary mirror, it was found that the radius of curvature (ROC) of the reflective surface of the mirror changed in a nearly linear fashion with the radial temperature gradient, with little additional aberration. A solid-state ROC controller using the thermal gradient effect was implemented and verified.

Applewhite, Roger W.↗

NASA NTRS1993

Thermal-mechanical behavior of high precision composite mirrors

Composite mirror panels were designed, constructed, analyzed, and tested in the framework of a NASA precision segmented reflector task. The deformations of the reflector surface during the exposure to space enviroments were predicted using a finite element model. The composite mirror panels have graphite-epoxy or graphite-cyanate facesheets, separated by an aluminum or a composite honeycomb core. It is pointed out that in order to carry out detailed modeling of composite mirrors with high accuracy, it is necessary to have temperature dependent properties of the materials involved and the type and magnitude of manufacturing errors and material nonuniformities. The structural modeling and analysis efforts addressed the impact of key design and materials parameters on the performance of mirrors.

Kuo, C. P.↗

NASA NTRS1991

Two-mirror projection systems for simulating telescopes

Optical instruments designed for use with large telescopes need to be tested before being installed at their work site. This is especially true for space-based instruments. To perform these tests, an auxiliary optical system is required which simulates the telescope exit pupil. Two-mirror projection systems can be used for this purpose. In this paper the first-order geometric properties and third-order aberrations of the general two-mirror system used at finite conjugates are examined. Relations are given in terms of five design parameters: object distance, image distance, exit pupil size, and the two mirror magnifications. A particular application of these relations is presented for a system designed to simulate the HST, for ground testing of the next generation of scientific instruments to be installed in the observatory. We show that a sufficient number of degrees of freedom are available to meet requirements when both mirrors are conics.

Hannan, Paul G.↗

NASA NTRS1991

Optical figure testing of prototype mirrors for JPL's Precision Segmented Reflector (PSR) program

JPL's PSR program is developing enabling technologies for large space telescopes employing segmented optics, and in particular, lightweight, thermally stable mirrors for telescopes operating at sub-mm wavelengths. JPL's vacuum cryointerferometric optical test facility includes a computer-controlled phase shifting interferometer operating at 10.59 microns and laser metrology for measurement of piston and absolute radius of curvature. The optical metrology has been integrated with a large vacuum chamber including a liquid nitrogen shroud capable of radiatively cooling 1.5 meter aperture mirrors down to 150 K. The facility is now being used to characterize prototype mirrors in both their room-temperature 'as-replicated' condition, and under orbital temperature conditions. The performance and limitations of the optical metrology hardware and software components are noted. Representative test results on prototype one meter-class composite mirrors being developed for PSR and related ground-based programs are also presented.

Hochberg, Eric B.↗

NASA NTRS1992

X-ray scattering measurements from thin foil X-ray mirrors

Thin foil X-ray mirrors are to be used as the reflecting elements in the telescopes of the X-ray satellites Spectrum-X-Gamma (SRG) and ASTRO-D. High resolution X-ray scattering measurements from the Au coated and dip-lacquered Al foils are presented. These were obtained from SRG mirrors positioned in a test quadrant of the telescope structure and from ASTRO-D foils held in a simple fixture. The X-ray data is compared with laser data and other surface structure data such as STM, atomic force microscopy (AFM), TEM, and electron micrography. The data obtained at Cu K-alpha(1), (8.05 keV) from all the mirrors produced on Al foils shows a scatter which limits the obtainable half-power width to above 1.5 arcmin. Mirrors based on electroformed Ni foils, however, show local regions with a factor of 4 better performance, and they are being developed for future applications.

Christensen, F. E.↗

NASA NTRS1993

Mirror fusion propulsion system - A performance comparison with alternate propulsion systems for the manned Mars mission

The performance characteristics of several propulsion technologies applied to piloted Mars missions are compared. The characteristics that are compared are Initial Mass in Low Earth Orbit (IMLEO), mission flexibility, and flight times. The propulsion systems being compared are both demonstrated and envisioned: Chemical (or Cryogenic), Nuclear Thermal Rocket (NTR) solid core, NTR gas core, Nuclear Electric Propulsion (NEP), and a mirror fusion space propulsion system. The proposed magnetic mirror fusion reactor, known as the Mirror Fusion Propulsion System (MFPS), is described. The description is an overview of a design study that was conducted to convert a mirror reactor experiment at Lawrence Livermore National Lab (LLNL) into a viable space propulsion system. Design principles geared towards minimizing mass and maximizing power available for thrust are identified and applied to the LLNL reactor design, resulting in the MFPS. The MFPS' design evolution, reactor and fuel choices, and system configuration are described. Results of the performance comparison shows that the MFPS minimizes flight time to 60 to 90 days for flights to Mars while allowing continuous return-home capability while at Mars. Total MFPS IMLEO including propellant and payloads is kept to about 1,000 metric tons.

Deveny, M.↗

NASA NTRS1993

Mirror fusion propulsion system: A performance comparison with alternate propulsion systems for the manned Mars Mission

Schulze, Norman R.↗

NASA NTRS1991

High accuracy switched-current circuits using an improved dynamic mirror

The switched-current technique, a recently developed circuit approach to analog signal processing, has emerged as an alternative/compliment to the well established switched-capacitor circuit technique. High speed switched-current circuits offer potential cost and power savings over slower switched-capacitor circuits. Accuracy improvements are a primary concern at this stage in the development of the switched-current technique. Use of the dynamic current mirror has produced circuits that are insensitive to transistor matching errors. The dynamic current mirror has been limited by other sources of error including clock-feedthrough and voltage transient errors. In this paper we present an improved switched-current building block using the dynamic current mirror. Utilizing current feedback the errors due to current imbalance in the dynamic current mirror are reduced. Simulations indicate that this feedback can reduce total harmonic distortion by as much as 9 dB. Additionally, we have developed a clock-feedthrough reduction scheme for which simulations reveal a potential 10 dB total harmonic distortion improvement. The clock-feedthrough reduction scheme also significantly reduces offset errors and allows for cancellation with a constant current source. Experimental results confirm the simulated improvements.

Zweigle, G.↗

NASA NTRS1993

Control of micromachined deformable mirrors

A micromachined deformable mirror with pixelated electrostatic actuators is proposed. The paper begins with a physical description of the proposed mirror. Then a mathematical model in the form of a nonlinear partial differential equation describing the mirror surface deformations is derived. This model is used to derive the required voltages for the actuators to achieve a specified static deformation of the mirror surface. This is followed by the derivation of a static nonlinear feedback controller for achieving noninteracting actuation. Then the structure for a complete control system for wavefront correction is proposed. The paper concludes with a discussion of the physical implementation of the proposed control system.

Agronin, M. L.↗

NASA NTRS1994

Design and implementation of a beam-waveguide mirror control system for vernier pointing of the DSS-13 antenna

The design and implementation of an antenna beam-waveguide (BWG) mirror position control system at the DSS-13 34-m antenna is presented. While it has several potential applications, a positioner on the last flat-plate BWG mirror (M6) at DSS 13 is installed to demonstrate the conical scan (conscan) angle-tracking technique at the Ka-band (32-GHz) operating frequency. Radio frequency (RF) beam-scanning predictions for the M6 mirror, computed from a diffraction analysis, are presented. From these predictions, position control system requirements are then derived. The final mechanical positioner and servo system designs, as implemented at DSS 13, are illustrated with detailed design descriptions given in the appendices. Preliminary measurements of antenna Ka-band beam scan versus M6 mirror tilt made at DSS 13 in December 1993 are presented. After reduction, the initial measurements are shown to be in agreement with the RF predicts. Plans for preliminary conscan experimentation at DSS 13 are summarized.

Alvarez, L. S.↗

NASA NTRS1993

Kinetic physics of the mirror instability

Kinetic mechanisms for the growth and saturation of the mirror instability are described using one-dimensional hybrid simulations. Two parameter regimes are considered. In the first regime, a relatively small ion anisotropy excites a slowly growing instability that produces small-amplitude waves; most ions respond to the waves as an adiabatic fluid. In the second regime a large anisotropy excites a rapidly growing instability that generates large-amplitude waves; the response of many ions in this case is nonadiabatic. The difference in ion response is due to the relative importance of two ion populations, resonant and nonresonant. Resonant ions, those ions with low velocities parallel to the background magnetic field, contribute to the growth of the instability as a result of their gyrointeractions with the noncoplanar component of the waves electric field and respond to the mirror waves nonadiabatically. Nonreasonant ions, those with large parallel velocities, respond as an adiabatic fluid. In both regimes, ion anisotropy is reduced by means of the magnetic mirror force; in the second regime, the anisotropy reduction reduces the free energy available for wave growth and leads to the saturation of the mirror instability.

Mckean, M. E.↗

NASA NTRS1995

SXI prototype mirror mount

The purpose of this contract was to provide optomechanical engineering and fabrication support to the Solar X-ray Imager (SXI) program in the areas of mirror, optical bench and camera assemblies of the telescope. The Center for Applied Optics (CAO) worked closely with the Optics and S&E technical staff of MSFC to develop and investigate the most viable and economical options for the design and fabrication of a number of parts for the various telescope assemblies. All the tasks under this delivery order have been successfully completed within budget and schedule. A number of development hardware parts have been designed and fabricated jointly by MSFC and UAH for the engineering model of SXI. The major parts include a nickel electroformed mirror and a mirror mount, plating and coating of the ceramic spacers, and gold plating of the contact rings and fingers for the camera assembly. An aluminum model of the high accuracy sun sensor (HASS) was also designed and fabricated. A number of fiber optic tapers for the camera assembly were also coated with indium tin oxide and phosphor for testing and evaluation by MSFC. A large number of the SXI optical bench parts were also redesigned and simplified for a prototype telescope. These parts include the forward and rear support flanges, front aperture plate, the graphite epoxy optical bench and a test fixture for the prototype telescope. More than fifty (50) drawings were generated for various components of the prototype telescope. Some of these parts were subsequently fabricated at UAH machine shop or at MSFC or by the outside contractors. UAH also provide technical support to MSFC staff for a number of preliminary and critical design reviews. These design reviews included PDR and CDR for the mirror assembly by United Technologies Optical Systems (UTOS), and the program quarterly reviews, and SXI PDR and CDR. UAH staff also regularly attended the monthly status reviews, and made a significant number of suggestions to improve the design, assembly and alignment of the telescope. Finally, a high level assembly and alignment plan for the entire telescope was prepared by UAH. This plan addresses the sequence of assembly, the required assembly and alignment tolerances, and the methods to verify the alignment at each step during the assembly process. This assembly and alignment plan will be used to assemble and integrate the engineering model (EM) of the telescope. Later on, based on this plan more detailed assembly and alignment procedures will be developed for the lower-level assemblies of SXI.

Source record↗

NASA NTRS1994

Replicate Wolter-I x-ray mirrors

Cylindrical (hyperbolic - parabolic Wolter I) mirrors have been electroformed from nickel over an electroless nickel-phosphorous (NiP) plated aluminum mandrel in support of the NASA AXAF-S x-ray spectrometer program. The electroless nickel was diamond turned and polished to achieve a surface finish of 10 angstroms rms or better. Gold was then plated on the nickel alloy after an electrochemical passivation step. Next a heavy layer of pure nickel was plated one millimeter thick with controlled stress at zero using a commercial PID program to form the actual mirror. This shell was removed from the NiP alloy coated mandrel by cryogenic cooling and contraction of the aluminum to release the mirror. It is required that the gold not adhere well to the NiP but all other plated coatings must exhibit good adherence. Four mirrors were fabricated from two mandrels prepared by this method. The area of each part is 0.7 square meters (7.5 square feet).

Engelhaupt, D. E.↗

NASA NTRS1995

Polarized Nuclei in a Simple Mirror Fusion Reactor

The possibility of enhancing the ratio of output to input power Q in a simple mirror machine by polarizing Deuterium-Tritium (D- T) nuclei is evaluated. Taking the Livermore mirror reference design mirror ratio of 6.54, the expected sin(sup 2) upsilon angular distribution of fusion decay products reduces immediate losses of alpha particles to the loss cone by 7.6% and alpha-ion scattering losses by approx. 50%. Based on these findings, alpha- particle confinement times for a polarized plasma should therefore be 1.11 times greater than for isotropic nuclei. Coupling this enhanced alpha-particle heating with the expected greater than 50% D- T reaction cross section, a corresponding power ratio for polarized nuclei, Q(sub polarized), is found to be 1.63 times greater than the classical unpolarized value Q(sub classical). The effects of this increase in Q are assessed for the simple mirror.

Noever, David A.↗