Astronomical Telescopes and Instrumentation Symposium
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Intrumentation Astronomy↗
Engineering topics
Meinel, Aden B.
Publications and source records attributed to Meinel, Aden B..
Corrective Optics For Camera On Telescope
Assembly of tilted, aspherical circularly symmetric mirrors used as corrective optical subsystem for camera mounted on telescope exhibiting both large spherical wave-front error and inherent off-axis astigmatism. Subsystem provides unobscured camera aperture and diffraction-limited camera performance, despite large telescope aberrations. Generic configuration applied in other optical systems in which aberations deliberately introduced into telescopes and corrected in associated cameras. Concept of corrective optical subsystem provides designer with additional degrees of freedom used to optimize optical system.
Macenka, Steven A.↗
Determination of the Hubble Space Telescope effective conic-constant error from direct image measurements
Direct measurement of discernible features in the Hubble Space Telescope (HST) imagery has enabled a self-consistent determination to be made of the effective conic constant of HST images taken with planetary camera 6 (PC-6) of the wide field and planetary camera. Before being corrected for the contribution from PC-6, the conic constant is -1.01429 +/- 0.0002. The correction for PC-6 is less accurately determined but probably lies between -0.0002 and 0.0004. As a result the HST optics are characterized best by a conic constant of -1.0140 +/-0.0003 as obtained from direct image measurements.
Meinel, Aden B.↗
Two-stage optics - High-acuity performance from low-acuity optical systems
The concept of two-stage optics, developed under a program to enhance the performance, lower the cost, and increase the reliability of the 20-m Large Deployable Telescope, is examined. The concept permits the large primary mirror to remain as deployed or as space-assembled, with phasing and subsequent control of the system done by a small fully assembled optical active element placed at an exit pupil. The technique is being applied to correction of the fabrication/testing error in the Hubble Space Telescope primary mirror. The advantages offered by this concept for very large space telescopes are discussed.
Meinel, Aden B.↗
Cameras Would Withstand High Accelerations
Very rugged cameras with all-reflective optics proposed for use in presence of high accelerations. Optics consist of four coaxial focusing mirrors in Cassegrain configuration. Mirrors are conics or aspherics. Optics achromatic,and imaging system overall passes light from extreme ultraviolet to far infrared. Charge-coupled-device video camera, film camera, or array of photodetectors placed at focal plane. Useful as portable imagers subject to rough handling, or instrumentation cameras mounted on severely vibrating or accelerating vehicles.
Meinel, Aden B.↗
Infrared and the search for extrasolar planets
Search for evidence concerning the existence of extrasolar planets will involve both indirect detection as well as direct (imaging). Indirect detection may be possible using ground based instrumentation on the Keck telescope, Imaging probably will require an orbiting system. Characterizing other planets for complex molecules will require a large orbiting or lunar-based telescope or inteferometer. Cryogenic infrared techniques appear to be necessary. Planning for a NASA ground and space-based program, Toward Other Planet Systems (TOPS), is proceeding.
Meinel, Aden B.↗
Wavefront control of large optical systems
Several levels of wavefront control are necessary for the optimum performance of very large telescopes, especially segmented ones like the Large Deployable Reflector. In general, the major contributors to wavefront error are the segments of the large primary mirror. Wavefront control at the largest optical surface may not be the optimum choice because of the mass and inaccessibility of the elements of this surface that require upgrading. The concept of two-stage optics was developed to permit a poor wavefront from the large optics to be upgraded by means of a wavefront corrector at a small exit pupil of the system.
Meinel, Aden B.↗
Precision segmented reflectors for space applications
A project to develop precision segmented reflectors (PSRs) which operate at submillimeter wavelengths is described. The development of a light efficient means for the construction of large-aperture segmented reflecting space-based telescopes is the primary aim of the project. The 20-m Large Deployable Reflector (LDR) telescope is being developed for a survey mission, and it will make use of the reflector panels and materials, structures, and figure control being elaborated for the PSR. The surface accuracy of a 0.9-m PSR panel is shown to be 1.74-micron RMS, the goal of 100-micron RMS positioning accuracy has been achieved for a 4-m erectable structure. A voice-coil actuator for the figure control system architecture demonstrated 1-micron panel control accuracy in a 3-axis evaluation. The PSR technology is demonstrated to be of value for several NASA projects involving optical communications and interferometers as well as missions which make use of large-diameter segmented reflectors.
Lehman, David H.↗
Compensation for primary reflector wavefront error
In a telescope having primary and secondary reflectors, wherein the actual primary reflector surface deviates from an ideal primary reflector surface, such deviation is compensated for. At least one intermediate element forms an image of the primary surface onto the secondary surface, so each point on the secondary surface corresponds to a point on the primary surface. The secondary surface is formed with a deviation from an ideal secondary surface, with the piston distance of each point on the actual secondary surface equal to the piston distance of a corresponding point on the actual primary surface from the ideal primary surface. It is found that this results in electromagnetic (e.g., light) rays which strike a deviating area of the actual primary surface being brought to the same focus as if the actual primary surface did not have a deviation from an ideal primary surface.
Meinel, Aden B.↗
Attaching Precise Mirrors To Lightweight Supports
Mirrors formed on optical masters and glued in place. Technique forms precise mirror surfaces on lightweight, rigid, imprecise graphite-composite substrates. Resembles that used to make lightweight replica mirrors and gratings. Layer of parting material deposited on master optical surface of precise desired shape. Parting layer must be very thin to minimize degradation of replica. Enables fabrication of lightweight mirrors of high surface finish suitable for use at short wavelengths.
Meinel, Aden B.↗
Error-Compensated Telescope
Proposed reflecting telescope includes large, low-precision primary mirror stage and small, precise correcting mirror. Correcting mirror machined under computer control to compensate for error in primary mirror. Correcting mirror machined by diamond cutting tool. Computer analyzes interferometric measurements of primary mirror to determine shape of surface of correcting mirror needed to compensate for errors in wave front reflected from primary mirror and commands position and movement of cutting tool accordingly.
Meinel, Aden B.↗
Optical testing of off-axis parabolic segments without auxiliary optical elements
The traditional optical test for an off-axis segment of a parabolic mirror utilizes an autocollimation flat and requires considerable test-bay space. Several other test configurations that will minimize space requirements are described. One method involves a null corrector, and three others require no auxiliary test optics. Combinations of the methods described will be useful in providing full independent evaluation of the figure of the segment under test.
Meinel, Aden B.↗
Active wavefront control challenges of the NASA Large Deployable Reflector (LDR)
The 20-m Large Deployable Reflector will have a segmented primary mirror. Achieving diffraction-limited performance at 50 microns requires correction for the errors of tilt and piston of the primary mirror. This correction can be obtained in two ways, the use of an active primary or a correction at a demagnified pupil of the primary. A critical requirement is the means for measurement of the wavefront error and maintaining phasing during the observation of objects that may be too faint for determining the error. Absolute phasing can only be determined using a cooperative source. Maintenance of phasing can be done with an on-board source. A number of options are being explored as discussed below. The many issues concerning the assessment and control of an active segmented mirror will be addressed with an early construction of the Precision Segmented Reflector testbed.
Meinel, Aden B.↗
The Lunar Configurable Array Telescope (LCAT)
The desire for a much larger space telescope than HST by astronomers is clearly demonstrated by the attendance at this Workshop. The reality is that a much larger space telescope than the HST collides with cost scaling reality. Coupled with this reality is the fact that any multi-billion dollar science project must have broad-based support from the science community and solid political support at both Presidential and Congressional levels. The HST successor is certainly in the same multi-billion dollar class as the Super Collider of the physics community, a project that has finally achieved the broad support base necessary for funding to follow. Advocacy of a bigger HST on the general grounds that 'bigger is better' will not be sufficient. A new concept needs to be developed that clearly diverges from scaling up of a traditional HST-type space telescope. With these realities in mind we have a few comments regarding the nature of a possible space telescope that may depart from what the organizers of this Workshop had in mind. The national goal declared by the President is Space Station, the Moon and Mars, in that order. Space Station is a potential location where a large system could be assembled prior to being sent into a high orbit. It is not a desirable environment for a large space telescope. Mars is not relevant as an observatory site. The Moon is very relevant for reasons we will address. Our comments are based on the premise of a permanent Lunar Outpost. One of the main arguments for a lunar telescope is a degree of permanency, that is, as long as a Lunar Outpost is maintained. In contrast, the relatively short lifetime of an orbiting telescope is a disadvantage, especially as a cost penalty. Access to a telescope in a 100,000 km orbit for refurbishment and resupply is a major problem with no solution in the present NASA planning. A telescope in conjunction with a Lunar Outpost means the possibility for continual upgrading or modifying the telescope to meet changing science objectives. The two main technical disadvantages of the Moon are: 1) its gravity field; and 2) direct Sun and Earth light. The gravity term is manageable. It also appears to be feasible to shield the telescope from direct sun and Earth light and from scattering from nearby lunar terrain. Thermal disturbances to the telescope also appear to be manageable by proper shielding, enabling the telescope to become as cold as if it were at a lunar pole crater. If these conditions are met, the telescope could be at a logistically convenient location near the Lunar Outpost. We want to address a concept that is significantly different from those presented in the preliminary communications from Garth Illingworth in order to help fill in the matrix of possibilities. This option, moreover, is of special interest to JPL and could be an area where JPL can contribute in future studies.
Meinel, Aden B.↗
Laser agile illumination for object tracking and classification - Feasibility study
The 'agile illumination' concept for discrimination between ICBM warheads and decoys involves a two-aperture illumination with coherent light, diffraction of light by propagation, and a resulting interference pattern on the object surface. A scanning two-beam interference pattern illuminates one object at a time; depending on the shape, momentum, spinning, and tumbling characteristics of the interrogated object, different temporal signals will be obtained for different classes of objects.
Scholl, Marija S.↗
Making Optical Correctors by Diamond Turning
Large Optics Diamond Turning Machine (LODTM) at Lawrence Livermore National Laboratory used to make highly amorphic reflecting wavefront-corrector plates with rms difference between desired and measured reflector surfaces of only 0.075 wave. Measured errors correspond to one standard deviation of uncertainties in digitization and reduction of interferograms of surface. Appears accuracy of LODTM-generated surface exceeds current ability to measure it. Work demonstrates feasibility of single-point diamond turning for manufacture of generalized wavefront-control surfaces or other unusual surfaces desired by optical designers.
Meinel, Aden B.↗
Telescope structures - An evolutionary overview
A development history is presented for telescope structural support materials, design concepts, equatorial and altazimuthal orientational preferences, and mechanical control system structural realizations. In the course of 50 years after Galileo, the basic configurations of all reflecting telescopes was set for the subsequent 300 years: these were the Cassegrain, Gregorian, and Newtonian designs. The challenge of making a lightweight ribbed pyrex glass primary mirror for the 5-m Palomar telescope was met by von Karman's use of finite element analysis. Attention is given to the prospects for a 20-m deployable space-based reflecting telescope.
Meinel, Aden B.↗
Optical and infrared space optics challenges
A number of optical design and technology challenges are discussed with reference to specific space optics projects. The projects examined include the Large Deployable Reflector, multiple-mirror telescopes, the Hubble Space Telescope, and the Circumstellar Imaging Telescope. Other projects discussed include a voyage to a distance of 1000 astronomical units, the Shuttle Imaging Spectrometer Experiment, and directional optical systems. The ultimate challenge is the detection of and communication with any planets that may be discovered around nearby stars.
Meinel, Aden B.↗