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At least 1,297 records · Page 72

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NASA NTRS1993

Optical design of zero-power Hubble Space Telescope wave-front correctors for null testing

The optical design of the second-generation wide-field/planetary-camera instrument for the Hubble Space Telescope has been modified to compensate for the spherical aberration of the optical telescope assembly (OTA) by introduction of undercorrected spherical aberration into the wave front. This instrument can be tested in a simple manner to ensure that its aberration contribution has the proper sign and magnitude. We present designs for a near-zero power doublet lens that can be used to generate a spherically aberrated wave front that is similar to the OTA wave front. When this lens is used in combination with the instrument, a near-perfect or nulled wave front should be produced, resulting in a high-quality point image on axis. We also present lens designs for a similar test that can be performed on the OTA simulators now being built to verify the other second-generation instruments.

Hannan, Paul G.↗

NASA NTRS1993

Hubble Space Telescope COSTAR asphere verification with a modified computer-generated hologram interferometer

To correct for the spherical aberration in the Hubble Space Telescope primary mirror, five anamorphic aspheric mirrors representing correction for three scientific instruments have been fabricated as part of the development of the corrective-optics space telescope axial-replacement instrument (COSTAR). During the acceptance tests of these mirrors at the vendor, a quick and simple method for verifying the asphere surface figure was developed. The technique has been used on three of the aspheres relating to the three instrument prescriptions. Results indicate that the three aspheres are correct to the limited accuracy expected of this test.

Feinberg, L.↗

NASA NTRS1991

Space Infrared Telescope Facility science instruments overview

The Space Infrared Telescope Facility (SIRTF) will contain three cryogenically cooled infrared instruments: the Infrared Array Camera (IRAC), the Infrared Spectrograph (IRS), and the Multiband Infrared Photometer for SIRTF (MIPS). These instruments are sensitive to infrared radiation in the 1.8-1,200 micrometer range. This paper will discuss the three instruments' functional requirements and their accommodation in the SIRTF telescope system.

Bothwell, Mary↗

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 NTRS1992

In-flight performance of the Broad-Band X-Ray Telescope

The Broad-Band X-Ray Telescope (BBXRT) was designed to carry out moderate resolution spectrophotometry of cosmic X-ray sources in the 0.3-12 keV band from the Space Shuttle. It consists of a pair of coaligned conical foil telescopes, with cryogenically cooled Si(Li) spectrometers as focal instruments. It was flown as part of the Astro-1 mission in December, 1990. The in-flight performance of the instrument was essentially as predicted on the basis of ground calibration and modelling. We discuss the performance of the system, with emphasis on the conical mirror systems, and present some preliminary scientific results which illustrate the power of broad band, high sensitivity X-ray spectrophotometry.

Petre, R.↗

NASA NTRS1992

Solar observations with the Multi-Spectral Solar Telescope Array

The Multi-Spectral Solar Telescope Array (MSSTA) is a sounding rocket-borne solar observatory which was succesfully launched on May 13, 1991, from the White Sands Missile Range, NM. Ultrahigh resolution, full-disk solar X-ray, EUV, and FUV images were obtained with the MSSTA Herschelian, Cassegrain, and Ritchey-Chretien telescopes. We describe the payload and provide some preliminary scientific results from the flight.

Hoover, Richard B.↗

NASA NTRS1992

Photographic films for the Multi-Spectral Solar Telescope Array

The rocketborne Multi-Spectral Solar Telescope Array (MSSTA) uses an array of Ritchey-Chretien, Cassegrain, and Herschelian telescopes to produce ultrahigh-resolution full-disk images of the sun within the soft X-ray, EUV, and FUV ranges. Such imaging of the solar disk and corona out to several solar radii placed great demands on the MSSTA's data storage capabilities; in addition, its photographic films required very low outgassing rates. Results are presented from calibration tests conducted on the MSSTA's emulsions, based on measurements at NIST's synchrotron facility.

Hoover, Richard B.↗

NASA NTRS1992

The Soft X-ray Telescope for Solar-A - Design evolution and lessons learned

The Japanese Solar-A satellite mission's Soft X-ray Telescope uses grazing-incidence optics, a CCD detector, and a pair of filter wheels for wavelength selection. A coaxially-mounted visible-light lens furnished sunspot and magnetic plage images, together with aspect information which aids in aligning the soft X-ray images with those from the satellite's Hard X-ray Telescope. Instrument electronics are microprocessor-based, and imbedded in a tightly integrated distributed system. Control software is divided between the instrument microprocessor and the spacecraft control computer.

Bruner, Marilyn E.↗

NASA NTRS1992

Operations analysis for a large lunar telescope

Consideration is given to a study of the operations and assembly of a 16-m large lunar telescope (LLT), which deals with the operations and assembly of the telescope from LEO to the lunar surface for assembly. The study of LLT operations and assembly is broken down into three divisions to allow easier operations analysis: earth to orbit operations, LEO operations (transfer to lunar surface operations), and lunar surface operations. The following guidelines were set down to ensure a reasonable starting point for a large, lunar, untended installation: the existence of a lunar base, a space transportation system from LEO to the lunar surface, continuous manning of the lunar base during the assembly period, and availability/capability to perform lunar assembly with the lunar base crew. The launch/vehicle packaging options, lunar site selection and assembly options, and assembly crew assumptions are discussed.

Thyen, Christopher↗

NASA NTRS1992

Laboratory evaluation of footings for lunar telescopes

Presented here are the results of laboratory experiments with diffferent footing shapes for lunar telescopes. These experiments used a variety of soils including some to simulate regolith response. Based on what is known of regolith and regolith-structure interaction, a shallow-multiple-contact points footing foundation can be adequately designed to support lunar telescopes. Plane-strain load-displacement tests were conducted with different footings and different lunar simulants in a deep transparent plexiglass container. The model footings considered include the rectangular, hemispherical, and spudcan designs. Simulants used to reproduce the mechanical properties of the lunar regolith were fly ash, crushed basalt with and without glass, and a processed lunar simulant. Load-displacement curves were obtained for the different footings in Ottawa sand and in the crushed basalt with glass. The spudcan footing was found to be self-digging and yet stiff, thus providing excellent lateral stability in a large variety of soils.

Chua, Koon M.↗

NASA NTRS1991

Phase retrieval for the Hubble Space Telescope using iterative propagation algorithms

Phase retrieval algorithms, including the iterative transform algorithm and gradient search algorithms, were generalized to include the effects of propagation through a complicated optical system and to discount the effects of bad CCD pixels. For the gradient search algorithms, analytic gradients were derived that greatly speed up the computation over finite difference methods. For the Hubble Space Telescope (HST), the aperture function was reconstructed and the phase errors were retrieved. This information is useful to design correction optics for the telescope and for the deconvolution of blurred images from the HST.

Fienup, J. R.↗

NASA NTRS1991

Telescope optical systems program overview

Telescope Optical Systems is a new focused program of technology development that will shape and enable the new 'telescope' missions being studied and planned by NASA. The program structure contains six major elements: systems, optics, materials, structures, controls, and integration and test. Activities in each element will address key technology issues that support a wide range of user needs. Program goals, technology needs, and technology performance objectives are summarized in outline form.

Hirschbein, Murray S.↗

NASA NTRS1994

Reflective Baffles For Telescope

Nonimaged light causing unacceptable heating rejected instead of absorbed. Precise reflective baffles incorporated into reflective telescope to prevent undesired portion of incident light from entering sensitive optical and electronic instruments in focal region of main reflector. In original intended application, telescope and associated instruments placed in geostationary orbit to observe selected area of Earth; undesired light solar reflected from adjacent areas of Earth or coming directly from Sun when line of sight to Sun lies near field of view. Terrestrial optical instruments also improved by installation of reflective baffles.

Hovis, Warren A.↗

NASA NTRS1993

Model of optical scatter from microimpacts on the Hubble Telescope

The investigation and modelling of optical scatter from damaged or contaminated mirrors is of interest to those who wish to estimate the working life cycle of an optical system. A space born telescope faces a threat to its survival from naturally occurring micrometeoroids and man-made debris. High velocity, in the range of 4 to 14 km/s, impacts of small particles, in the range of 1 to 100 microns, will produce small craters on the impacted surface. These microcraters will typically have a size range of 3 to 300 microns for debris impacts and 6 to 600 microns for micrometeoroid impacts. If the microcraters accumulate on a telescope mirror, there will be an increase in optical scatter and a loss of image resolution. The micrometeoroid model of Cour-Palais and the orbital debris model of Kessler have been encoded in a computer program (SPENV) by the author. The output from this program has been matched with previous calculations and compared with impact data on the LDEF satellite. Subsequent work has been done to marry this computer program with an algorithm to compute optical scatter. The optical scatter algorithm employs Mie theory of scatter from small particles.

Crowell, L. B.↗

NASA NTRS1993

Space Shuttle Mission STS-61: Hubble Space Telescope servicing mission-01

This press kit for the December 1993 flight of Endeavour on Space Shuttle Mission STS-61 includes a general release, cargo bay payloads and activities, in-cabin payloads, and STS-61 crew biographies. This flight will see the first in a series of planned visits to the orbiting Hubble Space Telescope (HST). The first HST servicing mission has three primary objectives: restoring the planned scientific capabilities, restoring reliability of HST systems and validating the HST on-orbit servicing concept. These objectives will be accomplished in a variety of tasks performed by the astronauts in Endeavour's cargo bay. The primary servicing task list is topped by the replacement of the spacecraft's solar arrays. The spherical aberration of the primary mirror will be compensated by the installation of the Wide Field/Planetary Camera-II and the Corrective Optics Space Telescope Axial Replacement. New gyroscopes will also be installed along with fuse plugs and electronic units.

Source record↗

NASA NTRS1993

The polarization sensitivity of the liquid xenon imaging telescope

The properties and the expected performance of a liquid xenon (LXe) gamma ray imaging telescope, optimized for the MeV energy region, are presented. The unique potential of this telescope as a Compton polarimeter is particularly emphasized. Based on Monte Carlo simulations we show that the modulation factor is as high as 40 percent at 1 MeV with a detection efficiency close to 20 percent. These figures of merit combined with the excellent background suppression capability of the three dimensional position sensitive LXe detector yield sensitivity at the three sigma level to polarization fractions as small as a few percent for strong sources, even in a balloon flight.

Aprile, Elena↗

NASA NTRS1992

Deconvolution of Hubble Space Telescope images using simulated point spread functions

Presented is a study of the use of simulated point spread functions (PSF's) to deconvolve Hubble Space Telescope images. We concentrate on images from the Wide Field and Planetary Camera (WFPC) and examine the affect of position dependence of the PSF and the telescope focus position on deconvolutions. Comparisons will be made to what will be expected from WFPC 2, which will include corrective optics. Since PSF's can be simulated for any specific observation, with the added advantage of being noise free and the ability to subsample them, they may be more suitable for deconvolution than observed ones in some cases. And since finding a suitable observed PSF may be difficult, simulated ones may be easier to use.

Krist, J. E.↗

NASA NTRS1994

Lunar Ultraviolet Telescope Experiment (LUTE), phase A

The Lunar Ultraviolet Telescope Experiment (LUTE) is a 1-meter telescope for imaging from the lunar surface the ultraviolet spectrum between 1,000 and 3,500 angstroms. There have been several endorsements of the scientific value of a LUTE. In addition to the scientific value of LUTE, its educational value and the information it can provide on the design of operating hardware for long-term exposure in the lunar environment are important considerations. This report provides the results of the LUTE phase A activity begun at the George C. Marshall Space Flight Center in early 1992. It describes the objective of LUTE (science, engineering, and education), a feasible reference design concept that has evolved, and the subsystem trades that were accomplished during the phase A.

Mcbrayer, Robert O.↗