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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

A flat array large telescope concept for use on the moon, earth, and in space

An astronomical optical telescope concept is described which can provide very large collecting areas, of order 1000 sq m. This is an order of magnitude larger than the new generation of telescopes now being designed and built. Multiple gimballed flat mirrors direct the beams from a celestial source into a single telescope of the same aperture as each flat mirror. Multiple images of the same source are formed at the telescope focal plane. A beam combiner collects these images and superimposes them into a single image, onto a detector or spectrograph aperture. This telescope could be used on the earth, the moon, or in space.

Woodgate, Bruce E.↗
NASA NTRS2016

Aperture, A Large Telescope Using Magnetostriction For Post Deployment Corrections: Final Technical Report of NASA Innovative Advanced Concepts (NIAC) Phase I

In summary, astronomical as well as Earth observing applications of the future are counting on larger aperture telescopes than are currently available. Several groups have been working on the topic of enabling large (about 16-m diameter) UV-Vis telescopes for many years. The unique feature of our concept is that magnetic films are used rather than electrostatic films or piezo-electrostatic pads. Our magnetic film concept allows for contiguous correction along the surface, does not require a hard wire connection, and does not require continuous external application of the field. There are many unknowns related to the initial accuracy of the deployed figure prior to the magnetic write head corrections. The length scale over which the corrections need to be applied is also of concern. For, although approximately mm length scale corrections can be made with the MSM plus write head technology, the number of 1 mm² patches in a 16 m diameter mirror is too large to contemplate applying individual corrections to each individual patch. However, deployment strategies and the materials available continue to evolve, in particular shape memory composites (SMCs) [34] or alloys (SMAs) [41], such that at this time we see no show-stoppers for this concept. Furthermore, the ability to tune deformations down to much (factors of 10-100) smaller (m) scale opens the futuristic possibility of improving the figure well beyond Strehl values of 90%.

APERTURE↗
NASA NTRS1972

Research study to determine critical optical/mechanical properties of materials considered for selection as substrates for the primary mirror on a large telescope

An investigation was conducted to evaluate the stability of a specific low expansion glass-ceramic material relative to its use as a large, lightweight mirror substrate for diffraction-limited spaceborne optical applications. These evaluations were made on a segment (0.44 meter diameter by 0.31 meter thick) of a 2 to 3 meter diameter mirror blank. The dimensional stability of this mirror was measured interferometrically before and after lightweighting, as a function of rough machining, etching, thermal environment, and support configuration. A special computer analysis program was used to plot the coefficients corresponding to aberrations with sixfold symmetry (caused by the mirror's self-weight deflection on a three point support). The objective was to enhance the test sensitivity. Results indicate that any such effects due to self-weight deflection are of the order of 0.015 lambda rms. The rms and peak-to-peak figure changes associated with each processing operation are summarized.

Slomba, A. F.↗
NASA NTRS2013

A Combined Very Large Telescope and Gemini Study of the Atmosphere of the Directly Imaged Planet, Beta Pictoris b

We analyze new/archival VLT/NaCo and Gemini/NICI high-contrast imaging of the young, self-luminous planet Beta Pictoris b in seven near-to-mid IR photometric filters, using advanced image processing methods to achieve high signal-to-noise, high precision measurements. While Beta Pic b's near-IR colors mimic those of a standard, cloudy early-to-mid L dwarf, it is overluminous in the mid-infrared compared to the field L/T dwarf sequence. Few substellar/planet-mass objects-i.e., κ And b and 1RXJ 1609B-match Beta Pic b's JHKsL photometry and its 3.1 micron and 5 micron photometry are particularly difficult to reproduce. Atmosphere models adopting cloud prescriptions and large (approx. 60 micron)dust grains fail to reproduce the Beta Pic b spectrum. However, models incorporating thick clouds similar to those found forHR8799 bcde, but also with small (a fewmicrons) modal particle sizes, yield fits consistent with the data within the uncertainties. Assuming solar abundance models, thick clouds, and small dust particles (a = 4 micron), we derive atmosphere parameters of log(g) = 3.8 +/- 0.2 and Teff = 1575-1650 K, an inferred mass of 7+4 −3 MJ, and a luminosity of log(L/L) approx. −3.80 +/- 0.02. The best-estimated planet radius, is approx. equal to 1.65 +/- 0.06 RJ, is near the upper end of allowable planet radii for hot-start models given the host star's age and likely reflects challenges constructing accurate atmospheric models. Alternatively, these radii are comfortably consistent with hot-start model predictions if Beta Pic b is younger than is approx. equal to 7 Myr, consistent with a late formation well after its host star's birth approx. 12+8 −4 Myr ago.

overluminous↗
NASA NTRS1982

Active wavefront correction in large telescopes

Astronomical progress with the MMT telescope, which attains high-resolution imaging by partial compensation for atmospheric distortion, is discussed. The small tertiary and beam combiner mirrors at the MMT bring six images to a common focus, where there is a TV system for acquisition and guiding. Individual image positions can be controlled by stepper motors driving actuators on the secondaries, each step moving an image 0.05 arc seconds in the focal plane. The instrument's correction for image jiggle due to atmospheric turbulence and drift of the relative positions of the images due to gravitational and thermal effects on the structure are described. A scheme for correcting residual structural errors is discussed. It appears that the telescope can work to about the 17th visual magnitude. For faint sky limited objects comparable performance would require a perfectly rigid single mirror of the same aperture to have 50 percent more collecting area and cost at least 1.5 times more.

Angel, J. R. P.↗
NASA NTRS1984

Thermal expansion uniformity of materials for large telescope mirrors

Uniformity of thermal expansion has been measured for fused quartz and borosilicate glass. The variation of expansion coefficient for three melts of TO8E was 5 x 10 to the -9th/K over a temperature range of 300 to 100 K and was found to vary linearly with position in the melt. This spatial gradient averaged 3.5 x 10 to the -11th/K-cm. The room-temperature thermal expansivity variation of Duran (Tempax) glass was about 27 x 10 to the -9th/K, while that of E6 glass was about 52 x 10 to the -9th/K.

Jacobs, S. F.↗
NASA NTRS1988

Study Of Large Telescopes

Document considers selection of suitable telescope for advanced space laboratory. Analyzes and compares two- and four-mirror telescopes, both practical and structurally similar. Emphasizes analysis of four-mirror telescope systems, since design and performance characteristics of two-mirror telescopes well known. Three-mirror systems not considered.

Korsch, Dietrich↗
NASA NTRS2001

High Resolution Near-IR Spectroscopy of Protostars With Large Telescopes

It is now possible to measure absorption spectra of Class I protostars using D greater than or = 8m telescopes equipped with sensitive cryogenic IR spectrographs. Our latest high-resolution (R approx. 20,000) Keck data reveal that Class I protostars are indeed low-mass stars with dwarf-like features. However, they differ from T Tauri stars in that Class I protostars have much higher IR veilings (tau(sub k) greater than or = 1 - 3+) and they are rotating quickly, v sin i greater than 20 km/s. Interestingly, the vast majority of protostellar absorption spectra show stellar - not disk - absorption features. A preliminary H-R diagram suggests that protostellar photospheres may have different physical structures than T Tauri stars, perhaps due to their higher accretion rates.

Greene, Tom↗
NASA NTRS1994

A Large-Telescope Natural Guide Star AO System

None given. From overview and conclusion:Keck Telescope case study. Objectives-low cost, good sky coverage. Approach--natural guide star at 0.8um, correcting at 2.2um.Concl- Good performance is possible for Keck with natural guide star AO system (SR>0.2 to mag 17+).AO-optimized CCD should b every effective. Optimizing td is very effective.Spatial Coadding is not effective except perhaps at extreme low light levels.

Keck telescope telescope guideance star AO system↗
NASA NTRS2010

Large Telescope Segmented Primary Mirror Alignment

A document discusses a broadband (white light) point source, located at the telescope Cassegrain focus, which generates a cone of light limited by the hole in the secondary mirror (SM). It propagates to the aspheric null-mirror, which is optimized to make all the reflected rays to be normal to the primary mirror (PM) upon reflection. PM retro-reflects the rays back through the system for wavefront analysis. The point source and the wavefront analysis subsystems are all located behind the PM. The PM phasing is absolute (white light) and does not involve the SM. A relatively small, aspheric null-mirror located near the PM center of curvature has been designed to deliver the high level of optical wavefront correction. The phasing of the segments is absolute due to the use of a broadband source. The segmented PM is optically aligned independently and separately from the SM alignment. The separation of the PM segments alignment from the PM to the SM, and other telescope optics alignments, may be a significant advantage, eliminating the errors coupling. The point source of this concept is fully cooperative, unlike a star or laser-generated guide-star, providing the necessary brightness for the optimal S/N ratio, the spectral content, and the stable on-axis position. This concept can be implemented in the lab for the PM initial alignment, or made to be a permanent feature of the space-based or groundbased telescope.

Rud, Mayer↗