Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “optical alignment”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

An approach to optical structures control

The stabilization of a large, spaceborne Cassegrain telescope is examined. Modal gain factors and known characteristics of disturbances are used to determine which structural model affect line of sight (LOS) the most and are candidates for active control. THe approach is to: (1) actively control and maintain alignment of optical components; (2) place structural control actuators for optimum impact on the selected modes for active vibration control; and (3) feed back the best available estimate of LOS error for direct LOS control. Local analog loops are used for lower bandwidth control and multivariable digital control for lower bandwidth control. The control law is synthesized in the frequency domain using the characteristic gain approach. Robustness is measured by employing conicity, which is an outgrowth of the positivity approach to robust feedback system design. The feasibility of the design approach will be demonstrated by conducting a lab experiment on a structure similar to a scaled version of the telescope.

Iwens, R. P.↗
NASA NTRS2005

Vibrating Optical Fibers to Make Laser Speckle Disappear

In optical systems in which laser illumination is delivered via multimode optical fibers, laser speckle can be rendered incoherent by a simple but highly effective technique. The need to eliminate speckle arises because speckle can make it difficult to observe edges and other sharp features, thereby making it difficult to perform precision alignment of optical components. The basic ideas of the technique is to vibrate the optical fiber(s) to cause shifting of electromagnetic modes within the fiber(s) and consequent shifting of the speckle pattern in the light emerging from the fiber(s). If the frequency of vibration is high enough, a human eye cannot follow the shifting speckle pattern, so that instead of speckle, a human observer sees a smoothed pattern of light corresponding to a mixture of many electromagnetic modes. If necessary, the optical fiber(s) could be vibrated manually. However, in a typical laboratory situation, it would be more practical to attach a vibrating mechanism to the fiber(s) for routine use as part of the fiber-optic illuminator. In experiments, a commercially available small, gentle, quiet, variable- speed vibratory device was used in this way, with the result that the appearance of speckle was eliminated, as expected. Figures 1 and 2 illustrate the difference.

McGill, Matthew↗
NASA NTRS1995

Development of microchannel plate x-ray optics

The goal of this research program was to develop a novel technique for focusing x-rays based on the optical system of a lobster's eye. A lobster eye employs many closely packed reflecting surfaces arranged within a spherical or cylindrical shell. These optics have two unique properties: they have unlimited fields of view and can be manufactured via replication of identical structures. Because the angular resolution is given by the ratio of the size of the individual optical elements to the focal length, optical elements with size on the order of one hundred microns are required to achieve good angular resolution with a compact telescope. We employed anisotropic etching of single crystal silicon wafers for the fabrication of micron-scale optical elements. This technique, commonly referred to as silicon micromachining, is based on silicon fabrication techniques developed by the microelectronics industry. We have succeeded in producing silicon lenses with a geometry suitable for a 1-d focusing x-ray optics. These lenses have an aspect ratio (40:1) suitable for x-ray reflection and have very good optical surface alignment. We have developed a number of process refinements which improved the quality of the lens geometry and the repeatability of the etch process. In addition to the silicon fabrication, an x-ray beam line was constructed at Columbia for testing the optics. Most recently, we have done several experiments to find the fundamental limits that the anisotropic etch process placed on the etched surface roughness.

Kaaret, Philip↗
NASA NTRS1990

Non-steller light from high-redshift radiogalaxies

With the aid of a new IRCAM image of 3C356, researchers question the common assumption that radiosource-stimulated starbursts are responsible for the extended optical emission aligned with radio structures in high-redshift radiogalaxies. They propose an alternative model in which the radiation from a hidden luminous quasar is beamed along the radio axis and illuminates dense clumps of cool gas to produce both extended narrow emission line regions and, by Thomson scattering, extended optical continua. Simple observational tests of this model are possible and necessary if we are to continue to accept that the color, magnitude and shape evolution of radiogalaxies are controlled by the active evolution of stellar populations.

Rawlings, Steve↗
NASA NTRS2015

Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES) for WFIRST/AFTA

Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES) is a prototype lenslet array based integral field spectrometer (IFS) designed for high contrast imaging of extrasolar planets. PISCES will be used to advance the technology readiness of the high contrast IFS baselined on the Wide-Field InfraRed Survey TelescopeAstrophysics Focused Telescope Assets (WFIRSTAFTA) coronagraph instrument. PISCES will be integrated into the high contrast imaging testbed (HCIT) at the Jet Propulsion Laboratory and will work with both the Hybrid Lyot Coronagraph (HLC) and the Shaped Pupil Coronagraph (SPC). We will present the PISCES optical design, including the similarities and differences of lenslet based IFSs to normal spectrometers, the trade-off between a refractive design and reflective design, as well as the compatibility to upgrade from the current 1k x 1k detector array to 4k x 4k detector array. The optical analysis, alignment plan, and mechanical design of the instrument will be discussed.

Integral Field Spectrometer↗
NASA NTRS2017

Design and characterization of a low cost CubeSat multi-band optical receiver to map water ice on the lunar surface for the Lunar Flashlight mission

Lunar Flashlight is an innovative NASA CubeSat mission dedicated to mapping water ice in the permanently shadowed regions of the Moon, which may act as cold traps for volatiles. To this end, a multi-band reflectometer will be sent to orbit the Moon. This instrument consists of an optical receiver aligned with four lasers, each of which emits sequentially at a different wavelength in the near-infrared between 1 μm and 2 μm. The receiver measures the laser light reflected from the lunar surface; continuum/absorption band ratios are then analyzed to quantify water ice in the illuminated spot. Here, we present the current state of the optical receiver design. To optimize the optical signal-to-noise ratio, we have designed the receiver so as to maximize the laser signal collected, while minimizing the stray light reaching the detector from solar-illuminated areas of the lunar surface outside the field-of-view, taking into account the complex lunar topography. Characterization plans are also discussed. This highly mass- and volume-constrained mission will demonstrate several firsts, including being one of the first CubeSats performing science measurements beyond low Earth orbit.

Sellar, Glenn R.↗
NASA NTRS2016

Laboratory Testing and Performance Verification of the CHARIS Integral Field Spectrograph

The Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) is an integral field spectrograph (IFS) that has been built for the Subaru telescope. CHARIS has two imaging modes; the high-resolution mode is R82, R69, and R82 in J, H, and K bands respectively while the low-resolution discovery mode uses a second low-resolution prism with R19 spanning 1.15-2.37 microns (J+H+K bands). The discovery mode is meant to augment the low inner working angle of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) adaptive optics system, which feeds CHARIS a coronagraphic image. The goal is to detect and characterize brown dwarfs and hot Jovian planets down to contrasts five orders of magnitude dimmer than their parent star at an inner working angle as low as 80 milliarcseconds. CHARIS constrains spectral crosstalk through several key aspects of the optical design. Additionally, the repeatability of alignment of certain optical components is critical to the calibrations required for the data pipeline. Specifically the relative alignment of the lens let array, prism, and detector must be highly stable and repeatable between imaging modes. We report on the measured repeatability and stability of these mechanisms, measurements of spectral crosstalk in the instrument, and the propagation of these errors through the data pipeline. Another key design feature of CHARIS is the prism, which pairs Barium Fluoride with Ohara L-BBH2 high index glass. The dispersion of the prism is significantly more uniform than other glass choices, and the CHARIS prisms represent the first NIR astronomical instrument that uses L-BBH2as the high index material. This material choice was key to the utility of the discovery mode, so significant efforts were put into cryogenic characterization of the material. The final performance of the prism assemblies in their operating environment is described in detail. The spectrograph is going through final alignment, cryogenic cycling, and is being delivered to the Subaru telescope in April 2016. This paper is a report on the laboratory performance of the spectrograph, and its current status in the commissioning process so that observers will better understand the instrument capabilities. We will also discuss the lessons learned during the testing process and their impact on future high-contrast imaging spectrographs for wavefront control.

Coronagraphic High Angular Resolution Imaging Spec↗
NASA NTRS2000

Horizon: A Proposal for Large Aperture, Active Optics in Geosynchronous Orbit

In 1999, NASA's New Millennium Program called for proposals to validate new technology in high-earth orbit for the Earth Observing-3 (NMP EO3) mission to fly in 2003. In response, we proposed to test a large aperture, active optics telescope in geosynchronous orbit. This would flight-qualify new technologies for both Earth and Space science: 1) a future instrument with LANDSAT image resolution and radiometric quality watching continuously from geosynchronous station, and 2) the Next Generation Space Telescope (NGST) for deep space imaging. Six enabling technologies were to be flight-qualified: 1) a 3-meter, lightweight segmented primary mirror, 2) mirror actuators and mechanisms, 3) a deformable mirror, 4) coarse phasing techniques, 5) phase retrieval for wavefront control during stellar viewing, and 6) phase diversity for wavefront control during Earth viewing. Three enhancing technologies were to be flight- validated: 1) mirror deployment and latching mechanisms, 2) an advanced microcontroller, and 3) GPS at GEO. In particular, two wavefront sensing algorithms, phase retrieval by JPL and phase diversity by ERIM International, were to sense optical system alignment and focus errors, and to correct them using high-precision mirror mechanisms. Active corrections based on Earth scenes are challenging because phase diversity images must be collected from extended, dynamically changing scenes. In addition, an Earth-facing telescope in GEO orbit is subject to a powerful diurnal thermal and radiometric cycle not experienced by deep-space astronomy. The Horizon proposal was a bare-bones design for a lightweight large-aperture, active optical system that is a practical blend of science requirements, emerging technologies, budget constraints, launch vehicle considerations, orbital mechanics, optical hardware, phase-determination algorithms, communication strategy, computational burdens, and first-rate cooperation among earth and space scientists, engineers and managers. This manuscript presents excerpts from the Horizon proposal's sections that describe the Earth science requirements, the structural -thermal-optical design, the wavefront sensing and control, and the on-orbit validation.

Chesters, Dennis↗
NASA NTRSDate not supplied

The Roman Space Telescope Optical System: Status, Test, and Verification

The Nancy Grace Roman Space Telescope (“Roman”) was prioritized by the 2010 Decadal Survey in Astronomy & Astrophysics and is NASA’s next flagship observatory. Launching no earlier than 2026, Roman will explore the nature of dark energy, as well as expand the census of exoplanets in our galaxy via microlensing. Roman will also demonstrate key technology needed to image and spectrally characterize extra-solar planets. Roman’s large field of view, agile survey capabilities, and excellent stability enable these scientific objectives, yet present unique challenges for the design, test, and verification of its optical system. The Roman optical system comprises an optical telescope assembly (OTA) and two instruments: the primary science wide-field instrument (WFI) and a technology demonstration coronagraph instrument (CGI), and the instrument carrier (IC), which meters the OTA to each instrument. This paper presents a status of the optical system hardware as it begins integration and test (I&T), as well as describes key optical test, alignment, and verification activities as part of the I&T program.

space telescope↗
NASA NTRS1992

Wavefront sensing, control, and pointing

A majority of future NASA astrophysics missions from orbiting interferometers to 16-m telescopes on the Moon have, as a common requirement, the need to bring light from a large entrance aperture to the focal plane in a way that preserves the spatial coherence properties of the starlight. Only by preserving the phase of the incoming wavefront, can many scientific observations be made, observations that range from measuring the red shift of quasi-stellar objects (QSO's) to detecting the IR emission of a planet in orbit around another star. New technologies for wavefront sensing, control, and pointing hold the key to advancing our observatories of the future from those already launched or currently under development. As the size of the optical system increases, either to increase the sensitivity or angular resolution of the instrument, traditional technologies for maintaining optical wavefront accuracy become prohibitively expensive or completely impractical. For space-based instruments, the low mass requirement and the large temperature excursions further challenge existing technologies. The Hubble Space Telescope (HST) is probably the last large space telescope to rely on passive means to keep its primary optics stable and the optical system aligned. One needs only look to the significant developments in wavefront sensing, control, and pointing that have occurred over the past several years to appreciate the potential of this technology for transforming the capability of future space observatories. Future developments in space-borne telescopes will be based in part on developments in ground-based systems. Telescopes with rigid primary mirrors much larger than 5 m in diameter are impractical because of gravity loading. New technologies are now being introduced, such as active optics, that address the scale problem and that allow very large telescopes to be built. One approach is a segmented design such as that being pioneered by the W.M. Keck telescope now under construction at the Mauna Kea Observatory. It consists of 36 hexagonal mirror segments, supported on a framework structure, which are positioned by actuators located between the structure and the mirrors. The figure of the telescope is initialized by making observations of a bright star using a Shack Hartmann sensor integrated with a white light interferometer. Then, using sensed data from the mirror edges to control these actuators, the figure of the mosaic of 36 segments is maintained as if it were a rigid primary mirror. Another active optics approach is the use of a thin meniscus mirror with actuators. This technique was demonstrated on the European Southern Observatory's New Technology Telescope (NTT) and is planned for use in the Very Large Telescope (consists of four 8-m apertures), which is now entering the design phase.

Pitts, Thomas↗
NASA NTRS2018

Optical and Mechanical Designs of the Multi-band SWIR Receiver for the Lunar Flashlight CubeSat Mission

Mapping and quantifying lunar water ice addresses one of NASA’s Strategic Knowledge Gaps to understand the lunar resource potential for future human exploration of the Moon. Lunar Flashlight is an innovative NASA CubeSat mission dedicated to mapping water ice in the permanently-shadowed and occasionally-sunlit regions in the vicinity of the lunar South Pole. Lunar Flashlight will acquire these measurements from lunar orbit using a multi-band laser reflectometer composed of an optical receiver aligned with four lasers emitting different wavelengths in the shortwave infrared spectral region between 1 µm and 2 µm. The receiver measures the laser radiance reflected from the lunar surface in each spectral band and continuum/absorption reflectance band ratios are then analyzed to quantify water ice concentration in the illuminated spot. The receiver utilizes a 70×70-mm, aluminum, off-axis paraboloidal mirror with a focal length of 70 mm, which collects the incoming light onto a single, 2 mm diameter InGaAs detector with a cutoff wavelength of 2.4 µm. We present the optical and mechanical designs of the receiver, including its optimization for rejection of solar stray-light from outside its intended field of view. This highly mass- and volume-constrained instrument payload will demonstrate several firsts, including being one of the first instruments onboard a CubeSat performing science measurements beyond low Earth orbit and the first planetary mission to use multi-band active reflectometry from orbit.

Sellar, R. Glenn↗
NASA NTRS2011

Alignment and Characterization of High Uniformity Imaging Spectrometers

Imaging spectrometers require precise adjustments, in some cases at the sub-micrometer level, in order to achieve auniform response over both the spectral and spatial dimensions. We describe a set of measurement techniques and theircorresponding alignment adjustments to achieve the 95% or higher uniformity specifications required for Earthobservingimaging spectrometers. The methods are illustrated with measurements from the Next Generation Imaging Spectrometer system that has been built at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Offner spectrometer↗
NASA NTRS1967

Star/horizon simulator used to test space guidance system

Star/horizon simulator is used for alignment and optical plus photoelectric tests of the sextant for the Apollo guidance and navigation system optical unit assembly. The unit is basically a refractive collimator with a two inch objective lens system and a twenty-four inch focal length.

Schmidt, W. C.↗
NASA NTRS1972

Solar experiment alignment system

Sensor system determines absolute alignment of optical axis of experiment package relative to solar vector and provides control information to permit pointing experiment anywhere on solar disc to absolute accuracy of the order of two arc seconds in center and five arc seconds on limb.

Fain, D. L.↗
NASA NTRS1975

Experiment definition phase shuttle laboratory: LDRL-10.6 experiment

Progress is reported in the development of the space shuttle laboratory laser data relay link. The system transmittance of various surfaces was considered in order to examine the coating tradeoffs for the beryllium mirrors. The results of six coating combinations considered are summarized. It is recommended that silver coatings be used throughout the system. Design of the pre-expander and a preliminary alignment procedure implemented to align all optical elements to the reference mechanical axis (the rotational axis of the outer gimbal bearing located between the two Gregorian telescopes) are included. The local oscillator subsystem, consisting of the laser, Stark cell, Stark cell electronics, power supply, starting circuit, and conditioning optics were completed and installed in the optimechanical subsystem and operation against a 10.6 micrometer source was attempted. Preliminary measurements of the HgCdTe mixer showed that this critical element was inoperative and in subsequent tests the receiver front end electronics had also failed. Possible reasons for these failures and corrective action and steps to prevent future recurrence are discussed.

Source record↗
NASA NTRS1975

Pulsed electromagnetic gas acceleration

Terminal voltage measurements with various cathodes and anodes in a high power, quasi-steady magnetoplasmadynamic (MPD) are discussed. The magnitude of the current at the onset of voltage fluctuations is shown to be an increasing function of cathode area and a weaker decreasing function of anode area. Tests with a fluted cathode indicated that the fluctuations originate in the plasma adjacent to the cathode rather than at the cathode surface. Measurements of radiative output from an optical cavity aligned to examine the current-carrying portion of a two-dimensional, 56 kA magnetoplasmadynamic discharge reveal no lasing in that region, consistent with calculations of electron excitation and resonance radiation trapping. A voltage-swept double probe technique allows single-shot determination of electron temperature and electron number density in the recombining MPD exhaust flow. Current distributions within the cavity of MPD hollow cathodes for various static prefills with no injected mass flow are examined.

Jahn, R. G.↗
NASA NTRS1977

Recombination lasing in a magnetoplasmadynamic arcjet

The plasmadynamic recombination laser concept is verified experimentally in a high power quasi-steady MPD arcjet operating at 4 kA and 12 g/sec of argon. Measurements of the spatial variation of electron temperature, electron density, and population densities in the arc exhaust flow confirm that inverted populations of the 4p to 4s Ar II transitions are established by collisional-radiative recombination of the Ar III ion. Using an optical cavity aligned transversely to the flow, recombination lasing of four such transitions, 5145, 4880, 4764 and 4727 A, is observed spectro-photographically and photoelectrically over the entire 1-msec discharge.

Campbell, E. M.↗
NASA NTRS1977

Recombination lasing in a magnetoplasmadynamic arcjet

The plasmadynamic recombination laser concept is verified experimentally in a high-power quasisteady MPD arcjet operating at 4 kA and 12 g/sec of argon. Measurements of the spatial variation of electron temperature, electron density, and population densities in the arc exhaust flow confirm that inverted populations of the 4p to 4s ArII transitions are established by collisional-radiative recombination of the ArIII ion. Using an optical cavity aligned transversely to the flow, recombination lasing of four such transitions, 5145, 4880, 4764, and 4727 A, is observed spectrophotographically and photoelectrically over the entire 1-msec discharge.

Campbell, E. M.↗