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At least 145 records · Page 8

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NASA NTRS2012

Molecular Mechanisms of Circadian Regulation During Spaceflight

The physiology of both vertebrates and invertebrates follows internal rhythms coordinated in phase with the 24-hour daily light cycle. This circadian clock is governed by a central pacemaker, the suprachiasmatic nucleus (SCN) in the brain. However, peripheral circadian clocks or oscillators have been identified in most tissues. How the central and peripheral oscillators are synchronized is still being elucidated. Light is the main environmental cue that entrains the circadian clock. Under the absence of a light stimulus, the clock continues its oscillation in a free-running condition. In general, three functional compartments of the circadian clock are defined. The vertebrate retina contains endogenous clocks that control many aspects of retinal physiology, including retinal sensitivity to light, neurohormone synthesis (melatonin and dopamine), rod disk shedding, signalling pathways and gene expression. Neurons with putative local circadian rhythm generation are found among all the major neuron populations in the mammalian retina. In the mouse, clock genes and function are more localized to the inner retinal and ganglion cell layers. The photoreceptor, however, secrete melatonin which may still serve a an important circadian signal. The reception and transmission of the non-visual photic stimulus resides in a small subpopulation (1-3%) or retinal ganglion cells (RGC) that express the pigment melanopsin (Opn4) and are called intrisically photoreceptive RGC (ipRGC). Melanopsin peak absorption is at 420 nm and all the axons of the ipRGC reach the SCN. A common countermeasure for circadian re-entrainment utilizes blue-green light to entrain the circadian clock and mitigate the risk of fatigue and health and performance decrement due to circadian rhythm disruption. However, an effective countermeasure targeting the photoreceptor system requires that the basic circadian molecular machinery remains intact during spaceflight. We hypothesize that spaceflight may affect ipRGC and melanopsin expression, which may be a contributing cause of circadian disruption during spaceflight.

Zanello, S. B.↗

NASA NTRS2004

A Miniature Solid-State Spectrometer for Space Applications: Field Tests

A solid state infrared spectrometer has been developed under the Planetary Instrument Definition and Development Program PIDDP to implement a small rugged spectrometer principally for landed applications. The instrument uses the high index of refraction and waveguide properties of a silicon slab to achieve good spectral resolution and high throughput in a small instrument footprint (less than 25 cm). Light enters the silicon slab and is reflected off a grating (Ebert configuration), utilizing the silicon index of refraction to achieve high dispersion. An array of microthermopiles is used to measure the amplitude of the dispersed light. Input optics are typically utilized to focus light on the input aperture and a chopper is used to compensate system drift.

Smythe, W. D.↗

NASA NTRS2007

Recirculation of Laser Power in an Atomic Fountain

A new technique for laser-cooling atoms in a cesium atomic fountain frequency standard relies on recirculation of laser light through the atom-collection region of the fountain. The recirculation, accomplished by means of reflections from multiple fixed beam-splitter cubes, is such that each of two laser beams makes three passes. As described below, this recirculation scheme offers several advantages over prior designs, including simplification of the laser system, greater optical power throughput, fewer optical and electrical connections, and simplification of beam power balancing. A typical laser-cooled cesium fountain requires the use of six laser beams arranged as three orthogonal pairs of counter-propagating beams to decelerate the atoms and hold them in a three-dimensional optical trap in vacuum. Typically, these trapping/cooling beams are linearly polarized and are positioned and oriented so that (1) counter-propagating beams in each pair have opposite linear polarizations and (2) three of the six orthogonal beams have the sum of their propagation directions pointing up, while the other three have the sum of their propagation directions pointing down. In a typical prior design, two lasers are used - one to generate the three "up" beams, the other to generate the three "down" beams. For this purpose, the output of each laser is split three ways, then the resulting six beams are delivered to the vacuum system, independently of each other, via optical fibers. The present recirculating design also requires two lasers, but the beams are not split before delivery. Instead, only one "up" beam and one oppositely polarized "down" beam are delivered to the vacuum system, and each of these beams is sent through the collection region three times. The polarization of each beam on each pass through the collection region is set up to yield the same combination of polarization and propagation directions as described above. In comparison with the prior design, the present recirculating design utilizes the available laser light more efficiently, making it possible to trap more atoms at a given laser power or the same number of atoms at a lower laser power. The present design is also simpler in that it requires fewer optical fibers, fiber couplings, and collimators, and fewer photodiodes for monitoring beam powers. Additionally, the present design alleviates the difficulty of maintaining constant ratios among power levels of the beams within each "up" or "down" triplet.

Enzer, Daphna G.↗

NASA NTRS1991

Soybean stem growth under high-pressure sodium with supplemental blue lighting

To study high-pressure sodium (HPS) lamps used for plant lighting because of their high energy conversion efficiencies, 'McCall' soybean plants were grown for 28 days in growth chambers utilizing HPS lamps, with/without supplemental light from blue phosphor fluorescent lamps. Total photosynthetic photon flux levels, including blue fluorescent, were maintained near 300 or 500 micromol/sq m s. Results indicate that employment of HPS or other blue-deficient sources for lighting at low to moderate photosynthetic photon flux levels may cause abnormal stem elongation, but this can be prevented by the addition of a small amount of supplemental blue light.

Wheeler, R. M.↗

NASA NTRS1977

Photovoltaic, gravitationally-stabilized solid-state, satellite solar power station /GSS4PS/

The salient feature of a gravitationally-stabilized satellite solar power system (SSPS) for a photovoltaic system is that the large solar array is separated into smaller segments or subunits, joined together in a linear array oriented along the local vertical. Applicability of gravitational stabilization to the design of photovoltaic SSPS is demonstrated. Both actively controlled systems using multiple solar panels oriented to the sun and passively controlled systems requiring no sun orientation are considered and determined to be feasible. Expressions for gravity-gradient induced tension and restoring torques about the local vertical are assessed. Particular attention is directed to the applicability of solid-state approaches to the design of SSPS. It is shown that an all solid-state SSPS utilizing the LITOMIC (light-to-microwave conversion) concept is feasible but that a hybrid system employing a combination of both solid-state and cryogenic cooled low-voltage techniques to the design of the power management and distribution subsystem may also provide a solution.

Cantafio, L. J.↗

NASA NTRS1979

Remote sensing of phytoplankton density and diversity in Narragansett Bay using an airborne fluorosensor

An aircraft-borne remote system is presented that utilizes narrow-band light from multiple dye lasers to excite selected algae photopigments and then measures the resultant flourescence emitted from chlorophyll a at 685 nm. Tests were conducted with both pure and mixed cultures of marine algae from a series of field tests taken from piers and bridges of Narragansett Bay, and a prototype remote fluorosensor was flown over the Bay during the 1978 winter-spring diatom bloom. Remote fluorescence obtained at hover points over sea-truth stations showed correlations with in situ fluorescence, total chlorophyll a, and cell count. It was concluded that the ratio of remote fluorescence to direct chlorophyll a concentration was less variable than expected, and the distribution of total chlorophyll a between two major photoplankton color groups showed three distinct areas, within the Bay, of green and golden-brown species.

Farmer, F. H.↗

NASA NTRS1980

Solar cell angular position transducer

An angular position transducer utilizing photocells and a light source is disclosed. The device uses a fully rotatable baffle which is connected via an actuator shaft to the body whose rotational displacement is to be measured. The baffle blocks the light path between the light source and the photocells so that a constant semicircular beam of light reaches the photocells. The current produced by the photocells is fed through a resistor, a differential amplifier measures the voltage drop across the resistor which indicates the angular position of the actuator shaft and hence of the object.

Sandford, M. C.↗

NASA NTRS1984

Stimulus factors in motion perception and spatial orientation

The Malcolm horizon utilizes a large projected light stimulus Peripheral Vision Horizon Device (PVHD) as an attitude indicator in order to achieve a more compelling sense of roll than is obtained with smaller devices. The basic principle is that the larger stimulus is more similar to visibility of a real horizon during roll, and does not require fixation and attention to the degree that smaller displays do. Successful implementation of such a device requires adjustment of the parameters of the visual stimulus so that its effects on motion perception and spatial orientation are optimized. With this purpose in mind, the effects of relevant image variables on the perception of object motion, self motion and spatial orientation are reviewed.

Post, R. B.↗

NASA NTRS1986

Origins of the solar wind in the corona

The coronal origins of the solar wind are considered. Potential sources of low-speed wind which are consistent with current data, including streamers and the interfaces between them and other coronal regions, await mass flow measurements for confirmation. A Doppler-dimming technique utilizing a white-light coronagraph and UV coronal spectrometer is to be employed aboard the Space Shuttle SPARTAN program, and its usage on Ulysses may provide information on mass flows in streamers and their surroundings.

Withbroe, G. L.↗

NASA NTRS1987

A review of recent activities in the NASA CELSS program

A CELSS (Controlled Ecological Life Support System) is a device that utilizes photosynthetic organisms and light energy to regenerate waste materials into oxygen and food for a crew in space. The results of studies with the CELSS program suggest that a bioregenerative life support system is a useful and effective method of regenerating consumable materials for crew sustenance. The data suggests that the operation of a CELSS in space is practical if plants can be made to behave predictably in the space environment. Much of the work centers on the biological components of the CELSS system. Ways of achieving high efficiency and long term stability of all components of the system are examined. Included are explorations of the conversion of nonedible cellulose to edible materials, nitrogen fixation by biological and chemical methods, and methods of waste processing. A description is provided of the extent to which a bioregenerative life support system can meet the constraints of the space environment, and the degree is assessed to which system efficiency and stability can be increased during the next decade.

Macelroy, R. D.↗

NASA NTRS1987

A review of recent activities in the NASA CELSS program

A CELSS (Controlled Ecological Life Support System) is a device that utilizes photosynthetic organisms and light energy to regenerate waste materials into oxygen and food for a crew in space. The results of theoretical and practical studies conducted by investigators within the CELSS program suggest that a bioregenerative life support system can be a useful and effective method of regenerating consumable materials for crew sustenance. Experimental data suggests that the operation of a CELSS in space will be practical if plants can be made to behave predictably in the space environment. Much of the work currently conducted within the CELSS program centers on the biological components of the CELSS system. The work is particularly directed at ways of achieving high efficiency and long term stability of all components of the system. Included are explorations of the conversion of nonedible cellulose to edible materials, nitrogen fixation by biological and chemical methods, and methods of waste processing. It is the intent of the presentation to provide a description of the extent to which a bioregenerative life support system can meet the constraints of the space environment, and to assess the degree to which system efficiency and stability can be increased during the next decade.

Macelroy, R. D.↗

NASA NTRS1990

Noncontact measurement of high temperature using optical fiber sensors

The primary goal of this research program was the investigation and application of noncontact temperature measurement techniques using optical techniques and optical fiber methods. In particular, a pyrometer utilizing an infrared optical light pipe and a multiwavelength filtering approach was designed, revised, and tested. This work was motivated by the need to measure the temperatures of small metallic pellets (approximately 3 mm diameter) in free fall at the Microgravity Materials Processing Drop Tube at NASA Marshall Space Flight Center. In addition, research under this program investigated the adaptation of holography technology to optical fiber sensors, and also examined the use of rare-earth dopants in optical fibers for use in measuring temperature. The pyrometer development effort involved both theoretical analysis and experimental tests. For the analysis, a mathematical model based on radiative transfer principles was derived. Key parameter values representative of the drop tube system, such as particle size, tube diameter and length, and particle temperature, were used to determine an estimate of the radiant flux that will be incident on the face of an optical fiber or light pipe used to collect radiation from the incandescent falling particle. An extension of this work examined the advantage of inclining or tilting the collecting fiber to increase the time that the falling particle remains in the fiber field-of-view. Those results indicate that increases in total power collected of about 15 percent may be realized by tilting the fiber. In order to determine the suitability of alternative light pipes and optical fibers, and experimental set-up for measuring the transmittance and insertion loss of infrared fibers considered for use in the pyrometer was assembled. A zirconium fluoride optical fiber and several bundles of hollow core fiber of varying diameters were tested. A prototype two-color pyrometer was assembled and tested at Virginia Tech, and then tested on the Drop Tube at Marshall Space Flight Center. Radiation from 5 mm diameter niobium drops falling in the Drop Tube was successfully detected, and recorded for later analysis. Subsequent analysis indicated that the imaging of light output from the light pipe onto the detector active areas was not identical for both detectors.

Claus, R. O.↗

NASA NTRS1991

Fiber optic sensing system

A fiber optic interferometer utilizes a low coherence light emitting diode (LED) laser as a light source which is filtered and driven at two RF frequencies, high and low, that are specific to the initial length of the resonator chamber. A displacement of a reflecting mirror changes the length traveled by the nonreferencing signal. The low frequency light undergoes destructive interference which reduces the average intensity of the wave while the high frequency light undergoes constructive interference which increases the average intensity of the wave. The ratio of these two intensity measurements is proportional to the displacement incurred.

Adamovsky, Grigory↗

NASA NTRS1993

High surface area, low weight composite nickel fiber electrodes

The energy density and power density of light weight aerospace batteries utilizing the nickel oxide electrode are often limited by the microstructures of both the collector and the resulting active deposit in/on the collector. Heretofore, these two microstructures were intimately linked to one another by the materials used to prepare the collector grid as well as the methods and conditions used to deposit the active material. Significant weight and performance advantages were demonstrated by Britton and Reid at NASA-LeRC using FIBREX nickel mats of ca. 28-32 microns diameter. Work in our laboratory investigated the potential performance advantages offered by nickel fiber composite electrodes containing a mixture of fibers as small as 2 microns diameter (Available from Memtec America Corporation). These electrode collectors possess in excess of an order of magnitude more surface area per gram of collector than FIBREX nickel. The increase in surface area of the collector roughly translates into an order of magnitude thinner layer of active material. Performance data and advantages of these thin layer structures are presented. Attributes and limitations of their electrode microstructure to independently control void volume, pore structure of the Ni(OH)2 deposition, and resulting electrical properties are discussed.

Johnson, Bradley A.↗

NASA NTRS1992

Elastic modulus measurements of LDEF glasses and glass-ceramics using a speckle technique

Elastic moduli of five glass types and the glass-ceramic Zerodur, exposed to a near-earth orbit environment on the Long Duration Exposure Facility (LDEF), were compared to that of unexposed samples. A double exposure speckle photography technique utilizing 633 nm laser light was used in the production of the speckle pattern. Subsequent illumination of a double exposed negative using the same wavelength radiation produces Young's fringes from which the in-plane displacements are measured. Stresses imposed by compressive loading produced measurable strains in the glasses and glass-ceramic.

Wiedlocher, D. E.↗

NASA NTRS1994

An introduction to the Astro Edge solar array

The Astro Edge solar array is a new and innovative low concentrator power generating system which has been developed for applications requiring high specific power, high stiffness, low risk, light modular construction which utilizes conventional materials and technology, and standard photovoltaic solar cells and laydown processes. Mechanisms, restraint/release devices, wiring harnesses, substrates, and support structures are designed to be simple, functional, lightweight, and modular. A brief overview of the Astro Edge solar array is discussed.

Spence, B. R.↗

NASA NTRS1997

Micro-Optic Color Separation Technology for Efficient Projection Displays

Phase 1 of this project focused on development of an overall optical concept which incorporated a single liquid crystal spatial light modulator. The system achieved full color by utilizing an echelon grating, which diffracted the incident light into three orders with different color spectra, in combination with a microlens array, which spatially separated RGB bands and directed the light of the appropriate wavelength to the appropriate color dot. Preliminary echelon grating designs were provided by MIT/LL and reviewed by Rockwell. Additional Rockwell activities included the Identification of microlens designs, light sources (ILC), and projection optics to fulfill the overall design requirements. An Internal subcontract was established with Rockwell's Collins Avionics and Communications Division (CACD) which specified the liquid crystal SLM (Sharp Model No. LQ 46EO2) and built the projection display baseline projector. Full Color projected video images were produced and shown at the 1995 HDS meeting in Washington. Analysis of the luminance performance of the projector and detailed parameter trade studies helped define the dependence of overall display efficiency on lamp collimation, and indicated that a lamp with very small arc dimension is required for the optical concept to be viable.

Gunning, W. J.↗

NASA NTRS1996

A Fiber Optic Probe for Monitoring Protein Aggregation, Nucleation, and Crystallization

Protein crystals are experimentally grown in hanging drops in microgravity experiments on-board the Space Shuttle orbiter. The technique of dynamic light scattering (DLS) can be used to monitor crystal growth process in hanging droplets (approx. 30 (L)) in microgravity experiments, but elaborate instrumentation and optical alignment problems have made in-situ applications difficult. In this paper we demonstrate that such experiments are now feasible. We apply a newly developed fiber optic probe to various earth and space (micro- gravity) bound protein crystallization system configurations to test its capability. These include conventional batch (cuvette or capillary) systems, hanging drop method in a six-pack hanging drop vapor diffusion apparatus (HDVDA), a modified HDVDA for temperature- induced nucleation and aggregation studies, and a newly envisioned dynamically controlled vapor diffusion system (DCVDS) configuration. Our compact system exploits the principles of DLS and offers a fast (within a few seconds) means of quantitatively and non-invasively monitoring the various growth stages of protein crystallization. In addition to DLS capability, the probe can also be used for performing single-angle static light scattering measurements. It utilizes extremely low levels of laser power (approx. few (W)) without a need of having any optical alignment and vibration isolation. The compact probe is also equipped with a miniaturized microscope for visualization of macroscopic protein crystals. This new optical diagnostic system opens up enormous opportunity for exploring new ways to grow good quality crystals suitable for x-ray crystallographic analysis and may help develop a concrete scientific basis for understanding the process of crystallization.

Ansari, Rafat R.↗