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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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

On the reflectivity of complex mesh surfaces

Poorer than expected surface reflectivity was observed in an early Tracking and Data Relay Satellite System antenna utilizing a tricot mesh weave. This poor reflectivity was determined to be caused by inadequate electrical contact at wire crossover points. A proper mathematical and numerical approach to assess the impact of wire junctions on reflectivity performance is developed. A mathematical method is presented for computing the surface reflectivity of complex mesh configurations like those on unfurlable-type spacecraft antennas. The method is based on the Floquet mode expansion to establish an integral equation for mesh wire currents. The equation is solved using the method of moments with triangular basis functions. It is observed that it is necessary to give special attention to the junction treatment among different branches of the mesh configurations. A vector junction current approach that resulted in satisfactory solutions for the current is described. The results of numerical simulations are compared against measured data and excellent agreement is observed.

Imbriale, William A.↗
NASA NTRS1990

A multi-aperture spectrometer design for the Atmospheric Infrared Sounder (AIRS)

The baseline multiaperture echelle spectrometer for the Atmospheric IR Sounder (AIRS) is described in terms of design and applications. The functional requirements for the optical design are set forth including the 1-K measurement goal, the 3.4-15.4 spectral bandpass, and the full global coverage twice daily. The multiaperture spectrometer is compared to the cross-dispersed spectrometer, and the multiaperture model is found to permit specific adjustments to the signal-to-noise ratio. The optical design of the spectrometer is described in terms of the focal-plane constraints, the multiaperture pupil-imaging relay, the spectrometer collimator, and the grating format and efficiency. The multiaperture design is found to have a good spectral-response function, and a 1.2 percent signal change is noted for a 95-percent unpolarized scene. The AIRS instrument is illustrated in its deployment configuration and is concluded to be capable of fulfilling the performance requirements.

Pagano, Robert↗
NASA NTRS1992

Space Network Interoperability Panel (SNIP) study

The Space Network Interoperability Panel (SNIP) is described in terms of the panel's composition, purpose, history, and ongoing activities. SNIP is a consortium comprising NASA, ESA, and NASDA that is dedicated to the study of interoperability of the data-relay satellite (DRS) systems of the three groups. S-band and Ka-band interoperability are addressed by the SNIP study program by means of defining operations concepts, technical subjects, and other matters relevant to international DRS system compatibility. The potential users of the interoperability scheme are listed, cross-support techniques are described, and the load situations of the three agencies are characterized. A common 'interoperability frequency framework' is proposed, and both left-and right-hand circular polarization are incorporated to enhance flexibility and minimize interference. An operations concept is outlined based on these and other recommendations as developed by the international SNIP study.

Ryan, Thomas↗
NASA NTRS1992

Space network interoperability panel (SNIP) study

The history and status of the SNIP study conducted by NASA, ESA, and NASDA are reviewed. Particular attention is given to data relay systems development plans; agency load situations; cross support; the top managers agreement about implementation of S-band interoperability and accelerating the K-alpha band high data rate exploration; testing of actual systems; NASA interim architecture for an S-band era system to make NASA spacecraft and TDRSS/TDRS-II compatible with ESA and NASDA systems; tropical rainfall measuring mission support; S-band cross support; and K-alpha band status.

Fahnestock, Dale↗
NASA NTRS1992

Results of telerobotic hand controller study using force information and rate control

To increase quantified information about the effectiveness and subjective workload of force information relayed through manipulator input control devices, a space related task was performed by eight subjects with kinesthetic force feedback and/or local force accommodation through three different input control devices (i.e., hand controllers) operating in rate control mode. Task completion time, manipulator work, and subjective responses were measured. Results indicated a difference among the hand controllers. For the Honeywell six degree-of-freedom hand controller, the overall task completion times were shortest, the amount of work exerted was the least, and was the most preferred by test subjects. Neither force accommodation with or without reflection resulted in shorter task completion times or reduced work although those conditions were better than no force information for some aspects. Comparisons of results from previous studies are discussed.

Willshire, Kelli F.↗
NASA NTRS1992

Orbiter attitude design for the Astro-1 Spacelab mission

The methods utilized to design orbiter attitudes that satisfied the various Space Shuttle program and payload constraints of the Astro-1 Spacelab astronomy mission are described. The premission methods developed for attitude design and how those methods were applied to accomplish the large amount of real-time replanning required during the flight are presented. Some of the attitude concerns for Astro-1 included orbiter window thermal constraints, two separate telescope fields-of-view, tracking and data relay satellite Ku-band access, and telescope sun avoidance.

Olsen, C. D.↗
NASA NTRS1991

Trajectory and navigation system design for robotic and piloted missions to Mars

Future Mars exploration missions, both robotic and piloted, may utilize Earth to Mars transfer trajectories that are significantly different from one another, depending upon the type of mission being flown and the time period during which the flight takes place. The use of new or emerging technologies for future missions to Mars, such as aerobraking and nuclear rocket propulsion, may yield navigation requirements that are much more stringent than those of past robotic missions, and are very difficult to meet for some trajectories. This article explores the interdependencies between the properties of direct Earth to Mars trajectories and the Mars approach navigation accuracy that can be achieved using different radio metric data types, such as ranging measurements between an approaching spacecraft and Mars orbiting relay satellites, or Earth based measurements such as coherent Doppler and very long baseline interferometry. The trajectory characteristics affecting navigation performance are identified, and the variations in accuracy that might be experienced over the range of different Mars approach trajectories are discussed. The results predict that three sigma periapsis altitude navigation uncertainties of 2 to 10 km can be achieved when a Mars orbiting satellite is used as a navigation aid.

Thurman, S. W.↗
NASA NTRS1992

Galileo trajectory design

The trajectory design of the Galileo spacecraft is examined. The Galileo spacecraft was launched on a six-year long trip to Jupiter in October 1989. A new Venus-Earth-Earth-Gravity Assist (VEEGA) trajectory mode is being used for the transfer to Jupiter and involves two phasing orbits around the sun and gravity-assist flybys with Venus. The aggregate delta V acquired from these flybys is 18.3 km/s. The interplanetary trajectory includes a close flyby of asteroid 951-Gaspra in October 1991 and a possible flyby of 243-Ida in August 1993. After arrival at Jupiter in December 1995, the previously released Galileo atmospheric probe will relay data to earth via the Galileo Orbiter. The orbital phase of the mission will involve 10 orbits of Jupiter over a 22 month period. In this phase the Orbiter will use repeated gravity-assisted flybys of Europa, Ganymede and Callisto during which Jupiter, its magnetosphere and the Galilean satellites will be investigated. The mission is scheduled to end in October 1997.

D'Amario, Louis A.↗
NASA NTRS1991

The 4-meter lunar engineering telescope

The 16-meter diffraction limited lunar telescope incorporates a primary mirror with 312 one-meter segments; 3 nanometer active optics surface control with laser metrology and hexapod positioners; a space frame structure with one-millimeter stability; and a hexapod mount for pointing. The design data needed to limit risk in this development can be obtained by building a smaller engineering telescope on the moon with all of the features of the 16-meter design. This paper presents a 4.33-meter engineering telescope concept developed by the Summer 1990 Student Program of the NASA/JHU Space Grant Consortium Lunar Telescope Project. The primary mirror, made up of 18 one-meter hexagonal segments, is sized to provide interesting science as well as engineering data. The optics are configured as a Ritchey-Chretien with a coude relay to the focal plane beneath the surface. The optical path is continuously monitored with 3-nanometer precision interferometrically. An active optics processor and piezoelectric actuators operate to maintain the end-to-end optical configuration established by wave front sensing using a guide star. The mirror segments, consisting of a one-centimeter thick faceplate on 30-cm deep ribs, maintain the surface figure to a few nanometers under lunar gravity and thermal environment.

Peacock, Keith↗
NASA NTRS1991

SALSA - A Synthesis Array for Lunar Submillimeter Astronomy

A conceptual design is described for a lunar submillimeter wavelength interferometer called SALSA, a Synthesis Array for Lunar Submillimeter Astronomy. Its design is greatly simplified over conventional submillimeter wavelength arrays because it takes advantage of a beam waveguide to relay signals to a centrally-located receiver system. The array is optimized to synthesize images at wavelengths between 60 and 300 microns, and it has an angular resolution of 10 milliarcsecs at 60 microns. Observations in this region provide unique insights into fundamental issues in astrophysics such as star formation, but are impossible from the earth's surface because of atmospheric absorption. The baseline design for SALSA consists of twelve, 3.5-meter diameter antennas arranged in a Y-shaped configuration consisting of three 0.5-km long arms, each with four antennas distributed according to a power-law function of distance. Such a beam-waveguide approach has significant advantages, since all the high-power-consumption items (active cryogenics, correlator) are at a central location and could share a single power source. In addition, the antennas can be quite simple and maintenance is greatly reduced. The primary technology challenges for developing such an array are the coherent detectors (mixers and local oscillator sources), and ensuring the dimensional stability of the optical elements under the extreme lunar thermal environment (85-385 K).

Mahoney, M. J.↗
NASA NTRS1992

Microwave systems applications in deep space telecommunications and navigation - Space Exploration Initiative architectures

The general support requirements of a typical SEI mission set, along with the mission operations objectives and related telecommunications, navigation, and information management (TNIM) support infrastructure options are described. Responsive system architectures and designs are proposed, including a Mars orbiting communications relay satellite system and a Mars-centered navigation capability for servicing all Mars missions. With the TNIM architecture as a basis, key elements of the microwave link design are proposed. The needed new technologies which enable these designs are identified, and current maturity is assessed.

Hall, Justin R.↗
NASA NTRS1991

Load flows and faults considering dc current injections

The authors present novel methods for incorporating current injection sources into dc power flow computations and determining network fault currents when electronic devices limit fault currents. Combinations of current and voltage sources into a single network are considered in a general formulation. An example of relay coordination is presented. The present study is pertinent to the development of the Space Station Freedom electrical generation, transmission, and distribution system.

Kusic, G. L.↗
NASA NTRS1991

A method for interference mitigation in space communications scheduling

Increases in the number of user spacecraft and data rates supported by NASA's Tracking and Data Relay Satellite System (TDRSS) in the S and Ku bands could result in communications conflicts due to mutual interference. A method to mitigate interference while minimizing unnecessary scheduling restrictions on both TDRSS network and user resources, based on consideration of all relevant communications parameters, was developed. The steps of this method calculate required separation angles at TDRSS and produce interference intervals, which can be used in the production of schedules free of unacceptable interference. The method also can be used as the basis for analysis, evaluation, and optimization of user schedules with respect to communications performance. Described here are the proposed method and its potential application to scheduling in space communications. Test cases relative to planned missions, including the Earth Observing System, the Space Station Manned Base, and the Space Shuttle are discussed.

Wong, Yen F.↗
NASA NTRS1991

Optoelectronics research for communication programs at the Goddard Space Flight Center

Current optoelectronics research and development of high-power, high-bandwidth laser transmitters, high-bandwidth, high-sensitivity optical receivers, pointing, acquisition and tracking components, and experimental and theoretical system modeling at the NASA Goddard Space Flight Center is reviewed. Program hardware and space flight milestones are presented. It is believed that these experiments will pave the way for intersatellite optical communications links for both the NASA Advanced Tracking and Data Relay Satellite System and commercial users in the 21st century.

Krainak, Michael A.↗
NASA NTRS1992

A deterministic method for estimating attitude from magnetometer data only

A new deterministic algorithm which estimates spacecraft attitude utilizing magnetometer data only is presented. This algorithm exploits the dynamic equations of motion to propagate attitude and thus requires knowledge of both internal and external torques, except in the special case of a spacecraft rotating with constant angular velocity. Preliminary results obtained for the uncontrolled Relay Mirror Experiment satellite utilizing real telemetry data are reported.

Natanson, G. A.↗
NASA NTRS1993

Monitor For Electrical-Discharge Machining

Circuit monitors electrical-discharge-machining (EDM) process to detect and prevent abnormal arcing, which can produce unacceptable "burn" marks on workpiece. When voltage between EDM electrode and workpiece behaves in manner indicative of abnormal arcing, relay made to switch off EDM power, which remains off until operator attends to EDM setup and resets monitor.

Burley, Richard K.↗
NASA NTRS1993

Switching An Image Processor Between Two Computers

Remote-control parallel switching circuit connects either of two computers (but not both simultaneously) to image processor. Includes two parallel switches actuated mechanically by solenoids. Each solenoid controlled by solid-state relay connected to remote-control line from associated computer. One or other solenoid energized to connect image processor to computer requesting access according to protocol implemented in software.

Bodis, Jim↗
NASA NTRS1993

Improved Large-Field Focusing Schlieren System

System used to examine complicated two- and three-dimensional flows. High-brightness large-field focusing schlieren system incorporates Fresnel lens instead of glass diffuser. In system with large field of view, image may also be very large. Relay optical subsystem minifies large image while retaining all of light. Facilities candidates for use of focusing schlieren include low-speed wind and water tunnels. Heated or cooled flow tracers or injected low- or high-density tracers used to make flows visible for photographic recording.

Weinstein, Leonard M.↗