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At least 199 records · Page 11

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NASA NTRS1988

Chemical vapor deposited silica coatings for solar mirror protection

A variety of techniques is available to apply protective coatings to oxidation susceptible spacecraft components, and each has associated advantages and disadvantages. Film applications by means of chemical vapor deposition (CVD) has the advantage of being able to be applied conformally to objects of irregular shape. For this reason, a study was made of the oxygen plasma durability of thin film (less than 5000 A) silicon dioxide coatings applied by CVD. In these experiments, such coatings were applied to silver mirrors, which are strongly subject to oxidation, and which are proposed for use on the space station solar dynamic power system. Results indicate that such coatings can provide adequate protection without affecting the reflectance of the mirror. Scanning electron micrographs indicated that oxidation of the silver layer did occur at stress crack locations, but this did not affect the measured solar reflectances. Oxidation of the silver did not proceed beyond the immediate location of the crack. Such stress cracks did not occur in thinner silica films, and hence such films would be desirable for this application.

Gulino, Daniel A.↗

NASA NTRS1988

Vision sensing techniques in aeronautics and astronautics

The close relationship between sensing and other tasks in orbital space, and the integral role of vision sensing in practical aerospace applications, are illustrated. Typical space mission-vision tasks encompass the docking of space vehicles, the detection of unexpected objects, the diagnosis of spacecraft damage, and the inspection of critical spacecraft components. Attention is presently given to image functions, the 'windowing' of a view, the number of cameras required for inspection tasks, the choice of incoherent or coherent (laser) illumination, three-dimensional-to-two-dimensional model-matching, edge- and region-segmentation techniques, and motion analysis for tracking.

Hall, E. L.↗

NASA NTRS1989

On trajectory generation for flexible space crane: Inverse dynamics analysis by LATDYN

For future in-space construction facility, one or more space cranes capable of manipulating and positioning large and massive spacecraft components will be needed. Inverse dynamics was extensively studied as a basis for trajectory generation and control of robot manipulators. The focus here is on trajectory generation in the gross-motion phase of space crane operation. Inverse dynamics of the flexible crane body is much more complex and intricate as compared with rigid robot link. To model and solve the space crane's inverse dynamics problem, LATDYN program which employs a three-dimensional finite element formulation for the multibody truss-type structures will be used. The formulation is oriented toward a joint dominated structure which is suitable for the proposed space crane concept. To track a planned trajectory, procedures will be developed to obtain the actuation profile and dynamics envelope which are pertinent to the design and performance requirements of the space crane concept.

Chen, G.-S.↗

NASA NTRS1989

Infrared radiometric technique for rapid quantitative evaluation of heat flux distribution over large areas

This paper describes a novel approach for rapid, quantitative measurement of spatially distributed heat flux incident on a plane. The technique utilizes the spatial temperature distribution on an opaque thin film at the location of interest, as measured by an imaging infrared radiometer. Knowledge of film radiative properties, plus quantitative estimates of convection cooling permit the steady state energy balance at any location on the film sheet to be solved for the incident heat flux. Absolute accuracies on the order of 10-15 percent have been obtained in tests performed in air. The method is particularly useful for evaluation of spatial heat flux uniformity from distributed heat sources over large areas. It has recently been used in several applications at the Jet Propulsion Laboratory, including flux uniformity measurements from large distributed quartz lamp arrays used during thermal vacuum testing of several spacecraft components, and flux mapping of a low power NdYg laser beam.

Glazer, Stuart↗

NASA NTRS1991

Gamma radiation survey of the LDEF spacecraft

The retrieval of the Long Duration Exposure Facility (LDEF) spacecraft after nearly 6 years in orbit offered a unique opportunity to study the long term buildup of induced radioactivity in the variety of materials on board. The first complete gamma ray survey was conducted of a large spacecraft on LDEF shortly after its return to Earth. A surprising observation was the large Be-7 activity which was seen primarily on the leading edge of the satellite, implying that it was picked up by LDEF in orbit. This is the first known evidence for accretion of a radioactive isotope onto an orbiting spacecraft. Other isotopes seen during the survey, the strongest being Na-22 and Mn-54, are all attributed to activation of spacecraft components in orbit. Be-7 is a spallation product of cosmic rays on nitrogen and oxygen in the upper atmosphere. However, the observed density is much greater than expected due to cosmic ray production in situ. This implies transport of Be-7 from much lower altitudes up to the LDEF orbit.

Phillips, G. W.↗

NASA NTRS1992

Gamma radiation survey of the LDEF spacecraft

The retrieval of the Long Duration Exposure Facility spacecraft in January 1990 after nearly six years in orbit offered a unique opportunity to study the long term buildup of induced radioactivity in the variety of materials on board. We conducted the first complete gamma-ray survey of a large spacecraft on LDEF shortly after its return to earth. A surprising observation was the Be-7 activity which was seen primarily on the leading edge of the satellite, implying that it was picked up by LDEF in orbit. This is the first known evidence for accretion of a radioactive isotope onto an orbiting spacecraft. Other isotopes observed during the survey, the strongest being Na-22, are all attributed to activation of spacecraft components. Be-7 is a spallation product of cosmic rays on nitrogen and oxygen in the upper atmosphere. However, the observed density is much greater than expected due to cosmic-ray production in situ. This implies transport of Be-7 from much lower altitudes up to the LDEF orbit.

Phillips, G. W.↗

NASA NTRS1990

Space segment configuration of the Canadian mobile satellite system

The performance requirements, the main parameters, and the configuration of the MSAT spacecraft are reviewed. The major features of the communications subsystem are discussed in some detail. Key technology items include the L-band Radio Frequency (RF) power amplifier which must operate with a high DC to RF power efficiency and generate low intermodulation when loaded with multi-carrier signals; and the large diameter deployable L-band antenna. The development status and expected performance of these spacecraft components is examined.

Bertenyi, Elemer↗

NASA NTRS1991

A space crane concept for performing on-orbit assembly

The topics are presented in viewgraph form and include: in-space assembly and construction enhances future mission planning flexibility; in-space assembly and construction facility concept; space crane concept with mobile base; fundamental characteristics; space crane research approach; spacecraft component positioning and assembly test-bed; and articulating joint testbed.

John T Dorsey↗

NASA NTRS1992

Magellan flight operations update

The flight operations of the Magellan spacecraft are discussed with specific attention given to spacecraft conditions, the execution of a limbtracking maneuver, and results of mapping Venus. A list of spacecraft component failures is given, and the mapping effort is shown to yield information on the subsurface Venusian magma, the south pole, and the impact craters. The Magellan is capable of further mapping cycles, radio-science investigations of the solar corona, and aiding in the development of a high-resolution 'gravity model' to characterize the mass distribution of Venus.

Doody, Dave↗

NASA NTRS1992

High performance polymers and polymer matrix composites for spacecraft structural applications

A program implemented by NASA Langley Research Center to develop and evaluate new polymers and polymer matrix composites for spacecraft structural applications is examined. Various polymeric films, moldings, and adhesives are evaluated for resistance to atomic oxygen and high energy electron and UV radiation. Thin films from the poly(arylene ether)s containing phenylphosphine oxide groups and the siloxane-epoxies exhibited minor weight loss compared to Kapton polyimide after exposure. Large doses (greater than 10 exp 9 rads) of electron radiation, simulating 30 yr of exposure in GEO, are found to alter the chemical structure of epoxies by both chain scission and cross-linking. The thermal cycling representative of both LEO and GEO environments can cause microcracking in composites which can in turn affect the dimensional stability and produce mechanical property reductions. The processing and fabrication issues associated with precision composite spacecraft components are also addressed.

Bowles, D. E.↗

NASA NTRS1992

Structurally adaptive space crane concept for assembling space systems on orbit

Many future human space exploration missions will probably require large vehicles that must be assembled on orbit. Thus, a device that can move, position, and assemble large and massive spacecraft components on orbit becomes essential for these missions. A concept is described for such a device: a space crane concept that uses erectable truss hardware to achieve high-stiffness and low-mass booms and uses articulating truss joints that can be assembled on orbit. The hardware has been tested and shown to have linear load-deflection response and to be structurally predictable. The hardware also permits the crane to be reconfigured into different geometries to satisfy future assembly requirements. A number of articulating and rotary joint concepts have been sized and analyzed, and the results are discussed. Two strategies were proposed to suppress motion-induced vibration: placing viscous dampers in selected truss struts and preshaping motion commands. Preliminary analyses indicate that these techniques have the potential to greatly enhance structural damping.

Dorsey, John T.↗

NASA NTRS1992

Developing satellite ground control software through graphical models

This paper discusses a program of investigation into software development as graphical modeling. The goal of this work is a more efficient development and maintenance process for the ground-based software that controls unmanned scientific satellites launched by NASA. The main hypothesis of the program is that modeling of the spacecraft and its subsystems, and reasoning about such models, can--and should--form the key activities of software development; by using such models as inputs, the generation of code to perform various functions (such as simulation and diagnostics of spacecraft components) can be automated. Moreover, we contend that automation can provide significant support for reasoning about the software system at the diagram level.

Bailin, Sidney↗

NASA NTRS1992

Transfer Orbit Plasma Interaction Experiment (TROPIX)

Viewgraphs on the Transfer Orbit Plasma Interaction Experiment (TROPIX) are presented. Objectives of this research are (1) to map the charged particles in Earth's magnetosphere from LEO to GEO at high inclinations; (2) to measure plasma current collection and resulting shifts in vehicle electrical potential from LEO to GEO across range of orbital inclinations; (3) to study spacecraft interaction with plasma environment using solar electric propulsion (SEP) thrusters as plasma contactors; (4) to measure array degradation over mission duration; (5) to evaluate the potential of various microelectronics, spacecraft components, and instruments for future space missions; and (6) to demonstrate SEP technology applied to a flight vehicle. An overview of TROPIX is presented.

Hickman, Mark↗

NASA NTRS1993

Lunar Science: Using the Moon as a Testbed

The Moon is an excellent test bed for innovative instruments and spacecraft. Excellent science can be done, the Moon has a convenient location, and previous measurements have calibrated many parts of it. I summarize these attributes and give some suggestions for the types of future measurements. The Lunar Scout missions planned by NASA's Office of Exploration will not make all the measurements needed. Thus, test missions to the Moon can also return significant scientific results, making them more than technology demonstrations. The Moon is close to Earth, so cruise time is insignificant, tracking is precise, and some operations can be controlled from Earth, but it is in the deep space environment, allowing full tests of instruments and spacecraft components. The existing database on the Moon allows tests of new instruments against known information. The most precise data come from lunar samples, where detailed analyses of samples from a few places on the Moon provide data on chemical and mineralogical composition and physical properties.

Taylor, G. J.↗

NASA NTRS1993

Efficient development and processing of thermal math models of very large space truss structures

As the spacecraft moves along the orbit, the truss members are subjected to direct and reflected solar, albedo and planetary infra-red (IR) heating rates, as well as IR heating and shadowing from other spacecraft components. This is a transient process with continuously changing heating loads and the shadowing effects. The resulting nonuniform temperature distribution may cause nonuniform thermal expansion, deflection and stress in the truss elements, truss warping and thermal distortions. There are three challenges in the thermal-structural analysis of the large truss structures. The first is the development of the thermal and structural math models, the second - model processing, and the third - the data transfer between the models. All three tasks require considerable time and computer resources to be done because of a very large number of components involved. To address these challenges a series of techniques of automated thermal math modeling and efficient processing of very large space truss structures were developed. In the process the finite element and finite difference methods are interfaced. A very substantial reduction of the quantity of computations was achieved while assuring a desired accuracy of the results. The techniques are illustrated on the thermal analysis of a segment of the Space Station main truss.

Warren, Andrew H.↗

NASA NTRS1993

The properties of perfluoropolyethers used for space applications

The perfluoropolyether (PFPE) class of liquid lubricants has been used for space applications for over two decades. At first, these fluids performed satisfactorily as early spacecraft placed few demands on their performance. However, as other spacecraft components have become more reliable and lifetimes have been extended, PFPE lubricant deficiencies have been exposed. Therefore, the objective of this paper is to review the PFPE properties that are important for successful long term operation in space.

Jones, William R., Jr.↗

NASA NTRS1993

The MSAT spacecraft of Telesat Mobile Inc.

The MSAT spacecraft of the Canadian mobile satellite operator, Telesat Mobile Inc. (TMI) is described. When launched in 1994, the large geostationary MSAT spacecraft which is currently under construction by Hughes Aircraft Co. and Spar Aerospace Ltd. will enable TMI to provide mobile and transportable communications services to its customers even in the most remote parts of the North American continent. The main elements of TMI's mobile satellite system (described in a companion paper) are the space segment and the ground segment. TMI's space segment will employ one of two nearly identical satellites, one of which will be owned and operated by TMI, the other by the U.S. mobile satellite operator, American Mobile Satellite Corporation (AMSC). The two companies are participating in a joint spacecraft procurement in order to reduce the nonrecurring costs and to ensure system compatibility between the two systems; and they have also agreed to provide in-orbit backup to each other in the event of a catastrophic satellite failure. The program status, performance requirements, main parameters, and configuration of the MSAT spacecraft are reviewed. The major features of the communications subsystem are discussed in some detail, and a brief summary is presented of the spacecraft service module. Key technology items include the L-band RF power amplifier, which must operate with a high DC to RF power efficiency and generate low intermodulation when loaded with multi-carrier signals; and the large diameter deployable L-band antenna. The development status and expected performance of these spacecraft components is examined.

Bertenyi, E.↗

NASA NTRS1994

Properties of Perfluoropolyethers for Space Applications

Jones, William R., Jr.↗