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At least 181 records · Page 10

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NASA NTRS1982

Inorganic spark chamber frame and method of making the same

A spark chamber frame, manufactured using only inorganic materials is described. The spark chamber frame includes a plurality of beams formed from inorganic material, such as ceramic or glass, and are connected together at ends with inorganic bonding material having substantially the same thermal expansion as the beam material. A plurality of wires formed from an inorganic composition are positioned between opposed beams so that the wires are uniformly spaced and form a grid. A plurality of hold down straps are formed of inorganic material such as ceramic or glass having substantially the same chemical and thermal properties as the beam material. Hold down straps overlie wires extending over the beams and are bonded thereto with inorganic bonding material.

Heslin, T. M.↗

NASA NTRS1982

An approximation concepts method for space frame synthesis

A method is presented for the minimum mass design of three dimensional space frames constructed of thin walled rectangular cross-section members. Constraints on nodal displacements and rotations, material stress, local buckling, and cross sectional dimensions are included. A high quality separable approximate problem is formed in terms of the reciprocals of the four section properties of the frame element cross section, replacing all implicit functions with simplified explicit relations. The cross sectional dimensions are efficiently calculated without using multilevel techniques. Several test problems are solved, demonstrating that a series of approximate problem solutions converge rapidly to an optimal design.

Mills-Curran, W. C.↗

NASA NTRS1984

Test Frame Simulates Zero Gravity

Counterweighted frame simulates zero gravity in tests of solar-array wing. Net effect close simulation of zero-gravity environment in which wing must function. Frame also facilitates testing and replacement of solar-cell elements and panels.

Chung, D.↗

NASA NTRS1982

A comparison of frame synchronization methods

Different methods are considered for frame synchronization of a concatenated block code/Viterbi link. Synchronization after Viterbi decoding, synchronization before Viterbi decoding based on hard-quantized channel symbols are all compared. For each scheme, the probability under certain conditions of true detection of sync within four 10,000 bit frames is tabulated.

Swanson, L.↗

NASA NTRS1984

Formulation of blade-flutter spectral analyses in stationary reference frame

Analytic representations are developed for the discrete blade deflection and the continuous tip static pressure fields in a stationary reference frame. Considered are the sampling rates equal to the rotational frequency, equal to blade passing frequency, and for the pressure, equal to a multiple of the blade passing frequency. For the last two rates the expressions for determining the nodal diameters from the spectra are included. A procedure is presented for transforming the complete unsteady pressure field into a rotating frame of reference. The determination of the true flutter frequency by using two sensors is described. To illustrate their use, the developed procedures are used to interpret selected experimental results.

Kurkov, A. P.↗

NASA NTRS1984

A catalog of selected compact radio sources for the construction of an extragalactic radio/optical reference frame

A catalog of 234 strong compact extragalactic radio sources that display optical counterparts is presented. This catalog identifies proposed sources for establishing an almost inertial reference frame against which the motions of the earth, solar system, galactic objects, and spacecraft may be measured. This catalog also defines those sources for which precise optical positions should be determined in order to relate this reference frame with the optical FK 5 fundamental system. The accuracy of the radio source positions of these sources is not greater than 0.1 arcsec with the majority not greater than 0.01 arcsec. Further refinement to not greater than 0.005 arcsec by future observations is expected soon.

Argue, A. N.↗

NASA NTRS1985

Alternative approximation concepts for space frame synthesis

A structural synthesis methodology for the minimum mass design of 3-dimensionall frame-truss structures under multiple static loading conditions and subject to limits on displacements, rotations, stresses, local buckling, and element cross-sectional dimensions is presented. A variety of approximation concept options are employed to yield near optimum designs after no more than 10 structural analyses. Available options include: (A) formulation of the nonlinear mathematcal programming problem in either reciprocal section property (RSP) or cross-sectional dimension (CSD) space; (B) two alternative approximate problem structures in each design space; and (C) three distinct assumptions about element end-force variations. Fixed element, design element linking, and temporary constraint deletion features are also included. The solution of each approximate problem, in either its primal or dual form, is obtained using CONMIN, a feasible directions program. The frame-truss synthesis methodology is implemented in the COMPASS computer program and is used to solve a variety of problems. These problems were chosen so that, in addition to exercising the various approximation concepts options, the results could be compared with previously published work.

Lust, R. V.↗

NASA NTRS1985

Relating the Planetary Ephemerides and the Radio Reference Frame

The positions of Venus, Mars, and Jupiter were obtained in the VLBI radio reference frame by measuring the position of a satellite (natural or artificial) of each planet relative to an extragalactic source in the radio catalogue. From the results for Mars and Venus it is concluded that the offset in right ascension of the radio frame from the dynamical equinox defined in DE200 is 0.00 sec +/- 0.04 sec. The observations for Jupiter imply a correction to its position from DE200 of -0.18 sec +/- 0.04 sec in right ascension and -0.06 +/- 0.05 sec in declination on 1983 April 29. The right ascension of Jupiter relative to the inner planets has been measured independently using Doppler tracking data near Jupiter encounter from Pioneers 10 and 11 and from Voyagers 1 and 2 by tying the tracking station positions, through previous spacecraft missions, to the DE200 ephemerides of the inner planets. This technique yielded a correction to Jupiter's right ascension of -0.22 +/- 0.05 sec, in good agreement with the results from the direct radio measurements.

Niell, A. E.↗

NASA NTRS1985

Spline Curves, Wire Frames and Bvalue

The methods that were developed for wire-frame design are described. The principal tools for control of a curve during interactive design are mathematical ducks. The simplest of these devices is an analog of the draftsman's lead weight that he uses to control a mechanical spline also create Ducks for controlling differential and integral properties of curves were created. Other methods presented include: constructing the end of a Bezier polygon to gain quick and reasonably confident control of the end tangent vector, end curvature and end torsion; keeping the magnitude of unwanted curvature oscillations within tolerance; constructing the railroad curves that appear in many engineering design problems; and controlling the frame to minimize errors at mesh points and to optimize the shapes of the curve elements.

Smith, L.↗

NASA NTRS1986

Modeling fault diagnosis as the activation and use of a frame system

Twenty pilots with instrument flight ratings were asked to perform a fault-diagnosis task for which they had relevant domain knowledge. The pilots were asked to think out loud as they requested and interpreted information. Performances were then modeled as the activation and use of a frame system. Cognitive biases, memory distortions and losses, and failures to correctly diagnose the problem were studied in the context of this frame system model.

Smith, Philip J.↗

NASA NTRS1986

Word and frame synchronization with verification for PPM optical communications

A method for obtaining word and frame synchronization in pulse position modulated optical communication systems is described. The method uses a short sync sequence inserted at the beginning of each data frame and a verification procedure to distinguish between inserted and randomly occurring sequences at the receiver. This results in an easy to implement sync system which provides reliable synchronization even at high symbol error rates. Results are given for the application of this approach to a highly energy efficient 256-ary PPM test system.

Marshall, William K.↗

NASA NTRS1988

Source and event selection for radio-planetary frame-tie measurements using the Phobos Landers

The Soviet Phobos Lander mission will place two spacecraft on the Martian moon Phobos in 1989. Measurements of the range from Earth-based stations to the landers will allow an accurate determination of the ephemerides of Phobos and Mars. Delta Very Long Base Interferometry (VLBI) between the landers and compact radio sources nearby on the sky will be used to obtain precise estimates of the angular offset between the radio and planetary reference frames. The accuracy of this frame-tie estimate is expected to be in the vicinity of 10 mrad, depending on how well several error sources can be controlled (calibrated or reduced). Many candidate radio sources for VLBI measurements were identified, but additional work is necessary to select those sources which have characteristics appropriate to the present application. Strategies for performing the source selection are described.

Linfield, R.↗

NASA NTRS1988

Frame synchronization performance and analysis

The analysis used to generate the theoretical models showing the performance of the frame synchronizer is described for various frame lengths and marker lengths at various signal to noise ratios and bit error tolerances.

Aguilera, C. S. R.↗

NASA NTRS1988

Determination of the inner planet frame tie using VLBI data

The problem of connecting the independent reference frames formed by the planetary ephemeris and the radio source catalog is one of growing importance to spacecraft navigation. Using quasar-relative VLBI delay data collected by the Deep Space Network, and Soviet coherent data from the Venus flyby of the Soviet Vega 1 and 2 spacecraft, a self-consistent estimate of the frame tie offset has been found, along with its uncertainty.

Mcelrath, Timothy P.↗

NASA NTRS1988

Few-nanoradian deep space navigation in local reference frames

Angular navigation with Very Long Baseline Interferometry is performed at the 15-100 nanoradian level by differencing the interferometric delays of a spacecraft and nearby radio source. Clock rate, earth orientation and atmospheric effects limit the accuracy. By observing several radio sources along with the spacecraft, these dominant errors can be reduced by parameter estimation. Using improved instrumentation, the technique analyzed below, which can potentially yield 1-3 nanoradian accuracy, locates the spacecraft in a local reference frame of radio sources. In this paper, observation strategies and covariance results will be presented for the local reference frame technique. The error contributions of system noise and tropospheric fluctuations will be evaluated. An application of this few-nanoradian technique to Jovian approach is also presented.

Treuhaft, R. N.↗

NASA NTRS1988

Hypervelocity impact studies using a rotating mirror framing laser shadowgraph camera

The need to study the effects of the impact of micrometeorites and orbital debris on various space-based systems has brought together the technologies of several companies and individuals in order to provide a successful instrumentation package. A light gas gun was employed to accelerate small projectiles to speeds in excess of 7 km/sec. Their impact on various targets is being studied with the help of a specially designed continuous-access rotating-mirror framing camera. The camera provides 80 frames of data at up to 1 x 10 to the 6th frames/sec with exposure times of 20 nsec.

Parker, Vance C.↗

NASA NTRS1988

Deep space tracking in local reference frames

A self-calibrating deep space tracking technique is described which can potentially produce two nanoradian angular spacecraft determinations. The technique uses very long base interferometric observations of a spacecraft and several radio sources. The currently employed single source technique is described as a parameter estimation procedure. Then, the number of parameters and observations leads to the proposed local reference frame technique. Station clock, Earth rotation, and tropospheric parameters are estimated along with spacecraft position from the multisource observation sequence. The contributions to spacecraft angular uncertainty from system noise, tropospheric fluctuations, and uncalibrated radio source structure are evaluated. Of these experimental errors, radio source structure dominates the determination of the spacecraft position in the radio reference frame. It is shown, however, that the sensitivity of relative spacecraft position accuracies to time-invariant radio source structure effects may be on the order of 2 nanoradians.

Treuhaft, R. N.↗

NASA NTRS1989

Integrated optimization of nonlinear R/C frames with reliability constraints

A structural optimization algorithm was researched including global displacements as decision variables. The algorithm was applied to planar reinforced concrete frames with nonlinear material behavior submitted to static loading. The flexural performance of the elements was evaluated as a function of the actual stress-strain diagrams of the materials. Formation of rotational hinges with strain hardening were allowed and the equilibrium constraints were updated accordingly. The adequacy of the frames was guaranteed by imposing as constraints required reliability indices for the members, maximum global displacements for the structure and a maximum system probability of failure.

Soeiro, Alfredo↗