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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 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Design and control of remote manipulators

Results of investigations on vibrational modes of manipulators revealed: (1) any arbitrary manipulator may be analyzed for its small motion compliances; (2) a simulation of the Martin-Marietta shuttle boom with a 65,000 lb. payload attached, indicated three natural frequencies; and (3) simulations can be made of rigid limbs and flexible joints as well as for flexible limbs and locked joints and combinations thereof. Trajectories for arms were determined so that some integral criterion such as integral of kinetic energy or control torque magnitude is minimized over a motion of the arm. Experiments performed to evaluate various TV displays in conjunction with manipulator control modes showed that when mounted directly to the manipulator control arm and arranged to look approximately along the arm to the hand the operator could perform the task almost as quickly as when viewing the task directly.

Whitney, D. E.↗
NASA NTRS1972

Measurements of speed of response of high-speed visible and IR optical detectors

A technique for measuring speed of response of high speed visible and IR optical detectors to mode-locked Nd:YAG laser pulses is described. Results of measurements of response times of four detectors are presented. Three detectors that can be used as receivers in a 500-MHz optical communication system are tested.

Rowe, H. E.↗
NASA NTRS1972

Simulation of a flexible spinning vehicle

Results are presented of experimental investigation of the controlled and uncontrolled dynamical behavior of a rotating or artificial gravity space station including flexible body effects. A dynamically scaled model was supported by a spherical air bearing which provided a nearly moment free environment. Reaction jet system were provided for spin-up and spin-down and for damping of wobble motion. Two single-gimbal gyros were arranged as a control moment gyro wobble damping system. Remotely controllable movable masses were provided to simulate mass shift disturbances such as arise from crew motions. An active mass balance wobble damping system which acted to minimize the wobble motions induced by crew motions was also installed. Flexible body effects were provided by a pair of inertia augmentation booms. Inertia augmentation booms are contemplated for use on rotating space stations to cause the spin axis moment of inertia to be the largest of the three moments of inertia as is necessary to assure gyroscopic stability. Test runs were made with each of the control systems with the booms locked (rigid body) and unlocked (flexible body).

Baudry, W. A.↗
NASA NTRS1972

Investigation of forming curved ablative panels from flat panels for space shuttle

The purpose of this study was to determine the feasibility of reforming flat ablative panels to a curved configuration. The study indicated that if the panels could be shaped to a radius of 2.54 m (100 in.) then 88.7% of the surface area of the orbiter could be covered, and that if they could be shaped to a radius of 3.81 m (150 in.) then 77.2% of the surface could be covered. Two basic approaches were followed to determine the best method for forming the flat panels to a curved shape. The first was to determine if partially cured panels could be formed, allowing the forming heat cycle to complete the curing of the ablator. The second method was to form fully cured flat panels into the desired curvature through a secondary heat cycle. Measurements made on the panels during storage indicated that they continued to straighten out over time. This was attributed to residual stresses locked into the panels that had not been fully relaxed by the heat cycle.

Chandler, H. H.↗
NASA NTRS1970

Multipath error in range rate measurement by PLL-transponder/GRARR/TDRS

Range rate errors due to specular and diffuse multipath are calculated for a tracking and data relay satellite (TDRS) using an S band Goddard range and range rate (GRARR) system modified with a phase-locked loop transponder. Carrier signal processing in the coherent turn-around transponder and the GRARR reciever is taken into account. The root-mean-square (rms) range rate error was computed for the GRARR Doppler extractor and N-cycle count range rate measurement. Curves of worst-case range rate error are presented as a function of grazing angle at the reflection point. At very low grazing angles specular scattering predominates over diffuse scattering as expected, whereas for grazing angles greater than approximately 15 deg, the diffuse multipath predominates. The range rate errors at different low orbit altutudes peaked between 5 and 10 deg grazing angles.

Sohn, S. J.↗
NASA NTRS1971

Measurement of total electron content with a geostationary satellite during the solar eclipse of March 7, 1970.

This note deals with the measurement of the total electron content of the ionosphere at the Goddard Space Flight Center, looking towards the geostationary satellite ATS 3 during the solar eclipse of Mar. 7, 1970. Obscuration at this site was nearly total. Faraday rotation was measured with a stationary circularly polarized antenna and a dual-channel phase-lock receiver tuned to 137.350 MHz. By comparing the electrical phase of the two opposite circularly polarized components, a continuous chart recording was made of Faraday rotation vs local time. A depletion of about 25% in electron content was observed from first contact to the time of minimum electron content. The time variations of the electron content during the eclipse are briefly examined in the light of current theories of ionospheric processes.

Rangaswamy, S.↗
NASA NTRS1971

On the selection of an optimum design point for phase-coherent receivers employing band-pass limiters.

Discussion of the optimum power allocation problem associated with the design of a phase-coherent receiver employing a bandpass limiter. A single channel system is treated in detail, and an optimization technique is proposed that makes use of up-to-date phase-locked loop and bandpass limiter theories recently contributed by Lindsey (1969) and Springett and Simon (1971). It is shown how this technique can be extended to a two-channel system.

Simon, M. K.↗
NASA NTRS1971

A nuclear powered air cushion freighter for the 1980's.

A design for a transoceanic, dry cargo-carrying freighter is suggested; its use and operation in port are discussed. With a gross weight of 4500 metric tons (5000 tons), more than 50 percent of which is cargo, it will cruise at 50 meters per second (100 knots) in waves 2.4 meters (8 ft) high. Its peripheral jet-flexible skirt air cushion concept and air thrustors will let the freighter go over waves 8 meters high at reduced velocity. Power comes from a 1280 megawatt, helium-cooled thermal reactor. It could dock at any major port in the world, but because it needs no surface contact, it could also travel inland to land-locked ports. A modular terminal design and methods of cargo transfer are suggested. The concept of cargo containerization influences both the freighter and terminal design.

Anderson, J. L.↗
NASA NTRS1972

Theory of two coupled lasers.

A transmitting window is used to weakly couple two resonant optical cavities. When active medium is placed in one cavity, the system describes a laser coupled to a resonant cavity, while active medium in both cavities describes two coupled lasers. Equations of motion for the fields in the two cavities are found. These equations are solved in the steady state when the cavities are sufficiently closely tuned that the lasers in the two cavities oscillate with the same frequency. In the locked situation, the second cavity tends to stabilize the frequency of operation against changes in length of the first cavity. When there is no active medium in the second cavity, and that cavity becomes very long, the laser acts as if it were looking into free space.

Spencer, M. B.↗
NASA NTRS1972

A versatile pulse programmer for pulsed nuclear magnetic resonance spectroscopy.

A digital pulse programmer producing the standard pulse sequences required for pulsed nuclear magnetic resonance spectroscopy is described. In addition, a 'saturation burst' sequence, useful in the measurement of long relaxation times in solids, is provided. Both positive and negative 4 V trigger pulses are produced that are fully synchronous with a crystal-controlled time base, and the pulse programmer may be phase-locked with a maximum pulse jitter of 3 ns to the oscillator of a coherent pulse spectrometer. Medium speed TTL integrated circuits are used throughout.

Tarr, C. E.↗
NASA NTRS1972

Efficient second harmonic generation of picosecond laser pulses.

Efficient conversion to the second harmonic (SH) using KD2PO4 and CsH2AsO4 crystals inside a folded cavity of a high-power-dye mode-locked neodymium-glass laser is reported. For the first time, frequency-doubled picosecond light pulses have been obtained in CsH2AsO4 with peak powers of the order of 1 GW/sq cm at 0.531 micron for an effective pump power density of 4 GW/sq cm.

Rabson, T. A.↗
NASA NTRS1972

Digital simulation of hybrid loop operation in RFI backgrounds.

A digital computer model for Monte-Carlo simulation of an imperfect second-order hybrid phase-locked loop (PLL) operating in radio-frequency interference (RFI) and Gaussian noise backgrounds has been developed. Characterization of hybrid loop performance in terms of cycle slipping statistics and phase error variance, through computer simulation, indicates that the hybrid loop has desirable performance characteristics in RFI backgrounds over the conventional PLL or the costas loop.

Ziemer, R. E.↗
NASA NTRS1972

A surface wave spread spectrum communication link.

This development has resulted in a fast lock-up, 8-MHz bandwidth, 8-KHz data rate, spread spectrum communication link breadboard that is implemented using surface wave devices as the primary signal generators and signal processing elements. It uses surface wave tapped delay lines (SWTDL's) in the transmitter to generate the signals and in the receiver to match filter detect them. The system also incorporates a re-entry delay line (circulating integrator) which increases the effective code length per data bit by eight-fold.

Fugit, B. R.↗
NASA NTRS1972

Radiation-pressure-driven mass loss from quasi-stellar objects.

It is shown that radiation pressure acting on the material in the outer envelopes of QSOs will cause mass outflow unless the mass M of the QSO exceeds a critical value Ms. If the QSOs are at cosmological distances, Ms is on the order of 10 to 100 billion solar masses, and otherwise scales according to intrinsic luminosity. Radiation-pressure-driven mass loss could be responsible for the absorption-line spectra observed in many QSOs. If so, the presence of blueshifted absorption lines in some but not all QSOs indicates that typically M is of the same order as Ms. It is also suggested that under radiative acceleration certain ratios of emission-line to absorption-line redshifts may be preferred as a result of a line-locking mechanism. Inferences are made concerning the magnitude of the gravitational component of the redshift. Possible tests of various aspects of the model are discussed.

Mushotzky, R. F.↗
NASA NTRS1972

Dynamical characteristics of Phobos and Deimos.

The orbital properties of the two small Martian satellites, Phobos and Deimos, are discussed, as well as those dynamical constants of Mars that can be determined from the satellite orbits. The secular acceleration of the mean motion of Phobos is shown to be very small. Of mechanisms that could cause any such acceleration, only tidal friction appears to be important. From the orbital evolution of the Martian satellites under tidal forces, Phobos and Deimos seem to have originated in nearly circular orbits of low inclination fairly close to the distance at which a satellite's orbital period is the planet's rotation period. It is proposed that the Martian satellites were born at the same time as Mars from equatorial dust clouds. The satellites are predicted to be locked in synchronous rotation, with their axes of minimum moment of inertia pointing on the average toward Mars, whereas their maximum axes are approximately normal to their orbit planes.

Burns, J. A.↗
NASA NTRS1972

Direct observation of the orientational Kerr effect in the self-focusing of picosecond pulses.

Direct measurements of the relaxation time of the birefringence within the self-focusing region of mode-locked laser pulses in several anisotropic liquids establish the importance of the orientational Kerr effect in the picosecond time regime. This result leads to some speculation as to the origin of the high degree of symmetry in the phase-modulated filament spectra observed with picosecond pulses.

Reintjes, J.↗
NASA NTRS1972

Nutational stability of a dual-spin satellite under the influence of applied reaction torques.

The nutational stability of a dual-spin satellite under the influence of an applied reaction torque is analyzed. It is assumed that since the solar paddle attachments to the hub of the spacecraft are not rigidly locked, the effect of the solar panels can be replaced by a constant reaction torque acting on the hub of the spacecraft. This could result in the satellite having an equilibrium motion about an axis displaced from the nominal axis of symmetry. The variational equations of motion are developed about such an equilibrium position using the SAS-A spacecraft as a model. Energy dissipation on the rotor as well as the main body is included. This nonautonomous set of differential equations are linearized and transformed to an autonomous set using the Lyapunov Reducibility Theorem. The stability of the kinematically similar system is examined numerically using representative SAS-A parameters for the case when either pair of solar panels is assumed to be loosely attached. Stability is verified for small system nutation angles (0.1 degree) although the time constant associated with the least damped mode is approximately one order of magnitude larger than that for the SAS-A system without the influence of the reaction torques.

Bainum, P. M.↗
NASA NTRS1972

Stimulated parametric fluorescence induced by picosecond pump pulses.

Stimulated parametric fluorescence emission tunable over the range from 0.96 to 1.16 microns has been obtained using a barium sodium niobate crystal pumped by a frequency-doubled and mode-locked neodymium:glass laser. The pump radiation in the form of a train of picosecond pulses produced infrared parametric fluorescence pulses, less than 10 psec in duration and with average peak powers on the order of 300 W when pumped with a power density of 300 MW/sq cm.

Rabson, T. A.↗