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This device is characterized by an elongated body having predetermined elastic properties. An applied tensile force of any magnitude, within a given range, imparts to the body an elongation of a predetermined length. The magnitude of applied tensile force is indicated as a function of the angular motion afforded the threaded sleeve mounted on the body.
Tests of the Viking 16.15-meter nominal-diameter disk-gap-band parachute were conducted at Mach number and dynamic pressure conditions which bracketed the range postulated for the Viking '75 mission to Mars. Parachutes were deployed at supersonic, transonic, and subsonic speeds behind a simulated Viking entry capsule. All parachutes successfully deployed, inflated, and exhibited sufficient drag and stability for mission requirements. Basic parachute data including loads, drag coefficients, pull-off angles, and canopy area ratios are presented. Trajectory reconstruction and onboard camera data methods were combined to yield continuous histories of both parachute and test-vehicle angular motions which are presented for the period from parachute deployment through steady inflation.
The linear and angular motions of the Zond 6 and Zond 8 spacecraft imaging camera during the exposure cause displacements of the optical image points. In the case of instantaneous exposure of each individual point and the nonsimultaneous exposure of the complete frame, this leads to finite geometric shifts of the points without causing blurring of the photographic image. Therefore, when measuring the resulting photographic pictures, the problem arises of reducing the picture point positions to a common instant of time. This reduction is performed by means of dynamic corrections to the measured picture point coordinates. These corrections are found by using formulas of dynamic photogrammetry. Their use with the Zond space probe photographs is described.
The development of a three axis stabilized balloon platform capable of being operated in three modes of increasing accuracy is discussed. The system relies on angular motion sensing for primary feedback with linear accelerometers, magnetometers, and a star sensor for positional information. When under primary control the system will acquire and stabilize on any accessible part of the celestial sphere. A video verification system is included to provide pointing confirmation. Under improved accuracy control, the star sensor is used to lock onto a target star.
A comprehensive model of vestibular organ function is presented. The model is based on an analogy with the inertial guidance systems used in navigation. Three distinct operations are investigated: angular motion sensing, linear motion sensing, and computation. These operations correspond to the semicircular canals, the otoliths, and central processing respectively. It is especially important for both an inertial guidance system and the vestibular organs to distinguish between attitude with respect to the vertical on the one hand, and linear velocity and displacement on the other. The model is applied to various experimental situations and found to be corroborated by them.
The two-region model of the solar wind divides the interplanetary space into two regions: it assumes that the solar wind is one-fluid in an inner region within 0.4 AU and two-fluid in an outer region beyond 0.4 AU. This paper includes the angular motion of the solar wind in the two-region model. The flow in the one-fluid region is governed by the one-fluid magnetohydrodynamic equations. The second and third moment equations of the Vlasov equation together with other conservation equations are used to describe the solar-wind flow in the two-fluid region. The predicted azimuthal velocity at 1 AU is less than 2 km/s. All other macroscopic and microscopic properties from this model are in good agreement with experimental quiet-time observations at 1 AU. The numerical results also confirm that when the azimuthal velocity is included in the analysis, the amount of magnetic-field energy converted into kinetic energy in the solar wind is only a small fraction of the total expansion energy flux and has little effect upon the final radial expansion velocity.
Time-varying features of an electron-photon cascade are considered, particularly those associated with radio emission. The cosmic ray shower is represented as a superposition of collinear 10 GeV electron-photon cascades launched at different heights in the atmosphere. Actual simulations are performed for only 10 cascades at each of 40 heights and the results are scaled to represent the total number of cascades required. The apparent angular motions of the cascade particles as detected by antennas located at various positions up to 300 m from the shower axis are simulated. The radio pulse waveform and the corresponding frequency spectrum are obtained from these motions.
The stability and control of a high-performance aircraft was analyzed, and a design methodology for a departure prevention stability augmentation system (DPSAS) was developed. A general linear aircraft model was derived which includes maneuvering flight effects and trim calculation procedures for investigating highly dynamic trajectories. The stability and control analysis systematically explored the effects of flight condition and angular motion, as well as the stability of typical air combat trajectories. The effects of configuration variation also were examined.
A 91.5 cm aperture telescope installed aboard NASA-Lockheed C-141A aircraft for the performance of infrared astronomy is described. A unique feature of the telescope is that its entire structure is supported by a 41 cm spherical air bearing which effectively uncouples it from aircraft angular motion, and with inertial stabilization and star tracking, limits tracking errors to less than 1 arc second in most applications. A general description of the system, a summary of its performance, and a detailed description of an offset tracking mechanism is presented.
The dynamic structure of large-amplitude Alfven disturbances of the interplanetary magnetic field is examined by transforming one-hour intervals of Explorers 33 and 35 magnetometer data from the solar ecliptic coordinate system to a coordinate system defined by the principal axes of the variance matrix. It is demonstrated how some interplanetary magnetic field fluctuations observed by both Explorers are consistent with local properties theoretically predicted for plane large-amplitude Alfven waves by Barnes and Hollweg (1974). The different types of angular motion of the magnetic field component normal to the direction of minimum variance may be indicative of the detailed conditions of the solar coronal plasma in the regions generating the Alfven waves, or some aspect of local generation.
A rendezvous of an unmanned probe to an earth-approaching asteroid has been given a high priority in the planning of interplanetary missions for the 1990s. Even without a space mission, much could be learned about the history of asteroids and comet nuclei if more information were available concerning asteroids with orbits which cross or approach the orbit of earth. It is estimated that the total number of earth-crossers accessible to ground-based survey telescopes should be approximately 1000. However, in connection with the small size and rapid angular motion expected of many of these objects an average of only one object is discovered per year. Attention is given to the development of the software necessary to distinguish such rapidly moving asteroids from stars and noise in continuously scanned CCD exposures of the night sky. Model and input parameters are considered along with detector sensitivity, aspects of minimum detectable displacement, and the point-spread function of the CCD.
A thermally induced spin rate ripple hypothesis is proposed to explain the spin rate anomaly observed on ISEE-B. It involves the two radial 14.5 meter beryllium copper tape ribbons going in and out of the spacecraft hub shadow. A thermal lag time constant is applied to the thermally induced ribbon displacements which perturb the spin rate. It is inferred that the averaged thermally induced ribbon displacements are coupled to the ribbon angular motion. A possible exponential build up of the inplane motion of the ribbon which in turn causes the spin rate ripple, ultimately limited by damping in the ribbon and spacecraft is shown. It is indicated that qualitative increase in the oscillation period and the thermal lag is fundamental for the period increase. found that numerical parameter values required to agree with in orbit initial exponential build up are reasonable; those required for the ripple period are somewhat extreme.
The inertial pointing stability of a gimbal pointing system (AGS) was compared with a magnetic pointing/gimbal followup system (ASPS), under certain conditions of system structural flexibility and disturbance inputs from the gimbal support structure. Separate 3 degree-of-freedom (3DOF) linear models based on NASTRAN modal flexibility data for the gimbal and support structures were generated for the ASPS configurations. Using the models inertial pointing control loops providing 6dB of gain margin and 45 deg of phase margin were defined for each configuration. The pointing loop bandwidth obtained for the ASPS is more than twice the level achieved for the AGS configuration. The AGS limit is attributed to the gimbal and support structure flexibility. As a result of the higher ASPS pointing loop bandwidth and the disturbance rejection provided by the magnetic isolation ASPS pointing performane is significantly better than that of the AGS system. The low frequency peak of the ASPS transfer function from base disturbance to payload angular motion is almost 60dB lower than AGS low frequency peak.
This paper describes Landsat-4 sensors, spacecraft disturbances, and the methodology used to correct Thematic Mapper (TM) images. The discussion includes system requirements, mathematical modeling, in-orbit angular motion measurement, Fast Fourier Transformer (FFT) data analysis, and scan system correction. Emphasis is given to the cause and effect of the electromechanical disturbances beginning with the scan mirror and its interaction and sensitivity to externally and self-generated disturbances. Ground-testing results are compared with those obtained in orbit.
The NASA Langley Research Center has assembled a flexible grid on which control systems research can be accomplished on a two-dimensional structure that has many physically distributed sensors and actuators. The grid is a rectangular planar structure that is suspended by two cables attached to one edge so that out of plane vibrations are normal to gravity. There are six torque wheel actuators mounted to it so that torque is produced in the grid plane. Also, there are six rate gyros mounted to sense angular motion in the grid plane and eight accelerometers that measure linear acceleration normal to the grid plane. All components can be relocated to meet specific control system test requirements. Digital, analog, and hybrid control systems capability is provided in the apparatus. To date, research on this grid has been conducted in the areas of system and parameter identification, model estimation, distributed modal control, hierarchical adaptive control, and advanced redundancy management algorithms. The presentation overviews each technique and presents the most significant results generated for each area.
Scientific satellites may require translunar orbits aligned with the Sun-Earth line, with most of the period spent in either the sunward or antisunward direction. To maintain alignment, the orbit's line of apsides must rotate at a rate equal to mean angular motion of the Earth about the Sun. To maintain this rotation of the line of apsides by use of fuel onboard the spacecraft is prohibitively expensive. Farquhar and Dunham proposed a method for maintaining the desired alignment by gaining momentum at the expense of the Moon during a close approach (a lunar swingby) as the spacecraft passes beyond lunar orbit, then returning the momentum at the second lunar swingby as the spacecraft returns within the lunar orbit. The cycle of double-lunar swingbys may then be repeated. Dunham presented the orbit parameters necessary to achieve double-lunar swingby orbits which will maintain Sun-Earth line alignment. The details of the Keplerian approach to calculation of these parameters are presented. Methods for solution of the necessary equations for these parameters are presented.
A system composed of several interconnected elastic components that may experience large angular motion relative to each other during operation is referred to as a flexible multibody structure. Several formulations were proposed for the determination of the dynamic response of controlled flexible multibody structures. In general, these formulations consist of superposing elastic deformations of the component body onto the large rigid body motion of the component. It was shown that this particular methodology for combining linear structural deformations with nonlinear kinematics can lead to erroneous response predictions when either the beam member is very flexible or the rotational speed is high. In addition, previous formulations introduce constraint equations to define the interrelations among system components. This approach increases the number of equations that must be solved, and may result in contraint violation when numerical error accumulates during the integration process. In order to overcome the difficulties, a new approach was suggested. The approach is essentially a finite element formulation which takes advantage of the fact that many multibody structures are joint dominated. The Large Angle Transient Dynamic Analysis (LATDYN) program for clarity of documentation, ease of use, user friendliness, modeling generality, and accuracy of results was evaluated. This required gaining a working familiarity with the code and performing several case studies.
A methodology for model-independant controller design for controlling large angular motion of multi-body dynamic systems is outlined. The controlled system may consist of rigid and flexible components that undergo large rigid body motion and small elastic deformations. Control forces/torques are applied to drive the system and at the same time suppress the vibration due to flexibility of the components. The proposed controller consists of passive second-order systems which may be designed with little knowledge of the system parameter, even if the controlled system is nonlinear. Under rather general assumptions, the passive design assures that the closed loop system has guaranteed stability properties. Unlike positive real controller design, stabilization can be accomplished without direct velocity feedback. In addition, the second-order passive design allows dynamic feedback controllers with considerable freedom to tune for desired system response, and to avoid actuator saturation. After developing the basic mathematical formulation of the design methodology, simulation results are presented to illustrate the proposed approach to a flexible six-degree-of-freedom manipulator.