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Results for “LIBRATIONAL MOTION”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

The dynamics and control of large flexible space structures. Volume 3, part B: The modelling, dynamics, and stability of large Earth pointing orbiting structures

The dynamics and stability of large orbiting flexible beams, and platforms and dish type structures oriented along the local horizontal are treated both analytically and numerically. It is assumed that such structures could be gravitationally stabilized by attaching a rigid light-weight dumbbell at the center of mass by a spring loaded hinge which also could provide viscous damping. For the beam, the small amplitude inplane pitch motion, dumbbell librational motion, and the anti-symmetric elastic modes are all coupled. The three dimensional equations of motion for a circular flat plate and shallow spherical shell in orbit with a two-degree-of freedom gimballed dumbbell are also developed and show that only those elastic modes described by a single nodal diameter line are influenced by the dumbbell motion. Stability criteria are developed for all the examples and a sensitivity study of the system response characteristics to the key system parameters is carried out.

Bainum, P. M.↗
NASA NTRS1980

On the dynamics of large orbiting flexible beams and platforms oriented along the local horizontal

The dynamics and stability of large orbiting flexible beams and platforms oriented along the local horizontal are treated both analytically and numerically. It is assumed that such structures could be gravitationally stabilized by attaching a rigid lightweight dumbbell at the center of mass by a spring loaded hinge which also could provide viscous damping. For the beam it is seen that the small amplitude inplane pitch motion, dumbbell librational motion, and the anti-symmetric elastic modes are all coupled. The three dimensional equations of motion for a circular flat plate in orbit with a two-degree-of-freedom gimballed dumbbell are also developed and show that only those elastic modes described by a single nodal diameter line are influenced by the dumbbell motion. Stability criteria are developed for both examples and a parametric study of the least damped mode characteristics together with numerically simulated transient responses are carried out.

Bainum, P. M.↗
NASA NTRS1991

Libration in the earth's rotation

External luni-solar torque exerted on the difference (B-A) of the earth's two equatorial principal moments of inertia gives rise to two types of librational motions in the earth's rotation: the semidiurnal libration in spin and the prograde diurnal libration in polar motion. Formulas for the librations considering a realistic earth model and their tidal decompositions are derived and evaluated. The spin libration has a maximum peal-to-peak amplitude of 0.90 milliarcseconds, that of the polar libration is 0.06 milliarcseconds. Implications concerning their detectability and role in the tidal variation of earth rotation are discussed.

Chao, B. F.↗
NASA NTRS1965

The Libration of Mercury

Numerical solutions for librational motion of Mercury obtained by applying Runge-Kutta integration

NUMERICAL ANALYSIS↗
NASA NTRS1992

On the dynamical structure of the Trojan group of asteroids

Using a semi-analytical approach, domains of possible motion for Trojan asteroids were established. It is shown that stable librating motion is possible for both high inclination and high eccentricity. Frequency distributions were also produced for real Trojan asteroids, against differing libration amplitudes and libration periods.

Zagretdinov, R. V.↗
NASA NTRS1992

Interaction dynamics of an orbiter and a flexible space structure undergoing incremental in-space construction

A theoretical investigation is presented pertaining to the use of a Shuttle based remote manipulator system to construct and assemble the Space Station at the primary stage. The equations of motion for an on-orbit Space Shuttle with flexible or rigid remote manipulator system are developed including the effect of librational motion, starting and stopping motion constraints, and contact/impact conditions in maneuvering the Space Shuttle Remote Manipulator System (SRMS). Preliminary results indicated that the orbiting system may become unstable when certain disturbances have been triggered that provided a guideline in maneuvering the SRMS.

Chiou, J. C.↗
NASA NTRS1980

Atmospheric perturbation and control of a shuttle/tethered satellite

A simplified model of the strong atmospheric perturbation of a small satellite attached to the orbiter by a long, rigid tether predicts undesirable uncontrolled libration motions similar to those from sophisticated models. The simplified model is used to compare performance limitations of two simple control systems that rely only on tether tension for three-dimensional control. Because the effects on libration of both the changing kinematic and atmospheric drag torques caused by changing length are largely predictable, the controller that models these changes has substantially better performance. In particular, the altitude variation of the tethered satellite above an oblate earth can be controlled substantially better with a controller that uses a length command adapted to these predictable changes than one that only reacts to tension changes. Also, small amplitude out-of-plane librations, that are coupled only to second-order with changing length, can be damped substantially faster by the controller that periodically commands properly phased length changes than by the controller that only reacts to the second-order changes in tension.

Spencer, T. M.↗