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Attitude performance of GEOS 2 gravity gradient spacecraft, discussing prelaunch design and postlaunch analyses

GEOS-C will be the third of a series of spacecraft designed for the National Geodetic Satellite Programme. The two earlier and successful spacecraft were designated GEOS-I and II. In these, geocentric stabilisation was acheived to optimise the usage of the radiated and reflected radio and optical power of the geodetic observations. It was the atmospheric attenuation of the optical beacons, by which the spacecraft could be photographed against a star background, which imposed the accuracy requirement of earth pointing to within 5°. Descriptions as well as performance analyses of these attitude control systems have been published. In each, the proper mass distribution was obtained through an end mass on a de Havilland extendible boom. Since initial misorientation and perturbing torques induce motion about the equilibrium orientation in a gravity-gradient system, a mechanism for energy dissipation is necessary. A Magnetically Anchored Eddy Current Damper was used for this purpose. It consists of a magnet assembly that is free to lock onto the geomagnetic field and rotate freely within a conducting spherical shell. Relative motion of the two produces eddy currents in the conductor which in turn impede the relative motion.

Magnetic hysteresis rods have been used successfully for damping the attitude motions of passively stabilized near-Earth satellites. This paper describes the implementation of a model of magnetic hysteresis that is suitable for digital computer simulations of such motions. The model is based on the domain theory of magnetization which assumes that associated with each domain is a shifted rectangular hysteresis loop. Coefficients used by the model are determined by least-squares fitting data from experimental hysteresis loops. For a type of hysteresis rod commonly in use, it is shown that a simplified version of the model may be used. Results from the theoretical model are compared with experimentally generated loops and show good agreement. Nomenclature a, b = axes of increasing and decreasing H in the theoretical hysteresis model B = magnetic flux density in a damping rod Bn = B(Hn)j the normal flux density in a rod Br = B(Hr) — B(Q), the residual flux density in a rod dA = weighted differential area in the Preisach plane F = function minimized in determining kQ and the fct-/s H = ambient magnetic field component along the longitudinal axis of a damping rod Hn = normal magnetizing force along the axis of a rod Hr = 0, the residual magnetizing force along the axis of a rod kotkij = coefficients determined by least-squares fitting experimental data to the theoretical model N = parameter that determines the order of the polynomials Pij Pij = polynomials in terms of H and Hn used in the theoretical model aij,pij = coefficients of Hn when only the normal and residual experimental magnetization data are used

4 Rastogi, R. P. and Baijal, S. K., "Heterogeneous Combustion of Boron-Containing Polymers," AIAA Journal, Vol. 9, No. 12, Dec. 1971, pp. 2399-2403. 5 Magnusson, U. I. F., "A Fuel for Hybrid Rockets," World Aerospace System, Vol. 2, Feb. 1966, pp. 50-52. 6 Magnusson, U. I. F., "Svenst Bransile for Hybrid Rocket Motor," Teknisk Tidskrift, Vol. 96, April 1966, pp. 365-368. 7 Moore, G. E. and Berman, K., "A Solid Liquid Rocket Propellant System," Jet Propulsion, Vol. 26, Nov. 1956, pp. 965-968. 8 Munjal, N. L. and Srivastava, M. L., "Ignition Delay of Hybrid Rocket Propellants: Aniline Nitrate-Red Fuming Nitric Acid System," Indian Journal of Chemistry, Vol. 5, No. 7, 1967, pp. 320-322. 9 Rastogi, R. P., Girdhar, H. L., and Munjal, N. L., "Ignition Catalysts for Rocket Propellants with Red Fuming Nitric Acid as Oxidant," ARS Journal, Vol. 32, No. 6, June 1962, p. 952. 10 Munjal, N. L., "Ignition Catalysts for Furfuryl Alcohol—Red Fuming Nitric Acid Bipropellants," AIAA Journal, Vol. 8, No. 5, May 1970, pp. 980-981. 11 Munjal, N. L., Prasad, J., and Ghosh, S. C, "Ignition of NonHypergolic Rocket Fuels with Fuming Nitric Acid under Suitable Conditions," AIAA Journal, Vol. 10, No. 10, Oct. 1972, pp. 13451346. 12 Munjal, N. L. and Prasad, J., "Ignition of Nonhypergolic Rocket Fuels," AIAA Journal, Vol. 10, No. 12, Dec. 1972, pp. 1722-1723. 13 Munjal, N. L., "Ignition of Nonhypergolic Propellants with Hypergolic Fluids," AIAA Journal, Vol. 6, No. 9, Sept. 1968, pp. 17821783. 14 Munjal, N. L., "Spontaneous Ignitability of Nonhypergolic Propellants under Suitable Conditions," AIAA Journal, Vol. 1, No. 8, Aug. 1963, p. 1963. 15 Rastogi, R. P., Kaushal, K., and Munjal, N. L., "Ignitability of Nonhypergolic Propellants in Presence of Potassium Permanganate," AIAA Journal, Vol. 3, No. 3, March 1965, p. 554. 16 Dixon, J. K. and Longfield, J. E., Catalysts, Vol. 12, Reinhold, New York, 1960, p. 325. 17 Thomas, J. M. and Thomas, W. J., Introduction to the Principles of Heterogeneous Catalysts, Academic Press, New York, 1967, p. 380.

Fur elliptische Umlaufbahnen mit Exzentrizitaten nahe eins ist es moglich, mit Hilfe eines kontinuierlich verstellbaren Steuerrads Schwerkraft-Stabilisierung anzuwenden. Das Radsteuergesetz sowie die sich daraus ergebenden stabilen Gebiete sind in einer fruheren Arbeit beschrieben worden, und zwar fur den Fall eines Rads, dessen Geschwindigkeit phasenmasig mit der wirklichen Anomalie genau ubereinstimmt. In der vorliegenden Arbeit werden die sich fur verschiedene Werte der Phasenverschiebung ergebenden invarianten Flachen untersucht. Gravity gradient stabilization can be used effectively in elliptic orbits with eccentricities approaching unity by the use of a variable speed control wheel. The wheel control law and the resulting stable regions have been described in a previous paper for the case where the wheel speed is exactly in phase with the true anomaly. Here, the invariant surfaces resulting for different values of the phase shift are investigated.

Both analytical and numerical techniques are used to study the oscillations and regions of stability of a gravity-gradient satellite in an eccentric orbit. A stroboscopic study of the results of a digital simulation of the equations of attitude motion yields stable regions that are considerably larger than those reported previously. The analytic study is conducted via a perturbational technique, and the results show good agreement with the numerical results in magnitude but not in phase. (Author)

External perturbation effects of near earth environment on dynamics and attitude of slowly spinning multibody satellite

Earth-pointing satellites joined by tether, discussing reel back and drag brake orbital deployment techniques and dynamic behavior

Equation providing nodal angle for largest roll libration with twice orbital frequency derived for gravity gradient satellite