Spacecraft spin axis attitude determination

1992 ◽  
Vol 28 (2) ◽  
pp. 529-534 ◽  
Author(s):  
H.E. Emara-Shabaik
Keyword(s):  
Attitude Determination ◽  
Spin Axis ◽  
Spacecraft Spin

Impact of Flexibility on the Clock Controller of the Galileo Spacecraft

1994 ◽  
Vol 116 (3) ◽  
pp. 521-528
Author(s):  
F. O. Eke ◽  
G. A. Macala ◽  
G. K. Man
Keyword(s):  
Stability Analysis ◽  
Time Domain ◽  
Spin Axis ◽  
Structural Flexibility ◽  
Simulation Studies ◽  
Time Domain Simulation ◽  
Control Loop ◽  
Control Loops ◽  
Control Subsystem ◽  
Spacecraft Spin

This paper presents a study of the effects of structural flexibility on one of the control loops that constitute the Attitude and Articulation Control Subsystem of the Galileo Spacecraft. Both stability analysis and time domain simulation studies are discussed. Results obtained indicate that the control loop of interest—the Clock Controller—will interact stably with the spacecraft structure as long as the spacecraft scan platform boresight points at least 30 deg away from the spacecraft spin axis (poles). Flexibility effects become more and more pronounced with proximity of the bore-sight to the poles as several structural modes become excitable to resonance.

Models of comets with strongly variable nongravitational effects

1999 ◽  
Vol 173 ◽  
pp. 381-387
Author(s):  
M. Królikowska ◽  
G. Sitarski ◽  
S. Szutowicz
Keyword(s):  
Cometary Nucleus ◽  
Spin Axis ◽  
Reactive Force ◽  
Orbital Elements ◽  
Cometary Nuclei ◽  
Short Period ◽  
Basic Parameters ◽  
Polar Radius ◽  
Cometary Activity ◽  
Nongravitational Effects

AbstractThe nongravitational motion of five “erratic” short-period comets is studied on the basis of published astrometric observations. We present the precession models which successfully link all the observed apparitions of the comets: 21P/Giacobini-Zinner, 31P/Schwassmann-Wachmann 2, 32P/Comas Solá, 37P/Forbes, and 43P/Wolf-Harrington. We used the Sekanina's forced precession model of the rotating cometary nucleus to include the nongravitational terms into equations of the comet's motion. Values of six basic parameters (four connected with the rotating comet nucleus and two describing the precession of spin-axis of the nucleus) have been determined along the orbital elements from positional observations of the comets. The solutions were derived with additional assumptions which introduce instantaneous changes of modulus of reactive force,Aand of maximum of cometary activity with respect to perihelion time. The present precession models impose some contraints on sizes and rotational periods of cometary nuclei. According to our solutions the nucleus of 21P/Giacobini-Zinner with oblateness along the spin-axis of about 0.32 (equatorial to polar radius of 1.46) is the most oblate among five investigated comets.

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