The Precession of a Spinning Spacecraft due to Radiation Pressure Torque

Details The Precession of a Spinning Spacecraft due to Radiation Pressure Torque The Precession of a Spinning Spacecraft due to Radiation Pressure Torque

Sep 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999dda....31.1402r&link_type=abstract

American Astronomical Society, DDA meeting #31, #14.02

Astronomy and Astrophysics

Astronomy

Scientific paper

For a spacecraft with a large, nearly flat, optically uniform solar shield, the torque due to solar radiation pressure can be described simply. The FAME astrometric mission will use radiation pressure on such a shield, orthogonal to the nominal spin axis, to drive an Hipparcos-style observing pattern (Reasenberg and Phillips, SPIE 3356, 1998). The spacecraft, which has nominal periods of 20 min for rotation and 10 days for precession around the Sun direction, will be a precessing "fast top." FAME will measure 40 million stars with bright-star accuracy of 0.05 milli-arcsecond (mas). The full set of (six) first-order differential equations for the motions of the instrument axes may need to be integrated numerically to describe the motion to the required sub-mas accuracy. However, a useful understanding of the FAME rotation can be obtained by ignoring the Eulerian nutations and the (approximately zero) torque around the spin axis. One can then write a pair of first-order nonlinear differential equations for the motion of the angular momentum vector in a rotating coordinate system with the Sun along the x axis. These equations have been solved, ignoring the eccentricity of Earth's orbit, as a series expansion in a small quantity proportional to the precession period (in years). The solution was confirmed and extended by multiple numerical integrations of the equations of motion. In the limit of fast precession, the motion around the Sun is circular and of uniform rate. As the precession period is increased, the first (and higher) order correction to the uniform circular path and the second (and higher) order correction to the period become important. For the FAME mission, these terms must be incorporated in the data analysis, but do not materially affect the quality of the observing schedule.

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