Fig.1
As it was explained earlier non nominal direction of the principal axes has caused some unavoidable side effect of thruster operation nominally to be used for angular momentum vector control. For nominally supported principal axes this thruster does not generate the moment along spin axis Z. But for actual case it does generate moment along new principal axis Zn and accelerates s/c spin rate.
As a result of the previous attitude maneuvers and solar light pressure the spin rate was raised and period has been changed from 55.5 seconds to 42 seconds.
So decision has been taken for the last attitude maneuver to use so -R pair of thrusters with the moment directed as old Z axis. In new situation this pair could change the angular momentum direction and also diminish the spin rate.
It has been successfully done. The spin period has been raised to the 100 seconds, the angle of the angular momentum vector with the Sun has been diminished to about 15 degrees with the maximum nutation amplitude about 5 degrees.
Results are illustrated on Fig.1 and Fig 2.
By the described maneuver two goals have achieved: targeting the principal axis towards Sun with simultaneous nutation damping and the slow down spin rate of the s/c. The last one is needed to explore the real possibility of attitude control using light pressure. Theoretical estimations have shown that for such mode of attitude control the 300 second period as the least is necessary.
Back to the Latest News Last updated 14 Nov 1995