STATIONKEEPING OF GEOSTATIONARY SATELLITES WITH SIMULTANEOUS ECCENTRICITY AND LONGITUDE CONTROL

Because of increasingly stringent deadband requirements (+/- 0.05-degr ees) in conjunction with larger solar radiation perturbations caused b y higher area-to-mass ratios on current and future satellites, east/we st stationkeeping has become significantly more complicated. An algori thm that simultaneously controls the mean eccentricity and longitudina l motion of a geostationary satellite placed at any station longitude is developed. Eccentricity control is achieved based upon an expanded version of the sun pointing perigee method to include the long-period luni-solar effects in the eccentricity vector targeting scheme. Simult aneous control of the longitudinal motion is achieved by apportioning the required DELTAV for eccentricity control amongst N maneuvers to ma intain longitude within a +/- 0.05-degrees deadband. Upon completing t he Nth maneuver, the satellite begins a period of free drift with star ting conditions coinciding with the optimal free-drift cycle initial c onditions. Modeling of the sun, Earth, and moon effects on the satelli te's motion allows for an arbitrary station longitude (and in particul ar for longitudes at or near an equilibrium point). A detailed simulat ion of the spacecraft's operating environment incorporating the maneuv er strategy was used to verify the feasibility of the algorithm and to illustrate its robustness in the presence of measurement and executio n errors.