Stationkeeping Techniques for Libration-Point Satellites

Orbits about collinear libration points are unstable, requiring stationkeeping maneuvers to maintain. Several different methods for calculating libration-point orbit stationkeeping maneuvers have been proposed. A tight control technique was used by the third International Sun-Earth Explorer (ISEE-3), the first libration-point mission. An easily-implemented “orbital energy balancing” loose control strategy was developed later and has been used successfully by the Solar Heliospheric Observatory (SOHO) and Advanced Composition Explorer (ACE). For SOHO, this loose control has resulted in station-keeping Δ V costs of just over 2 m/sec per year with maneuvers performed about four times a year, an improvement of almost a factor of four over ISEE-3’s tight control. Part of the gain probably results from better trajectory determinations from improved radiometric tracking data for SOHO. All three missions, especially SOHO, have had operational mishaps that have resulted in temporary expenditures of fuel that were much larger than expected, but in spite of these, it appears that the spacecraft can be kept in their designed halo orbits for periods longer than planned before launch.