This work presents fuel-optimal altitude maintenance of Low-Earth-Orbit (LEO) spacecrafts experiencing non-negligible air drag and J2 perturbation. A pseudospectral (direct) method is first applied to roughly estimate an optimal fuel consumption strategy, which is employed as an initial guess to precisely determine itself. Based on the physical specifications of KOrea Multi-Purpose SATellite-2 (KOMPSAT-2), a Korean artificial satellite, numerical simulations show that a satellite ascends with full thrust at the early stage of the maneuver period and then descends with null thrust. While the thrust profile is presumably bang-off, it is difficult to precisely determine the switching time by using a pseudospectral method only. This is expected, since the optimal switching epoch does not coincide with one of the collocation points prescribed by the pseudospectral method, in general. As an attempt to precisely determine the switching time and the associated optimal thrust history, a shooting (indirect) method is then employed with the initial guess being obtained through the pseudospectral method. This hybrid process allows the determination of the optimal fuel consumption for LEO spacecrafts and their thrust profiles efficiently and precisely.

1. INTRODUCTION
 2. PROBLEM FORMULATION
  2.1 Altitude Maintenance Problem
  2.2 Necessary Conditions for Optimality
 3. ALTITUDE MAINTENANCE ALGORITHM
 4.SIMULATION RESULTS AND DISCUSSIONS
 5. CONCLUSION
 ACKNOWLEDGMENTS
 REFERENCES

• Kyung-Ha Kim(Astrodynamics and Control Laboratory, Department of Astronomy, Yonsei University, Seoul 03722, Korea)
• Chandeok Park(Astrodynamics and Control Laboratory, Department of Astronomy, Yonsei University, Seoul 03722, Korea) Corresponding Author
• Sang-Young Park(Astrodynamics and Control Laboratory, Department of Astronomy, Yonsei University, Seoul 03722, Korea)