Atmospheric drag force is an important source of perturbation of Low Earth Orbit (LEO) orbit satellites, and solar activity is a major factor for changes in atmospheric density. In particular, the orbital lifetime of a satellite varies with changes in solar activity, so care must be taken in predicting the remaining orbital lifetime during preparation for post-mission disposal. In this paper, the System Tool Kit (STK®) Long-term Orbit Propagator is used to analyze the changes in orbital lifetime predictions with respect to solar activity. In addition, the STK® Lifetime tool is used to analyze the change in orbital lifetime with respect to solar flux data generation, which is needed for the orbital lifetime calculation, and its control on the drag coefficient control. Analysis showed that the application of the most recent solar flux file within the Lifetime tool gives a predicted trend that is closest to the actual orbit. We also examine the effect of the drag coefficient, by performing a comparative analysis between varying and constant coefficients in terms of solar activity intensities.

1. INTRODUCTION
 2. ANALYSIS OF SOLAR FLUX AND ORBITALLIFETIME
  2.1 Solar Flux Analysis
  2.2 Relationship between Basic Parameters and Solar Flux
  2.3 Orbital Lifetime Trends
 3. CHARACTERISTICS OF THE LOP ANDLIFETIME TOOL
  3.1 LOP and Atmospheric Density Models
  3.2 Sensitivity of the Lifetime Tool to SolFlx Data
 4. LOP AND LIFETIME TOOL RESULTS
  4.1 Solar Flux and LOP Results
  4.2 Solar Flux and Lifetime Tool Results
 5. CONCLUSION
 ACKNOWLEDGMENTS
 REFERENCES

• Ha–Yeon Choi(Aerospace System Engineering, Korea University of Science and Technology, Daejeon 34113, Korea)
• Hae-Dong Kim(IT Convergence Technology Team, Korea Aerospace Research Institute, Daejeon 34133, Korea) Corresponding Author
• Jae-Dong Seong(Aerospace System Engineering, Korea University of Science and Technology, Daejeon 34113, Korea)