1. C.C. Chao, MEO disposal orbit stability and direct reentry strategy, in: Proceedings of the Spaceflight Mechanics 2000, Advances in the Astronautical Sciences Series, 105, Part II, Univelt Inc., San Diego, California, USA, 2000, pp. 817–838.
2. R.A. Gick, C.C. Chao, GPS disposal orbit stability and sensitivity study, in: Proceedings Spaceflight Mechanics 2001, Advances in the Astronautical Sciences Series, V108, Part II, Univelt Inc., San Diego, California, USA, 2000, pp. 2005–2018.
3. Long-term evolution of navigation satellite orbits: GPS/GLONASS/GALILEO;Chao;Advances in Space Research,2004
4. K. Merz, R. Jehn, Stability of MEO disposal orbits, in: Proceedings of the 22nd Inter-Agency Space Debris Coordination (IADC) Plenary Meeting, CD-ROM, ASI, Abano Terme, Italy, April 2004.
5. N.N. Balashova, E.I. Ignatovich, A.I. Serdjukov, L.N. Sintsova, Research of MEO navigating systems stability, in: Proceedings of the 22nd Inter-Agency Space Debris Coordination (IADC) Plenary Meeting, CD-ROM, ASI, Abano Terme, Italy, April 2004.