1. S. Di Girolamo, L. Caporicci: “Aircraft navigation using global positioning system improved with geostationary satellites”. ION GPS-90, 3rd International Technical Meeting, Colorado Springs, Sep. 1990.
2. S. Di Girolamo, M. Marinelli: “HEO constellations for multifunctional mobile communications.”, The Space Congress — Bremen, Germany, May, 23–25th 1995.
3. S. Di Girolamo, C. Soddu: “Use of Highly elliptic orbits for new communications services”, International Symposium on Spacecraft Ground Control and Flight Dynamics, SCD1, Sao Josè dos Campos, Brazil, February 7–11,1994.
4. S. Di Girolamo, C. Soddu: “Use of multistationary inclined orbits for new communications services”, International Symposium on Space Flight Dynamics, St. Petersburg — Moscow, May 22–28, 1994.
5. G. Perrotta, S. Di Girolamo: “INAVS:a ICO satellite constellation navigation system”, AIAA Guidance, Navigation & Control, New Orleans, USA, 10–14 August 1997.