The Geostationary Satellite X00639 (静止衛星X零零陸参玖), or simply just X00639, is a satellite mentioned in AI: THE SOMNIUM FILES.
X00639 is a satellite placed in geosynchronous orbit around the equator, located at longitude 100º East. Reported to be 50 meters long (around 150 feet by Iris), the satellite was first identified by the Bisei Spaceguard Center and reported by a space advocacy group on April 4th, 2002 in Japan. An urban legend sprung up about X00639's potential origins as a secret US military satellite.
- The term Geostationary Satellite X00639 was a keyword featured in the announcement trailer for AI: THE SOMNIUM FILES, floating in the background at the beginning.
- Day 4: Monday –syuurAI–
- Wikipedia page for Geostationary Satellites, specifically the section on "Unknown Details of Geostationary Satellites" (only in Japanese)