Boeing ES-21 UFO

The UFO (UHF Follow-On) system is a series of geostationary communication satellites, commissioned in the 1990s by the U.S. Navy to supplant and eventually replace the older FLTSATCOM (Fleet Satellite Communications) and Leasat satellites. Prime contractor was Hughes Space, now Boeing Satellite Systems.

The first three UFO satellites were of Block 1 configuration, and were equipped with a UHF (Ultra-High Frequency) and an SHF (Super-High Frequency) payload. Block 2, satellites UFO-4 to -6, added an EHF (Extremely High Frequency) payload, whose capacity was doubled in the final Block 2 satellite, UFO-7. In Block 3, satellites UFO-8 to -10, the SHF system was replaced by a new Ka-band Global Broadcast Service (GBS) payload. The final satellite UFO-11 was of Block 4 configuration, with enhanced UHF and EHF payloads.

Image: Boeing

ES-21A (UFO Block 3)

The successor to UFO is MUOS (Mobile User Objective System). In 2021, responsibility for the remaining UFO assets was transferred from the Navy to the newly-established U.S. Space Force, which allocated the MDS designation ES-21A to the satellites. As of early 2024, at least 4 UFO satellites are still operational.

UFO Launch List

• No.: Sequential flight number for the GSSAP (Hornet) program
• Name: Unclassified name of the satellite. Since June 1984, U.S. military satellites get a sequential "USA" number.
• COSPAR ID: International designation of the satellite

UFO launches

Main Sources

[1] Wikipedia: UHF Follow-On Satellite
[2] Gunter Krebs: UFO 1, 2, 3, UFO 4, 5, 6, 7, UFO 8, 9, 10, UFO 11
[3] USSF: Army, Navy SATCOM Mission Areas Shifting to U.S. Space Force

Back to Directory of U.S. Military Rockets and Missiles, Appendix 3

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Last Updated: 2 August 2024