Mobile User Objective System (MUOS)

The Mobile User Objective System (MUOS) is a US military narrowband satellite communications system developed as the successor to the UHF Follow-On (UFO) constellation. MUOS comprises five geostationary satellites, including one on-orbit spare, and operates in the same UHF frequency ranges as its predecessors (approximately 292–317 MHz uplink and 243–270 MHz downlink), ensuring backward compatibility with legacy 5-kHz and 25-kHz narrowband terminals.

A new waveform is provided to increase capacity tenfold to approximately 10 Mbps per satellite (between 75 bps to 384 kbps to users). Multiple access is via Wideband CDMA (WCDMA)—nonetheless, notching is provided to avoid interference with ground stations in the same frequency. Each satellite uses a 14-m, 16-beam transmit/receive antenna supporting four 5-MHz WCDMA carrier frequencies.

The satellite payload operates as a simple bent-pipe transponder using a Ka-band feeder link to ground radio access facilities (RAF) between latitudes of 65°N and 65°S—four in the US, one in Italy and one in Australia. Launch dates: MUOS-1 (2 Nov 2012); MUOS-2 (19 Jul 2013); MUOS-3 (21 Jan 2015); MUOS-4 (2 Sep 2015); MUOS-5 (24 Jun 2016). The four currently operational MUOS satellites are stationed at longitude 100°W (MUOS-1); 177°W (MUOS-2); 15°W (MUOS-3); and 75°E (MUOS-4). Full operational capability was declared on 17 October 2019.

MUOS supports a wide range of user terminals across land, maritime, and aeronautical platforms, including manpack, shipborne, and airborne radios, enabling secure mobile voice and data communications for tactical and strategic military users. Manpack terminals conform to MILSTD 118-117 (January 2015), and terminals include General Dynamics AN/PRC-155 and the Harris AN/PRC-117G. Shipborne terminal is General Dynamics AN/USC-61C. Airborne terminals are Raytheon AN/ARC-231 (rotary), Rockwell Collins AN/ARC-210 (fixed wing) and Northrop Grumman Freedom 450.