Ground Mobile Forces
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'Ground Mobile Forces (GMF) refers to the tactical satellite communications (SATCOM) component of the Tri-Service Tactical (TRI-TAC) program.[1] Developed by GTE-Sylvania in the mid-1970s, TRI-TAC was a joint-service military command, control, and communications initiative.[1] The program aimed to field advanced multichannel switched equipment, eliminate redundant acquisitions across military branches, and establish seamless interoperability between tactical and strategic communications systems.[1]
Architecture and technical specifications
[edit]GMF systems operate in a hub-and-spoke network topology.[1] In this configuration, a central hub terminal can simultaneously ingest up to four primary data feeds from outlying spoke terminals.[1]
Terminal classifications
[edit]The system utilizes four primary designated SATCOM terminals categorized by their operational role:
- Hub Terminals (AN/TSC-85B and AN/TSC-100A): Equipped for point-to-point and hub operations.[1]
- Spoke Terminals (AN/TSC-93B and AN/TSC-94A): Designated remote terminals that connect directly back to a hub.[1]
Data capacities and throughput
[edit]- Hub Performance: Standard hub configurations ingest up to 48 multiplexed, encrypted channels from a maximum of four spoke terminals simultaneously.[1] Utilizing an external multiplexer doubles this capacity to 96 channels.[1]
- Channel Configuration: Channels operate at 16 kbit/s or 32 kbit/s, translating to an effective true capacity of 48 kbit/s when accounting for protocol overhead.[1]
- Spoke Performance: Outlying terminals support up to 24 multiplexed channels (16/32 kbit/s).[1]
| Terminal Type | Designation | Primary Role | Max Capacity (Channels) | Antenna Type |
|---|---|---|---|---|
| Hub | AN/TSC-85B / AN/TSC-100A | Point-to-Point / Hub | 48 (96 with external mux)[1] | 20 ft (6.1 m) QRSAG dish[1] |
| Spoke | AN/TSC-93B / AN/TSC-94A | Remote Spoke | 24[1] | 8 ft (2.4 m) parabolic dish[1] |
Radio frequency and environmental protection
[edit]GMF terminals communicate via Super High Frequency (SHF) X-band through the Defense Satellite Communications System (DSCS) satellite constellation.[1][2]
All GMF terminals feature external interfaces for field telephones, a 70 MHz Intermediate Frequency (IF) wideband input, and connection to an AN/TSQ-111 Tech Control Facility.[1] To support sustained tactical deployments, equipment shelters are sealed for operations in Chemical, Biological, Radiological, and Nuclear (CBRN) environments.[1]
Obsolescence and legacy
[edit]While legacy TRI-TAC and GMF hardware provided foundational field communications for decades, the bulky circuit-switched equipment has largely become obsolete.[1]
Over time, these systems were largely phased out in favor of modern, IP-based fly-away quad-band systems equipped with compact routers, switches, and advanced encryption hardware.[1] Despite their technical obsolescence, select GMF terminals remained active in field operations under severe conditions during military engagements in Iraq and Afghanistan.[1]
See also
[edit]References
[edit]Further reading
[edit]- "AN/TTC-39 Technical Manual / Document" (PDF). Archived (PDF) from the original on February 11, 2026. Retrieved July 29, 2026 – via RadioNerds.
- Carestio, R.; McLeskey, F.; Coyle, D. (16 June 1986). An Analysis of Planned Army Ground Mobile Forces (GMF) Satellite Use in Support in Mobile Subscriber Equipment (PDF) (Report). M/A-COM Government Systems, Inc. Archived (PDF) from the original on 26 August 2022. Retrieved 26 August 2022 – via Defense Technical Information Center.
- Shively, Robert G. (15 April 1993). Updating The Joint Common User Communications Architecture — A Case For The Army's View (PDF). United States Army War College (Report). Carlisle Barracks, Pennsylvania. ADA263904. Archived from the original (PDF) on 1 March 2021. Retrieved 24 August 2022 – via Defense Technical Information Center.