WASHINGTON — Mobile satellite fleet operator Inmarsat is putting the finishing touches on what the company describes as a low-cost service that will allow mobile military forces and other government users to communicate from almost anywhere in the world through existing but modified tactical radios.

Called L-TAC, the new offering is similar to the mobile services provided by UHF satellites but uses commercial L-band frequencies. The U.S. Navy currently operates an aging fleet of UHF satellites to provide mobile services to ships at sea and tactical forces operating in hard-to-reach areas, but current demand far outstrips supply.

To help remedy that shortage and fill a niche in the marketplace, Inmarsat quickly developed the L-TAC service, sprinting from conception to late-stage testing in a little over a year. Inmarsat announced July 9 that the service had been successfully tested on a vehicle traveling at 116 kilometers per hour. 

London-based Inmarsat has long been a provider of L-band services, primarily for maritime and military customers, and operates a robust fleet of L-band satellites. The L-TAC service will work with Inmarsat’s I-4 constellation, whose capacity will be dramatically increased following the successful July 25 launch of the Inmarsat 1-4A F4, or Alphasat, satellite.

The U.S. Defense Department “has a very good system; they just need more” capacity, said David Helfgott, president and chief executive of Inmarsat Government, the fleet operator’s Herndon, Va.-based marketing arm.

Even with the capacity boost expected from the Navy’s next-generation Mobile User Objective System, demand for UHF capacity, used mainly for tactical military applications including mobile services, is expected to exceed supply. This has led multiple companies to try to fill the gap.

In July 2012, Harris CapRock Communications of Fairfax, Va., announced it was teaming with Astrium Services of Europe to provide managed network services using UHF satellite capacity to international and U.S. government customers. The capacity is being provided initially by the British government-funded but commercially operated Skynet satellite fleet.

Meanwhile, Intelsat of Washington and Luxembourg, the world’s largest satellite operator, has added UHF military payloads to two of its satellites, one of which was lost in a launch failure early this year. 

The L-TAC service is ideally suited for a platoon of Marines operating in an area without significant infrastructure — such as Afghanistan — who want to communicate not only with one another but also with commanders in the United States, Helfgott said as an example.  

Inmarsat executives believe the service will be attractive to many users because it does not require land-based infrastructure. 

Like UHF frequencies, L-band provides very good voice and low-speed data transmissions, Helfgott said.  

For the service, users would need only an antenna adapter, about the size of a soda can,  for their existing UHF radio. The adapter, known as the SlingShot, was developed by the Spectra Group.

The device will have push-to-talk technology, which allows several different people to communicate on the same channel at once.

“The operational benefits for soldiers on the ground are enormous, providing low risk, highly resilient and easy to use connectivity independent of local infrastructure or terrain,” Andy Start, president of Inmarsat’s Global Government business unit, said in a statement in February.

So far, Helfgott said, L-TAC has generated “very strong interest” from potential customers. He expects the Defense Department, including special operations forces and intelligence customers, to be the service’s biggest user. Federal law enforcement agencies have also shown interest in L-TAC, he said.

L-band capacity leases for the new service will be available for terms as short as one month, Helfgott said. The service is expected to go on the market in August.

Mike Gruss is a senior staff writer for SpaceNews. He joined the publication in January 2013 to cover military space. Previously, he worked as a reporter and columnist for The Virginian-Pilot in Norfolk, Va. and The Journal Gazette in Fort Wayne, Ind. He...