Commercial satellite capacity leased from Loral Skynet appears to be the leading candidate to fill a gap in UHF-band mobile satellite communications coverage that some U.S. military leaders fear could materialize within the next three years.

Pentagon officials have grown

worried in recent years that some of the U.S. Navy’s UHF Follow-On (UFO)

satellites that are on orbit today may not last until the service begins launching the new-generation Mobile User Objective System (MUOS) satellites in March 2010. The geostationary-orbiting UFO satellites are used by mobile forces as well as headquarters staff in fixed locations


The most recent analysis

by the Navy’s Communications Satellite Program Office in San Diego

estimates there is a less-than-70 percent chance that the full UHF Follow On constellation will be healthy between December 2008 and when the MUOS satellites begin launching,

according to Steven Davis, a spokesman for the Space and Naval Warfare Systems Command in San Diego.

Options for filling any coverage gap that might materialize

include leasing commercial UHF services, and adjusting the Navy’s



, Davis said Oct. 25 in a written response to questions


Citing classification restrictions, U.S. Navy Lt. Denver Applehans, a spokesman for U.S. Strategic Command in Omaha, Neb., declined to comment on whether

a degradation of the UFO constellation would leave certain areas of the

globe without coverage or simply reduce the amount of

bandwidth available worldwide.

U.S. Air Force Gen. Kevin Chilton, commander of

Strategic Command, was briefed on the gap concerns

Oct. 18, Applehans said Oct. 26 in a written response to questions. One option under consideration – and likely the only one feasible prior to the first MUOS launch – is leasing UHF services from satellite operator Loral Skynet of Bedminster, N.J., beginning in 2008, Applehans said.

Another option is

leasing a payload aboard a spacecraft operated by Intelsat of Washington that would be available

around 2010, Applehans said.

Still another option is

a concept called

Netted Iridium

that Iridium Satellite LLC of Bethesda, Md., has demonstrated with the Marine Corps. However, that capability will

not be available until around the time of

the first MUOS launch, he said.

Iridium operates a global constellation of 66 satellites in low orbit. Scott Scheimreif, assistant vice president for government programs at Iridium, said


Netted Iridium

concept enables mobile forces to communicate over ad-hoc networks and

includes a push-to-talk feature

. A prototype of this system

has seen limited

use in Iraq, he said.

Iridium is


a five-year contract with the Marine Corps that could lead to improvements

including better access, range and signal security, Scheimreif said. In the interim, however, the prototype network could be expanded to help fill any UHF Follow On gap, he said.

Strategic Command also has

asked the Pentagon’s newly established

Operationally Responsive Space program office

to look at gap-filler options

, Applehans said.

But the type of system typically associated with Operationally Responsive Space, a relatively small satellite built and launched on relatively short notice, probably would not fill the military’s needs in the desired time frame, he said.


such systems have yet to demonstrate the ability to meet troops’ coverage and capacity needs. Small

satellites like the ones being developed under the Pentagon’s experimental

series might not able to handle software algorithms that increase the number of troops who can access a single communications channel, a technique

used on the UHF Follow On system

today. “This time division algorithm needs a stable platform in a specific orbit to be effective and it is unclear if a TacSat can meet this requirement,” he said.

However, the military may gain insight that can be applied to future use of small satellites to augment communications coverage through the planned TacSat-4 experiment, Applehans said. That spacecraft is expected to launch in late 2008.

In a written response to questions, Col. James Haywood, Air Force deputy director for space acquisitions, said the Operationally Responsive Space program office received a cost estimate of around $60 million to build a small satellite to help fill the potential UHF gap, but added that the figure had not been independently validated. Other options that the office looked at to address the gap included aerial platforms like balloon relays, he said.