While overcrowded skies already are causing the U.S. Defense Department to consider scaling back its planned unmanned aerial vehicle (UAV) purchases, industry officials say even a smaller fleet is still likely to strain the limits of the Pentagon's satellite communications capacity.

Army officials have been considering canceling two of the four UAV rollouts planned under the Future Combat Systems program. The existing plan would give four types of UAVs to each Army brigade, and a review is currently being done to see whether all four are necessary or whether they would unnecessarily weigh down the brigades. The Army also is experiencing traffic problems in places like Baghdad where the skies are increasingly congested from the growing numbers of UAVs.

Even if it does cut back on its current UAV plans, there may not be enough satellite capacity available to handle the demands of an already extensive UAV program.

As military use of UAVs has grown, government officials have looked at adding more advanced sensors, weapon capabilities and the ability to transfer high-speed, full-motion video back to commanders. And while some of the enhancements for UAVs such as stealth capabilities do not take up bandwidth, many applications will dramatically increase the amount of bandwidth needed, industry officials said.

David Helfgott, president and chief executive officer of Americom Government Services of McLean, Va., said some UAVs need to transmit high-definition data at speeds that can exceed 45 megabits per second. Americom Government Services sells commercial satellite capacity to U.S. government users.

Helfgott said another challenge is that UAVs require a rather small antenna, which limits the rate of data transfer. Surveillance UAVs, which transfer multispectral data from infrared and ultraviolet sensors, take up a great deal of bandwidth, as do both regular definition and high-definition video, Helfgott said.

As a result, the Department of Defense already has problems allocating the necessary bandwidth to serve the several hundred UAVs already in the field.

A Predator or Globalhawk UAV as it exists today can take up to a full transponder on a satellite to transfer its data, Helfgott said.

"Can you imagine somebody having to get 1,000 of those up into the air?" Helfgott said. "You're not going to probably have a situation where all those are being used at once, but even 100 is an issue." UAVs require Ku-band capacity to transfer their data, and in certain parts of the world, such as in the Middle East, this can be hard to come by, he said.

Commercial providers have stepped in to help fill the military's need for UAV bandwidth, but while that has been beneficial, it might not always be a viable option, said Victoria Samson, an analyst with the Center for Defense Information in Washington.

"The U.S. military lucked out when at the same time they had a strong need for extra capabilities, the commercial world had stuff [available] to sell," Samson said. "There's going to be a time when that's just not going to be there."

Industry officials say the military often expects them to build capacity with the Pentagon's needs in mind, but without a formal contract in place. Helfgott said AGS is keeping UAVs in mind as it develops payloads that provide capacity in the Ka-band of the spectrum, which allows a higher throughput than Ku- or C-band.

Military officials have said that when the Transformational Communications Satellite (T-Sat) program, slated to launch in 2013, is completed, the laser crosslinks and IP-router technology it uses will help solve the Pentagon's bandwidth needs.

But "T-Sat is really stumbling badly," Samson said, citing the budget cuts and technical difficulties the project has faced; after cutting $200 million from the 2006 budget for T-Sat last year, the Senate Armed Services Committee is looking at trimming another $70 million in 2007.

"This means the only solution you have is possibly decades away," Samson said. By then, the demand for bandwidth will have increased exponentially.

"T-Sat may be able to meet the demand," said Jim Lewis, a senior fellow with the Center for Strategic and International Studies. "But the problem is that people keep discovering ways to use more bandwidth, to add more sensors. "

Military officials have made some efforts to conserve satellite bandwidth, said Dan White, vice president of engineering for DataPath of Duluth, Ga., which provides satellite connectivity solutions, largely for military customers. DataPath worked with the Marines to develop an IP accelerator, which transmits data from the ScanEagle UAVs in real time; before transmission took an hour.

But some industry officials say the military isn't doing enough to examine creative ways of using existing bandwidth.

Richard DalBello, vice president of government relations for Intelsat General of Washington, said the Pentagon needs to look into a more "network-style" approach to capacity rather than point-to-point systems. They need to prioritize and reroute communications to free up more bandwidth for UAVs, Dalbello said.

The military also could explore relying on near-space communications platforms to provide additional bandwidth, Lewis said.

Dyke Weatherington, deputy for the UAV planning task force for the Office of the Secretary of Defense, could not be reached for comment at press time. Calls to the Office of the Secretary of Defense press office were not returned.

Greg Grant contributed to this article from Washington.