Flexibility drives new Pentagon satellite plans
DOD officials seek to balance the need for speed with investment protection
New technology is always faster and better than its immediate predecessor, sometimes significantly so. But the financial case for switching to a new platform is more complicated if the move requires pulling the plug on a large and still perfectly functional installed base of equipment.
Defense Department officials faced these kinds of trade-offs when designing their newest fleet of communications satellites under the Wideband Global SATCOM program.
Among other more advanced features on the WGS satellites, new Ka-band transmission technology gives each spacecraft 10 times the bandwidth capacity of the X-band Defense Satellite Communications System (DSCS) satellites they are replacing.
However, U.S. military forces still use thousands of X-band radios and terminals in various theaters of operation, a significant investment in equipment and training that leaders are reluctant to abandon.
Therefore, officials decided to use some of the WGS satellites’ premium onboard processing capacity to continue support for X-band radios while allowing them to communicate with newer Ka gear.
“The satellite has all its expense upfront, but the long tail of the cost is in the terminals, so we want the satellite to be as terminal-friendly as possible and not drive a lot of changes,” said Col. Donald Robbins, commander of the Military Satellite Communications Systems Wing's Wideband Satellite Communications Group at Los Angeles Air Force Base, Calif. Robbins is responsible for the WGS and DSCS programs.
WGS’ embrace of existing X-band gear is important, but it’s only one of several benefits the satellites offer to support more flexible, rapidly evolving warfighter capabilities.
The new program also arrives on the scene as the military adjusts its satellite plans to increasingly use commercial services to meet surge needs rather than always building its own spacecraft.
The three operational WGS satellites — the third went online in June — support all combatant commands, with WGS 1 and 2 at 35 percent and 54 percent of capacity, respectively, and operating an even split of X-band and Ka-band use, Robbins said.
A digital channelizer on each satellite lets ground forces using an X-band terminal or radio communicate with other forces using a Ka-band terminal or radio. In the past, an X-band radio could only communicate with another X-band radio. Now deployed forces that are already using one type of device don't need to carry another.
Communications via the Ka band are increasing because it has faster data rates and a higher capacity. For example, transmitters on unmanned aerial vehicles are transitioning to the Ka band to better handle live and high-definition video streams.
Each of the first three WGS satellites is equipped with 10 Ka-band antennas. Eight of them provide narrow coverage, and the other two provide wider area coverage. The coverage of the oval-shaped beam coming from the Ka-band antennas spans 600 miles, and the beam can be steered through a gimbal system, a feature not available with previous-generation satellites.
“If you have a conflict in a certain area of the globe, you can gimbal the antenna and move that 600-mile footprint to wherever you want to put it,” said Mark Spiwak, Boeing's program director for WGS.
Each WGS satellite also includes two X-band phased array faces; one to transmit communications and one to receive them. Like the Ka-band antenna, the X-band phased arrays are also steerable. They also can change shape to more effectively cover terrain.
“Let’s say I have comms around the coast of New Jersey,” Robbins said. “If I put a circular beam down in Asbury Park, half of my beam might be in the Atlantic Ocean, even though I don’t have any people in the Atlantic. Instead, I can shape the beam so it follows the New Jersey coastline.”
A satellite can also use the shaping feature to tailor its beam to avoid a signals jammer on the ground.
Road Map Revisions
For now, the WGS satellites will coexist with the eight DSCS satellites in orbit until their fuel runs out. Boeing is building WGS satellites 4, 5 and 6, known as Block II satellites. They will have modifications from the first three WGS satellites that allow them to provide more bandwidth to support the unmanned aerial vehicle airborne intelligence, surveillance and reconnaissance mission.
The WGS 7-12 Block II Follow On satellites would be clones of those in construction for Block II, though there are a variety of studies under way to add more capacity to those satellites to compensate for the canceled Transformational Communications Satellite (TSAT) rogram. That program was scheduled to play an important role in Warfighter Information Network-Tactical Increment 4 and other programs.
Although the military is adding significantly more bandwidth through the WGS program, it anticipates that it will still need surge capacity for future conflicts and to pick up slack from the canceled TSAT program. For that, the military turns to private-sector satellites, such as satellites owned by Inmarsat and Intelsat. Those companies have started programs to build new commercial satellites that will include hosted payloads that the military can lease.
“Comms-on-the-move for land, mobile users and ISR for unmanned aerial systems were big drivers for TSAT,” said J.J. Shaw, director of North America and global naval programs at Inmarsat. “The requirements are being recategorized with the cancellation of TSAT, but they are still there.”
In August, Inmarsat contracted with Boeing to build three Ka-band satellites with 89 total Ka-band antennas. The Inmarsat-5 satellites support the same waveforms and terminals that are supported by the WGS satellites. Intelsat also has contracted with Boeing to build four communications satellites under a 2009 agreement, and two of those four satellites will include an ultra-high-frequency hosted payload.
ViaSat is another company seeking to provide bandwidth for the military, though it’s taking a different approach. Rather than using a satellite built for broadcast, ViaSat plans to launch a satellite, named ViaSat-1, in 2011 that is specifically designed for two-way communications. Instead of having a capacity of 2.5 gigabits/sec, as WGS satellites have, it will support communications as fast as 140 gigabits/sec, said Ric VanderMeulen, vice president of government satellite communications at ViaSat.