FROM GAPFILLER TO GLOBAL
FROM GAPFILLER TO GLOBAL
No Longer Seen as an Interim Step, Wideband Global
Satellite System is Becoming a Major Link in Military Communications.
by Tom Marlowe, MIT Correspondent
The Wideband Global Satellite Communications (WGS) system, designed to provide faster and more robust communications to warfighters in the field, is already proving itself capable of speeding delivery of service to U.S. forces in more ways than one.
Not only does one WGS satellite provide more throughput and flexibility than the entire constellation of nine Defense Satellite Communication Systems (DSCS) satellites but also the satellite was being used by military operations within six months of its launch— an unprecedented feat.
The Air Force declared the first WGS satellite operational this spring, following its launch last October. Today, it is relaying communications to forces in the Pacific region, providing a tremendous boost to military bandwidth and the capability to communicate across satcom channels.
“WGS provides the capability to work in both X-band and Ka-band to augment the DSCS satellites and the Global Broadcast System [GBS] respectively,” said Joe Davidson, a spokesperson for Space and Missile Systems Center at Air Force Space Command. “Because of the cross-band capabilities of WGS, a signal received in one frequency band can be transmitted in the other,” Davidson explained. “In addition, WGS supports twoway Ka-band communications—while prior GBS capabilities only supported one-way communications— as well as frequency reuse and bandwidth switching.”
The ability to transmit communications from one frequency band to another enables warfighters to send a file or stream up an X-band, for example, and down to a Ka-band terminal or the other way around. In addition, the WGS satellites can support UAVs at rates previously unheard of. Once all six of the satellites are launched by 2012, the first three could support eight UAVs transferring data simultaneously at 137 Mbps and the latter three could support two additional UAVs at 274 Mbps.
Support for UAVs is just one example of communications capabilities provided by WGS satellites, which will also assist U.S. Strategic Command and the combatant commands, tactical and deployed troops, the Defense Information Systems Network, Defense Dissemination System, C4I Afloat, Diplomatic Telecommunications System, White House Communications Agency, Defense Support Program and U.S. intelligence agencies.
Although the acronym has remained the same, the name of the program was changed during the course of its development, from a “gapfiller” to a “global” system. The Department of Defense initially conceived of WGS as a means of meeting needs on an interim basis pending institution of the Transformational Satellite Communications (TSAT) system, but instead settled on WGS as a modern standard.
DoD also struck the gapfiller designation from WGS because the system has at least one capability not provided by TSAT that warfighters will continue to need in the future.
“The main rationale for this is knowing that the capabilities that will eventually be provided by TSAT do not include continued support of X-band users,” Davidson elaborated. “What TSAT offers in protected communication, WGS makes up for with increased capacity and data rates. Continued support of X-band will not end in the foreseeable future. One capability of a next generation of WGS would be enhanced aerial intelligence surveillance and reconnaissance support.”
REVOLUTIONARY ELEMENTS
The U.S. military breaks down satcom services into the categories of protected, wideband and narrowband communications.
TSAT and the legacy MILSTAR satellites provide protected communications, which incorporate very secure channels and could survive a nuclear attack, according to Mark Spiwak, WGS program director for prime contractor Boeing.
When military forces need to send large data files or stream video in wideband applications, they would rely upon the DSCS satellites, but now they can use WGS as well. For narrowband communications, warfighters utilize the UHF or UHF Follow-On (UFO) satellites.
Boeing is currently under contract for six WGS satellites, although it is involved in several of the other prominent satcom programs, Spiwak elaborated. The next two WGS satellites are scheduled to launch in the fall of this year. DoD is targeting an October launch date for the second of the satellites, while the third satellite is less than a month behind it in terms of readiness.
The next three satellites, which constitute block two of WGS, are in production. The first of those, the fourth WGS satellite, is planned to launch in 2011. The final one should be in orbit in 2012.
One WGS satellite is able to surpass the entire constellation of DSCS satellites in wideband signal bandwidth due in part to several innovations Boeing introduced to the satellites, Spiwak added.
“There are two key elements to focus on,” Spiwak explained. “First, the satellite handles X-band and Ka-band communications. We have an X-band phased array. The phased array technology is remarkable. It can handle 1,900 independently routable channels. It’s a very flexible system.
“When you have a historical satellite, you have a fixed antenna that provides a shape on the ground and that satellite is able to provide communications coverage and capability to a certain area on the ground and a certain throughput on the ground. These phased array antenna can be digitally steered and digitally commanded dynamically to change the shape it provides on the ground and the throughput,” he said.
So DoD might determine that a specific area requires higher bandwidth capability specifically for X-band. It could then enlarge the pipe for X-band communications via WGS, changing the shape of the antenna and steering signal as necessary.
“It can provide a larger pipe, a smaller pipe or a tailored pipe to provide communication to the area on the ground to the troops that need it when DoD says it needs to change the shape of the beam to a specification and provide capability to a specific area,” Spiwak observed. “That ability, that throughput and flexibility, is extremely valuable.”
The second key element that revolutionizes satellite capabilities deals with the capability to transmit messages between X-band and Ka-band systems via the satellites’ digital channelizer. In the past, X-band and Ka-band communications have required their own dedicated ground equipment, which provided little or no capability for cross-band communications. But now the digital channelizer can route communications between the bands.
“So when you are in a battle anywhere in the world, you are not worried about having to talk just to X-band or Ka-band,” Spiwak remarked. “You want to call in air support or ground support without having to worry which channel it is using. When you need support, this satellite allows flexibility for capability to talk to those resources.”
ON-ORBIT PERFORMANCE
The WGS satellite on-orbit has so far impressed DoD officials with its other capabilities as well. It can transmit data at a rate greater than 3 GB per second, much more than an estimated quarter GB per second for the entire DSCS constellation, Spiwak noted. “It is very tailorable. The customer can have a very narrow band and provide significantly more than 3 gigabits per second, or it can have a broader band and provide less than that,” he said.
In addition, WGS has six globally positioned ground stations with equipment capable of handling the tailored beams along with the cross-band communications. Those capabilities sprung from DoD requirements, which drove the specifications of the WGS satellites, which in turn drove specifications for the ground hardware.
Once these requirements were fulfilled, DoD recognized it had achieved a modern wideband communications system and not merely a “gapfiller” system, Spiwak revealed. “The WGS gapfiller was once meant to fill gaps before DoD went to its advanced wideband systems,” Spiwak described. “As the design matured and the WGS capability became more real as hardware was delivered and validated, the DoD looked and said this is our staple program.”
Economics also play a role as DoD is eager to save money with more cost-effective satcom solutions. The department must lease a great deal of commercial satcom capability to meet its communications needs. That commercial bandwidth costs a lot more than governmentowned bandwidth. WGS’s capabilities to deliver both X-band and Ka-band communications in addition to its signal flexibility promise to deliver a great deal of cost savings to DoD in the future.
The military also has the potential to realize these savings much faster than it might have in the past due to the speed with which WGS satellites have proven ready for operations, Spiwak reported. Boeing delivered WGS capability in less than six months from launch of the satellite.
“That is the cleanest and quickest system the Air Force has ever been able to deliver. Boeing is very proud of having such a capable system being delivered six months after launch,” Spiwak declared.
“This satellite has an additional 50 percent margin on its propellant life because of the performance in getting to orbit and 25 percent margin on downlink power, which allows the Air Force to put increased power and increased flexibility into the field of regard,” he continued. “Those are figures of merit that are unprecedented in terms of delivering satellite systems.”
The time from launch to availability for previous SATCOM systems like MILSTAR ran perhaps four or five times longer than WGS, Spiwak estimated, making WGS the fastest satcom vehicle ever to swing into action for the military. ♦
