Sunday, October 01, 2006

Last round of Wideband Gapfiller Satellite tests

The Boeing Company has completed Spacecraft Thermal Vacuum (SCTV) testing for the first of its Wideband Gapfiller Satellites (WGS). The tests, conducted at the Boeing Satellite Development Center in El Segundo, Calif., evaluated the WGS operating systems' ability to withstand the extreme temperatures of space.

"WGS has completed one of the most difficult and highest risk tests in the build process to evaluate its ability to withstand the extreme hot and cold temperatures of space," said U.S. Air Force Lt. Col. David Lee, WGS Block I program manager. "The completion of these tests moves WGS closer to its scheduled 2007 launch date."

Over a two-month period, Boeing completed the demanding tests inside its largest thermal-vacuum chamber, which provided the best representation of the space environment by removing all air and eliminating the ability to dissipate heat through convection. WGS testers cycled between hot and cold temperature extremes to ensure that all subsystems perform properly throughout all mission phases.

"With the thermal-vacuum test complete, the team now is conducting final reviews of all environmental test data to confirm that the satellite is ready to proceed with final factory testing and shipment to the launch site," said Charles Toups, vice president of Navigation and Communications Systems for Boeing Space & Intelligence Systems. "Once it's launched, WGS will provide a tremendous boost in capacity and operational flexibility for our U.S. Department of Defense customers. We are extremely proud to deliver these satellites to support our nation's needs."

WGS is the key element of a high-capacity satellite communications system designed to quickly disseminate large amounts of data to the warfighter. With a growing need for bandwidth, including two-way, point-to-point, multicast and broadcast communications, WGS will provide additional network-centric communications capabilities for troops in the field.

WGS will support the DoD's warfighting information exchange requirements, enabling execution of tactical command and control, communications, and computers; intelligence, surveillance, and reconnaissance (C4ISR); battle management; and combat support information. WGS will also augment the current Ka-band Global Broadcast Service (on UHF F/O satellites) by providing additional information broadcast capabilities.

Each WGS can route 2.4 to 3.6 Gbps of data -- providing more than 10 times the communications capacity of the predecessor DSCS III satellite. Using reconfigurable antennas and a digital channelizer, WGS also offers added flexibility to tailor coverage areas and to connect X-band and Ka-band users anywhere within the satellite field of view. The system provides tremendous operational flexibility and delivers the needed capacity, coverage, connectivity and control in support of demanding operational scenarios.

The WGS space segment will initially consist of three geostationary satellites operating over Pacific, Indian and Atlantic regions. Plans are in place for procurement of additional satellites to meet the warfighter's evolving SATCOM bandwidth requirements. Follow-on satellites will include enhanced capabilities, such as an RF bypass to support ultra-wide terminals needed for airborne ISR missions.

Boeing was awarded the WGS contract in January 2001, and has been authorized for production of the first three satellites, plus the associated ground-based command and control elements. Integrated logistics, training, and sustaining engineering support are also provided by Boeing. The procuring agency is the U.S. Air Force Space Command's Space and Missile Systems Center (USAF/SMC) at Los Angeles AFB, California.

With an initial launch scheduled in 2007 aboard an Air Force Evolved Expendable Launch Vehicle, WGS will provide early transformational capabilities supporting government objectives for the Transformational Communications Architecture in the next decade and beyond.

Capacity: WGS supports communications links within the Government's allocated 500 MHz of X-band and 1 GHz of Ka-band spectrum. The WGS payload can filter and route 4.875 GHz of instantaneous bandwidth. Depending on the mix of ground terminals, data rates and modulation schemes employed, each satellite can support data transmission rates ranging from 2.4 Gbps to more than 3.6 Gbps. By comparison, a DSCS III satellite will support up to 0.25 Gbps.

Coverage: The WGS design includes 19 independent coverage areas that can be positioned throughout the field of view of each satellite. This includes eight steerable and shapeable X-band beams formed by separate transmit and receive phased arrays; 10 Ka-band beams served by independently steerable, diplexed antennas, including three with selectable RF polarization; and transmit/receive X-band Earth coverage beams.

Connectivity: The enhanced connectivity capabilities of WGS enable any user to communicate with any other user with very efficient use of satellite bandwidth. A digital channelizer divides the uplink bandwidth into nearly 1,900 independently routable 2.6 MHz subchannels, providing connectivity from any uplink coverage area to any downlink coverage area (including the ability to cross-band between X and Ka frequencies). In addition, the channelizer supports multicast and broadcast services and provides an effective and flexible uplink spectrum monitoring capability to support network control.

Command and Control: Control of the WGS communications payloads is accomplished from four Army Wideband Satellite Operations Centers (WSOCs), using ground equipment hardware and software developed by Boeing, ITT Industries, and Raytheon Corp. Each Gapfiller Satellite Configuration and Control Element (GSCCE) has the capability to control up to three satellites at a time, via "in-band" (X-band or Ka-band) telemetry and command links. Spacecraft platform control is accomplished by the 3rd Space Operations Squadron (3 SOPS) at Schriever AFB in Colorado Springs, using WGS mission unique software and databases provided by Boeing, hosted on the Command and Control Segment Consolidated (CCS-C) systems that are being fielded by Integral Systems, Inc. The satellite is designed for compatibility with the current S-band SGLS TT&C capability, as well as the planned Unified S-band (USB) formats and frequencies.

Boeing 702 Platform: The Boeing 702 satellite is the industry leader in capacity, performance and cost-efficiency. Enabling technologies for the advanced 702 design are the xenon-ion propulsion system (XIPS), highly efficient triple-junction gallium arsenide solar cells, and deployable radiators with flexible heat pipes.

XIPS is 10 times more efficient than conventional bipropellant systems. Four 25-cm thrusters remove orbit eccentricity during transfer orbit operations and are used for orbit maintenance and to perform station change maneuvers as required throughout the mission life. Deployable radiators with flexible heat pipes provide substantially more radiator area, resulting in a cooler, more stable thermal environment for both bus and payload. This increases component reliability and reduces performance variations over life.

The figure below shows how the X-band and Ka-band antenna suites are interconnected via the digital channelizer to provide the unique flexibility and connectivity of WGS. Contrary to one report passed around the radio hobby, and based on publicly released information, it does not not appear as though these WGS platforms will carry any dedicated UHF downlink capability.