Seventh WGS satellite readied for launch atop ULA Delta IV booster
CAPE CANAVERAL, Fla — After launching the GPS IIF10 satellite on July 15, Colorado-based United Launch Alliance is now preparing a Delta IV+ Medium (5,4) rocket for liftoff, which, if it flies on schedule, will see the seventh Wideband Global SATCOM (WGS 7) communications satellite sent aloft. In slightly more than a week, ULA will have fielded two of the three rockets that the aerospace firm currently employs.
The WGS system is a partnership between the United States Department of Defense (DoD) and Australia’s Department of Defence. Operation and usage of the system are divided into three segments: terminal, control, and space. The spacecraft being fielded atop ULA’s Delta IV rockets work alongside Terminal Segment users and the Control Segment operators.
These services are currently provided by the Defense Satellite Communications System (DSCS) and Global Broadcast Service (GBS) satellites already on orbit. According to a report appearing on SpaceFlight Now, a single WGS satellite will provide as much bandwidth as the entire DSCS system.
The communications services provided by the WGS fleet will be used by members of the Canadian, U.S., and Australian armed services. The satellites will provide additional bandwidth and communications resources to allow for better communications for soldiers on the battlefield.
The WGS constellation will serve to strengthen the existing Ka-band Global Broadcast Service (on UHF F/O satellites). This service will be accomplished by utilizing new two-way abilities on that band.
WGS-7 will connect the X-band and Ka-bands and is the first Block II follow-on satellite. Both Block I and II spacecraft are capable of filtering as well as downlinking up to 4.575 MHz from 39 primary channels. WGS-7 can filter and downlink up to 5.375 MHz from 46 primary channels (according to information obtained from United Launch Alliance).
WGS-7 is incorporated with a high-bandwidth radio frequency (RF) bypass capability; this gives the satellite the ability to handle a larger bandwidth. Each WGS satellite should be able to provide data transmission rates between 2.1 and 3.6 Gbps.
According to ULA, the WGS 7 should, if it functions as advertised, deliver up to ~800 MHz of additional bandwidth through the use of “Redundant Port Activation”.
With nineteen independent coverage areas, 18 can be focused on positions across the satellite’s purview. WGS-7 has eight steerable/shapeable X-band beams that are formed by different transmission and reception beams. The spacecraft has 10 Ka-band beams that are managed by independently steerable diplexed antennas.
The system has been designed to be flexible with each satellite able to customize the coverage it provides. WGS can connect either X-band and Ka-band users with one another anywhere within the satellite’s field of vision.
The fleet of WGS satellites are managed by five Army Wideband SATCOM Operations Centers which have been strategically positioned at different points across the globe. These sites are meant to provide 24-hour operations support for the GPS fleet. To help get this new spacecraft on its way into the black of space, the company has tapped one of the three rockets that it currently fields.
ULA has employed one of the heavier versions of the Delta IV Medium rocket to launch these satellites to their orbital destinations. This flight should see a slight variation in the four Orbital ATK-provided GEM 60 solid rocket boosters that are affixed to the booster’s first stage. SpaceFlight Insider has received a report that one of the four SRBs will be about one to two feet longer than the others. Apparently, one thrust cone will be steerable during flight, and the other three will have fixed thrust cones. There are several core components that comprise the Delta IV Medium launch system.
Payload Fairing (PLF) – The PLF is the component of the rocket that will shield WGS-7 through Earth’s dense atmosphere. The PLF, composed of a composite bisector, measures about five meters in diameter.
The PLF stands at an impressive 47 feet (14 meters) in height. With this component in place, the Delta IV Medium’s height is brought to 217 feet (66 meters).
Delta Cryogenic Second Stage (DCSS) – Positioned beneath the PLF, the DCSS contains propellant tanks that are structurally rigid and constructed of isogrid aluminum ring forgings and spun-formed aluminum domes. Fueled by super-cooled (cryogenic) liquid hydrogen and liquid oxygen, the DCSS employs a single RL10B-2 rocket engine.
The RL-10B-2, produced by Aerojet Rocketdyne, is capable of generating some 24,750 lbf (110 kN) of thrust. Each of the DCSS’ tanks is insulated with sprayed-on as well as bonded-on insulation blankets. Support for the stage’s electronics contained within the DCSS is provided by an equipment shelf.
Booster – The Delta IV design is based on what is called the Common Booster Core or “CBC”. This design allows for more of the boosters to be attached together (as is the case with the Heavy version of the booster).
The single CBC used on the Medium version of the rocket gets its power from a single Aerojet Rocketdyne RS-68A engine at its base. Like the RL-10B-2, the RS-68A is fueled by cryogenic liquid hydrogen and liquid oxygen, and is capable of producing some 705,250 lbf (3.137 MN) of thrust at sea level.
Like the DCSS, the CBC is covered by a combination of sprayed-on and bonded-on insulation along with helium-purged insulation blankets. The CBC is controlled by avionics located within the DCSS which guides and controls the rocket as it carries its charge to orbit.
GEM-60 – This version of the Delta IV Medium will use four strap-on Orbital ATK GEM-60 solid rocket boosters. These are affixed to the CBC. Each of the SRBs is capable of generating an additional 191,400 lbf (851.4 kN) of thrust.
United Launch Alliance still has several flights on its 2015 manifest. The next launch currently scheduled will be that of the fourth spacecraft Mobile User Objective System. Planned for a August 31, 2015 flight, ULA will employ the most powerful version of the Atlas V rocket – the 551. Liftoff will occur from Cape Canaveral’s Space Launch Complex 41 in Florida.
Jason Rhian spent several years honing his skills with internships at NASA, the National Space Society and other organizations. He has provided content for outlets such as: Aviation Week & Space Technology, Space.com, The Mars Society and Universe Today.