United Launch Alliance’s first Delta IV launch of 2017 carried a Wideband Global Satcom spacecraft (WGS-9) into orbit Saturday. The lift off from Cape Canaveral Air Force Station occurred at 20:18 local time (00:18 UTC), following a slightly delay related to the Swing Arm system at the pad.
Delta IV Launch:
Saturday’s launch will deploy the ninth satellite of the US Air Force’s Wideband Global Satcom (WGS) constellation. WGS-9, which was purchased for the Air Force by a group of other nations in exchange for access to the WGS system, will join the eight satellites already in orbit which launched between 2007 and 2016.
Boeing was awarded a contract to develop the WGS system – with two satellites and an option for a third – in 2001, with the first launch scheduled for 2004. The option in the contract was converted to a firm order for a third spacecraft early in 2003.
The WGS program – named Wideband Gapfiller Satellite until 2007 – was initiated to augment the Defence Satellite Communications System (DSCS), providing new and enhanced capabilities and replacing older satellites as they reached the end of their operational lives. WGS spacecraft provide more than ten times the bandwidth of their predecessors – with a single spacecraft having greater bandwidth than the entire DSCS constellation combined. DSCS and WGS would have been replaced by the Transformational Satellite System (TSAT) constellation, however this was canceled in 2009.
Even before TSAT was canceled, the Air Force had begun to expand WGS; increasing the planned number of satellites from three to five in 2006. The Australian government agreed to finance a sixth satellite in exchange for access to the whole constellation, and this was ordered in October 2007. From the fourth satellite onwards the spacecraft have been upgraded with radio frequency (RF) bypass functionality for applications requiring extremely high bandwidth, such as unmanned aerial vehicles (UAVs) deployed on reconnaissance missions.
Four further satellites, including the WGS-9 spacecraft which will launch on Saturday, were ordered between 2010 and 2012. These are designated as Block II Follow-On missions. From WGS-8 onwards, the satellites have been equipped with an upgraded digital channelizers, almost doubling the available downlink bandwidth.
Built by Boeing, WGS satellites are based on the BSS-702 platform and designed for fourteen years of service. Each spacecraft is equipped with an Aerojet Rocketdyne R-4D-15 High Performance Apogee Thruster (HiPAT) to perform insertion into geosynchronous orbit and four Xenon-Ion Propulsion System (XIPS-25) thrusters for stationkeeping.
The WGS-9 satellite carries X and Ka-band transponders. The satellite will use a phased array antenna to provide eight jam-resistant X-band beams, while ten individual antennae will provide Ka-band beams. An additional X-band payload will be used to provide Earth coverage. The satellite can support 8.088 gigahertz of bandwidth, with an expected downlink speed of up to 11 Gbps.
The first WGS satellite, USA-195 or WGS-1, launched aboard an Atlas V 421 in October 2007. The second satellite was also deployed by an Atlas, launching in April 2009.
Beginning with the third launch – in December 2009 – the Delta IV has been used for all subsequent launches, flying in the Delta IV Medium+(5,4) configuration.
The Delta IV was developed by Boeing under the US Air Force’s Evolved Expendable Launch Vehicle (EELV) program. Boeing inherited the Delta IV design from McDonnell Douglas in a 1997 merger, having had its own EELV proposal rejected the previous year. The Delta IV first flew in November 2002, three months after Lockheed Martin’s rival design, the Atlas V, which was developed under the same program.
In 2003, following revelations that Boeing had illegally obtained tens of thousands of pages of documents from Lockheed Martin during the initial competition for EELV launch contracts, the Department of Defense (DoD) moved several launches which had been awarded to Boeing to the Atlas V and temporarily suspended Boeing from bidding for new launch contracts.
The dispute was resolved when the companies agreed to merge their launch operations, forming United Launch Alliance in December 2006 to offer Delta II, Delta IV and Atlas V launches to the US Government.
Saturday’s launch was the thirty-fifth flight of the Delta IV, which has achieved thirty-three successful launches in its previous missions.
The Delta IV Medium+(5,4) configuration has only been used for WGS launches. It is one of five configurations in which the Delta IV has launched; the Medium, which had a single core, no solid rocket motors and a four-metre DCSS, was the smallest version. Used for two launches in 2003 and a third in 2006, it is now effectively retired as no launches are scheduled and no new medium-class payloads are being assigned to the Delta.
The largest configuration, the Delta IV Heavy, uses three cores and a five-metre upper stage. Three intermediate, or Medium+, configurations – the M+(4,2), M+(5,2) and M+(5,4) – are used to launch intermediate payloads. These add two solid rocket motors, a five-metre upper stage and two further solid rocket motors respectively to the single-core vehicle.
United Launch Alliance intends to retire the single-core version of the Delta IV by 2019, with the Atlas V launching all medium and intermediate-class payloads until the introduction of a new rocket, Vulcan, which will replace both the Atlas V and Delta IV.
The Delta IV Heavy will remain flying until Vulcan has been upgraded to carry the US military’s heaviest payloads, which can currently only fly aboard the Delta. Saturday’s launch will be the second-to-last flight for the Delta IV Medium+(5,4).
The Delta IV departed from Space Launch Complex 37B at the Cape Canaveral Air Force Station (CCAFS). The Delta launch complex is built on the site of a pad which was used in the 1960s for early test flights supporting the Apollo program.
The original Launch Complex 37B was the site of the first orbital launch of the Saturn I rocket, SA-5, in January 1964, before five further launches with boilerplate Apollo spacecraft. After the Saturn I was retired, two Saturn IB launches were made from LC-37B, the first testing the rocket’s S-IVB stage in orbit and the second, Apollo 5, marked the first unmanned test flight of the Apollo Lunar Module.
The Saturn launch complex having been demolished in the 1970s, Delta’s launch pad at Complex 37 was constructed in preparation for the Delta IV’s maiden flight, which occurred from SLC-37B in November 2002.
Saturday’s launch began with ignition of the Delta IV’s RS-68A main engine, five seconds before the countdown reached zero. Burning liquid hydrogen and liquid oxygen, the RS-68A powers the Common Booster Core (CBC) that form’s Delta’s first stage. At the zero-second mark in the countdown, the four GEM-60 solid rocket motors ignited, and the rocket – whose mission number was Delta 377 – lifted off.
Seven seconds into its flight, Delta 377 began a series of pitch, yaw and roll manoeuvres to place it on course for orbit. The rocket flew east downrange along an azimuth of 93.46 degrees, passing through the area of maximum dynamic pressure – Max-Q – 46.1 seconds after liftoff.
The solid rocket motors began to burn out 92.8 seconds after launch, with boosters three and four burning out 2.3 seconds ahead of boosters one and two. The two pairs of boosters separated eight seconds after their respective burnouts.
Three minutes and 14.6 seconds into the mission, the payload fairing separated from around the WGS-9 satellite at the nose of the rocket. By this point, the rocket cleared the lower regions of Earth’s atmosphere and the fairing was no longer needed to protect the spacecraft.
The Common Booster Core completed its burn three minutes and 56.5 seconds after liftoff. The spent stage was jettisoned 6.6 seconds later. After stage separation, the second stage – a five-metre Delta Cryogenic Second Stage (DCSS) – deploy the extendible nozzle of its RL10B-2 engine ahead of ignition. The RL10B-2 ignited thirteen seconds after staging to begin its first burn.
The DCSS, which like the first stage burns liquid hydrogen and liquid oxygen, made two burns to deploy WGS-9 into its planned orbit, with a third burn after spacecraft separation to deorbit itself. The first burn was the longest, lasting fifteen minutes and 37.5 seconds, and established the rocket in an initial parking orbit. Nine minutes and 33 seconds after the first burn ends the second began, raising the apogee of Delta 377’s orbit. This burn lasted three minutes and 9.7 seconds.
Spacecraft separation occurred at 41 minutes, 45.6 seconds mission elapsed time, nine minutes and 10.3 seconds after the end of the second burn. WGS-9 was deployed into a supersynchronous transfer orbit with a perigee of 435 kilometers (270 miles, 235 nautical miles), an apogee of 44,372 kilometers (27,572 miles, 23,959 nautical miles) and an inclination of 27 degrees to the equator. From this orbit, the satellite will use its R-4D apogee motor to raise itself into geostationary orbit.
The second stage began its third and final burn twenty-nine minutes and 59 seconds after spacecraft separation.
This ten-second deorbit burn lowered its orbit’s perigee so that the stage reenters Earth’s atmosphere at the end of its first orbit.
Because of the orbit’s high apogee, the stage will take another eleven hours to complete this one revolution, while the Earth rotates underneath such that the stage will reenter over the western Pacific. ULA states that the expected impact time for any debris surviving reentry will be twelve hours, twelve minutes and 9.6 seconds mission elapsed time.
Saturday’s launch was the third of the year for United Launch Alliance, who conducted Atlas V launches in January and early March to deploy the SBIRS-GEO-3 missile-detection satellite and NROL-79 – a pair of Intruder signals intelligence satellites – respectively. ULA’s next launch is scheduled for next Saturday, with another Atlas V due to carry the SS John Glenn – Orbital ATK’s OA-7 Cygnus mission to resupply the International Space Station.
The next Delta launch is scheduled for September, with the National Oceanic and Atmospheric Administration’s (NOAA) JPSS-1 weather satellite lifting off aboard the penultimate flight of ULA’s venerable Delta II rocket. The Delta IV’s next launch will occur in October, with the NROL-47 satellite, which is expected to be a Topaz radar imaging spacecraft.
Only one further WGS satellite, WGS-10, is currently scheduled for launch. This is slated to lift off in 2019, aboard the final single-core Delta IV launch.
(Images via ULA).