Screenshot from ULA Webcast of the launch of WGS-7. The orange cryo insulation foam is visible
Mission Rundown: ULA - Delta IV M +5,4 - WGS-7
Written: December 21, 2022
Last satellite to ‘follow on’ in orbit
Flying with an upgraded first stage, United Launch Alliance’s Delta IV rocket successfully deployed the seventh Wideband Global Satcom communications satellite.
Departing from Cape Canaveral’s Space Launch Complex 37B on Cape Canaveral Air Force Station occurred at 20:07 EDT on Thursday, July 23, 2015 - 00:07 UTC next Friday.
Delta IV M+5,4 flight path. Point 4 is BECO. Point 7 is MECO-1. Point 8-9 is MES-2 to SECO-2 doing the GTO burn. Point 10 is WGS-7 deployment. Delta IV CCB lands 3000 km downrange after BECO
The WGS-7 Payload
The Delta IV Medium+ rocket’s mission was to deliver the Wideband Global Satcom 7 (WGS-7) communications satellite in a super synchronous geostationary transfer orbit.
The first Block II Follow-On spacecraft in the US Air Force’s WGS program, WGS-7 introduces enhancements over its Block II predecessors with increased downlink channels and bandwidth. Further upgrades are expected to follow from the next satellite.
The 6,000 kilogram (13,000 lb) spacecraft carries a Ka and X-band communications payload. The spacecraft is designed for a service life of fourteen years.
Constructed by Boeing, the WGS spacecraft are based on the BSS-702 satellite bus. Twin solar arrays provide power for the spacecraft’s systems while an R-4D-15 liquid propellant motor will be used for major maneuvers such as orbit circularization.
An electric propulsion system, consisting of four XIPS-25 ion thrusters, will be used for stationkeeping. The contract to build WGS-7 was signed in September 2011, although long-lead parts had been under construction from August 2010.
Initiated and led by the United States Air Force, the WGS program has become multinational with Australia financing the sixth spacecraft in return for participation and international investment also facilitating a further vehicle.
The Delta IV Medium Launch
In the Delta IV Medium configuration, this is flown without boosters while the Delta IV Medium+ can fly with two or four solid rocket motors.
For the launch, which had flight number Delta 372, the Medium+(5,4) configuration was used. This featured 4 GEM-60 solid rocket motors and a 5 meter diameter upper stage.
Departing from Cape Canaveral’s Space Launch Complex 37B, Delta 372’s mission began with ignition of the first stage main engine five seconds ahead of liftoff. The solid rocket motors ignited a fraction of a second before the countdown reaches zero, with the Delta achieving liftoff when the thrust from the RS-68A engine exceeded her weight.
Beginning a series of pitch, yaw and roll maneuvers to attain attitude for her ascent to geosynchronous transfer orbit, Delta 372 aligned herself along a launch azimuth of 93.46 degrees heading East over the Atlantic Ocean. Forty five seconds into the flight the vehicle experienced maximum dynamic pressure.
At the 91.6-second mark in the flight the solid motors burned out. Their spent casings were jettisoned in pairs, 2.4 seconds apart, with the first two separating 100 seconds after liftoff. The payload fairing separated from around WGS-7 three minutes and four seconds into the flight.
Three minutes and 56.4 seconds after lifting off from Cape Canaveral, the Delta’s first stage propellant was depleted and the stage cut off. Six seconds later it separated from the rocket, allowing the second stage to extend the nozzle of its RL10B-2 engine and, thirteen seconds after staging, igniting to continue its ascent.
The Delta IV upper stage, the Delta Cryogenic Second Stage (DCSS), is powered by the single RL10B-2 engine and can be flown in versions with diameters of four or five meters depending upon payload requirements. Like the CBC, the DCSS burns liquid hydrogen and liquid oxygen.
The first burn of the second stage lasted fifteen minutes and 41.4 seconds. Following a nine-minute, 25.3 second coast the DCSS restarted for a further three minutes and eighteen seconds to establish the final orbit for spacecraft separation.
WGS-7 separated nine minutes and 9.9 seconds later into a 441 by 66,870 kilometer orbit (274 by 41,551 miles; 238 by 36,107 nautical miles) at an inclination of 24 degrees.
The Delta IV Medium rocket
United Launch Alliance’s Delta IV Medium +(5,4) rocket launched on the rocket type’s thirtieth flight, had flight number Delta 372 (D372). The Delta IV, which first flew in 2002, is one of the two types of Delta Evolved Expendable Launch Vehicles (EELVs) operated by ULA, along with the Atlas V.
ULA also operates the older Delta II rocket, which will be retired later this year. ULA has operated these three rockets since it was formed in December 2006 – with Delta II and Delta IV having been previously operated by Boeing and Atlas V originally developed by Lockheed Martin before the merger between the two companies.
Delta IV is a two-stage rocket, with an all-cryogenic core vehicle – fuelled by liquid hydrogen propellant and liquid oxygen oxidizer. The first stage is a Common Booster Core (CBC), powered by a single improved RS-68A engine. In the Medium+(5,4) configuration this is augmented by four GEM-60 solid rocket motors.
Delta’s second stage, the five-meter (16.4-foot) diameter version of the Delta Cryogenic Second Stage (DCSS), will begin to deploy the extendible nozzle of its RL10B-2 engine, with full ignition burn coming on about 13 seconds after stage separation.
The timings of the upper DCSS burns are more mission-specific than earlier flight events and have not been published, however, the first burn is likely to be longer, typically around twelve-and-a-half minutes in duration, establishing an initial Earth parking orbit.
Following a coast phase, a much shorter second DCSS burn will circularize the orbit. This burn could take as little as fifteen seconds. Depending on mission type, objectives and payload mass DCSS can make several more burns.
DCSS first burn always puts the payload into an elliptical orbit, second burn has either a transfer objective or is to circularize the high Earth orbit. The transfer burn happens usually on the equator line over Africa where a yaw turn will reduce the inclination of the orbit with the equator line from 28 to 16-8 degrees.
DCSS will perform a third 10 minute burn to raise the first orbit to a steep elliptical 10 hour long transfer orbit with the aim to reach a geostationary orbit at 35 500 km altitude. The size and mass of the payload now dictates whether or not the payload will be deployed 5 minutes after the third burn shutdown.
Eight ton - 8 000 kg payloads are left to find the way to their geostationary orbit under their own power with an apogee engine and its propellant of choice. Smaller payloads 2-3 ton - 2-3 000 kg can be inserted by DCSS in a geostationary orbit with a fourth burn.
Delta IV Medium 5,2 split in its major parts. The DCSS tank capacity isn’t know in details yet
Now all there is left is the fourth deorbit burn or the fifth graveyard burn. DCSS have by now used all of its propellant but 10-12 seconds. That burn time is used to get out of the payload's way so it won't interfere with its orbit.
The graveyard orbit will take about 25 000 years to decay down to Earth and the deorbit burn will lower the perigee to below ocean level or below the 100 Km Karman line, where air friction will brake its mach 25 speed for good.
Delta IV M stands 67 meters - 220 feet tall, weighs about 340 194 kg - 750 000 pounds and is launched with a thrust of more than 4.45 MN - 1 000 000 foot pounds.
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