Screenshot from ULA Webcast of the launch of WGS-10. Don’t worry. I’ll hold you until you must go
Mission Rundown: ULA - Delta IV M+5,4 - WGS-10
Written: September 16, 2021 - Edit: December 3, 2022
Time to set up more antennas
United Launch Alliance deployed a Wideband Global Satcom satellite for the US Air Force Friday on a Delta IV M+5,4 rocket. WGS-10 lifted off from SLC-37B on the Cape Canaveral Air Force Station at 20:26 EDT on Friday, March 15, 2019 - 00:26 UTC on Saturday.
WGS-10 was carried into orbit by United Launch Alliance’s Delta IV rocket, which will be flying in its Medium+(4,5) configuration. Friday’s launch was expected to be the last time that this version of the Delta IV – which has been used exclusively to launch WGS satellites – flies. One more GPS launch was approved, so this Friday's launch was the penultimate second to last medium class Delta IV launch remaining on ULA’s manifest – July’s GPS launch will be the final flight of the Delta IV Medium+.
Friday’s launch was targeting a low-inclination geosynchronous transfer orbit; the rocket needs to fly to the East and be launched from the East Coast on SLC-37B.
The WGS-10 Payload
Wideband Global SATCOM - WGS-10 satellite vehicle is the latest part of a growing constellation of highly-capable communications satellites that serve the armed forces of the United States and its allies.
WGS satellites are based around Boeing’s BSS-702 bus, with each satellite equipped for a service life of at least fourteen years. The satellites are powered by solar panels, with propulsion coming from a liquid-fuelled R-4D-15 High Performance Apogee Thruster (HiPAT) and four Xenon-Ion Propulsion System 25 (XIPS-25) stationkeeping thrusters. Each satellite has a mass of about 6,000 kilograms (13,200 lb).
As WGS launches have continued, the capabilities of the satellites have been upgraded. The first three spacecraft were built to the Block I specification, while from the fourth spacecraft onwards the Block II spacecraft featured an RF bypass function to allow for extremely high bandwidth operations – such as relaying data from unmanned aerial vehicles (UAVs) on reconnaissance flights.
WGS-10 is the fourth Block II follow-on satellite and supports communications links in the X-band and Ka-band spectra. While Block I and II satellites can instantaneously filter and downlink up to 4.410 GHz, WGS-10 can filter and downlink up to 8.088 GHz of bandwidth. Depending on the mix of ground terminals, data rates and modulation and coding scheme employed, a single WGS satellite can support data transmission rates over 6 Gbps, and WGS-10 with its advanced digital channelization may support over 11 Gbps.
The Delta IV Medium+ launch
Delta IV is designed around the Common Booster Core (CBC), a modular rocket stage fuelled by liquid hydrogen and liquid oxygen, with an Aerojet Rocketdyne RS-68A engine providing thrust. In the rocket’s Medium configuration, one CBC serves as the rocket’s first stage, while the Medium+ versions augment this with two or four GEM-60 SRB’s.
Delta IV M+ first stage tank is being loaded with 416.4 cubic meters or 110,000 gallons of super-cold liquid hydrogen that is chilled to minus 222 degrees Celsius or -423 degrees Fahrenheit. The tank must be bigger to hold the hydrogen excess gas pressure.
The Oxygen tank holds 40 000 gallon of liquid Oxygen chilled to below -182,96 0C Celsius or -297,33 0F Fahrenheit in a tank measuring about 151,4 m3 in estimated tank volume.
I wonder how many gallons of liquid Oxygen can fit in the pipelines in the raceway?
The Delta Cryogenic Second Stage (DCSS) is powered by an RL10B-2 engine and also burns liquid hydrogen and oxygen. Versions of the DCSS with diameters of four and five meters have been used: 4 meters with the Medium and Medium+(4,2) configurations, and 5 meters with the remaining Medium+ versions and the Delta IV Heavy.
Delta IV Medium+(5,4) split in its major parts. The bottom tank holds 416.4 M3 liquid hydrogen.
Continuing up the rocket comes the second stage. The smaller Delta Cryogenic Second Stage (DCSS) is powered by a single, vacuum optimized RL10B-2 engine. For its fuel, the DCSS uses liquid hydrogen (LH2) and for the oxidizer, liquid oxygen (LOX).
The LH2 tank - volume of 38 m3 holding 10 000 gallon LH2 - being on top, has the job of supporting the payload and the payload fairing with a strut gage of two rings and is also structurally separated from the other ‘half’ of DCSS.
The even smaller LOX tank - volume of 23 m3 holding 6 000 gallon LOX - is suspended in a strut gage of two rings below it and is responsible for structurally supporting the RL10B-2 engine. The LOX tank is spherical in size of material, insulation and structural purpose.
The Delta IV Medium+(5,4) that will perform Friday’s launch had one five-meter Common Booster Core, four GEM-60 solid rocket motors, and a five-meter DCSS. The continuous numbering of Delta launches that began with NASA’s Thor-Delta vehicles in the 1960s, this launch will be marked as Delta 383.
Friday’s launch was the thirty-ninth flight for the Delta IV. The launch began with ignition of Delta 383’s first stage RS-68A engine with about 2.7 seconds remaining on the countdown clock. At zero, the four GEM-60 boosters ignited and Delta lifted off, beginning the journey into orbit. After clearing its launch pad, Delta executed a series of pitch, roll and yaw maneuvers beginning 5.8 seconds after liftoff to put it onto the correct trajectory for geosynchronous transfer orbit.
A little over 35 seconds after liftoff, Delta IV reached Mach 1, the speed of sound. At 47.2 seconds into its flight, the rocket passed through Max-Q, the area of maximum dynamic pressure. This is the point in Friday’s launch at which the rocket experienced the greatest stress from aerodynamic forces, as a result of the combined effect of its increasing velocity, and the outside air density which decreases as the rocket climbs.
Delta 383’s solid rocket motors burned out and separated in pairs. The first two – motors 3 and 4 – burned out 93.4 seconds into the mission, with the second pair following a second later. The first pair of boosters separated at 100 seconds mission elapsed time, with the second booster separation after another 2.4 seconds.
Once it reached space, Delta IV no longer needed its payload fairing – the structure at the nose of the rocket which was used to protect WGS-10 from the atmosphere during ascent. This was jettisoned three minutes and 19 seconds into the flight, separating into two halves that fall away from the rocket as it continues toward orbit. Booster Engine Cutoff (BECO) – the shutdown of the Common Booster Core’s engine after it has depleted its propellant – came at three minutes and 55.8 seconds after launch.
The spent first stage separated six and a half seconds after cutoff, with the second stage’s RL10B-2 engine deploying its extendable nozzle to prepare for its own startup. It lit 13 seconds after staging, to begin the first of three planned burns during Friday’s mission.
The first burn lasted fifteen minutes and 14.3 seconds, placing Delta and its payload into an initial parking orbit. Exactly ten minutes later the RL10 ignited again for its second burn – this three-minute, 20.4 second burn injected WGS-10 into its transfer orbit. The satellite separated from the launch vehicle four minutes later, at 36 minutes and 50 seconds mission elapsed time.
At separation, Delta and WGS-10 was in an elliptical geosynchronous transfer orbit with a perigee of 433.9 kilometers (269.6 miles, 234.3 nautical miles) and an apogee of 44315.6 kilometers (27536.4 miles, 23928.5 nautical miles), inclined at 27.0 degrees to the equator and with an argument of perigee of 178.0 degrees. This is a supersynchronous transfer orbit, taking WGS-10 slightly above the geostationary belt, which reduces the amount of fuel that the satellite needs to use to raise its orbit. WGS-10 will perform a series of maneuvers under its own power to reach its final slot in geostationary orbit.
Delta’s upper stage made its third and final burn 35 minutes and 10.2 seconds after spacecraft separation. Lasting just ten seconds, this deorbited the stage, placing it on course to re-enter the atmosphere over the Pacific Ocean a little under eleven hours later. The upper stage burns up when it re-enters the atmosphere, with any surviving debris falling harmlessly into the sea. The deorbit burn is performed to ensure that as little unnecessary debris is left in orbit as possible – since the stage serves no further useful purpose after deploying its payload.
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