United Launch Alliance (ULA) successfully delivered the latest member of the Wideband Global SATCOM (WGS) constellation to orbit. The launch of WGS-8 (ULA’s 114th overall and the 34th Delta IV) occurred on time with liftoff commencing at 6:53 p.m. EST (23:53 GMT) Dec. 7, 2016, precisely at the opening of its 49-minute launch window.
“Thank you to the U.S. Air Force and industry team whose flawless execution enabled today’s successful launch of the WGS-8 mission,” said Laura Maginnis, ULA vice president of Custom Services, in a news release. “Last week ULA celebrated our anniversary and 10 years of 100 percent mission success. This evening’s launch epitomizes why our customers continue to entrust ULA to deliver our nation’s most crucial space capabilities.”
The Delta IV, configured in its Medium+ (5,4) arrangement, took off from Cape Canaveral Air Force Station’s (CCAFS) Space Launch Complex 37 (SLC-37). It quickly left the pad as the four strap-on GEM-60 solid rocket motors (SRMs) ignited. This occurred approximately five seconds after the core stage’s RS-68A engine roared to life.
Clearing the tower a few seconds after liftoff, the Delta IV began its pitch, roll, and yaw maneuver as it rapidly gained speed on the “uphill” climb to orbit, and ultimately a supersynchronous transfer orbit.
With the RS-68A and four SRMs continuing to fire, the vehicle surpassed Mach 1 (the speed of sound) around 37 seconds after liftoff and encountered the greatest aerodynamic stress on the vehicle about 9 seconds later. This region of increased aerodynamic loads on the rocket is called “max Q” and is a function of the vehicle’s speed and atmospheric pressure.
The next milestone on the way to orbit was the burnout and jettisoning of the four SRMs, more than a minute-and-a-half after liftoff.
At two minutes into the flight, the vehicle was traveling at Mach 5 and doubled its speed only a minute later. As the vehicle continued to accelerate—with the RS-68A consuming nearly 2,000 pounds (907 kilograms) of propellant every second—it was high enough to be able to shed the protective payload fairing at three minutes and fourteen seconds into the flight.
Booster Engine Cutoff (BECO) successfully occurred just short of four minutes after liftoff, and the second stage, the Delta Cryogenic Second Stage (DCSS), separated a few seconds later. The DCSS’s RL10B-2 engine ignited shortly thereafter, and with its 24,750 pounds (110.1 kilonewtons) of thrust, the rocket continued to power the WGS-8 satellite to orbit.
This RL10B-2 burned for approximately fifteen minutes during this first burn, with main engine cut-off (MECO-1) occurring nearly twenty minutes into the flight. The DCSS and its WGS-8 payload then entered a 10-minute coast period, and re-ignition of the RL10B-2 initiated nearly 30 minutes after liftoff.
The second burn was significantly shorter than the first, lasting slightly more than three minutes, with MECO-2 occurring some 32 minutes after lifting off from SLC-37.
With its job nearly done, the DCSS and WGS-8 satellite coasted for approximately nine minutes before the spacecraft separated from the second stage, high above and slightly east of Madagascar. Now free-flying, the satellite will use its onboard propulsion system to reach its ultimate destination high above the equator in an undisclosed geostationary orbit.
While ULA notched their 114th successful launch, their success also rides on the shoulders of the men and women in uniform of the United States Air Force’s 45th Space Wing. Brig. Gen. Wayne Monteith, 45th Space Wing commander and mission Launch Decision Authority, was full of praise for his team.
“Thanks to the astounding commitment, focus on the mission, and teamwork the men and women of the 45th Space Wing share with our mission partners at SMC and ULA, we successfully launched the next satellite in the WGS constellation,” Monteith said. “This mission demonstrates the Air Force’s commitment to deliver secure and reliable satellite communications around the globe to U.S. forces and our allies. It also once again showcases why the 45th Space Wing is the ‘World’s Premiere Gateway to Space.’”
The successful launch and deployment of the WGS-8 satellite marks ULA’s 11th of 2016 and is the company’s penultimate mission on their manifest for the year. ULA’s next scheduled launch, on Dec. 16, 2016, from SLC-41 at CCAFS, is for an Atlas V carrying the EchoStar 19 satellite.
Written by: Curt Godwin
Original source: spaceflightinsider.com