On a sunny, sticky day at Cape Canaveral Air Force Station’s Space Launch Complex 41 (SLC-41), the United Launch Alliance (ULA) celebrated its seventh flight of the Atlas V 551 (the 63rd Atlas V mission overall) with the successful launch of the U.S. Navy’s fifth Mobile User Objective System (MUOS-5) satellite. For this launch, the 45th Space Wing had predicted an 80 percent chance of acceptable weather—improving to 100 percent as the countdown clock neared zero. With all systems go, the rocket rumbled off the pad right at the beginning of its planned 44-minute launch window, at 10:30 a.m. EDT (14:30 GMT) June 24.
“Today’s successful launch is the culmination of the 45th Space Wing, Space and Missile Systems Center, Navy and ULA’s close partnership and dedicated teamwork,” Brigadier General Wayne Monteith, 45th Space Wing commander and mission Launch Decision Authority, said in a press release. “We continue our unwavering focus on mission success and guaranteeing assured access to space for our nation, while showcasing why the 45th Space Wing is the ‘World’s Premier Gateway to Space’.”
This launch comes three months after an anomaly on the RD-180 Mixture Ratio Control Valve (MRCV) during a March 22 Atlas V flight caused the first stage on the vehicle to shut down five seconds early. Vehicle operations had been suspended until the source of the anomaly was determined and a resolution implemented.
ULA determined the cause and, after a month-and-a-half delay, the MUOS-5 mission finally got underway.
With over 2.5 million pounds-force (11.12 MN) of thrust at liftoff, the Atlas V 551 configuration uses a single Russian-built RD-180 kerosene/liquid oxygen main engine and five Aerojet Rocketdyne solid rocket boosters (SRBs) to rocket off the pad.
A Centaur upper stage, powered by a single Aerojet Rocketdyne RL-10 C-1 liquid hydrogen/liquid oxygen engine, fired three times over the course of three hours, finishing the payload’s journey into orbit and lifting the satellite to its final geostationary transfer orbit (GTO) of 2,074 × 19,280 miles (3,338 × 31,028 kilometers).
Following a final polling of the mission controllers, the Atlas V emerged from a planned hold in its countdown and began a four-minute final sequence of launch preparations, including topping off the liquid hydrogen and liquid oxygen tanks on the Centaur upper stage.
The five solid rocket boosters SRBs, creating a distinctive white plume over the Florida coast, provided the steering, compensating for gravity and the asymmetrical position of the boosters (three on one side and two on the other).
One minute and 48 seconds into the flight, three of the SRBs were jettisoned, followed by two others a few seconds later. The Atlas V’s main engine finished its work approximately four-and-half minutes into the flight before the first stage was jettisoned.
The Centaur upper stage ignited successfully twice, once for just under eight minutes, followed by a second six-minute burn 20 minutes, 27 seconds into the flight. Then, at two hours, 49 minutes into the flight, the Centaur upper-stage engine burned for a third time for approximately four minutes.
After the final engine cutoff, the MUOS-5 satellite separated from the upper stage about less than five minutes later.
In addition to the MRCV fix, ULA engineer and flight commentator Andrea Lenhoff noted that this Atlas V 551 fielded a new acoustic protection system, which will improve protection of payloads during flight.
Lockheed Martin served as prime contractor and system integrator for the MUOS satellites. MUOS-5 is the latest and final spacecraft in a constellation used by the Navy to support communications for mobile users with a MUOS terminal.
Once the spacecraft circularizes its trajectory into a geostationary-Earth orbit (GEO), MUOS-5 will serve as an on-orbit spare satellite for the constellation. The spacecraft has a projected lifetime of about 15 years.
MUOS-5 will support users of the Wideband Code Division Multiple Access (WCDMA) system—the same protocol used by smartphones to communicate—as well as the legacy ultrahigh-frequency (UHF) system. Among its features is a 14-meter reflecting mesh antenna, which will be deployed when the satellite is on station.
With MUOS in place, WCDMA users will be able to communicate and share data within each satellite’s area of operations as well as any satellite within line of sight of others within the system, ensuring global communications.
Once operational, the MUOS constellation is expected to provide 16 times the capacity of the legacy UHF system. According to the MUOS outreach video, this will ensure that warfighters will be “able to call from DC to the Middle East all in one system.”
During the post-launch commentary, Commander Peter Sheehy also indicated that warfighters using MUOS should notice an immediate difference in voice quality over the legacy system.
“In some cases, you should even be able to detect tone of voice,” Sheehy said.
Following this successful flight, ULA expects the remaining launches on its 2016 manifest to proceed on schedule.
After Friday’s launch, the next Atlas V flight will loft a classified payload for the National Reconnaissance Office (NRO). That Atlas V will carry NROL-61 in the 421 configuration (4-meter fairing, two solid rocket boosters, and a single-engine Centaur upper stage). Liftoff will occur in a classified launch window sometime between 8 a.m. and noon EDT (12:00–16:00 GMT) July 28.
Additionally, an Atlas V will launch NASA’s OSIRIS-REx spacecraft from the Cape Sept. 8
Written by: Bart Leahy
Original source: spaceflightinsider.com