ULA set to launch Atlas V with MUOS-5
After being delayed a month-and-a-half due to a March 2016 in-flight anomaly, the United Launch Alliance (ULA) is gearing up to fly its next Atlas V rocket. The payload for this mission is the U.S. Navy’s fifth Mobile User Objective System (MUOS-5).
Slated to lift off at the beginning of a 44-minute window on Friday, June 24, at 10:30 a.m. EDT (14:30 GMT) from Cape Canaveral Air Force Station’s Space Launch Complex 41 (SLC-41), the launch will resume normal operations of the Atlas V rocket. ULA expects to fly all eight of its remaining originally scheduled manifest for this year, including MUOS-5.
Friday’s launch is expected to have an 80 percent chance of favorable conditions with only cumulous clouds having the potential to interfere with the mid-morning launch. This scheduled liftoff comes after engineers determined what caused the performance shortfall on the last Atlas V launch, which delivered the OA-6 Cygnus cargo spacecraft to orbit.
According to a statement by ULA on June 15, an unexpected shift in fuel pressure differential in the mixture ratio control valve in the Russian-built RD-180 engine caused the engine to run oxidizer-rich. As such, the oxygen tank was depleted early causing the engine to shut down around five seconds prematurely. This resulted in the Centaur upper stage having to make up for the velocity shortfall.
ULA said a minor change has been made to the valve to prevent the problem from occurring again. The company said this change has been verified in hot-fire tests.
The payload launching on Friday, MUOS-5, is a Navy communications satellite for mobile military forces. It will be placed into a high perigee geostationary transfer orbit (GTO) of 2,074 × 19,280 miles (3,338 × 31,028 kilometers).
Eventually, the onboard propellant will circularize the orbit of the spacecraft to some 22,500 miles (36,200 kilometers) in geostationary orbit (GEO), not far from where MUOS-4 resides, over the Indian Ocean. It is the final piece of a $7.7 billion mobile communications network and its 15-year lifespan serves partially as an on-orbit spare.
Those with MUOS terminals can connect with “smartphone-like” capabilities, which includes voice, text, video, and mission data transmission on a high-speed Internet Protocol-based system.
Built by Lockheed Martin, the satellite has a 14-meter-diameter reflecting mesh antenna. Each MUOS satellite has two payloads supporting Wideband Code Division Multiple Access (WCDMA) waveform capabilities and a UHF satellite system.
MUOS-5 will act as an on-orbit spare for WCDMA capabilities in addition to actively supporting the UHF system. The current constellation of four satellites and associated ground stations provide near global coverage for the Navy.
With the payload fairing, the Atlas V in the 551 configuration (5-meter fairing, five solid rocket boosters, and a single-engine Centaur upper stage) stands 206 feet (62.7 meters) tall.
The core booster is 12.5 feet (3.8 meters) in diameter and 106.5 feet (32.4 meters) tall. It has two fuel tanks, one for liquid oxygen (LOX) and the other for rocket-grade kerosene (RP-1), which feed the dual-thrust chamber RD-180 engine.
At liftoff, the RD-180 engine delivers 860,200 pounds-force (3,826 kilonewtons) of thrust. With the five strap-on solid rocket boosters, each of which provides 348,500 pounds-force (1,550 kilonewtons) of thrust, the total take-off thrust comes to 2.6 million pounds-force (11,564 kilonewtons).
The five solid rocket boosters will be jettisoned between 108 and 110 seconds after liftoff. Two first, then, two seconds later, the remaining three. About 207 seconds into the flight, the payload fairing will fly away, revealing the satellite.
Atlas Booster Engine Cutoff will occur less than a minute later after burning for four minutes and 25 seconds. The single-engine Centaur upper stage will separate and fire about 16 seconds later continuing the flight toward GTO.
Twelve minutes and 28 seconds after launching, the First Engine Cutoff (MECO-1) for Centaur will occur, placing the upper stage and payload into a stable parking orbit. Eight minutes later, the Centaur will fire again to burn toward GTO. That burn will last about six minutes.
After coasting to the top of the highly elliptical GTO orbit, taking just over two hours, the Centaur engine will ignite for a third time to raise the lower point in its orbit to 2074 miles (3,338 kilometers).
Spacecraft separation will occur less than five minutes later, some two hours and 53 minutes after liftoff.
This will be the 63rd Atlas V launch, the seventh in the 551 configuration. The first launch of this variant was Jan. 19, 2006—the launch of the New Horizons spacecraft that visited Pluto last summer.
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.
Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a blog about the International Space Station, called Orbital Velocity.