The bulbous payload fairing and MUOS-3 undergo preparations for installation atop the Atlas V 551. Photo Credit: ULA

The MUOS-3 payload, encapsulated within its bulbous payload fairing, is readied for installation atop the Atlas V 551. Photo Credit: ULA

The Atlas V 551 benefits from a large payload fairing to accommodate the heavyweight MUOS-3 satellite. Photo Credit: John Studwell/AmericaSpace

MUOS-3 communications satellite for the US Navy awaits launch atop an Atlas V rocket at pad 41 at Cape Canaveral Air Force Station, FL on Jan. 20, 2015. Credit: John Studwell/AmericaSpace

The Atlas V 551 rockets into the darkened Florida sky at 8:04 p.m. EST Tuesday, 20 January, to deliver MUOS-3 into orbit. Photo Credit: Mike Killian / AmericaSpace

Description:

• Atlas V rocket—flying for only the fifth occasion in its most powerful configuration, the “551,” equipped with a 5.4-meter (17.7-foot) payload fairing, five solid-fueled boosters, and a single-engine Centaur upper stage—to lift off from SLC-41 at Cape Canaveral Air Force Station” Capable of delivering up to 41,480 pounds (18,814 kg) to low-Earth orbit and up to 19,620 pounds (8,900 kg) to geostationary transfer orbit, the 551 heavylifter has been used previously to deliver MUOS-1 in February 2012 and MUOS-2 in July 2013, as well as NASA’s Pluto-bound New Horizons spacecraft in January 2006 and the Juno orbiter to Jupiter in August 2011. With MUOS-4 targeted to fly in August, 2015 promises to be the first time that a pair of Atlas V 551s will have launched within the span of a single calendar year.
• Launch will get underway at T-2.7 seconds, with the ignition of the Russian-built RD-180 first-stage engine, which burns liquid oxygen and a highly refined form of rocket-grade kerosene (known as “RP-1”) and generates 860,000 pounds (390,000 kg) of propulsive yield. The five Aerojet-built solid-fueled boosters, each measuring 67 feet (20.4 meters) tall, will also ignite and produce a total thrust of 1.7 million pounds (790,000 kg) to supplement the initial boost away from Florida. Climb-out of the 206-foot-tall (62.8-meter) stack from SLC-41 will commence at T+1.1 seconds, beginning an apparently slow ascent to about 85 feet (25.9 meters), after which the avionics of the Centaur upper stage will command a pitch, roll, and yaw program maneuver to establish the Atlas onto the proper flight azimuth of 94.58 degrees in order to deliver the MUOS-3 payload into orbit.
• Fifty-one seconds into the flight, the vehicle will pass through a period of maximum aerodynamic turbulence—colloquially known as “Max Q”—and the rapidly ascending stack will throttle down its RD-180 engine and begin a nominal zero-pitch and zero-yaw angle of attack to minimize these loads. At T+110.7 seconds, now exhausted, two of the strap-on boosters will be jettisoned, followed by the others about 1.5 seconds later. A little over 3.5 minutes into the mission, with the RD-180 still burning hot and hard, the bulbous payload fairing will be discarded, and when the 551 reaches a peak load of 4.6 G the engine will be throttled back to maintain this level.
• Shutdown is scheduled to take place at T+267.6 seconds, after which the 41.5-foot-long (12.6-meter) Centaur and its attached MUOS-3 payload will separate. To support the delivery of the satellite into its correct orbital “slot,” the Centaur will perform three lengthy firings of its 23,900-pound-thrust (10,840-kg) RL-10C engine. First trialed during last month’s NROL-35 mission for the National Reconnaissance Office, the liquid oxygen/hydrogen-fueled RL-10C measures 7 feet (2.2 meters) long and 4.5 feet (1.4 meters) in diameter and has a dry mass of 420 pounds (190 kg). Although its overall thrust is slightly higher than the 22,300 pounds (10,100 kg) of the earlier RL-10A, the upgraded engine’s specific impulse is a little lower than its counterpart.
• The first burn will last almost eight minutes, kicking off at T+283.6 seconds and terminating at T+750.4 seconds. The Centaur/MUOS-3 combo will then coast for a further eight minutes, before the RL-10C ignites for its second burn at 20 minutes and 32 seconds into the mission. This firing is scheduled to run for just under six minutes, steering the payload stack into an intermediate transfer orbit, and will be followed by a substantially longer period of coasting—more than two hours—before the third and final burn gets underway at T+2 hours and 48 minutes. This burn will last about 59 seconds and will deliver MUOS-3 into the Spacecraft Separation Transfer Orbit. When the Centaur’s targeted orbital parameters are achieved, Main Engine Cutoff (MECO) will be initiated by guidance command and the satellite will separate from the upper stage about two hours and 53 minutes after leaving Cape Canaveral Air Force Station. Nominal insertion orbit will be at an apogee of 22,240 miles (35,790 km) and a perigee of 2,370 miles (3,820 km), inclined 19.11 degrees to the equator.
• Launch preparations:
  Formal countdown operations got underway Tuesday afternoon Januari 20, at T-6 hours and 20 minutes, with the activation of flight control systems, shortly after 1:20 p.m. The flight computer will be tested both for flight control and guidance operations, the countdown clock will be started and other activities preparing for the Terminal Countdown will be carried out. Ground Command Systems testing occupied about 3.5 hours, as engineers verified communications between the Atlas V and the Launch Control Center (LCC).
• The Atlas V’s Common Core Booster (CCB) is fueled by a mixture of liquid oxygen and a highly refined form of rocket-grade kerosene (known as “RP-1”). Since the former undergoes cryogenic boil-off and must be continuously replenished until close to T-0, it was loaded relatively late in the countdown, whereas the RP-1 experiences “no leakage or reduction in capacity during the interval before launch” and consequently was pumped aboard the rocket yesterday. At 5:20 p.m., a built-in hold got underway, prior to the onset of liquid oxygen loading, and propellant storage areas were chilled down, in order to avoid thermally shocking and fracturing the hardware.
• At length, shortly before 6 p.m., as the Sun set over the marshy Florida landscape, the Launch Director authorized the lengthy process to begin. This was followed by the loading of a pair of cryogens—liquid oxygen and hydrogen—aboard the Atlas V’s Centaur upper stage, whose RL-10C engine would execute three “burns” to deliver the MUOS-3 satellite into its correct geostationary position. Liquid oxygen tanking passed smoothly through Slow Fill and Fast Fill modes, before finally transitioning to Topping by 6:20 p.m., in order to continuously replenish the effects of boil-off. Shortly after 6:30 p.m., the process of loading liquid hydrogen aboard the Centaur got underway.
• Overall, the Atlas V was enjoying a trouble-free countdown, as described by the Launch Tracker at T-60 minutes. The weather remains favorable at 80-percent Go and we are not aware of any issues being worked at this time. High-altitude balloon data in the final minutes before launch confirmed an improvement in the likelihood of acceptable weather conditions to 90 percent favorable.
• With all tanks confirmed at flight levels, the final checkout of the Flight Termination System (FTS)—which is tasked with destroying the vehicle in the event of a major accident during ascent—was performed and the ascent software was updated. At 7:24 p.m., the countdown entered its final 15-minute built-in hold at T-4 minutes, during which time ULA Launch Conductor Scott Barney took the opportunity to undertake last checks on the vehicle, payload, and weather situation.
• At 8:00 p.m., with the Range interference issue finally rectified, the clock was released from its final hold point at T-4 minutes and the Terminal Countdown got underway. During this phase, the Atlas V systems were transferred to internal power, the FTS was armed, and at T-60 seconds the Launch Control System was enabled and the vehicle’s computer assumed primary command of all critical functions. “Range Green!” came the call from the Range Operations Co-ordinator (ROC).
• Launch got underway at T-2.7 seconds, with the ignition of the Russian-built RD-180 first-stage engine, burning liquid oxygen and RP-1 and generating 860,000 pounds (390,000 kg) of propulsive yield. The five Aerojet-built solid-fueled boosters, each measuring 67 feet (20.4 meters) tall, also ignited and produced a total thrust of 1.7 million pounds (790,000 kg) to supplement the initial boost away from the darkened Cape. Climb-out of the stack from SLC-41 commenced at T+1.1 seconds, beginning a fast climb to about 85 feet (26 meters), after which the avionics of the Centaur upper stage—flying for the 200th time in conjunction with a member of the Atlas rocket family—commanded a pitch, roll, and yaw program maneuver to establish the Atlas onto the proper flight azimuth of 94.58 degrees in order to deliver the MUOS-3 payload into orbit.
• Shutdown—properly identified as Booster Engine Cutoff (BECO)—took place at T+267.6 seconds, after which the 41.5-foot-long (12.6-meter) Centaur and its attached MUOS-3 payload separated. To support the delivery of the satellite into its correct orbital “slot,” the Centaur will perform three lengthy firings of its 23,900-pound-thrust (10,840-kg) RL-10C engine.