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Today's launch of the Atlas 5 rocket will be the third flight of the vehicle's 551 configuration, which is distinguished by the combination of a five-meter payload fairing, five solid rocket boosters and a single-engine Centaur upper stage, the most powerful version of the Atlas 5 currently available.
Depending on a payload's weight and desired orbit, mission planners add strap-on solid boosters to the United Launch Alliance-made rocket to incrementally increase the vehicle's performance.
Atlas 5 vehicles are capable of flying with as many as five boosters, an option that was employed to generate as much thrust as possible to launch NASA's New Horizons space probe bound for Pluto in 2006 and NASA's Juno to Jupiter last August. For this particular mission, the weight of MUOS drove the selection of the 551 and the plan to fire the Centaur upper stage three times instead of the usual two burns.
"Weighing nearly 15,000 pounds, MUOS 1 is the heaviest satellite launched to date by an Atlas launch vehicle. Our customers for this mission asked for a mission design that would launch this very heavy and capable satellite in a manner that would minimize the amount of energy (and propellant) that the satellite would have to consume to position itself into the final geosynchronous orbit," said Jim Sponnick, United Launch Alliance's vice president of mission operations.