Pummeling the ground with an estimated 2.5 million pounds (1.1 million kg) of thrust, the largest and most powerful member of United Launch Alliance’s (ULA) Atlas V fleet roared aloft earlier tonight (Saturday, 14 April), to deliver a multi-purpose payload into orbit on behalf of the U.S. Air Force Space Command. Liftoff of the Atlas V 551—equipped with a 17-foot-wide (5-meter) payload fairing, five strap-on solid-fueled rockets and a single-engine Centaur upper stage—occurred from Space Launch Complex (SLC)-41 at Cape Canaveral Air Force Station, Fla., at 7:13 p.m. EDT, right on the opening of tonight’s two-hour “window”. The AFSPC-11 complement reportedly includes a classified primary customer, together with a geostationary-bound research satellite and a group of other technology demonstration, on-orbit imaging and risk-reduction payloads.
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Copyright 2018 by Rob van Mackelenbergh for Space-Site.com
Althought tonight’s flight represented the 77th mission by an Atlas V since its debut back in August 2002, AFSPC-11 is actually only the eighth outing by the rarely-used 551 variant, which carries the potential to deliver up to 41,470 pounds (18,814 kg) to low-Earth orbit and up to 19,620 pounds (8,900 kg) to geostationary altitude, some 22,300 miles (35,900 km) above the planet. This offers an indicator of the size and mass to be delivered to orbit on this mission. First used in January 2006 to loft NASA’s New Horizons spacecraft to Pluto, and described by ULA CEO Tory Bruno as “the bruiser”, the 551 has since seen service to deliver the Juno polar orbiter to Jupiter in August 2011 and five heavyweight Mobile User Objective System (MUOS) narrow-band military communications satellites, between February 2012 and June 2016. Following its AFSPC-11 duty, the power of the 551 will be unleashed again in June 2018 to boost the next Advanced Extremely High Frequency communications satellite (AEHF-5) into geostationary orbit.
Jeroen Wouda, Space-Site.com