Atlas-5/551

The Atlas V Common Core Booster (CCB) for this mission arrives in Florida in January 2020. Measuring 107 feet long (32.6 meters), the CCB provides much of the muscle to get the Atlas V 551 airborne. Photo Credit: ULA/Twitter

Photo: ULA

AEHF-6 being encapsulated for launch in its protective bullet-like payload fairing. Photo: ULA / Lockheed Martin

Photo: ULA

ULA′s Atlas V with AEHF-6 on the launch pad. Photo: ULA

Credit: Jeff Seibert / AmericaSpace.com

Description:

• In readiness for the AEHF-6 launch campaign, the Atlas V Common Core Booster (CCB) and Centaur upper stage left Decatur on 4 January, 2020 aboard ULA′s newly-renamed R/S RocketShip vessel, and arrived at Cape Canaveral on the 11th. The booster was immediately transferred to the holding bay at the Atlas Spacecraft Operations Center (ASOC) for receiving checks and horizontal processing, whilst the Centaur—which will be powered by the 500th RL-10 engine—was moved directly to the Vertical Integration Facility (VIF) at SLC-41 to begin the lengthy process of installation of its inter-stage adapter, payload fairing base segments and support ring. Processing entered high gear last month, when the 107-foot-long (32.6-meter) booster arrived at the VIF on 19 February for the Launch Vehicle On Stand (LVOS) milestone. “The Atlas program called this event Booster On Stand (BOS), while the Delta program used Vehicle On Stand (VOS). Now it is simply LVOS.”
• The process required the booster to be hauled horizontally by semi-truck across a distance of four miles (6.4 km) from the ASOC to the VIF. It was then parked at the doorway of the 30-story facility, as ULA engineers set up ground handling equipment and a pair of cranes grappled and raised the CCB from its carrier and secured its aft section in a rail dolly. This allowed the booster to be elevated to a vertical configuration. “Once vertical, the aft structure was disengaged and the crane holding the forward end of the rocket slowly and carefully hoisted the stage into the VIF and positioned it aboard the MLP,” ULA noted.
• The five solid-fueled rocket boosters (SRBs)—which will generate three-quarters of the 551′s total thrust at liftoff, some 1.7 million pounds (790,000 kg)—were then mounted around the base of the booster. “All 5 SRBs hung,” tweeted ULA CEO Tory Bruno on 28 February, by which point the 41.5-foot-tall (12.6-meter) Centaur upper stage had also been added to the stack.
• Next came the AEHF-6 payload itself. The satellite was delivered aboard a C-5 Galaxy cargo aircraft from Sunnyvale to the Cape′s Shuttle Landing Facility (SLF) on 11 January 2020. It was moved to Astrotech′s payload processing facility in Titusville for checkout, fueling and encapsulation in its 17-foot-wide (5-meter) Short Payload Fairing (SPF). On 12 March, the payload was installed atop the rocket, topping-off the stack at a total height of 197 feet (60 meters).
• The Atlas V has flown 82 missions since August 2002, of which ten have previously utilized the 551, which is the booster′s most powerful configuration, capable of hauling up to 19,620 pounds (8,900 kg) to geostationary altitude. It was first employed to deliver NASA′s New Horizons mission to Pluto in January 2006 and the agency′s Juno spacecraft to Jupiter in August 2011, before boosting five heavyweight Mobile User Objective System (MUOS) military communications satellites between February 2012 and June 2016, the dedicated AFSPC-11 payload for Air Force Space Command in April 2018 and most recently the AEHF-4 and AEHF-5 birds in October 2018 and last August. In fact, the Atlas V—in its 531 configuration, with three solid-fueled boosters—also lofted the AEHF-1, AEHF-2 and AEHF-3 satellites between August 2010 and September 2013.

• The launch has slipped a couple of times in recent weeks. Originally scheduled to fly on 19 March, it was announced by ULA earlier this month that a delay of at least two days would be needed to swap out a troublesome valve which had exhibited an off-nominal reading. Additional time required to complete testing of the replacement valve led ULA and the Eastern Range to settle on 26 March as the next available launch date.
• As the day wore on, the forecast brightened to 90-percent favorable. And even a glitch with a temperature sensor on the Centaur′s RL-10 engine was quickly verified as posing no constraint to launch by Anomaly Chief David McFarland. The countdown ticked smoothly down to within one minute, before a “Hold, Hold, Hold” call was heard over the communications net at approximately T-46 seconds.
• The clock was promptly reset to T-4 minutes as engineers began to troubleshoot the problem. “Ground hydraulics accumulator fault,” tweeted ULA CEO Tory Bruno in the minutes after the hold was called. “Working it.” Further updates trickled out as the two-hour “launch window” began to trickle away. “Bad amplifier card on a ground system hydraulic pump controller,” Mr. Bruno confirmed at 3:45 p.m. EDT. “Working on a solution.” At length, a revised T-0 was set for 4:18 p.m., less than 40 minutes before the scheduled closure of Thursday′s window.
• With the dual nozzles of the Atlas V′s RD-180 main engine punching out 860,000 pounds (390,000 kg) of propulsive yield and a further 1.7 million pounds (790,000 kg) from the five strap-on solids, the launch certainly jolted the Space Coast. The vehicle commenced a fast climb away from SLC-41, with the solids exhausting their propellant and separating around 106 seconds into flight. Meanwhile, the RD-180 continued to burn hot and hard, before itself shutting down—precisely on time—at four and a half minutes after liftoff. By this time, the stack was in the rarefied high atmosphere and the payload fairing had also been jettisoned. The CCB was discarded shortly afterwards, leaving the single RL10C-1 engine of the Centaur to execute three “burns” to deliver AEHF-6 to orbit.
• Also deployed on the mission was the TDO-2 cubesat, a so-called “multi-manifest small satellite” laden with U.S. Government payloads for optical calibration and space domain awareness experiments. “The mission of TDO-2 is to support space domain awareness through optical calibration and satellite laser ranging.
• TDO-2 was released from its perch at the aft-facing end of the Centaur upper stage about 31 minutes after launch.