United Launch Alliance (ULA) has successfully delivered its first major payload on behalf of the newly-formed U.S. Space Force, following Thursday afternoon’s spectacular 4:18 p.m. EDT liftoff of the sixth and final member of the Advanced Extremely High Frequency (AEHF) constellation of military communications satellites. Built by Lockheed Martin and with a “protected communications payload” furnished by Northrop Grumman Corp., AEHF-6 is the capstone of a fleet which will connect civilian leaders with their warfighters all around the world.
Thursday’s launch was the second ULA flight of the year and also marked the 500th use of a production RL-10 engine in the Atlas’ Centaur upper stage to complete three “burns” to deliver the heavyweight satellite precisely into its orbital slot.
Final processing for this mission got underway Wednesday, when the Atlas V—flying in its powerful “551” configuration, with a 17-foot-diameter (5-meter) payload fairing, five strap-on solid-fueled boosters and a single-engine Centaur—was rolled the final 1,800 feet (550 meters) north from the Vertical Integration Facility (VIF) to the pad surface at Space Launch Complex (SLC)-41 at Cape Canaveral Air Force Station, Fla. In pride of place on the rocket’s payload fairing, in tandem with the Atlas V and AEHF logos, was the blue livery of the U.S. Space Force, which officially came into existence in December 2019.
“In the current dynamic environment, national security is of utmost importance,” said Gary Wentz, ULA vice president of Government and Commercial Programs. “We are proud to launch the first National Security Space mission for the U.S. Space Force and look forward to delivering the final AEHF asset to support our nation’s national defense and the warfighter community.”
Standing 197 feet (60 meters) tall, the 551 is the ultimate heavylifter of the Atlas V fleet, capable of hauling 19,620 pounds (8,900 kg) to geostationary altitude and 41,570 pounds (18,850 kg) to low-Earth orbit. Today it recorded its 11th launch in this configuration, with 551s having previously been utilized to boost NASA’s New Horizons spacecraft to Pluto back in January 2006, the agency’s Juno orbiter to Jupiter in August 2011, all five members of the Mobile User Objective System (MUOS) narrowband military communications network between February 2012 and June 2016, followed by the Air Force Space Command’s AFSPC-11 payload in April 2018 and more recently the AEHF-4 and AEHF-5 satellites in October 2018 and last August.
As outlined in AmericaSpace’s preview feature, the multi-month campaign to launch AEHF-6 has taken place on several fronts. In early January, the Atlas V Common Core Booster (CCB) and Centaur upper stage were delivered by ULA’s RocketShip vessel from Decatur, Ala., to the Cape, whereupon both went their separate ways for pre-flight processing. The Centaur was moved directly to the VIF at SLC-41, whilst the Atlas V itself headed initially to the holding bay of the Atlas Spacecraft Operations Center (ASOC). On 19 February, both of these huge rocket components came together in the VIF for the Launch Vehicle On Stand (LVOS) milestone and by month’s end all five solid-fueled boosters had been installed around the CCB base. Finally, on 12 March, the bullet-shaped Short Payload Fairing (SPF), housing the AEHF-6 cargo, was mounted atop the stack.
Hopes to fly as soon as 19 March were postponed by a few days, thanks to the need to swap out a troublesome valve which had exhibited off-nominal readings. Additional time to complete testing of the replacement valve obliged ULA to settle on 26 March as the earliest available launch date. And despite the steady worldwide march of the COVID-19 coronavirus, ULA CEO Tory Bruno expressed no reservations about the performance capability of the Atlas V. “Mighty Atlas will be socially distancing from you at around 20,000 mph (32,000 km/h),” he tweeted Wednesday, “but you can still see him from your backyard if you live in Florida or the Georgia/Carolina coast.”
With a predicted 80-percent likelihood of acceptable weather, Thursday promised to be an ideal day to fly. “High pressure remains in control through the weekend, resulting in mainly dry conditions and unusually warm temperatures,” noted the 45th Weather Squadron at Patrick Air Force Base in its L-1 briefing on Wednesday. “The primary concern for both Thursday and Friday remains the Cumulus Cloud Rule.” However, it was stressed that the likelihood of acceptable conditions would improve to 90-percent favourable in the event of a 24-hour scrub to Friday. Shortly after arrival at the pad, technicians and engineers began loading RP-1—a highly refined form of rocket-grade kerosene—into the Atlas V’s tanks, with cryogenic tanking of liquid oxygen and hydrogen slated to begin in the final hours prior to Thursday’s launch.
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 today’s 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,” noted the Space and Missile Systems Center (SMC) at Los Angeles Air Force Base in El Segundo, Calif. “This capability will assist the nation’s warfighters in performing their critical missions.” Built by Georgia Institute of Technology and sponsored by the Air Force Research Laboratory, TDO-2 was released from its perch at the aft-facing end of the Centaur upper stage about 31 minutes after launch.
Today’s Centaur actually boasted the 500th RL-10-class engine to fly. It was ground-tested at Pratt & Whitney’s Florida Research and Development Center in West Palm Beach, Fla., way back in 1959, before supporting its first Atlas-Centaur flight in November 1963. Last month, present manufacturer Aerojet Rocketdyne lauded the milestone. “This reliable engine has placed hundreds of military, NASA and commercial satellites into Earth’s orbit,” the organization tweeted, “and has helped send spacecraft to explore every planet in our Solar System.” These intrepid explorers included Mariner 10, which visited both Mercury and Venus, multiple voyages to Mars—including the Mariner 9 orbiter, the Curiosity rover and the InSight lander—and the twin Voyagers, launched in the summer of 1977, which explored all four outer gaseous planets. And if you still classify Pluto as being a “planet”, an RL-10 also helped boost New Horizons to this tiny world on the ragged edge of the Solar System on the very first Atlas V 551 mission in January 2006.
As well as powering successive variants of Atlas and Delta boosters, the RL-10’s impressive career is expected to continue with Northrop Grumman Corp.’s OmegA and ULA’s Vulcan, as well as NASA’s in-development Space Launch System (SLS), all three of which are expected to perform their maiden “shakedown” missions next year. “A single RL-10 will power the Interim Cryogenic Propulsion System during the first uncrewed test flight of SLS and Orion,” noted Aerojet Rocketdyne in a recent summary of the engine’s heritage. “Four RL-10 engines will support the more powerful Exploration Upper Stage that is being developed for future versions of SLS. Aerojet Rocketdyne is also working to qualify a modern version of the engine, known as the RL10C-X that will include major components built using 3D printing technology. Incorporating 3D printing into the manufacturing process will reduce lead times and cost while maintaining the outstanding performance and reliability customers have come to expect.”