Although relegated last February to second place on the list of the world’s most powerful operational rockets—sitting behind SpaceX’s Falcon Heavy—the United Launch Alliance (ULA) Delta IV Heavy roared to space earlier today (Saturday, 19 January), more than a month later than planned, due to hydrogen leaks and other technical woes. Already flown on ten occasions, and once in 2018 to loft NASA’s Parker Solar Probe, the triple-cored booster rose ponderously from Space Launch Complex (SLC)-6 at Vandenberg Air Force Base, Calif., at 11:10 a.m. PST to deliver the classified NROL-71 payload to orbit for the National Reconnaissance Office. As ULA plans to retire the remainder of its Delta IV Medium fleet in 2019, the Heavy will stand alone as the sole member of the Delta family in operational service, flying about once annually into the 2020s.
“Congratulations to our team and mission partners for successfully delivering this critical asset to support national security missions,” said Gary Wentz, ULA vice president of Government and Commercial Programs. “Thank you to the entire team for their perseverance, ongoing dedication and focus on 100% mission success.”
Equipped with three Common Booster Cores (CBCs), each boasting a single RS-68A engine, the Delta IV Heavy yields 2.2 million pounds (1 million kg) of thrust at T-0. Since its maiden voyage in December 2004, it has been employed to boost six classified NROL payloads into orbit, as well as a Defense Support Program (DSP) infrared early-warning satellite, Parker and the Exploration Flight Test (EFT)-1 mission of NASA’s Orion spacecraft. Details of today’s mission entered the public domain back in November 2015, when the Air Force announced it had awarded launch services contracts for the NROL-52—launched via an Atlas V in October 2017—and NROL-71, which was initially scheduled to fly no sooner than 15 September 2018. Lt. Gen. Samuel Greaves, Air Force Program Executive Officer (PEO) for space and commander of the Space Missile Systems Center (SMC) at Los Angeles Air Force Base in El Segundo, Calif., speaking at the time, described the pair of high-priority missions as critical in “providing innovative overhead intelligence systems for national security” and described the Air Force’s arrangement through the Evolved Expendable Launch Vehicle (EELV) Phase One Block-Buy contract with ULA as achieving balance “between mission assurance, meeting operational needs, lowering launch costs and reintroducing competition for National Security space missions”.
The original launch date for NROL-71 slipped to the right, with Spaceflight Now noting a movement to early December 2018 and stating that the Delta IV Heavy hardware had already been raised at SLC-6 by September. NRO also announced that the payload fairing was delivered to the pad for integration in October.
In anticipation of an opening launch attempt at 8:19 p.m. PST Friday, 7 December, the 300-foot-tall (100-meter) Mobile Service Tower (MST) was dramatically retracted from the vehicle, exposing the 236-foot-tall (72-meter) Delta IV Heavy in its crowning glory. Notwithstanding a gloomy 40-percent chance of acceptable weather conditions, tempered by recent rain and ground winds, the countdown proceeded, but was eventually scrubbed due to an issue with holdfire circuitry. This circuitry provides a redundant communications link between the vehicle and the control center and would be used to call off the launch if a contingency arose. Launch was rescheduled for 8:06 p.m. PST Saturday, 8 December, with a slightly improved weather outlook of 60-percent favorable. This outlook improved steadily to 70-percent favorable, and eventually 90-percent, but Saturday’s launch attempt ultimately fell foul to technical troubles. Sadly, the attempt was aborted during the terminal count, at T-7.5 seconds, and the engines were shut down and safed. The sparkler-like Radial Outward Flame Igniters (ROFIs) had already begun firing, which added a dramatic visual element to ULA’s second effort to get NROL-71 airborne.
Moving ahead towards a third attempt to get the gremlin-plagued mission away, ULA announced a revised launch target of 5:57 p.m. PST on Tuesday, 18 December. The Launch Readiness Review (LRR) was concluded on the morning of Monday 17th, but the attempt was scrubbed due to high ground winds. Another launch attempt was set for 5:44 p.m. PST on Wednesday 19th, which moved slightly back to 5:49 p.m., following efforts to close a troublesome valve on the Delta IV Heavy. Wednesday’s attempt was ultimately scrubbed by ULA Launch Director Lou Mangieri, due to elevated hydrogen concentrations and evidence of a leak in the port-side CBC. A 24-hour recycle to the evening of Thursday, 20 December was declared, but the leak prompted a much longer postponement. Efforts to get the Delta IV Heavy off the ground before year’s end proved fruitless, with initial tentative targets of 30 December and 6 January coming and going with no word of a new launch date. Earlier this month, ULA noted that it was “continuing to remedy” the technical issues which had scuppered December’s launch attempts.
At length, a new launch date was scheduled for Saturday, 19 January. The Launch Readiness Review (LRR) was satisfactorily completed one day prior and the 30th Weather Squadron at Vandenberg declared a 70-percent likelihood of acceptable conditions at T-0, tempered by a slight risk of ground winds. It was noted that, in the event of a 24-hour scrub to Sunday, the meteorological outlook would deteriorate to just 40-percent favorable.
In the final hours before Saturday’s T-0, the pad area was cleared of all personnel and, following polls by the ULA launch team, a three-step process got underway to fuel the rocket with liquid oxygen and liquid hydrogen. This process began by chilling-down the tanks and ground equipment, fuel transfer lines and valves, to prevent “thermal shocking” as the super-cold propellants begin to flow. After the chilling-down process, fueling got underway, with “fast-flow” until the tanks were almost full, before transitioning to “replenishment mode”, which involved a process of continuous topping-off to maintain flight-ready levels, replacing any boiled-off cryogens. All told, an estimated 440,000 pounds (200,000 kg) of propellants were loaded aboard the Delta IV Heavy, which weighs some 1.6 million pounds (725,750 kg) at liftoff.
Emerging from the final built-in “hold” in the countdown at T-4 minutes, ordnance aboard the rocket was armed and the tanks in the three CBCs were secured and pressurized for flight. At T-15 seconds, as is customary with Delta IV-class missions, the ROFIs were activated to burn-off excess gases dumped through the rocket’s engine nozzles, prior to ignition. At slightly staggered intervals, the three RS-68As came to life, ramping up to a combined 2.1 million pounds (1 million kg) of propulsive yield and the Delta IV Heavy roared away from SLC-6 precisely on time.
Delta IV Heavy launches are always somewhat disconcerting to the uninitiated in the opening seconds, as the enormous amount of hydrogen being dumped through the engines to condition them—ahead of opening the liquid oxygen valves and commencing the ignition sequence—generates a huge fireball, which visually appears to set the vehicle’s orange-colored insulation alight as it leaves the pad. Seconds after clearing the SLC-6 tower, the Delta IV Heavy began its computer-commanded pitch, yaw and roll program maneuver to establish itself onto the correct trajectory to insert NROL-71 into orbit.
Judging from the Delta IV Heavy’s capacity to loft up to 63,470 pounds (28,790 kg) into low-Earth orbit and up to 31,350 pounds (14,220 kg) to geostationary altitude, its use for this mission implies that NROL-71 is a heavyweight payload and it has been suggested that the satellite is an upgraded member of the KH-11 “Keyhole” digital imaging reconnaissance platforms, which are believed to weigh around 41,900 pounds (19,000 kg), and thought to operate in a slightly elliptical orbit at an altitude of 160 miles (260 km) x 620 miles (1,000 km).
Today’s flight represents the first of up to nine ULA launches planned for 2019, a year which will phase-out Delta IV Medium capability. ULA anticipates the final two flights of its “single-stick” Delta IV Medium fleet, a second Delta IV Heavy mission and as many as five Atlas V flights, including unpiloted and piloted tests of Boeing’s CST-100 Starliner spacecraft for the Commercial Crew Program.