Another countdown for United Launch Alliance’s next Delta 4-Heavy rocket mission ended without a liftoff Wednesday after a computer sequencer detected a potential problem just before engine ignition.
The rocket was set to blast off from Cape Canaveral with a U.S. government spy satellite at 11:54 p.m. EDT Wednesday (0354 GMT Thursday), but the countdown stopped at T-minus 7 seconds. ULA said the automated countdown sequencer controlling the rocket in the final moments before liftoff detected an “unexpected condition prior to the engine start sequence.”
“The team is currently reviewing all data and will determine the path forward,” ULA said in a statement.
Here’s a replay of the final seconds of the aborted Delta 4-Heavy countdown tonight.
This is the second abort inside T-minus 10 seconds for this mission.
Continuing coverage: https://t.co/gZCB2vhVYZ pic.twitter.com/Gt7Wf4Cgzb
— Spaceflight Now (@SpaceflightNow) October 1, 2020
It was the second abort for the Delta 4-Heavy rocket in the final 10 seconds of a countdown. A launch attempt Aug. 29 was halted at T-minus 3 seconds, after ignition of one of the rocket’s three RS-68A main engines.
ULA, a 50-50 joint venture between Boeing and Lockheed Martin, traced the problem uncovered Aug. 29 to a pressure regulator at the Delta 4’s launch pad at Cape Canaveral Air Force Station. Officials began assessing the cause of Wednesday night’s abort as the launch team “safed” the Delta 4-Heavy rocket and drained it of cryogenic propellant.
Tory Bruno, ULA’s president and CEO, tweeted after Wednesday night’s abort that the countdown automatically stopped after a “sensor reported a fault.” He added that the Delta 4’s automated safety system operated as intended.
“Bird and payload are safe and unharmed,” Bruno tweeted, referring to the launcher and the NRO spy satellite. He also confirmed that ignitors inside the rocket’s three Aerojet Rocketdyne RS-68A main engines were not figured, and the engine turbopumps were not “spun up” at the beginning of the ignition sequence.
“Mission safety first,” Bruno added.
We experienced an automated abort because a sensor reported a fault. Automated Safety System operated as intended. Bird and payload are safe and unharmed. Engine ROFI ignitors were not fired. Turbo pumps were not spun up. Mission safety first…
— Tory Bruno (@torybruno) October 1, 2020
The abort Wednesday night occurred after sparklers at the base of the rocket ignited to burn off any excess hydrogen gas around the vehicle before the engine startup sequence.
Bruno later tweeted it was too early to know how long engineers might need to investigate the cause of Wednesday night’s abort and ready the Delta 4-Heavy for another launch attempt. But the launch team was instructed to prepare for an “extended recycle,” suggesting officials did not anticipate another launch attempt this week.
In any event, it seemed likely early Thursday that the Delta 4-Heavy will remain grounded for at least several days, and perhaps longer. That would free up the military-run Eastern Range to support a pair of SpaceX Falcon 9 rockets slated to blast off from different pads on Florida’s Space Coast on Thursday and Friday.
A Falcon 9 launcher was being prepared for launch from pad 39A at NASA’s Kennedy Space Center at 9:17 a.m. EDT (1317 GMT) Thursday with SpaceX’s next 60 Starlink broadband satellites. A separate Falcon 9 rocket was standing on pad 40 at Cape Canaveral Air Force Station for launch at 9:43 p.m. EDT Friday (0143 GMT Saturday) with a GPS navigation satellite for the U.S. Space Force.
Read our earlier story for details on the Starlink and GPS missions.
The aborted countdown Wednesday night continued a series of delays for the Delta 4-Heavy mission, codenamed NROL-44.
ULA has delayed the launch from its original target date of Aug. 26. A pneumatics issue prevented the rocket from launching Aug. 27, and the Aug. 29 countdown stopped when the automated launch sequencer detected a problem with a pressure regulator on the launch pad designed to flow helium gas to spin up rocket’s center engine for ignition.
The regulator for the center engine did not open, prompting the countdown’s computer controller to stop the countdown.
Bruno said that engineers refurbished and tested all three pressure flow devices at pad 37B before proceeding with another launch attempt.
ULA set Sept. 26 for the next launch attempt for the NROL-44 mission, but officials delayed the mission again to investigate a concern with the swing arm retraction system at the Delta 4-Heavy’s seaside launch complex at Cape Canaveral. The swing arms, which feed liquid propellants and conditioned air to the vehicle, are designed to quickly retract away from the rocket at liftoff.
Officials kicked off a countdown Monday afternoon for a launch opportunity just after midnight Tuesday. But the threat of lightning prevented ground crews from retracting the launch pad’s towering mobile gantry, which is needed to attach satellites in a vertical configuration on the pad, and also provides protection for the rocket before launch.
Storms again delayed rollback of the Mobile Service Tower on Tuesday, but the weather cleared in time to allow technicians to begin moving the gantry. Then a hydraulic leak interrupted the gantry rollback procedure, causing ULA to scrub another launch attempt.
The repeated problems with different parts of the Delta 4-Heavy’s launch pad have raised questions about aging infrastructure at pad 37B, which was originally built to support Saturn rocket launches in the 1960s, then mothballed until Boeing took over the facility in the 1990s for the Delta 4 program.
Boeing built the towering mobile gantry for the Delta 4 rocket, along with a then-new fixed umbilical tower with huge swing arms designed to pull away from the launcher as it climbs away from the pad.
ULA is retiring the Delta 4 rocket family after five more launches — three more from Cape Canaveral and two froom Vandenberg Air Force Base in California. The company’s next-generation Vulcan Centaur rocket, scheduled to debut in the second half of next year, will replace ULA’s existing Delta 4 and Atlas 5 launch vehicles.
While SpaceX’s Falcon Heavy rocket is significantly less expensive and can lift heavier payloads into low orbits, the Delta 4-Heavy has demonstrated an ability to inject satellites directly into high-altitude circular geosynchronous orbits more than 22,000 miles (nearly 36,000 kilometers) above Earth.
The maneuvers required for such an orbital injection take place over roughly six hours. While the payload on the NROL-44 mission is classified, independent analysts say publicly-known parameters such as the rocket’s capabilities, its launch azimuth, and the launch window suggest the Delta 4-Heavy is set to carry a signals intelligence satellite into geosynchronous orbit.
In that orbit, the satellite is expected to unfurl a giant football field-sized antenna to eavesdrop on telephone calls and other data traffic from U.S. adversaries.
The Delta 4-Heavy also has a larger payload fairing than the Falcon Heavy, and the mobile shelters at Cape Canaveral and Vandenberg allow ground crews to mate satellites to the rocket in a vertical orientation. SpaceX plans to offer an enlarged payload shroud on the Falcon Heavy and build a vertical integration hangar at the Kennedy Space Center to support future national security missions that can currently only fly on the Delta 4-Heavy.
Space Force officials said last month that ULA’s next Delta 4-Heavy rocket was scheduled to take off no earlier than December from Vandenberg. Bruno said ULA is reviewing maintenance and test procedures at the Delta 4 pads at Cape Canaveral and Vandenberg to ensure the facilities are ready to support the remaining Delta 4 flights.
“We are conducting a very detailed and comprehensive review of all of our preventative maintenance and pre-launch testing processes at the Delta pads and will make whatever improvements are indicated going forward,” Bruno tweeted last month.
The final Delta 4-Heavy rocket is scheduled to launch in 2023.
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