A United Launch Alliance Atlas 5 rocket stands on pad 41 at Cape Canaveral Air Force Station on Tuesday, Nov. 3. Credit: United Launch Alliance
United Launch Alliance called off the planned launch of an Atlas 5 rocket Wednesday at Cape Canaveral to resolve a problem with valves at the launch pad, while a SpaceX team a mile-and-a-half to the south readied a Falcon 9 rocket for liftoff Thursday evening with a GPS navigation satellite for the U.S. military.
ULA’s launch team scrubbed the Atlas 5 launch attempt Wednesday shortly before 6 p.m. EST (2300 GMT) after unsuccessful attempts to fix the valve issue, first remotely and then with a team of technicians dispatched to the Atlas 5’s seaside launch pad.
The Atlas 5 rocket will carry a classified payload into orbit for the National Reconnaissance Office, the U.S. government’s spy satellite agency. The launch is designated NROL-101, and the NRO has not disclosed any specifics about the payload’s mission, other than it will help the agency in its mission to collect and disseminate information for the government’s intelligence agencies.
ULA started the Atlas 5’s countdown late Wednesday morning, powered up the rocket, and proceeded with guidance system testing and other checkouts before loading cryogenic propellants into the launcher ahead of a planned liftoff at 5:54 p.m. EST (2254 GMT).
But the launch team stopped the countdown clock after an “unexpected system response from remotely commanded ground system liquid oxygen valves,” ULA said in a statement.
“The team continues to analyze the system and will protect for our next launch attempt no earlier than Nov. 6,” ULA said.
The next opportunity to launch the Atlas 5 rocket will be Friday, ULA said. An exact time for Friday’s launch attempt was not immediately announced, but the mission’s launch time has moved about four minutes earlier per day. That would put Friday’s launch time at around 5:46 p.m. EST (2246 GMT).
The Atlas 5’s launch was previously scheduled for Tuesday, but ULA returned the rocket to its vertical hangar near the launch pad to replace an environmental control system duct feeding conditioned air to the top secret NRO payload on top of the 206-foot-tall (63-meter) vehicle.
Ground crews returned the Atlas 5 to its launch pad late Tuesday in preparation for the launch attempt Wednesday.
Before the next Atlas 5 launch opportunity, SpaceX plans to launch a Falcon 9 rocket from nearby pad 40 during a 15-minute window opening at 6:24 p.m. EST (2324 GMT) Thursday.
The 229-foot-tall (70-meter) Falcon 9 rocket was standing on pad 40 Wednesday in preparation for launch Thursday evening. Pad 40 is located about a mile-and-a-half (2.5 kilometers) south of the Atlas 5 launch pad at Cape Canaveral.
A SpaceX Falcon 9 rocket stands on pad 40 at Cape Canaveral Air Force Station on Nov. 4. Credit: Stephen Clark / Spaceflight Now
The Falcon 9 rocket is poised to loft the GPS 3 SV04 navigation satellite for the U.S. Space Force, replenishing the fleet of positioning and timing stations used by billions of military and civilian users around the world.
SpaceX tried to launch the GPS satellite Oct. 2, but an engine problem forced an automatic abort just two seconds prior to liftoff.
Engineers investigating the Oct. 2 abort found that two of the nine first stage engines on the rocket had a tendency to ignite a split-second earlier than expected. Inspections showed a blocked relief valve in the gas generators of the two engines caused pressures to rise sooner than designed at startup, and sensors on the engines detected the problem and halted the countdown.
SpaceX engineers inadvertently left behind in two Merlin engines as the cause of the aborted countdown last month.
“When we looked at the data, we saw that two of the engines attempted to start early, and the auto abort prevented that,” said Hans Koenigsmann, SpaceX’s vice president of build and flight reliability. “And by doing that, it prevented a possible hard start that could have been damaging to the engine hardware.”
The Merlin engines power up with help from an igniter fluid known as TEA-TEB — or triethylaluminium-triethylborane — that gives off a bright green flash at the start pf the ignition sequence.
“And then we have liquid oxygen, and we have kerosene, or RP-1 as its called,” Koenigsmann said last week in a conference call with reporters. “And you need to introduce these liquids in the right order. If you do this in the wrong order, if you happen to throw in the liquid oxygen and the RP-1 and the igniter fluid, then what would happen is we call it a hard start.”
A hard start would “rattle” the engine in most cases, but could cause damage, Koenigsmann said. “So in general, you do not want that. You want a good startup.”
SpaceX shipped the Merlin engines back to a test site in Central Texas, where inspections revealed a substance blocking a line leading to a pressure relief valve in the gas generator on two of the engines.
Koenigsmann said the vent port, which means just one-sixteenth of an inch wide, was obstructed by a hardened masking lacquer. He said liquid lacquer — similar to red nail polish — is used by a third-party vendor that anodizes aluminum engine components for SpaceX.
The lacquer protects certain parts during the anodizing treatment process, but the vendor — which officials did not identify — is supposed remove the material before shipping the components to SpaceX for engine manufacturing.
The gas generator on each Merlin engine drives a turbopump feeding kerosene and liquid oxygen propellants into the main combustion chamber.
Engineers at SpaceX’s McGregor test site demonstrated that the engines performed normally after removing the blockage from the vent valve. Koenigsmann said the issue was “very subtle, but can have obviously some negative impact on the engine operation.”
“The GPS 3-4 mission will still use the same booster as for the first launch attempt” said Walt Lauderdale, GPS 3-4 mission director from the Space Force’s Space and Missile Systems Center. “The two engines which gave rise to the launch abort were replaced with ones confirmed through inspection and pedigree review to not have any residual masking lacquer.”
SpaceX and Space Force officials verified all nine Merlin engines on the Falcon 9 rocket were ready for flight after a test-firing on pad 40 Saturday.
Besides the rocket for the GPS mission, the engine issue has also affected vehicles for a pair of upcoming NASA launches. So far, the problem has only impacted missions slated to use new Falcon 9 boosters.
The first operational flight of SpaceX’s Crew Dragon spaceship is set for liftoff Nov. 14 from the Kennedy Space Center with three NASA astronauts and a Japanese mission specialist to kick off a half-year expedition on the International Space Station.
SpaceX is replacing two Merlin engines on the Falcon 9 rocket for the Crew Dragon mission that engineers found suffered from the same early startup tendency exhibited by the engines on the rocket for the GPS mission. The problem delayed the Crew Dragon launch from Oct. 31 to Nov. 14.
Steve Stich, NASA’s commercial crew program manager, said last week that the agency’s engineers want to analyze engine data from the GPS launch before clearing the Crew Dragon for liftoff later this month.
The engine problem has also delayed the launch of the U.S.-European Sentinel-6 Michael Freilich oceanography satellite from Vandenberg Air Force Base in California. That mission was originally supposed to blast off Nov. 10, but is now scheduled for launch Nov. 21.