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SpaceX on Saturday tested a Falcon 9 rocket at Cape Canaveral in a pre-flight check designed to verify the launcher’s engines are ready to orbit a US military GPS navigation satellite on November 5.
An engine problem forced SpaceX to abandon a launch attempt in early October.
After identifying the problem, SpaceX re-tested the Falcon 9 rocket for the GPS mission on Saturday at 7 p.m. EDT (11 p.m. GMT) on Station 40 of the Cape Canaveral Air Station. The purpose of the test was to verify that the corrective actions resolved the problem.
SpaceX rolled the double-decker rocket – minus its GPS navigation satellite payload – onto Block 40 and lifted the Falcon 9 upright on Saturday. The launch team stationed at a nearby control center supervised the loading of kerosene and liquid oxygen propellants into the rocket on Saturday evening before the 7 p.m. test firing.
The rocket’s nine 1D Merlin engines ignited with a flash and rumble through the Cape Canaveral spaceport. The engines fired for several seconds, increasing to 1.7 million pounds of thrust as the holding clamps held the Falcon 9 firmly to the ground.
SpaceX later confirmed in a tweet that the test firing was complete, setting the stage for final launch preparations. The mission is scheduled to take off on Thursday, November 5, SpaceX wrote in a tweet.
The mission was previously scheduled to be launched on Wednesday, according to several sources.
The Falcon 9 rocket will be returned to its hangar, where SpaceX will mount the US Space Force’s 3 SV04 GPS navigation satellite to the vehicle. The spacecraft is already encapsulated in the Falcon 9 payload fairing.
The GPS 3 SV04 mission was ready for takeoff on October 2, but SpaceX interrupted the countdown at the start of the engine ignition sequence just two seconds before takeoff.
Engineers investigating the Oct. 2 abandonment found that two of the rocket’s engines tended to ignite a fraction of a second earlier than expected. Inspections showed that a stuck relief valve in the gas generators of both engines was pushing up pressure earlier than expected on startup, and sensors on the engines detected the problem and stopped the countdown.
SpaceX presumably replaced the two suspicious engines on the Falcon 9 rocket. A Space Force spokesperson referred inquiries to SpaceX, and a SpaceX spokesperson did not respond to questions about them. .
The Lockheed Martin built SV04 GPS 3 navigation satellite is the fourth in a new generation of GPS satellites with longer lifetimes, higher power and more precise navigation signals. The GPS 3 SV04 spacecraft is expected to join 31 operational GPS satellites orbit 12,550 miles (20,200 kilometers) above Earth.
SpaceX engineers have identified a masking treatment inadvertently left in two Merlin engines as the cause of the October 2 abandonment.
“When we looked at the data, we found that two of the engines had attempted to start early and the automatic shutdown prevented it,” said Hans Koenigsmann, vice president of construction and flight reliability at SpaceX. “And in doing so, it prevented a possible difficult starting that could have damaged the engine hardware.”
Merlin engines are powered up using an ignition fluid called TEA-TEB – or triethylaluminum-triethylborane – which emits a bright green flash at the start of the ignition sequence.
“And then we have liquid oxygen, and we have kerosene, or RP-1 as the name suggests,” Koenigsmann said last week on a conference call with reporters. “And you have to put those liquids in the right order. If you do that in the wrong order, if you throw out the liquid oxygen and the RP-1 and the ignition fluid, then what would happen is we call it a hard start.
Hard starting would “shake” the engine in most cases, but could cause damage, Koenigsmann said. “So usually you don’t want that. You want a good startup. “
“If we see the pressure building too soon, then we know the liquid is in there, and it shouldn’t be,” he said. “And the motor controller software then stops the whole process.”
Launch pad inspections revealed no signs of a hardware issue on the Merlin engines after the October 2 abandonment. After returning the Falcon 9 rocket to its hangar, technicians removed the engines and shipped them to SpaceX’s test facility in McGregor, Texas.
SpaceX was able to analyze the starting behavior of the engines at McGregor, and further inspections revealed a blockage in a narrow pipe leading to a relief valve on the gas generator.
Koenigsmann said the vent hole, which is just a sixteenth of an inch wide, was clogged with hardened masking lacquer. He said the liquid lacquer – similar to red nail polish – is used by a third-party vendor that anodizes aluminum engine components for SpaceX.
The lacquer protects some parts during the anodizing treatment process, but the supplier – whom officials have not identified – is supposed to remove the material before shipping the components to SpaceX for engine manufacturing.
The gas generator in each Merlin engine drives a turbopump feeding the kerosene and liquid oxygen propellants into the main combustion chamber.
“This is obviously a very important part,” Koenigsmann said. “This little red substance was blocking a relief valve which caused it to (increase the pressure) a little earlier than expected.”
“Probably during the wash or the cleaning process, some of that masking lacquer got into that vent hole and blocked it,” Koenigsmann said.
“How was it missed? The little hole that leads to the ventilation valve is tiny. It’s 60 thousandths of an inch… When something goes in there and gets hooked on it, you might miss it, ”Koenigsmann said. “You shouldn’t… but I can see how people forget about it and haven’t really seen it, even though it’s red.
Engineers at SpaceX’s McGregor test site also demonstrated that the engines were operating normally after removing the blockage from the vent valve. Koenigsmann said the problem was “very subtle, but obviously can have a negative impact on engine operation.”
“There is no doubt that the rocket is tough and requires a lot of attention to detail,” Koenigsmann said. “To me, it almost tells me that rockets make me humble every day I work with them. It’s always a challenge, and it’s always tough, and you have to be super diligent and vigilant to get it right.
SpaceX engineers had not detected the problem before. The old boosters from SpaceX’s reusable Falcon 9 rocket fleet don’t appear to feature an early ignition data signature, but the rockets for the GPS and Crew-1 missions are brand new.
“What we have noticed is that this is something that must have happened in the last couple of months, so it mainly affects the build dates of the engines which are on the new boosters and not on the old boosters. “said Koenigsmann.
Besides the rocket for the GPS mission, which will use a new Falcon 9 booster, the engine issue has also affected vehicles for a pair of upcoming NASA launches.
The first operational flight of SpaceX’s Crew Dragon spacecraft is scheduled to take off on November 14 from the Kennedy Space Center with three NASA astronauts and a Japanese mission specialist to launch a half-year expedition to the International Space Station.
SpaceX is replacing two Merlin engines on the Falcon 9 rocket for the Crew Dragon mission which engineers said suffered from the same early start-up tendency as the rocket engines for the GPS mission. The issue delayed the launch of Crew Dragon from October 31 to November 14.
A US-European oceanography satellite named Sentinel-6 Michael Freilich was supposed to be launched on another brand new Falcon 9 booster on November 10 from Vandenberg Air Force Base in California. Kathy Lueders, head of the human exploration and operations division of NASA, said on October 30 that the launch of Sentinel-6 Michael Freilich would be delayed later in November, “pending continued analysis of data from engines ”.
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Follow Stephen Clark on Twitter: @ StephenClark1.
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