On Wednesday, November 3, a United Launch Alliance (ULA) Atlas V 531 rocket was set to launch the NROL-101 mission – a classified payload for the National Reconnaissance Office (NRO) of the United States government – from Space Launch Complex 41 (SLC-41) at Cape Canaveral Air Force Station. At neighboring Space Launch Complex 40 (SLC-40) a SpaceX Falcon 9 stood ready and waiting to launch a US military GPS satellite just a day later.
Ultimately, due to an anomaly with launchpad ground support equipment, the ULA launch attempt of the Atlas V NROL-101 mission was scrubbed Wednesday evening. Admittedly, the weather did not look promising either with ground winds remaining a concern throughout the countdown window.
With an hour and forty-seven minutes to go – just five seconds after a planned fifteen-minute hold was released – the launch teams announced that an anomaly had been discovered with “a ground valve issue with the liquid oxygen system for the Atlas V first stage.” The discovery initiated an immediate stop to the countdown and launch teams entered into an unplanned hold that would delay the targeted launch time.
At first, ULA conducted remote troubleshooting, but the anomaly was not remedied and a return-to-pad team would be required to enter the secured launchpad to physically investigate.
An anomaly team was deployed to investigate the valve that was restricting the flow of liquid oxygen (LOx) to the first stage of the Atlas V rocket. The hold remained for over an hour allowing the propellant lines to warm to a temperature that would be needed to be re-cooled prior to resuming the countdown.
Eventually, the return-to-pad team was able to evacuate the pad securing it for launch once again. Chill-down procedures to return the propellant lines back to an operational temperature began but were halted almost immediately. The anomaly had not been completely rectified and not enough time remained in the launch window to re-address it and re-chill the propellant lines. This led to the scrubbed launch attempt.
Typically, a scrubbed ULA mission for the NRO means that a neighboring SpaceX mission has to wait until the problem is fixed and ULA gets its rocket off of the nearby launchpad. However, that was not the case with Wednesday’s scrub. ULA stood down for a 48 hour recycle – rather than a typical 24 hour recycle – to attempt to launch the Atlas V 531 again on Friday, November 6.
This cleared the way for SpaceX to keep its targeted launch date of Thursday, November 5 during a launch window that extends approximately fifteen minutes from 6:24 – 6:39 p.m. EST (2324-2339 UTC) from SLC-40.
Following a successful static fire test of all nine Merlin 1D engines, SpaceX will attempt to launch the GPSIII-SV04 satellite for the United States military for a second time on Thursday, November 5.
The previous launch attempt on Friday, October 2 was thwarted at T-2 seconds due to anomalous engine start-up behavior. The unexplained early start-up of two Merlin 1D engines was eventually determined to be caused by “unexpected pressure rise in the turbomachinery gas generator” as explained by SpaceX CEO Elon Musk.
The engine anomaly prompted a thorough investigation of all Merlin 1D engines on the launch vehicle, as well as, a thorough investigation of the engines on two Falcon 9 launch vehicles designated for future NASA missions – the first operational rotation mission of the Commercial Crew Program, Crew-1, and the launch of the NASA and European Space Agency Earth-observation satellite, the Micheal Freilich Sentinel-6. Engines were eventually replaced on all three Falcon 9 launch vehicles.
A live hosted webcast of Thursday’s launch attempt will be provided on the company website and is expected to be available for viewing approximately fifteen minuted before liftoff.
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