RE: SES 8 launch postponed to 28th Nov
Now again sad news
Falcon 9 Launch Scrubbed after Last-Second Countdown Abort
Photo: SpaceX Launch Webcast
The second launch attempt of a SpaceX Falcon 9 rocket on the company’s first GEO Transfer Mission was scrubbed on Thursday after the rocket’s engines were shut down just split seconds before liftoff. SpaceX says the next launch attempt will not take place for several days to allow engineers to complete inspections on the launch vehicle to determine the cause of a slow thrust build-up condition that was observed during ignition.
Thursday’s launch countdown was started 13 hours and 2 minutes ahead of the opening of the launch window which stretched from 22:39 to 23:44 UTC. After checkouts and initial reconfigurations of the rocket, the Falcon 9 was loaded with Liquid Oxygen and Rocket Propellant-1, going through an uneventful countdown sequence.
As teams were approaching terminal countdown, all Stations were polled for a GO or No GO for launch.
All was in readiness including the Falcon 9 launch vehicle, the SES-8 spacecraft, the Eastern Range and the launch weather that had not been an issue throughout the day. Pressing into the Terminal Countdown Sequence at T-10 minutes, the Falcon 9 started final reconfigurations to prepare for liftoff. The launch vehicle transitioned to internal power, the first stage ignition system was armed and Liquid Oxygen Loading was terminated to allow tank pressurization to start ahead of the retraction of the Strongback to clear the way for liftoff.
Inside the final four minutes of the countdown, the Flight Termination System Transferred to internal power & was armed, and the launch vehicle’s computer was aligned for flight before assuming control of the countdown at T-1 minute. The final minute included Thrust Vector Control Tests and propellant tank pressurization to flight level ahead of engine start.
Three seconds ahead of the planned launch time, the TEA-TEB ignition system of the first stage was initiated and Merlin 1D turbopumps were started. All nine engines came to life and started building up thrust until the Flight Computer triggered a shutdown – just about one second before liftoff. The launch team completed initial vehicle safing steps and started looking at the data to find out why the flight computer shut down the engines.
According to SpaceX CEO and Chief Designer Elon Musk, some of the Merlin 1D engines were slow to ramp-up thrust. As part of Falcon’s tight red-line limits, the computer aborted when the engine parameters during ignition were not within those limits. The launch team then looked at the data that was collected during the ignition sequence and determined that the engines appeared to the in good condition and were just slow to reach their nominal thrust level.
Photo: SpaceX Launch Webcast
Overly conservative red-line limits have caused a number of countdown aborts in Falcon 9’s short history. In the past, the launch team was able to confirm that no hardware problems were present and adjust the limits before trying again. That was also the thinking on Thursday and teams set up for another launch attempt at the end of the 65-minute window while working on data analysis in parallel, developing a plan to modify the engine start sequence to ensure the engines would reach the proper thrust levels at the expected time.
The Merlin 1D engines use high-pressure Helium to spin-up their turbopumps during the ignition sequence. According to Elon Musk, teams decided to increase the Helium pressure during start-up for the second attempt to see if that would allow the vehicle to pass all abort limits. A Tweet sent by Musk indicated that teams were not fully convinced that this modification would work, but decided to press on.
While setting up for a new launch attempt, the Propulsion Team was still analyzing the data acquired during the engine start and cutoff to ensure that no actual hardware problem was present on any of the nine engines. The end of the 65-minute launch window was targeted as T-0, keeping the option of a late abort in the Terminal Countdown in case the data analysis could not be completed in time.
Photo: SpaceX Launch Webcast
Heading back into the Terminal Countdown, Falcon 9 went through its nominal steps to get ready for launch. Inside one minute, the PROP Controller called a countdown abort because teams were not fully satisfied with the data analysis performed after the cutoff. To be completely safe, the countdown was stopped and a Scrub was called for the day to allow detailed analysis to be completed.
The Falcon 9 will be returned to the hangar where engineers will perform borescope inspections on the engines in question to rule out any hardware problems. Data from Thursday’s countdown will be used to determine whether the slow thrust build-up was in-family with data gathered during the testing of the Merlin 1D engines and the first stage. SpaceX completes test firings of each engine before the rocket reaches the launch pad, plus the Static Fire a few days prior to launch which provides them with a set of data on the specific performance of each engine.
A date for the next launch attempt will be selected when inspections are complete.
