SpaceX realign Falcon Heavy Static Fire test for Tuesday

The second most important part of Falcon Heavy’s debut has arrived: static fire.  With preparations continuing on schedule, SpaceX is anticipated to fire up the 27 engines at the base of Falcon Heavy in an event that will solidify the target launch date for the rocket’s maiden voyage – which will send Elon Musk’s Tesla Roadster on a journey to heliocentric Mars orbit. Last Thursday was the closest attempt, with a full prop loading cycle prior to a scrub of the attempt. The next attempt is likely to be Tuesday.

The main event had a NET (No Earlier Than) date of last Wednesday during a long static fire window that opened at 13:00 EST (1p local time, 18:00 UTC) and closed at 19:00 EST (7p local time, 00:00 UCT).  However, as of Wednesday morning, teams of workers were seen at the base of the pad, pointing to more work taking place, delaying the test to Thursday.

Thursday saw the loading of RP-1 and LOX into the vehicle for the first time. However, an abort was called, scrubbing the attempt for the day.

Crucially for this static fire, SpaceX was understood to be approaching the first attempt as a Wet Dress Rehearsal – everything but engine ignition – with a potential to proceed into a static fire had everything been is perfect.  Therefore, the test saw propellant pumped into all three first stage cores and the second stage without an initial intention to light the Falcon Heavy’s engines – exactly like the two Wet Dress Rehearsals performed last week at SLC-40 ahead of Zuma’s launch.

Information later noted this was a full prop load, meaning all three cores were loaded together for the first time.

As such, Thursday’s attempt was the first WDR for the big rocket.

Further work, relating to the Tail Service Masts (TSMs) and/or the hold down clamps – per previous work earlier in the week, is believed to be the focus as the Falcon Heavy was lowered off the pad on Friday morning. The rocket is now back erect on the pad, but is not expected to fire up until at least Tuesday.

Tuesday’s attempt will follow the same approach. If, and only if, everything proceeds perfectly with fueling and the entirety of the Wet Dress Rehearsal will SpaceX then roll the test directly into a static fire, lighting all 27 engines at the base of the massive rocket while keeping it firmly clamped to the launch mount and TEL (Transporter/Erector/Launcher) at Pad 39A at the Kennedy Space Center.

Given the dynamic and new nature to Falcon Heavy’s engine start sequence and initial run, it is now understood that the static fire will last an impressive 12 seconds – much longer than the customary three to seven second duration range as has been used on flight proven booster mission (of which Falcon Heavy has two flight proven boosters) static fires and missions of national security importance.

Static fire is a culmination of a great deal of work on Falcon Heavy, not the least of which involved the configuration of LC-39A at the Kennedy Space Center to host the world’s most powerful rocket – a role the pad is well accustomed to, having hosted Saturn V and the Space Shuttle fleet (the world’s most powerful rockets at their respective times) from 1967 to 2011.

The vast majority of work to prepare LC-39A for Falcon Heavy occurred during the pad’s transition from the Shuttle era to its host role for the Falcon family.  When Falcon 9 flights began off 39A in February 2017, SpaceX stated that 60 days worth of work remained – primarily with the TEL, electrical lines, plumbing and sound suppression water system – to finalize the pad for Falcon Heavy.

The original plan at the beginning of 2017 was to save all that work until SLC-40’s reactivation in August.  As that pad’s rebuild took longer than anticipated, SpaceX found an ability to perform almost all of the 60 days worth of work between Falcon 9 missions – aided greatly by a one month stand down in launch operations due to planned range maintenance by the 45th Space Wing in July.

By October, SpaceX had impressively shaved all work down to just 21 days.  By mid-November, they had reduced that to just 14 days, with all remaining work not possible until the clandestine Zuma satellite launched in mid-November and launch operations transferred to SLC-40 in early December.

The final 14 days worth of work could not proceed until all missions off 39A were complete because two of Falcon 9’s four hold down clamps had to be cut out from the TEL’s reaction frame – an operation that would eliminate the ability to launch single stick Falcon 9 missions from the pad in preparation for Falcon Heavy’s debut.

During its construction, Pad-A’s TEL was specifically designed to service both Falcon 9 and Falcon Heavy rockets – a configuration that required the east-west aligned hold down clamps of the Falcon 9 to be removable.  The single stick Falcon 9 is held onto the launch pad by four hold down clamps – which on Pad-A are aligned to the cardinal directions: north, south, east, and west.

NSF Forum

The east/west Falcon 9 hold down clamps have to be removed for Falcon Heavy as their presence overlaps with the Heavy’s side-mounted cores’ engines.  Thus, those east/west hold downs are installed on removable inserts to the TEL’s reaction frame.  Once removed, the needed space and exhaust holes for the side-mounted Falcon Heavy cores are present.

It is understood that when the east-west hold down inserts were initially constructed on the TEL reaction frame, they were not removable – thus they had to be physically cut away from the reaction frame in preparation for Falcon Heavy.

Now that they have been cut away, the removable inserts are designed to be reinstalled with relative ease, making Pad 39A easily configurable between Falcon 9 and Falcon Heavy – which will be highly important as Pad-A will serve as the launch pad for commercial crew operations later this year as well as host various single stick Falcon 9 missions to aid SpaceX’s busy 2018 manifest, which includes up to 30 missions.

For Falcon Heavy preps, once those east-west hold down inserts were removed, SpaceX needed to install two compression bridges at the base of the TEL’s reaction frame to help hold and distribute the Falcon Heavy’s weight.  These two compression bridges were mounted to the same points on the reaction frame that the east/west hold down clamps had been bolted to.

The compression bridges are not hold down clamps but rather specially designed pedestals that a portion of the mating brackets bolting the side cores of the Falcon Heavy to the central core will rest on top of.  (See image below for visual.)

Render of how Falcon Heavy sits on the compression bridges installed on the reaction frame of the TEL at LC-39A. Credit: NSF forum

With all prep work completed, the TEL was rolled into the Horizontal Integration Facility (HIF) where the inaugural Falcon Heavy was mated to it.  The TEL with Falcon Heavy then made the trip up the ramp to Pad 39A’s launch mount on 28 December 2017 for fit checks and electrical/data connection verification and validation ahead of the vehicle’s return to the HIF.

Now firmly back atop LC-39A, Falcon Heavy is preparing for its Wet Dress Rehearsal and static fire – a series of steps that will take Falcon Heavy through an entire launch countdown up to and including ignition of all 27 Merlin 1D engines at the base of the rocket.

The test will provide data not just on the ignition of all 27 engines but also verify and validate all of the electrical and data connections to the rocket, the pad’s ground support equipment systems, and cryogenic systems and propellant loading operations – which will mark the first time that three Falcon 9 cores and the second stage are fueled simultaneously.

If everything goes perfectly with fueling and the Wet Dress Rehearsal, personnel in charge of the test will have to agree to roll forward into static fire – should that emerge as the desired plan upon a successful fueling of Falcon Heavy.

It is possible the first fueling and Wet Dress Rehearsal will not result in static fire, which does not necessarily mean an issue will have presented but rather that the team wishes to review all data to make absolutely certain everything is ready for engine ignition.

Regardless, when static fire does occur, it will be the first time 27 Merlin 1D engines are lit together.  Due to thrust torque (a thrust-induced rotation) scenario that could destroy or severely damage the octawebs at the base of each Falcon core that house the Merlin 1D engines, the Falcon Heavy’s 27 engines will not be lit simultaneously like the Falcon 9 engines.

Instead, Falcon Heavy will take a page from the Space Shuttle’s book and will employ a staggered start sequence – like main engine start on Shuttle where each main engine started 120 milliseconds after the previous – as seen in the slow motion engineering video below.

For Falcon Heavy, it is understood that two engines will be lit simultaneously followed by the next two… and so on until all 27 are up and running.  The timing of this ignition sequence will be such that it will look simultaneous to the naked eye.

Once static fire is complete, teams will review the data collected during the test and determine whether a second static fire is necessary before proceeding into the launch campaign.

If only one static fire is needed, it is currently understood that Falcon Heavy will target the end of January for its maiden voyage – with publicly available proposed badging dates for media access to the Kennedy Space Center indicating that 25 January is the current No Earlier Than date if absolutely everything with static fire goes perfectly.

An end of January launch for Falcon Heavy would coincidentally place the flight within days of the planned GovSat-1/SES-16 launch of a Falcon 9 rocket from SLC-40, potentially setting up a scenario of two Falcon family missions from the Eastern Range within days of each other.

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