A SpaceX Falcon 9 booster had all four of its landing legs successfully retracted after a flawless fourth launch and landing, highlighting the impressive margins and durability of the rocket’s upgraded Block 5 design.
On April 22nd, Falcon 9 booster B1051 lifted off on its fourth orbital-class mission – also its second 60-satellite Starlink launch this. Around eight minutes later, B1051 successfully landed aboard drone ship Of Course I Still Love You (OCISLY), ending a back-to-back streak of failed ocean recoveries for SpaceX and verifying that the cause of a March 2020 in-flight engine failure had been rectified. After the loss of booster B1056 and B1048 in February and March, it was also simply a relief to have B1051 safe and sound aboard OCISLY, ensuring that the rocket should be able to support another launch in the near future.
After sailing in port on April 26th, SpaceX technicians lifted a booster off of drone ship OCISLY’s deck for the first time since late January – coincidentally (or maybe not) also Falcon 9 B1051. Two days after its arrival in port and transfer onto dry land, SpaceX successfully retracted all of the massive booster’s landing legs in less than three hours and had it ready for transport less than two hours after that. While B1051’s brisk fourth recovery didn’t break any records, it still serves as a reminder of Falcon 9’s impressive durability in light of the landing it experienced just ~85 days prior.
B1051’s successful leg retraction after its fourth launch and landing is particularly impressive for one main reason: after its third launch, the booster suffered perhaps the hardest drone ship landing any Block 5 rocket has thus far experienced.
Taken in March 2019 and February 2020 after Falcon 9 B1051’s first and third launches and landings, the photo below reveals just how hard a landing B1051 experienced after its Starlink-4 launch. Built almost entirely out of carbon fiber composites and mounted directly to the rocket’s tank walls, Falcon’s telescoping landing legs rely on something known as a ‘crush core’ – made out of aluminum honeycomb – that’s designed to intentionally collapse under a very specific amount of stress.
The crush core is situated in the very tip of the cylindrical leg booms and is easily visible above on the left, while it has nearly disappeared in the right (after) photo after an exceptionally hard landing used up what looks like 90+% of the booster’s safety margin. In other words, if B1051 had landed just a little harder after its third launch, it’s possible that the booster’s landing leg booms would have used up all their crush cores and been driven into the kerosene tank they attach to, potentially totaling the Falcon 9 first stage.
Instead, while clearly a rough landing, B1051 appears to have had its landing leg crush cores replaced and was made ready for another Starlink launch less than three months after that exceptionally hard landing. In other words, despite the rarity of similar hard landings over dozens of recent booster landings, SpaceX was apparently almost entirely unconcerned about the rocket’s state.
As usual, the company almost certainly checked the structural integrity of B1051’s major welds and landing leg hardware before certifying the vehicle for its fourth launch, but the fact that its reuse was so seemingly unexceptional is a testament to the sheer durability of SpaceX’s reusable rocket boosters. Thanks to the modularity of its design, B1051 should have no trouble performing at least several more orbital-class launches over the next several months (if not years). More likely than not, the Falcon 9 Block 5 rocket will fly again just two or so months from now on another Starlink mission, of which SpaceX has 20+ nominally scheduled this year alone.
