BN1

BN1 "booster nr 1" was the first Super Heavy booster to be assembled. Final stacking has been done on 18 March 2021. It is confirmed that BN1 will not support any mission with the second stage (starship). BN1 has been scrapped. The pathfinder prototype was never rolled out to the launch site.

## History

It was believed for some time, that BN1 could undergo some testing at the launch site. NSF author Chris Bergin later announced that "BN1 is not expected to fly. Instead, it will be stacked and rolled to the Starship suborbital pad for ground testing, including a potential Static Fire test. This will provide vital data ahead of the test flight of BN2, of which sections have already been spotted waiting for stacking." BN1 and BN2, along with SN15-17, represent “iterative improvements to the vehicles to improve the design and serve as production pathfinders” to aid the increasing production cadence.

Later, Elon Musk confirmed that BN1 won't fly as it is a production pathfinder in order to find out how to build and transport a 70 meter tall stage. BN2 will fly.

It was still unclear whether BN1 would roll out to the pad and if there would be some testing. Musk stated on March 30:

"BN1 is a manufacturing pathfinder, so will be scrapped. We learned a lot, but have already changed design to BN2. Goal is to get BN2 with engines on orbital pad before end of April. It might even be orbit-capable if we are lucky."

This indicated that the pathfinder would not even be rolled out to the pad, something that later turned out to be correct. Furthermore, it was revealed that the pathfinder differs from later prototypes in the tank order: While BN1 had its LOX tank at the top, BN3 will have the LOX tank at the bottom, just as Starship.

## Timeline

* 25 Jan 2021: Aft dome spotted
* 01 Feb 2021: Common dome flipped
* 05 Feb 2021: Aft dome sleeve spotted
* 07 Feb 2021: Aft dome liften onto sleeving stand
* 07 Feb 2021: Practice thrust dome moved around
* 08 Feb 2021: Aft dome sections ready for sleeving
* 09 Feb 2021: Aft dome sleeved
* 19 Feb 2021: Common dome ready for stacking
* 19 Feb 2021: Section rolled out for stacking, scaffolding errected, moved into highbay
* 23 Feb 2021: "Booster #2" four ring section ready infront of high bay
* 27 Feb 2021: Work on BN1 in high bay
* 28 Feb 2021: Stacking continued
* 07 March 2021: SN11 and BN1 changed places in high bay
* 07 March 2021: "Booster double" section (aft dome section plus two ring stack) moved onto new heavy stand
* 09 March 2021: Thrust rams installed, probably for testing BN1 [no?]
* 11 March 2021: Booster double section moved into high bay, stacking imminent
* 12 March 2021: Methane tank sections (lower part) including common dome section stacked on engine section
* 13 March 2021: Work continued
* 14 March 2021: Work platform installed for stacking LOX sections on CH4 sections
* 15 March 2021: Bluto/Tankzilla moved from pad to high bay, probably for BN1 stacking, laid down; extension for the crane moved
* 16 March 2021: Work platform and lead-ins attached for stacking LOX tank on CH4 section
* 18 March 2021: LOX tank **stacked** on CH4 tank (full height now visible), LOX tank previously was **cut off from its bottom ring**, thus BN1 now one ring short [?]
* 19 March 2021: Work continued
* 21 March 2021: Still attached to crane
* 23 March 2021: Disconnedted from crane, moved inside the high bay, possibly to make place for bridge crane installing
* 26 March 2021: SPMTs (blue) stacked with counterweights and connected, possibly for BN1 transport; other configuration than for SN transport [?]
* 28 March 2021: Work in high bay continued, work platform still up
* 13 Apr 2021: Scrapping continued throughout the day, stackes moved to scrapyard
* 13 Apr 2021: BN1 cut in half in the middle, bridge crane used (first time?)
* 14 Apr 2021: Scrapping in high bay continued (eg. BN1 Booster Qund3 section, started 5 January 21, completed 12 Jan 21)
* 25 Apr 2021: Final section hooked to crane for scrapping
* 25 May 2021: BN3 (some 12 rings high) moved in high bay, new stack moved into it and attached to bridge crane, stacking continued; LOX tank now at the bottom according to Elon Musk (unlike BN1)

## 18 March 2021 - Final Stacking

Timeline according to NSF:

* LOX tank cut off from lowest ring on stand
* LOX tank lifted by Tankzilla/Bluto in high bay
* CH4 tank shifted to the right, under the LOX tank
* LOX tank slowly lowered onto CH4 tank

## References

1. ↑ 1.0 1.1 https://www.nasaspaceflight.com/2021/03/starship-sn11-spacex-orbital-flight-summer/#more-76751
2. ↑ https://twitter.com/elonmusk/status/1376902791906611200
3. ↑ https://twitter.com/elonmusk/status/1397348226806665220