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Booster Number 1
Also CalledBN1

Booster Number 1 is a Superheavy prototype currently being assembled in Boca Chica, Texas.


The detailed design of Super Heavy remains the subject of speculation, as the only references are official SpaceX renders and the assembly of BN1 itself. The public consensus has changed several times throughout construction as new evidence comes to light. Even the internal SpaceX design appears to have been fluid, with evidence of sections being relabelled.

The current design appears to feature the Liquid Oxygen tank being the upper tank of the booster, with one or more downcomers passing through the lower Methane tank to the Raptors. The general construction is similar to the Starship tank section, however both Super Heavy tanks feature a number of stringers to support both the weight of Super Heavy itself and the Starship it carries on top. The aft dome structure appears to be similar to Starship's, with a inner ring of 8 gimballing Raptors mounted to a reinforced puck on the dome itself and an outer ring of 20 static Raptors mounted primarily to the skirt.

Booster Number 1 itself is expected to have a reduced design, with Elon tweeting that Super Heavy only needs two engines for a hop. The aft dome only has hardware for four of the eventual 8 inner Raptors, and it is unlikely that BN1 will receive the grid fins needed for high-altitude descent control.


Construction of BN1 commenced in September 2020, with the first sections being observed including LOX tank sections and the common dome sleeve. The first sections, marked 'LOX 1' and 'LOX 2', were moved into the High Bay on November 8, shortly followed by the top dome section. At this point, assembly appeared to halt for some time, although the reason for the delay remains unclear. Stacking resumed in late January 2021, with the total LOX tank section reaching 18 rings tall including the upper dome section - too tall for the methane tank. At this point, stacking halted whilst the internal layout of High Bay was reconfigured with the LOX tank section being moved to the rear right corner.

The Aft dome was observed at the end of January, with mounts and pumbing for four central Raptors. Also evident were 5 holes at the periphery of the dome, in locations that would support LOX feed lines to the outer Raptors. The dome was sleeved on the 8th of February, revealing that the 20 outer engine mounts were built into the skirt.

Stacking of the Methane tank began on the 19th of February, with the first four-ring stack being moved into the High Bay followed by the Common Dome section. A second four-ring stack was moved in on February 23.


BN1 is likely to undergo an intensive cryogenic testing phase to validate the design, as well as multiple static fires to verify engine plumbing. Should these be successful, a low-altitude (150m) hop can be expected.