[Update: Booster 4 rolls out, Starship 20 stacked] SpaceX works at stunning speed installing 29 Raptor engines overnight on Super Heavy Booster 4 ahead of Starship SN20 orbital flight

Update: Booster 4 has rolled to the launch site and is now awaiting integration with Starship 20, which has been stacked in the High Bay.


This morning Elon Musk showed off what appears to be a full complement of 29 Raptor engines in place on Starship Super Heavy Booster 4. The stunning overnight installation is the latest feat in a breathtaking surge of activity around SpaceX’s Starbase facilities as the company pushes hard toward a maiden orbital flight test for the fully stacked vehicle.

Starbase staff surge

In a somewhat expected fashion, SpaceX missed its own self-imposed (arguably over-ambitious) July deadline for Starship’s first orbital flight test. However, the company is clearly unphased as an unprecedented amount of activity has coalesced around its South Texas build site in the last two weeks.

With visible movements of Musk’s private jet and SpaceX transport vehicles ferrying large numbers of employees from their Florida and California locations to South Texas, it became apparent that the company had now adopted an all hands on deck approach to ramp up production for the approaching test.

Warp 9 speed

In the weeks after Booster 3’s first static fire on July 19, the final segements of the orbital launch integration tower were completed and stacked. This culminated with the long-awaited installation of the orbital launch table (the raised platform upon which the fully stacked Starship vehicle will stand) on July 31.

By then, Musk acknowledged on Twitter that “Starbase is moving at Warp 9” and that he had not even had time to shower for several days amid the “Starbase Surge”.

Fixed gridfins

At about the same time, a flurry of progress on Super Heavy Booster 4 caught even SpaceX’s most ardent optimists off-gaurd. Between July 30 and 31, all four of the booster’s gridfins were installed and painted black.

This came with the revelation that they would not actually retract like their Falcon 9 counterparts. Instead, they are in a fixed deployed position while remaining rotatable. This is a likely effort to strengthen their design for Musk’s stated plans to catch the returning booster by the fins with the use of enormous arms on the launch integration tower.

Musk has also implied on Twitter that gridfin designs could change through the course of the program as they explore the benefits of a design that would produce more drag and thus a lower terminal velocity for landing. This comes with the potential benefits of reducing landing propellants for an increased payload to orbit capability.

Raptors engaged

The gridfin installation was immediately followed by the stacking of the booster’s upper methane and lower liquid oxygen tank sections, bringing the booster to its full high bay-busting height of roughly 65m (215ft). Crews began installing Raptor engines on the lower section before stacking was even completed.

As the night of August 1 wore on and more Raptors were lined up underneath the booster, it became clear that SpaceX was pushing for the full complement of engines to be installed before the booster rolled out to the launch site.

By the morning of August 2, Musk all but confirmed this was the case with a picture of what appeared to be 29 Raptors installed on Booster 4, utterly smashing any previous benchmarks for Raptor installations in a 24 hour period.

Next for Starship

This breakneck pace of production is likely to only continue over the course of the next few days. Musk has indicated on Twitter that the orbital launch table will be checked for booster fitment around Tuesday, and transportation road closures for Highway 4 are already appearing to support this timeline.

Sources close to Space Explored have indicated that a full stack event could even happen as soon as August 5. This would require similarly rapid progress on Starship 20 in the coming days. This will entail stacking in the highbay once booster 4 has rolled out, completion of the hexagonal tile thermal protection system, and the first-time installation of the 3 vacuum-optimized Raptor engines currently on-site. (These are variants of atmospheric Raptor engines that are optimized for performance in the vacuum of space. They will constitute the outer ring of three engines on all orbit-class Starships.)

Booster 4 rolled out and Ship 20 nosecone stacked

UPDATE: Booster 4 rolled to the launch site amid much fanfare on August 3rd and is now in position to be lifted onto the launch table by “Frankencrane”, the enormous crane SpaceX has been using to build the launch integration tower. Only hours later that day, Starship 20 was rolled out of the Mid Bay and stacked with its nosecone in the High Bay by nightfall. Around 1AM Elon Musk shared a picture of the 3 vacuum Raptors installed. It appears the only remaining component of the ship left to finish is the rapidly expanding thermal protection system on its underside. A road closure for a potential rollout on Thursday was posted and then cancelled, so that event is now TBD. Once Ship 20 does make it to the launch site, “Frankencrane” will likely perform the final stacking atop Booster 4 as the system for doing so with the launch integration tower is not quite finished yet.

Stay tuned as we work to bring you the latest on this rapidly developing road to orbit for Starship Super Heavy.

Photos of SpaceX’s Booster 4 during rollout and Starship 20’s nosecone being stacked. Credit: Nic Ansuini

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Featured image credit: Elon Musk

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