SpaceX has finished the last major stacking event for the business half of its fifth full-scale Starship prototype, meaning that the company may be a week or less from having a fleet of Starships for the first time ever.
As of now, Starship serial number 5 (SN5) is on track to be completed in under a month, continuing a trend that SpaceX has managed over the entirety of 2020. Beginning in mid-January, SpaceX has completed several nosecone pathfinders, three test tanks, and three full-scale Starship prototypes – soon to be four once SN5 is finished. Once it is, however, SpaceX will be entering a new era of operations – fleet operations.
Up to this point, every full-scale Starship prototype and test tank SpaceX has built – excluding the tank SN2 was turned into in March – has been quickly destroyed over the course of one or two tests. For better or for worse, this has meant that SpaceX’s test and launch pad has always been more or less self-clearing, making way for the next prototype to roll out and begin testing after the scraps of its predecessor were removed. This time around, barring Starship SN4’s imminent demise, SpaceX will now have to deal with multiple completed Starship prototypes at the same time – a tiny taste of things to come.
For unknown reasons, SpaceX decided to swap out Starship SN4’s lone Raptor engine (likely SN18) after multiple wet dress rehearsals, partial engine tests, and two static fire tests – at least one of which was confirmed a success by CEO Elon Musk. Most recently, SpaceX removed Raptor SN18 to perform a more ambitious cryogenic pressure test, pushing Starship SN4’s propellant tanks all the way to 7.5 bar (~110 psi) at the same time as hydraulic rams simulated the thrust of three Raptor engines at the rocket’s base.
Instead of reinstalling Raptor SN18, SpaceX transported Raptor SN20 to the launch pad and installed it on Starship SN4 on May 10th, less than 24 hours after the prototype passed an orbital-class pressure test.
Aside from installing Raptor SN20, SpaceX teams have spent the last few days adding new COPVs (composite overwrapped pressure vessels) and plumbing to Starship SN4’s exterior – purpose largely unknown. While the new hardware is mostly a mystery, it is known that SpaceX is in the process of preparing SN4 and its new Raptor engine for a third wet dress rehearsal (WDR) and static fire test, necessary to ensure that Raptor SN20 is properly installed and functioning as expected.
Assuming that third static fire is successful, SpaceX’s will prepare Starship SN4 for its first flight, a ~150m (500 ft) hop test that will also be the first intentional flight of any full-scale Starship prototype since the program’s birth. For that hop test, SN4 will need some kind of attitude control system (ACS) thrusters to control its rotation and provide fine trajectory tuning to assist the ship’s lone Raptor engine. This is the likeliest explanation for the new hardware being installed on Starship SN4, as the ship does not currently appear to have ACS thrusters installed.
Of course, the first flight of a full-scale Starship prototype will probably be the riskiest test yet for the program and there’s a good chance that SN4 will meet its demise at some point during that flight. Enter Starship SN5.
As of May 12th, Starship SN5’s final two tank sections were stacked, effectively completing the most important half of the rocket (minus one final circumferential ring weld). SN5’s final outfitting of avionics and plumbing is still pending and will take at least a few days to a week or more, but that work can and has been completed after prototypes are transferred by road to the launch pad. Currently, Starship SN4 is occupying SpaceX’s one and only pad test stand, however, meaning that it wouldn’t make much sense to immediately move SN5 to the launch pad – at least until SN4 is done testing.
SN5 will also need a nose section and, perhaps, flaps installed, meaning that the full ship is likely still at least a week or two away from being finished, but that likely wont stop SpaceX from proof testing the rocket’s tanks if or when SN4 makes space at the launch pad.
According to comments made by Elon Musk, SN5 will likely become the first Starship prototype to have three Raptor engines installed and the first to attempt a truly high-altitude flight test if Starship SN4 is met with success in the coming weeks. As absurd as it feels to say, if SN5 completes triple-Raptor testing and a 20 km (~12 mi) flight test without issue, Musk has stated that the next step would be orbital flight tests. Starship SN6’s steel rings, meanwhile, are already being formed and stacked as SN5 nears completion.