Following in the footsteps of the late Mk1 vehicle, SpaceX’s latest Starship prototype has been outfitted with several Tesla battery packs and motors over the last few weeks.

CEO Elon Musk has confirmed in the past that SpaceX intends to try to use Tesla batteries to power Starship rockets and Tesla motors to drive the ships’ large aerodynamic control surfaces. By all appearances, a Tesla Model S motor’s appearance on the exterior of a Starship prototype recently moved to the launch pad is a first for SpaceX. However, in 2019, SpaceX at one point planned to use and even installed battery packs on Starship Mk1 components before the ship was prematurely destroyed during testing. The nosecone those battery packs were installed in still sits in the middle of SpaceX’s growing Boca Chica rocket factory.

For Starship SN3, the purpose of its ~200 kWh of battery power is rather self-explanatory. The purpose of the Tesla Model S motor recently installed on its side is much less clear.

SpaceX is in the midst of preparing Starship SN3 for its first tests after assembling the rocket from next to nothing in less than a month. SpaceX transported the building-sized prototype a mile down the road to its Boca Chica launch site on March 29th, where dozens of workers have been poring over it day and night ever since. SpaceX originally wanted to attempt the ship’s first two tests yesterday, April 1st, but the scheduled times have come and gone while work continues. Several backup windows are ready on April 2nd, beginning shortly before this article went live (1am CDT, 06:00 UTC).

Regardless, with any rocket prototype, test schedules can be extremely fluid and are always liable to change. While SpaceX relies heavily on agile development strategies, beginning with a minimum viable product and iterating to something approaching feature-complete, there is some value in not turning the “move fast and break stuff” dial to 100%. In the case of Starship, the equivalent of tens to hundreds of thousands of work hours and several million dollars of hardware go into each prototype – incredibly cheap on the scale of aerospace development norms but still a significant chunk of change and effort. A few days or weeks of delays are an annoyance that can be suffered if it better guarantees a successful test, versus the alternative of potentially rushing and cutting corners.

Sunrise greets Starship SN3 and a team of SpaceX workers on April 1st. (NASASpaceflight – bocachicagal)

SpaceX is now up to roughly five days of delays while preparing Starship SN3 for testing. Originally scheduled as early as April 1st, SpaceX has moved a planned Raptor engine static fire test to no earlier than (NET) April 6th, to be followed no fewer than several days later by a 150m (500 ft) hop test. Of course, before it can safely attempt its first static fire (or hop), SpaceX needs to verify that Starship SN3 – finished just days ago – is up to the task.

Enter Tesla hardware. During ground testing, Starship will likely be continuously connected to ground power sources. It’s also possible that SpaceX has chosen to use its Tesla battery packs as the main power source to insulate it from local outages. Either way, if or when Starship SN3 makes it to flight tests, the battery packs would power the ship’s onboard avionics, landing legs, and any other necessary equipment. That latter category may be where Starship’s apparent Model S motor comes in.

A member of the NASASpaceflight forum was first to realize that this appendage was almost certainly a Tesla Model S motor assembly. (NASASpaceflight – bocachicagal)

While it could simply be an early implementation test of the Tesla motors SpaceX wants to use to actuate Starship flaps and fins, there are no signs that SN3 will be outfitted with updated flaps and aerodynamic control surfaces more generally. For low-velocity testing, they’re simply unnecessary. Instead, it’s more likely that this Tesla motor is somehow involved in Starship’s autogenous pressurization system, a method of pressurizing tanks with the liquids they contain. Autogenous pressurization relies on a small portion of propellant (liquid oxygen and methane for Starship) being siphoned off and heated until it turns to gas. That oxygen or methane gas is then fed back into the tank it came from, keeping it at the pressure needed to feed Starship’s Raptor engines.

Autogenous pressurization is significantly more complex than the far more common use of helium or nitrogen pressurization systems. An electric pump could potentially be useful at several points throughout the process. Pump mystery aside, tune in to LabPadre’s 24/7 livestream below to follow along as SpaceX prepares to put Starship SN3 to the test for the first time.