# Why have SpaceX skipped the SpaceX Starship SN12, SN13, and SN14?

Something has happened to the SpaceX Starship SN11.

(For full details and answers regarding SN11, check out the question What happened to the SpaceX Starship SN11?)

Elon Musk recently posted this message on Twitter:

Why will SpaceX skip SN12, SN13, and SN14?

According to my opinion, SpaceX can just put the new technology in a rocket and call it SN12, why skip the numerical way? Is it just to show that the technology has advanced?

• Musk made a typo? Or lost track? I mean there must be a certain sameness to the project: you launch a rocket, it goes up, comes down, and explodes. Mar 30 at 22:49
• @jamesqf they wanted to skip unlucky 13 but added $\pm1$ for a margin of error
– uhoh
Mar 30 at 23:38
• @PeterMortensen The answer is: The new word I learned today. What is jeopardy compliance?" :-)
– uhoh
Mar 31 at 23:06
• So, SN15 could just as well have been SN2-1, and SN20 could be SN3-1 if the major revisions were numbered like software. Apr 1 at 23:36

SpaceX is doing two things in Boca Chica:

1. Prototyping Starship and Superheavy
2. Prototyping the factory for building Starship and Superheavy

The second one is probably even more important than the first one: SpaceX wants to build a thousand Starships. And they want to do this as cheap as possible. They also want at some point to be able to do it on Mars, with a minimal amount of infrastructure needed.

That's actually one of the reasons why they can afford to develop the way they do: the Starships that blow up, they would have built and then scrapped them anyway. In some sense, the Starships are just by-products of developing the factory.

So, shortly after they started building Starship SN11, they also started building SN12, SN13, and SN14. Parts for all of those were spotted at the build site, some of them were even partially stacked, if I remember.

However, according to Elon Musk, Starship SN15 has hundreds of major improvements over SN8–SN14, so at some point, it does not make sense to delay the flight testing of SN15 just to finish building SN12–SN14, when they already know that those are outdated.

And that's why they abandoned and scrapped the partially built Starships SN12–SN14.

It is expected that a similar thing is going to happen with Starships SN18 and SN19: SN20 will have another set of major upgrades, and SpaceX currently has the ambitious goal of flying SN20 to orbit with Superheavy BN3 before July. There is no way they are flying SN15, SN16, SN17, SN18, and SN19 in April–June.

You can also compare that to Superheavy BN1, which was always just a manufacturing pathfinder: it was built purely to test how to build it and how to transport it around the factory, then it will be scrapped again. There were speculations that it would be transported to the launch site and maybe do some pressure testing, but those speculations were proven wrong, when SpaceX just cut a piece off one of the tank sections, including plumbing and everything, in order to fit BN1 into the high bay.

At one point in the early development, SpaceX was also prototyping a second factory in Florida. Two competing teams were building Starship prototypes; they were required to share information with each other, but were free to decide whether they acted upon that information or not. The goal was to pit different approaches as well as the different locations (in terms of infrastructure, for example) against each other.

However, this approach was quickly abandoned, as Boca Chica proved clearly superior and the Starship prototype in Florida was scrapped.

• Elon Musk has stated on twitter that he wants "~1000 starships." Thousands may be hyperbole, but depending on the evolution of the project in 20 or 50 years, it doesn't seem unreasonable that the fleet may reach that size. Mar 31 at 16:30
• @CharlesBamford: I was searching for that tweet, but couldn't find it, and must have misremembered it. I got lost somewhere between thousandS of flights, hundreds of Raptor relights without refurbishment, hundreds of cargo flights before crew launches or landings, and a thousand Starships. (Interestingly, the timeline, and the renderings for #dearMoon seem to clash with the "hundreds of cargo flights". I can't imagine there being hundreds of cargo flights before 2023. I always assumed they would send crew up in a Dragon and transfer them to the vehicle in orbit for the first flights.) Mar 31 at 17:15
• @Michele "Musk said he hoped to build 1,000 Starships — the towering and ostensibly fully reusable spaceship that SpaceX is developing in South Texas — over 10 years. That's 100 Starships per year." businessinsider.com/… Mar 31 at 18:59
• They didn't start building SN12 through SN14 after finishing SN11, but well before that. They scrapped them before SN9 even launched. Twitter user @_brendan_lewis has weekly neat graphs of all the starships and super heavys that parts have been identified of. Apr 1 at 15:17
• This is the thing about SpaceX that excites me: it's a planned industrial revolution where everyone else's effort is a big science project. Everything they do is pitched at figuring out the machine, the engineering, the process and bankrolling the next iteration. Musk understands that despite a couple of tin cans in space humanity is not a spacefaring species, and he has a plan to change that. The only thing I think he could do better is get enough sleep. Apr 1 at 16:54

This is some unsourced conjecture, since much of this simply comes from public observations of operations in Texas by the countless fans.

They are running Boca Chica like a prototype Starship assembly line -- multiple test vehicles are under construction at all times. They roll sheet steel into rings, form bulkheads, stack the rings, etc in a multi week process.

At some stage, components were made for SNs 12, 13, & 14 -- But test flights of earlier models occurred while they were being built, and new design refinements were made that made existing work on 12-14 outdated.

Rather than expend time and expense completing prototypes that were already obsolete, they are scrapping the partial units and skipping ahead to the first unit built with the new enhancements in mind.

• Nice answer. But the first sentence is a fragment. Maybe consider rewording it, by starting with "Some of this is unsourced ..." Mar 30 at 18:11
• Certainly they're not scraping the partially assembled units. I'd wager they are just modifying/updating the work (since this is an obvious risk of producing multiple prototypes at once), and #15 just happened to be ready first. Mar 30 at 23:07
• Looks like they're actually scrapping them. SN 12, 13, and 14 seem to be less then 10% complete, only some arbitrary hardware bits are visible. If SN 15 has any changes to those completed parts then probably they'll be scrapped instead of updating them.
– csiz
Mar 31 at 3:17
• @SnakeDoc I don't think any of the prototypes so far are identical. Also they weren't pending the test, they are being built to also test out the build process (the situation with the first booster is similar in that it will not even have engines mounted for a test fire). And since they were very partially built (just a thrust puck or a header tank for those 3 models), they're clearly not dummies and simply stopped building them when they realized they're obsolete.
– csiz
Apr 2 at 1:07
• @SnakeDoc What makes it so bad? They are training to build Starships in a factory, so those partial builds are valuable practice. They also may have had different results in this test campaign, that required flying those. Apr 2 at 12:03

Possible that SN15 will be the first SN to be designed for a landing cradle. The new Superheavies are already designed to land in a cradle now being built at Boca Chica.

It's rocket science - there are limits to multistage engines that make integrated landing gear on heavy hulls impractical in Earth gravity (as we have seen). Cradles likely won't be required on the Moon or Mars.

Migrating to aerospike engines might make large SSTO spaceships with integrated landing gear practical on Earth. No such engine has ever made it to production without being cancelled for budgetary reasons.

The basic multistage engine design was developed during the Cold War at colossal expense, so it seems we are stuck with cradles for now.

• This is really interesting! In the past it was asked How much bigger could Earth be, before rockets wouldn't work?, a new question could be "How much bigger could rockets be, before reuse from Earth wouldn't work?" See also Why SpaceX want to land the rocket on the ground?
– uhoh
Apr 12 at 23:42
• SN-15 very likely has landing legs as SN-16 does. I'm of the opinion that they won't be attempting catching the SN's until after they're consistently getting through reentry and have very accurate landing profiles. We don't want expendable launch towers. Also gunna have to ask for a citation for BN2 and 3 being designed to be caught instead of using landing legs. Apr 12 at 23:54
• There is no reason to think that multistage engines originally designed to launch nuclear warheads in a fast one way trajectory would be also be capable of launching and landing heavy SSTO spaceships. New engines specifically designed for that (eg. aerospike) are required. Apr 14 at 17:41
• Raptors are designed to land on Earth, and Vacuum Raptors on Mars. You don't need Aerospikes which have always suffered fromf poor thrust to weight ratios, and poor efficiency in low (1-3) Mach realms. The XRS-2200 had a 35-1 ratio, with a production goal of increasing that to 80-1 at a similar thrust to Raptor. Even if it had met those audacious goals it still meant that using two Raptors, ground level and vacuum versions, would mass less and offer higher performance. For comparison, the XRS-2200 & Vacuum Raptor are both at 83% of theoretical max efficiency in space Apr 25 at 0:10
• But at ground level XRS only 64% & Raptor is 72%. XRS launch ISP only 339 using LH2, barely more than Raptor's 330 from Methane, while XRS also imposes the much heavier tanks that LH2 requires. So it seems far more effective to use the base Raptor for launch, and switch to Vacuum Raptors as the atmosphere thins. You save significant mass on engines and tanks, have no efficiency losses in Mach 1-3 regime, and have a fuel less prone to boil-off on long journeys. There is no useful space mission that requires Aerospikes to be able to be performed. Apr 25 at 0:23