SpaceX Stacks and Unstacks Starship

Yesterday, August 5, orbital Starship prototype S20 moved out of high bay and down the mile and a half road to the launch complex at Boca Chica.  

In the latest stage of SpaceX’s continually impressive “Starbase Surge,” the company rolled the first orbital-class Starship prototype’s aft tank section from its birthplace in the factory “midbay” to a much larger “high bay” around noon on August 3rd. Mere hours later, Elon Musk revealed that SpaceX had fitted the Starship with a full six Raptors – a first for any Starship prototype, though Super Heavy Booster 4 technically beat it to the punch with the installation of a staggering 29 Raptor engines hours prior.

The rocket’s conical nose section joined it in the high bay later that evening and SpaceX wasted no time stacking and welding the two Starship halves together early on August 4th, effectively completing the basic structure of Ship 20 (S20). After a day of final integration work, Starship S20 left the high bay around dawn on August 5th and took to the highway for a brief trip from SpaceX’s Boca Chica factory to launch and testing facilities just a mile and a half to the east.

It was a little surprising to see this.  As we were discussing in the comments on the 4th, there were no road closures for the day and a closure is required to move the transporter carrying the Starship - the multi-axled vehicle takes up the entire road.  Early in the morning Thursday, they announced a closure and S20 soon took the road, followed by a piece of ground support equipment also bound for the launch complex.  

By mid-morning, S20 was in the launch complex and eventually moved over near the Orbital Launch Integration Tower, but within a few hours, SpaceX announced over a PA in the area that further stacking operations were cancelled for Thursday due to winds in the area.  

Up early this morning, I was watching the Nerdle Cam by 7:30 EDT - 6:30 CDT and before sunrise in Boca Chica.  S20 was lifted and looked to be almost in place by 9:00 local.  This picture is from nearly an hour later.

Imagine my surprise when I went back to check on progress an hour later and found this: 

Unstacked?  S20 Taken down and put back on the transporter?  What?  Why?

S20 was unceremoniously loaded on the transporter and taken back to high bay.  

So what was this all about?  It seems to have simply been a test to see how things fit.  After all, these stages are 9 meters in diameter, about 30 feet.  No matter what sort of measuring instrument you use, it's not trivial to make two mating parts 30 feet in diameter and have them fit exactly.  Since the ultimate plan is to build many boosters and many Starships, all interchangeable, checking that things go together as expected is a good idea.  

Another thing to point out is the thermal tiles on S20.  This is the first time we've seen a Starship fully black like this, but if you look closely around the "flings" (the control surfaces at the front of the rocket) where they meet the body, you'll see unfinished areas.  SpaceX is running into a shortage of these thermal tiles; they've overloaded their suppliers.  It's true that tiles can be installed while on the launch pad, but that's easier with the facilities in the High Bay. 

Stacking Starship onto the booster seemed like a bold move.  They've never flown a Starship without static firing it, and they've changed out more than a couple of Raptor engines over the course of the testing all of the Starship prototypes.  Doing a test fire of S20 seems prudent since this configuration has never been tested.  The three Raptor Vacuum engines have never been tested on a vehicle before, although that doesn't seem particularly risky.  

The same concepts apply to the booster.  They've never tested the hardware to run cryogenics to 29 Raptor engines, and some sort of static test seems like a good idea.  Much as we can say against the SLS, they did their "green run" test firing of the full first stage to qualify it for flight.  A few different static firings, turning on a few engines at a time might be a valid way to test them if they're concerned about lighting up all 29 at the same time with all that other stuff so close to the launch pad.