SpaceX stacks Ship 25 and Booster 9, prepares for flight

by Alejandro Alcantarilla Romera

SpaceX has rolled out Ship 25 to the launch site and stacked it on top of Super Heavy Booster 9, bringing back a fully stacked Starship rocket to Starbase since April 20.

Several important additions have been made to Ship 25 ahead of this stacking and should make the vehicle ready for flight. SpaceX now eyes the last few days of preparations ahead of Starship’s second test flight, pending regulatory approval.

Ship 25 receives upgrades, gets stacked on Booster 9

Ship 25 stayed at Starbase’s Rocket Garden for the last month, having been rolled back from the launch site on August 5th.

Since then, the vehicle has not only undergone final preparations for flight with the addition of thermal protection system (TPS) tiles to its nosecone and the addition of its new livery but has also seen another number of changes as well.

Its lengthy stay and slow installation of TPS tiles indicated that there was more work to do than originally believed. Closeup pictures of the leeward side of the ship show that SpaceX has been very busy introducing a series of last-minute changes to the latest Starship prototype. 

A view of Ship 25’s common dome section showing the new set of charges added to the vehicle ahead of flight. (Credit: Jack Beyer for NSF)

One of these upgrades involves the addition of extra charges for the vehicle’s flight termination system (FTS). During the first flight of Starship, the automated FTS on both stages was triggered after the rocket lost control and veered off course. 

However, as stated by CEO Elon Musk a few days after launch, the charges were not powerful enough to break each stage apart as they were supposed to. This new upgrade was already implemented on Booster 9 a few months ago, and it is hoped that by adding extra explosive charges on each vehicle, these will indeed break apart if this system needs to activate during flight.

Teams have also added what appears to be a new set of openings or vents on the aft section of Ship 25 right above the engine shield of the vehicle. These vents’ location resembles Booster 9’s vent system on the aft end of the vehicle. These vents on Booster 9 are believed to be part of a carbon dioxide (CO2) purge system that prevents fires from starting and extending all over the engine section of the vehicle. 

This is another issue that was likely encountered on the first flight of Starship, where fires were visibly seen in between the booster engines. This fire might have been partially at fault for the loss of control of the vehicle less than two minutes into the flight. 

View of Ship 25’s aft section showing the new row of openings above the engine shields that should provide ventilation for these cavities. The reinforced welds and new set of pipes can also be seen in this picture (Credit: Jack Beyer for NSF)

With these new vents now also on Ship 25, SpaceX likely wants to ensure that no vehicle control is lost during flight due to any engine fire and that all of the important hardware in the engine section remains as intact as possible.

On this engine section, a new set of pipes have been added on the port and starboard of the leeward side of the ship. These look similar to the engine chill pipes already on the vehicle and from where gaseous oxygen is vented overboard so that it doesn’t pool inside the engine section.

These engine chill pipes have an extension on the booster side where they connect to allow this oxygen to be vented much further down the rocket than otherwise. However, the new set of pipes added recently to Ship 25 will not encounter a similar extension on the booster side.
For now, it is not clear what they could be for, but the absence of these extensions might mean that whatever is being vented via these pipes might not be vented during first stage flight like the gaseous oxygen and rather only while the engines are igniting. 

The aft end of Ship 25 has also seen the addition of reinforcements on the welds between the rings at and below the quick disconnect umbilical plate. This is not a new upgrade but rather an upgrade already implemented on Ship 24 for its own flight and that SpaceX had seemingly delayed for Ship 25.

It is believed these had to be installed for Ship 24 due to structural testing uncovering issues with this part of the vehicle. Nonetheless, these changes have now been implemented on Ship 25, and it should be ready for its upcoming flight.

Ship 25’s stacking on Sept. 5 gave observers the perfect opportunity to peer up into the engine section of the ship from below. Each of the engines on Ship 25 can be seen now fully shielded, and their turbomachinery is well protected from any potential damage.

While Booster 9 will feature the debut of a new electric thrust vector control (TVC) system, Ship 25 still sports the older hydraulically actuated TVC,, which involves using a hydraulic power unit (HPU) to drive this system. 

This HPU sits tucked inside the engine section and is surrounded by the same heavy-duty shielding that protects the engines. This should hopefully avoid the issues encountered during the first flight of Starship, with Booster 7’s own HPUs seen catching on fire during the ascent portion. 

The stacking on Tuesday also featured the first time a booster with the new hot staging ring held a ship above it. The careful lift of Ship 25 lasted for over an hour and ended with the vehicle being set on Booster 9 at around 2:20 PM CDT. This was made noticeable by the sudden wiggle of the whole rocket as the weight of the ship was settled on the booster.

With this additional ring on the booster adding an extra six feet (1.8 meters) to the total height of the rocket, SpaceX’s Starship has broken its own record for the tallest rocket in the world, which was set by the previous Ship 24 and Booster 7 stack.

The company CEO, Elon Musk, has stated on Twitter that the vehicles are ready for launch and that only FAA approval remains ahead. This could mean that SpaceX will not perform major rocket testing until launch. Depending on the time the FAA takes for approval, the company may decide to perform some testing to gather additional data ahead of the flight.

While this full stack is the first one since April 20, it will likely not be the last time before the next launch. It is expected that Ship 25 will be destacked a few days prior to launch in order to prepare its flight termination system for flight. 

This will involve teams going up to each of the vehicle’s FTS control boxes and removing the physical safety pins that prevent an accidental trigger of the explosives. 

It is expected that this could happen shortly after SpaceX receives approval from the FAA for this second flight of Starship, in a similar fashion to how it happened for the first flight.

(Lead Image: Ship 25 and Booster 9 at sunrise on Sept. 6. Credit: Jack Beyer for NSF)

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