by Chris Bergin


Booster 9 lifted by the Starship Launch Tower arms (Credit: SpaceX)


Booster 9 is the 7th complete booster and the 2nd flight-worthy booster ever produced. This vehicle represents an incremental upgrade compared to the Booster 7 and Booster 8 prototype series. Booster 9 began construction of its methane tank (top) in March 2022 and of its oxygen tank (bottom) in September 2022. Full stack of the booster was achieved on October 27th 2022.


Electric Thrust Vector Control (TVC) System

Booster 9 includes electric thrust vector control system instead of the hydraulic thrust vector control system that Booster 7 had. This hydraulic TVC used a pair of Hydraulic Power Units to drive the hydraulics for this system. With electric TVC the drive is direct from electric servos that move the engines using battery power so no more HPUs needed. This means less mass required on the booster and a system that they effectively have deleted. The new electric TVC hardware for Raptors can be seen as black cylinders on the TVC arms that connect to the booster aft cap.

Improved Engine Shielding

Booster 9 introduces a new engine shield that better protects the engines from other exploding engines nearby. It’s not clear in which way this shielding is better but it appears to be more sturdy, with a tougher appearance. Perhaps the plates separating the engines are thicker. The shields at the very base of the engines are now black which means they either have a black protective coating or they have used a new material that happens to be black. Either way, it’s new stuff all around. If Raptors are gonna be blowing up during this second flight, hopefully they don’t damage nearby ones.

Revamped Fire Suppression System

Booster 9 has a revamped fire suppression system. While Booster 7 had a fire suppression system, it was very inefficient. The system used and uses carbon dioxide to avoid these fires. Booster 7’s CO2 tanks were very long but very thin so their capacity was very limited. Booster 9’s CO2 tanks are now about the same in length but much wider which means a huge amount of extra volume in comparison. More volume more better, remember that. More CO2, more capacity to purge. SpaceX says it is now 15x more capable but who knows if that means 15x more volume or something else.

By the way, these tanks are located in the same location, in the chines that face the tower, but since they are larger now this means that all four aerodynamic chines are the same size. For Booster 7, the tower-facing chines were smaller than the ones opposite to the tower. Also, these tanks are normal metallic tanks, they’re NOT COPVs!

The CO2 is diffused into the engine compartments while the engines are running to precisely avoid these fires. Once diffused into the engine compartment, the CO2 mixes with all the other gases that might be there like gaseous methane, gaseous oxygen, etc. The mix of these gases is then vented out from 18 vents around the bottom ring of the booster for the outer 20 engines. Yes, I know, there are 20 outer engines and 18 vents, not sure why that’s the case but trust me, I’ve counted the vents (they’re also numbered!).

As for the mix of gases coming from the inner engines, it looks like they just vent it all from below since there’s not a really easy way to direct them overboard through the hull of the booster. Best part is no part so best vent is no vent, just dump it overboard.

Hot Staging Ring

One of the big changes for Flight 2 so far. The hot staging ring, also known as “vented interstage and heatshield”, allows the Ship to fire its engines while the booster engines are running. Not all engines will be running at staging, though, most engines will actually shut down and only a very few will remain ignited and at low throttle setting.

According to FAA documentation, this hot staging ring is about 9 metric tons in mass so it is quite heavy. The most likely reason is because it includes a massive shield to protect the top dome of the booster. Underneath this shield there’s a very heavy-duty set of stringers and reinforcements which is probably what makes it even heavier. Apart from that, it is a very simple structure.

It attaches at the top of the booster’s forward section using the same mechanisms used previously by the ship to attach to the top of the booster so no new hardware is needed – also no welding required. It is so simple that the same FAA documentation says for some missions it may be jettisoned which would be just as easy as opening the hooks on the pin connectors and letting it go – Frozen style. That’s on the bottom of the ring though, on the other side it has the other part of the connection system so that the Ship can still be attached to the top of the booster when said top is the hot staging ring.

According to Elon, hot staging is supposed to increment the payload performance by 10%, hence the change from the earlier kick separation system.

Flight Termination System (FTS)

Booster 7’s FTS charges were located right at the weld line of the common dome. The idea was that these would break apart the vehicle right between the tanks and that would mix the propellants and make it all go boom – yet, this didn’t happen. Booster 9’s FTS charges are located a ring higher up on the vehicle and are much larger. Other than that, there’s not a huge difference but hopefully this relocation and larger charges actually breaks the vehicle apart if it is needed.

Smaller Changes: Relocated CH4 Tank Vents and Starlink Antennas

Among some of the changes we see on Booster 9, there are two that are small but are interesting nonetheless.

The methane tank vents have been now relocated from a height on the vehicle right under the grid fins to being right under the hot staging ring. Overhead shots show that the top dome of the booster has a direct vent out from that location that splits in four and turns into the new methane tank vents. This could be so that the top dome can also be filled up with liquid methane during loading, maximizing the amount of methane loaded on the booster.

As mentioned above in this document, Booster 9’s HPUs have been removed and, as a consequence, the Starlink antennas previously located on top of them have been relocated to the top of the aerodynamic chines on Booster 9.


Ship 25 lifted by the Starship Launch Tower arms (Credit: SpaceX)


Ship 25th is the 8th complete Ship and the 2nd flight-worthy orbital Ship ever produced. This vehicle is within the same incremental upgrade group as Ship 24 with many similarities between the vehicles present. Ship 25 parts were first spotted in January 2022. Construction of its upper half began on May 25th 2022 with completion of that upper half happening on August 29th 2022. The bottom half of the vehicle started stacking on June 4th 2022 and was finished on August 5th 2022.  Full stack of the ship was achieved on September 12th 2022.


Aft Section Changes

The aft section has a row of openings that we really don’t know what is for. There are an extra two other openings on the port side of the aft section above the row of openings that we also don’t know what they’re for. The aft section also has an extra pair of pipes installed apart from the engine chill pipes that, once again, we don’t know what they’re for.

There’s plenty of theories as to what these openings and two new pipes might be for but not a general consensus. It could be that they’re related to avoiding fires on the ship engine section just like the fire suppression system on the booster but we’ll probably have to wait to see this being used during flight to figure out what they’re for.

Flight Termination System (FTS)

Just like Booster 7, Ship 24’s FTS was unable to break up the vehicle. Also like Booster 7, the charges were located right at the common dome of the ship with the hopes that it would mix the propellants and break the vehicle from the resultant explosion.

Given that, it’s no surprise that Ship 25’s FTS charges are like Booster 9’s. They are located a ring higher and they are larger as well.

Engine Shielding

Ship 25, like Booster 9, also features updated engine shielding to protect the Raptors during flight as they fire. Unlike for Booster 9, Elon never mentioned what was new for Ship 25’s engine shielding but one could assume it is also better and that it offers more protection than the older one.


Aerial view of the Starship Launch Site. The suborbital site is to the right and the orbital launch site is on the left. (Credit: Jack Beyer)


The Starship launch complex consists of an orbital site and a suborbital site. The suborbital site hosted the suborbital flights of ship prototypes from SN5 to SN15. That same general location is also from where Starhopper conducted its two flights and the static fires and other sort of testing back in 2019. The suborbital site has two pads, Pad A and Pad B.

Suborbital Pad A seems to not be in use anymore or, at the very least, it doesn’t appear to be in use for a while. After the suborbital flights, it was used mainly as a cryogenic proof test stand for ships but now that kind of testing is done at the Massey Outpost.

Suborbital Pad B has been used more than A, mainly as engine test stand for Ships. This pad has more concrete at the base of the stand to protect it from the engine firings, something that pad A doesn’t have.

The orbital launch site began construction all the way back in 2020 and first supported a vehicle all the way back in August 2021. However the first static fire test didn’t happen until a year later in August 2022. First launch occurred on April 20 2023 and now we’re just really close to the second launch from here.


Flame Deflector System

The flame deflector system is what we regularly call the water deluge system. This system was put in place to avoid the rock tornado from the first flight.

In order to install this system, the foundations were completely upgraded. About a couple dozen pilings about 30m (~100ft) deep were put into place underneath and around the area of the orbital launch mount. A roughly two stories tall layer of concrete was set up on top of that as well to strengthen the soil where the watercooled plate would eventually go on top of.

While the foundation should prevent the engines from digging into the ground, the plate prevents the engines from hitting the ground in the first place. On top of that, the steel plate is watercooled which means it won’t erode drastically – technical words, not mine – and therefore it’ll be easier to reuse.

The water used on this system is potable water taken from Brownsville and it is transported to the launch site and stored on seven storage tanks located to the southeast of the Starship Launch Tower. Next to these tanks, there’s a set of pressure tanks that help push the water out to the plate. This water flows from the storage tanks to the plate via two pipes and of these two one is thicker than the other. The thicker one splits in to near the orbital launch mount via a Y-shaped pipe that splits the flow of the water in two for two manifolds that are connected to the plate. The other pipe, the thinner one, is only connected to one manifold.

According to FAA documentation, this system could use up to 132,000 gallons of water during a launch event and the full storage capacity is of 358,000 gallons.

Faster Raptor Spin Up

For Starship’s second flight, the OLM has seen an upgrade to its Raptor startup hardware. In case you don’t know, the outer 20 engines on Super Heavy are directly started by the orbital launch mount through a dedicated quick disconnect umbilical that is connected to each outer engine. These umbilicals provide the high pressure helium that is injected in the engines to spin up their pumps, they also provide high pressure gaseous oxygen and gaseous methane for the preburner torch igniters for all outer engines – all fluids necessary for engine ignition. The Raptor umbilicals also provide nitrogen for purges but this is probably not used during engine ignition.

In any case, for flight 2 this system has had to be upgraded to support the faster start up sequence of the Raptor enignes. Now instead of igniting at T-8 seconds and taking several seconds to ignite all engines, the Raptors startup at T-3 seconds and all engines are ignited by the T0 mark.

Ship Quick Disconnect Umbilical

With Booster 9 now sporting a hot staging ring, this means Ship 25 is sitting a whole ring higher than Ship 24. This meant upgrading the Ship Quick Disconnect Umbilical to raise it and be able to connect to Ship 25 at its new height.

This also involved an upgrade to the access platforms on the Quick Disconnect Arm to access the Ship Quick Disconnect Port. However this upgrade didn’t involve automated deployment systems and the deployment and retraction of this is still hand-cranked.

Redesigned OLM Guiding Pins

With the removal of the Booster HPUs, the OLM guiding pins had to be redesigned to be able to, well, properly guide Booster 9 down onto the OLM. When SpaceX removed the HPUs, the hole where the guiding pins would connect to was instead installed directly onto the hull of the vehicle. This means that the new OLM pins are longer and are curved downwards in order to reach out to the hull of the vehicle and down into the OLM.

These pins have been removed several weeks ago, though, they would be blasted with the Raptor engine exhaust during launch and they weren’t needed anymore on the OLM once Booster 9 was lifted on it for a last time. Still, it’s interesting to note this because future vehicles also lack HPUs and, therefore, will make use of the new guiding pins to be guided down onto the OLM.


Here’s a rundown of the key events of the timeline ahead of Starship Flight Test 2. Events that are in italics will be those that are explicitly stated on SpaceX’s timeline.

12AM CST – T-7 hours. Road Closure Window Begins.

The road closure window, that stretches all the way to 2PM CST, will open. Evacuations will have already been underway at this point, SpaceX employees would not have shown up to work for the night shift, and police is likely to already have appeared before this time to clear the launch site area ahead of full closure.

The roadblock closest to the launch site will move up the road outside of the blast danger area right before or soon after the tank farm enters chilldown.

Undefined Time – Usually at around T-5 hours. Tank Farm Chilldown.

At some point during the count and a few hours after road closure is enforced, the tank farm will start its chilldown sequence. This will see this tank farm become substantially more active as it is conditioned to the right temperatures needed ahead of propellant load.

The methane and oxygen subcoolers will also get filled with liquid nitrogen which is used in the process of cooling down each propellant below its boiling temperature.

Approx. 45min Before Propellant Load. OLM Vent Starts. CO2 Load Indications

Once the tank farm is chilled down, the lines that supply propellants to the vehicles will start their own chilldown. This will be noticeable because the OLM and Tower will have a vent on the side that will be venting when this sequence starts.

The OLM vent comes always first and it usually takes about 45 minutes from its start to the start of propellant load. It initially begins as a very small vent off the side of the mount and it continually grows over time. In the last 5 minutes or so, the vent becomes large, entering what we normally call the “waterfall mode”.

The tower vent will begin after the OLM vent starts and will also die off before the OLM vent dies off. This is just the initial tower vent and may only last for about 12 minutes or so.

This time will also be when we’ll start seeing the CO2 tanks on the tower-facing chines venting and such. The chines will vent every now and then from this point till pretty much the end of the countdown. Heck, maybe they even vent during flight.

T-2 hours. GO For Propellant Load.

SpaceX’s Launch Director will poll controllers to give their GO/NO-GO decision to begin propellant load.

T-1 hour and 37 minutes. Booster Propellant Load Starts.

Once all is good to go, the propellant load will start on the booster. We’ll notice when this starts because the OLM vent will stop. Both methane and oxygen start loading at the same time for the booster. Frost should start to appear first on the LOX tank a few minutes after start of propellant load followed soon after by frost appearing on the methane tank.

At around the time frost starts building up on the booster, the tower vent will come back ahead of propellant load starting on the Ship.

T-1 hour and 17 minutes; T-1 hour and 13 minutes. Ship liquid methane and liquid oxygen load starts.

Well, just what it says. Ship propellant load will start, first with liquid methane and then with liquid oxygen. Despite the liquid methane starting up first, the liquid oxygen tank will see frost appearing on it first and then frost will appear on the methane tank.

Approx. T-1 hour. OLM Hold Down Clamps Open.

This is a not well known fact: Super Heavy is not held down for engine ignition. The hold down clamps open about one hour prior to liftoff and let the rocket free. From this point until liftoff, the weight of the rocket is just standing on the hold down arms.

T-19 minutes and 40 seconds. Engine Chill Starts.

Engine chilldown begins on both stages at this point of the count. Raptor engines use cryogenic propellants which means both methane and oxygen pumps need to be chilled down prior to engine ignition. The methane used on chill down is reclaimed while the oxygen is dumped overboard.

Approx. T-15 minutes. Ship Header Tank Activity.

Around this time in the count we’ll see venting on the ship header tanks, an indication that propellant load on them is well underway. With enough luck, we might also see frost on the tip of the nosecone right below the heatshield tiles on the tip of the nose.

Approx. T-5 minutes and T-3 minutes. Ship and Booster Propellant Load Complete.

After well over an hour of propellant load on both stages, the vehicles will have been fully loaded by around this point in the timeline.

T-40 seconds. Optional Hold Point.

SpaceX has the opportunity to hold at this point in the count for final checks, troubleshoot an issue, and/or catch up with any work still pending. This hold is optional, though, so they could just as easily not hold and go through that T-40 seconds in the count.

When the hold is released, a very peculiar and distinctive vent can be heard coming out from the side of the OLM that’s facing the tank farm. Before the OLM shields were installed, this vent was very visible but nowadays it is more complicated so we literally will have to play it by ear.

T-25 seconds. FireX System Activates.

This system activates in two steps, first a bit of nitrogen gas comes out from it, then both nitrogen and water come out at once. The FireX system displaces gaseous methane and gaseous oxygen that may be present under the engines.

T-10 seconds. Flame Deflector Activates

Just a few seconds after flame deflector activation starts, water starts flowing from the ground tanks to the steel plate under the pad. You’ll see the relief valves on the up-and-down water pipes to shoot water out first and then the plate will start shooting water. The relief valves will then close and the pressure will rise up on the system, meaning that the water will start coming out at full pressure from the steel plate. The process is quick and full pressure is achieved by the T-3 second mark.

T-3 seconds. Raptor Startup Sequence Begins

What the name says: Raptor start up sequence begins at this point in the count. The engines won’t start up at their full power but rather start at partial power.

T+2 seconds. Liftoff

Once 30 or more engines are confirmed running, they will throttle up. We don’t know at what throttle setting they’ll be throttling up but they will obviously have to throttle up high enough for the overall rocket thrust to be higher than the rocket’s weight. The general theory is that T+2 seconds marks the moment in the count when that happens and the rocket starts moving up the launch mount. This also means the engines most likely don’t reach full power until the rocket is already ascending and exiting the mount.


This is all the nominal plan posted by SpaceX. The real flight could and may very well deviate from all of these timings and events, especially if engines start to go out during ascent in which case the timing of these events will be all thrown off.

T+00:00:52 Max Q

This is the portion of the flight with maximum aerodynamic pressure on the vehicle. Not very clear whether Starship will throttle down for this period or not, Elon mentioned a number of years ago that they wouldn’t be throttling down for Max Q but that could have been just a goal, as usual for him.

T+00:02:39 Booster MECO (most engines cut off)

While Elon’s comments a few months ago suggested only three engines would remain lit at 50% throttle during hot staging… well, again, Elon comments. While obviously not a lot of engines should be igniting at that point, the number could have changed by now. Also, if the booster loses engines then that probably throws off the timing and the specific engines that shut down, I’m sure the booster will have some internal logic as to how to do that but go figure if that’s the case or not.

T+00:02:41 Hot-staging (Starship Raptor Ignition and stage separation)

We expect the Ship to only ignite the RVac engines first and then ignite the center engines very shortly after separation from the Booster.

T+00:02:53 Booster boostback burn startup

Once the Ship is off the hooks, the booster will initiate its flip back and boostback burn to cancel its horizontal velocity.

T+00:03:47 Booster boostback burn shutdown

T+00:06:18 Booster is transonic

Unlike Falcon 9, Super Heavy doesn’t perform an entry burn so it’ll scream down through the atmosphere and be transonic quicker than Falcon 9.

T+00:06:30 Booster landing burn startup

T+00:06:48 Booster landing burn shutdown

If it reaches this point, the booster will eventually be sunk on purpose and not recovered.

T+00:08:33 Starship engine cutoff

All six Ship engines shut down and the ship enters its ballistic trajectory to 100km off the coast of Kauai island in Hawaii.

T+01:17:21 Starship entry

T+01:28:43 Starship is transonic

T+01:30:00 Ocean impact

The ship will not perform a flip and landing burn, it will instead impact the ocean at terminal velocity.


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