Awaiting Static Fire as SpaceX sets up Starship's test campaign

It was December 29 of last year when Ship 20 performed its fourth and final static fire test. That was the last time any Starship vehicle had performed a static fire test. However, Ship 24 is now being readied to undergo a similar test campaign in preparation for the launch of Starship's first orbital test flight.

Meanwhile, SpaceX crews continue repairing Booster 7 and readying the next set of Starship vehicles poised to fly an orbital flight. Outside of Starbase, Raptor 2 testing has ramped up at McGregor, and SpaceX's Florida Starship operations are making progress with facility construction.

Booster 7 being repaired, Ship 24 about to fire its engines

Booster 7 began testing at the Orbital Launch Mount (OLM) the day after it was installed via the chopsticks on the Starship Launch Tower. Most of the testing, however, was only noticeable by the repeated venting of the vehicle tanks rather than signs of frost or condensation – a common feature of loading super cold cryogenic fluids into the vehicle.

Booster 7 during lift on to OLM via chopsticks – NSF Livestream.

These tests occurred in the weeks starting June 27 and July 4, while SpaceX teams also readied Ship 24 for rollout and testing. Finally, Ship 24 rolled out to the launch site on July 5 sporting new decals, a fresh set of Raptor engines, and a new look near the thermal protection system tiles on the sides of the vehicle and nose cone.

It was quickly installed on suborbital pad B for what was expected to be a dual flow test campaign: Booster 7 would continue to be tested at the OLM. At the same time, Ship 24 would start testing at suborbital pad B, eventually culminating in the stacking of Ship 24 on Booster 7 and the start of joint stacked operations.

However, these plans would be truncated on the afternoon of July 11. That day, SpaceX teams readied Booster 7 to perform an all-up 33-engine spin prime test.

Booster 7 and Ship 24 at the launch site – via Mary (@bocachicagal) for NSF/L2

On spin prime tests, the engine's liquid oxygen (LOX) pump is spun up to operating speeds, and LOX is flowed through it, effectively ensuring that the engine LOX pumps work as expected.

Before the test, frost and condensation started forming on the vehicle, indicating the loading of propellants on its tanks. Eventually, the engines began venting indicating engine chill was underway.

Finally, at 4:20 pm CDT, the spin prime test was conducted, but right at the end, a violent and fiery explosion occurred near the base of the vehicle.

While the explosion was violent, Booster 7 remained in one piece, and a few minutes after the event the tanks released an intense depress vent that is normal now to see after such tests.

SpaceX CEO Elon Musk responded on Twitter to NSF that the test was "actually not good. Team is assessing damage," indicating that a major problem had occurred during the test, as was evident by the blast.

https://twitter.com/elonmusk/status/1546639772621365248

In the following hours, the SpaceX teams slowly brought Booster 7 to a safe state, even amid some nearby fires of equipment and other materials near the base of the Launch Tower. Overnight assessment on the condition of the vehicle began, with Elon tweeting that he along with the rest of the crews had been inspecting the vehicle that night.

While the root cause of the incident is not fully understood, Musk's comments indicate it might have been related to an improper test configuration that allowed a fuel-air mixture to accumulate and catch fire. Usually, other rocket systems such as Delta IV and SLS utilize what are typically called ROFIs (Radially Outward Firing Igniters) before engine ignition to burn off residual hydrogen that is constantly flowing through the engine during chilldown operations.

During these operations, propellants are flowed through their pumps to cool them down ahead of high flow circulation during ignition; this avoids cavitation on the pumps due to sudden vaporization. However, these propellants normally turn into gas during the chilldown operations, so engines usually have what is called a "bleed" system, which is a system that allows the outflow of gas out of the engine cavities in the pumps.

On SpaceX's Merlin engine, there's only one cryogenic propellant, liquid oxygen, so when the engines are chilled down ahead of ignition, the engines only bleed gaseous oxygen. However, on Raptor, there are two cryogenic propellants, so both the liquid oxygen and the liquid methane pumps need to be chilled down ahead of ignition.

While an ignition was not in the cards for July 11's spin prime test, it is understood that SpaceX used liquid methane to chill down the methane pumps instead of using an inert cryogenic liquid like liquid nitrogen, which is what's typically used during engine tests that do not involve an ignition of any kind.

The day after the anomaly, Elon indicated on Twitter that Booster 7 would roll back to the production site to work on repairs to the vehicle and assess the next steps. Rollback occurred on July 14, and in the following days, it's been observed that several Raptor engines have been taken off from the vehicle, likely for further inspection and testing at SpaceX's McGregor test facility a few hours drive up north from Starbase.

As of writing, repairs are continuing on Booster 7, and it will likely still be undergoing repairs for the next week or two. So while an early retirement for the vehicle could be expected, the current target by teams is still an orbital flight by Booster 7 and Ship 24 with a notional target date of late August for the flight.

While these repairs are ongoing, Ship 24 has been undergoing several spin prime tests ahead of the long-awaited static fire test campaign. The first spin prime test occurred on July 18, with what appeared to be all six engines in a staggered sequence.

Two more six-engine spin prime tests occurred on July 19, and another pair of these tests happened on July 21, that time with one and two engines, respectively.

As usual, the test campaign sequence is not generally reported by SpaceX. It is likely testing will follow the path employed with Ship 20. It was the first time SpaceX tried to fire a Raptor Vacuum – or RVac – engine while attached to a ship, so precursor tests occurred before an all-up engine test. These involved the firing of one RVac engine first, then an RVac engine and a sea level Raptor engine to verify the simultaneous firing of both engines at the same time.

While Ship 24 also includes RVac engines, these are now of the upgraded Raptor 2 variant, so it wouldn't be surprising if SpaceX first tested one of these engines, or perhaps a sea level and an RVac engine at the same time to verify the nominal performance of these while attached to a vehicle.

However, regardless of the number of tests, the expected result is the same: a six-engine static fire test of Ship 24. This test will culminate and verify that the systems all work accordingly and the vehicle is cleared for flight.

Ship 24 waits its turn at the launch site – via Mary (@bocachicagal) for NSF L2

Once this is complete, it is likely that SpaceX teams will replace the potential heat shield tiles that may have gone missing at the conclusion of this campaign and ready Ship 24 for what is expected to be joint stacked operations with the booster that will push it into space.

Booster 8 nearing rollout, other vehicles line up for subsequent flights

While the Booster that will carry out the first orbital flight may still be Booster 7, SpaceX teams are readying the next one in the line, Booster 8, for potential rollout in the next few days. It is expected that Booster 8 will start its pre-launch test campaign sequence with ambient and cryogenic proof tests, just like previous vehicles did.

It is currently unknown whether this booster will be heading out to the OLM or structural test stand.

OLM repair work ongoing – via Mary (@bocachicagal) for NSF/L2

Most likely, Booster 8 will roll out in a similar state as Booster 7 did back on April 2 when it first rolled out to the launch site. Back then, the booster didn't have engines, grid fins, or even all the chines.

After all proof tests are completed, this hardware can be installed back at the Mega Bay and allow clearing of the orbital launch site for potentially more testing of Booster 7 and maybe even launch of the orbital flight test.

Ship 25, the vehicle currently paired with Booster 8, resumed stacking operations in the High Bay after a month's pause of these operations and a trip to the Mid Bay. Its nosecone can now be seen outside of the tents complete and with most of the heat shield tiles.

Future vehicles are also lining up as well at Starbase. Ship 26's mid-LOX section – a four-ring section that makes up the main body of the LOX tank – was seen out of the tents and with heat shield tiles installed as well which gives a good sense of progress on this upcoming ship.

Booster 9 has also started stacking in the Mega Bay beginning with its methane tank, and Booster 10's aft dome was sleeved as well. As of last month, this booster was expected to fly from Florida rather than Starbase but plans may have well changed by now. However, it is interesting to note SpaceX's desire to rapidly build vehicles at Starbase that will eventually fly from Florida rather than wait for the Starship factory at Kennedy Space Center to be fully built out.

Booster 10's pairing Starship, Ship 27, had its aft dome sleeved as well and another ship aft dome was also sleeved a few weeks later. Perhaps for a test tank of sorts or maybe for the following ship, Ship 28.

B9 and S26 to debut upgraded Raptor 2 engine, tests starting at McGregor

Among the information provided by Elon this past month was also the upgrades being done to Raptor 2 for upcoming boosters and ships. Particularly the new electric Thrust Vector Control (TVC) system that replaces the old hydraulic TVC system on Raptor. This will allow much more simplified control of the engine during flight and also simplified hardware and weight reductions on the vehicles, especially on the boosters where 13 of these engines will need to move.

Along with these upgrades, NASASpaceflight has been able to spot – and livestream – what are most likely tests of this new TVC system at SpaceX's McGregor test facility in Texas. These tests are being performed at the test site's Tripod stand, where several years ago Falcon 9 boosters would be test fired and where now Raptor engines are tested.

It is understood that Booster 9 and Ship 26 will be the first pair of vehicles to debut this upgraded Raptor 2 engine which will also see a slight upgrade in thrust and further simplification of their production.

Starship Launch Tower growing at KSC, Starfactory rises at Roberts Road

Starship's program is making serious progress on many fronts, including at SpaceX's facilities at the Kennedy Space Center in Florida. Over there, teams rolled out more tower sections to Launch Complex 39A (LC-39A) on July 20 and 27. Segment four was stacked the day after its rollout, July 21, with the latest rolling on Wednesday evening.

https://twitter.com/julia_bergeron/status/1552699384827187205

Several new developments are being seen at LC-39A including the appearance of a new tank in the form of large barrels and a huge stand to support it. The tank appears to be of similar construction as the cryogenic tanks built by SpaceX at Starbase with an inner shell and an outer shell.

This tank, however, looks larger, with the outer shell being about 20 meters in diameter and the inner shell being about 18 meters in diameter. It is yet unknown what this tank will be for but the design that can be guessed by these different barrel sizes seems to imply that this will be for a cryogenic fluid.

More progress is also being made on the tank farms at LC-39A with two new tanks arriving on July 24 and more groundwork occurring north of the former hydrogen sphere, where methane is expected to be stored not long from now in support of Starship operations at the complex.

At Roberts Road, more launch tower sections are being built, and the Mega Bay that will be used in the future for stacking ships and boosters is having its foundations completed.

Roberts Road this week via latest flyover (Julia Bergeron)

To the north of the complex the set of stacking and catching arms – nicknamed chopsticks – are still being built with more progress on the shoulders and main body of them occurring in the past month or so. The Ship QD arm and carriage system are also progressing as well.

(If you want to know all about the recent changes to SpaceX's facilities and more, be sure to check out our recent flyovers by NASASpaceflight members Julia Bergeron and Stephen Marr that are uploaded regularly on our YouTube channel.)

As observed, another development spotted at Roberts Road is the rise of the Starfactory building, the factory where future Starships and Super Heavy boosters will be built to fly from Florida.

Photos from Mary (@bocachicagal) and Nic (@NicAnsuini)

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