Starship Explosion

From AIAA’s “Daily Launch” email newsletter for Monday,  6-23-2025.  This ship was intended for Flight Test 10.  It blew up before they ever ignited the engines.  Quote: 

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SpaceX traces Starship test-stand explosion to failure of pressurized nitrogen tank

By Mike Wall published 3 days ago  (on Space.com)

"Initial analysis indicates the potential failure of a pressurized tank known as a COPV."

 

SpaceX thinks it knows why its newest Starship spacecraft went boom this week.

The 171-foot-tall (52-meter-tall) vehicle exploded on a test stand at SpaceX's Starbase site late Wednesday night (June 18) as the company was preparing to ignite its six Raptor engines in a "static fire" trial.

 

A day later, SpaceX narrowed in on a likely cause.

 

"Initial analysis indicates the potential failure of a pressurized tank known as a COPV, or composite overwrapped pressure vessel, containing gaseous nitrogen in Starship's nosecone area, but the full data review is ongoing," the company wrote in an update on Thursday (June 19).

 

"There is no commonality between the COPVs used on Starship and SpaceX's Falcon rockets," the company added. So, launches of the workhorse Falcon 9, which has already flown 75 times in 2025, should not be affected.

 

The Starship explosion did not cause any reported injuries; all SpaceX personnel at Starbase are safe, according to the update. People living around the site, which is near the border city of Brownsville, shouldn't be worried about contamination from the incident, SpaceX said.

"Previous independent tests conducted on materials inside Starship, including toxicity analyses, confirm they pose no chemical, biological, or toxicological risks," the company wrote. "SpaceX is coordinating with local, state, and federal agencies, as appropriate, on matters concerning environmental and safety impacts."

That said, the explosion did damage the area around the test stand, which is at Starbase's Massey site (not the orbital launch mount area, from which Starship lifts off).

"The explosion ignited several fires at the test site which remains clear of personnel and will be assessed once it has been determined to be safe to approach," SpaceX wrote in the update. "Individuals should not attempt to approach the area while safing operations continue."

Wednesday night's explosion occurred during preparations for Starship's 10th flight test, which SpaceX had hoped to launch by the end of the month. (Static fires are common prelaunch tests, performed to ensure that engines are ready to fly.) That timeline will now shift to the right, though it's not clear at the moment by how much.

The incident was the latest in a series of setbacks for Starship upper stages. SpaceX lost the vehicle — also known as Ship — on the last three Starship flight tests, which launched in January, March and May of this year.

Starship's first stage, called Super Heavy, has a better track record of late. For example, on Flight 7 and Flight 8, the huge booster successfully returned to Starbase, where it was caught by the launch tower's "chopstick" arms as planned.

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My take:  if the description “in the nosecone” for the location of the COPV is correct,  then it is located very close to the oxygen header tank (as the version 1 with 1200 metric tons propellant capacity was laid out),  which is also in the nose of the vehicle,  ahead of the “cargo bay” area.  Such a COPV explosion would easily rupture that oxygen header tank.  Compressed gases drive great explosive violence (with shrapnel) when such vessels burst.  See Figure 1.

Figure 1 – Inboard Profile of Starship Version 1

There would seem to be an oxygen header tank transfer piping line down the windward “belly” of the cargo bay section,  based on descriptions I have read.  In the explosion slow-motion video,  the cargo bay splits open through its heat shield,  right where that transfer line supposedly is,  with gush of something white (not fire) bursting through,  followed immediately by an explosion engulfing about the top half of the vehicle,  and a second or so later by a second explosion seemingly centered lower down.    

The main propellant tanks below the cargo bay would be the main methane tank forward,  with the methane header tank located inside,  at the base of that tank,  and finally the main oxygen tank,  just ahead of the engine bay.  The upgraded version 2 has a bigger propellant capacity,  but should be laid out similarly.  

I would hazard the guess that the COPV explosion and bursting oxygen header tank somehow put a large force on the transfer line,  which split open the belly at the cargo bay,  allowing liquid (and vapor) oxygen out through that split,  as well as releasing a few tons of liquid oxygen to fall down on top of the main methane tank. 

My guess is that spilled header oxygen and vented methane vapors are much of the first explosion.  Bear in mind that the impact of a few tons of liquid oxygen on the top of the main methane tank would rupture it as well,  adding some fuel to that first explosion pulse.  That first explosion pulse would massively rupture the main methane tank,  and also likely the main oxygen tank below it.  That’s the second pulse of the explosion,  which was larger and longer,  reflecting the larger mass of reactants. 

All of that scenario is just an educated guess on my part. 

As for the nitrogen tank,  said to be a “COPV”,  or “composite overwrapped pressure vessel”,  maybe that is not the right choice this early in the flight test program.  Such a design is a metal shell that is simply too thin to hold the pressure,  overwrapped by a yarn or fabric-reinforced composite material,  to bring it up to strength at a lighter weight. 

Here’s the problem:  no composite material has a large plastic (post-yield) strain capability.  If the COPV over-pressures for any reason whatsoever,  failure will be sudden,  without any warning!  Maybe a heavier all-metal nitrogen tank,  one with much more plastic strain capability,  would be a better choice until the other bugs all get worked out.  At least you could see it stretch before it explodes.  You do not want to fly even experimentally,  with too many possible failure modes!  See Figure 2.  

Figure 2 – Stress-Strain Curves for Low and High Plastic Strain Capability

Lots of things look good “on paper”,  but there are a lot of other things to worry about,  many of which cannot be put on that paper.  This is where the “older hands”,  with many years of school-of-hard-knocks experiences,  can be effectively very much wiser than youngsters fresh out of school.  SpaceX has no “old hands” on its staff:  they hire no one over about age 40 or 45.  There’s no gray heads visible anywhere in that organization.

PS:  note in Figure 1 the "typical" inert mass of the Starship Version 1 upper stage,  as 120 metric tons.  I do not have a figure for the Version 2 inert mass,  but it simply cannot be very much different from Version 1!  They are all built the same way.  The hearsay bandied about on the internet,  about 80 tons,  or even less,  is simply BS!