Comment by mholt
11 hours ago
Is it normal to load ALL the propellant when doing a static fire? (I presume that's the case, anyway, given the sheer magnitude of the kaboom.)
I know a WDR typically would, but I don't think they perform an ignition for those.
The weight of the propellant helps hold the rocket on the pad during the test fire, reducing how much force the hold-downs need to exert to keep the rocket on the pad, and stressing the rocket's structure in the same way it will be stressed at launch.
Test fires with a near-empty rocket would put considerably more force on the pad's hold-downs and the corresponding parts of the rocket's structure.
Blue also had a fuelled 2nd stage on top of the booster for the static fire, which is not out of the ordinary.
SpaceX has a "cap" that is held down with cables that it uses when it needs to test-fire a first stage by itself at its McGregor test site; static fires at launch sites are usually done with the 2nd stage on top.
It is also more realistic to do it fully loaded - very different forces are acting on a rocket based on how much propellant is loaded.
Right. The forces these things produce are massive. I only know the specifics for the Space Shuttle, but when it is at full liftoff thrust (liquid and solid boosters) there's just no way to keep it leashed to Earth. It's going up whether you want to or not.
The space shuttle stack has a net thrust (thrust minus weight) of about 9 MN at lauch [1]. High carbon steel has a yield strength of 700 MPa [2]. So you need a piece of steel with a cross section of 0.013 square meter to hold it down. That's a rod 6.5 cm / 2.5 inches in diameter. Hardly impossible. Your nearest road suspension bridge probably has cables bigger than this.
If you want to argue that it's impossible in practice, I'll point out that SpaceX's Starship first stage has a net thrust of 53 MN [3], and it does static fires (without the weight of the second stage on top) [4].
The space shuttle didn't do static fires because of the solid rocket boosters that would need to be teared down and reconstructed afterwards; not because it's physically impossible to hold it down.
[1] https://en.wikipedia.org/wiki/Space_Shuttle
[2] https://www.unionfab.com/blog/2024/03/yield-strength-of-stee...
[3] https://en.wikipedia.org/wiki/SpaceX_Starship
[4] https://www.dailymotion.com/video/xab20qa
In September 2016 almost exactly the same thing happened to a Falcon 9 at the Cape, also on a static fire. New Glenn is bigger, so bigger bang, but pretty much exactly the same thing.
Off the top of my head, I recall in SpaceX's case it was a helium tank failure- a helium tank weld failed and the helium tank itself shot through the cryogenic oxygen, hit the far wall, and gave off a spark. But that sort of failure is only apparent when everything is pressurized correctly, which means tanks have to be full. The goal of the test is that you detect that sort of failure before it goes boom and then can fix it.
https://www.youtube.com/watch?v=_BgJEXQkjNQ is a video of SpaceX's failure.
Wasn't a bad weld; it was a bad interaction between liquid or solid oxygen and what were previously thought to be inconsequential defects in the composite-overwrapped pressure vessel the helium was loaded into.
Quoting from one of the press releases:
"The recovered COPVs showed buckles in their liners. Although buckles were not shown to burst a COPV on their own, investigators concluded that super chilled LOX can pool in these buckles under the overwrap. When pressurized, oxygen pooled in this buckle can become trapped; in turn, breaking fibers or friction can ignite the oxygen in the overwrap, causing the COPV to fail. In addition, investigators determined that the loading temperature of the helium was cold enough to create solid oxygen (SOX), which exacerbates the possibility of oxygen becoming trapped as well as the likelihood of friction ignition.
"The investigation team identified several credible causes for the COPV failure, all of which involve accumulation of super chilled LOX or SOX in buckles under the overwrap."
https://web.archive.org/web/20170216160231/http://www.spacex...
Was that when a SpaceX engineer demanded immediate "roof" access to ULA's pad because they suspected someone at ULA had used a sniper rifle to shoot at the Falcon? Crazy times.
Edit: yes it was https://arstechnica.com/space/2025/05/spacex-pushed-sniper-t...
Incredible.
>Externally, they sent the site director for their Florida operations, Ricky Lim, to inquire whether he might visit the roof of the United Launch Alliance building... ULA told SpaceX’s Ricky Lim to get lost when he wanted to see the roof of their building in Florida.
The FAA letter:
https://cdn.arstechnica.net/wp-content/uploads/2025/04/Space...
> This theory appealed to SpaceX founder Elon Musk, who was asleep at his home in California when the rocket exploded. Within hours of hearing about the failure, Musk gravitated toward the simple answer of a projectile being shot through the rocket.
Man, the signs were always there, right? I think I only fully realized it in 2018 during the cave "incident".
I think this makes sense, but then what’s the learning - dont make bad welds? I imagine they were already trying to do as best they could. Or perhaps “however stringent you think your checks are, they need to be more stringent”. And then learning that repeatedly is somewhat spectacular.
> trying to do as best they could
There's another comment that it wasn't the weld but even if it was the welders would build to spec and "better" (if it's known what better is) only if it's straightforward. There are certainly scenarios where a fabricator could design a better jig or use a more precise process but if the spec doesn't call for it then it's probably not going to happen because there are also the dimensions of time and money that matter as well.
How do they determine the cause of failure in a things like this?
Lots and lots of telemetry.
a lot of sensor
I don't know anything about this particular launch, but one reason static fires sometimes load more fuel than you'd think is that the hold-down clamps aren't rated for the total thrust of the vehicle. Launch thrust is usually 1.2-1.6x the launch weight (if it's <1x you will not go to space today), so after subtracting gravity you've got 0.2-0.6x the weight acting upwards on the clamps. But rockets are mostly fuel by weight, so if you static fire it nearly empty, then that gravity term goes to ~zero, and the clamps have to hold the full 1.2-1.6x. You could overbuild them to handle that -- which isn't the end of the world, because they don't need to fly -- but it can be easier to just add extra fuel and detank it afterwards.
Why use fuel, though? Is there something about its specific density and weight distribution that rules out using other types of ballast?
Where would you put the other ballast?
You've got two large tanks making up the bulk of the stage's structure - one for oxidizer, one for fuel. They have large diameter pipes that feed propellant to the engines. You can't mix the ballast with either the oxidizer or fuel, and you can't feed the engines from anywhere but the propellant tanks...
If you are writing an integration test for some new and potentially bug-ridden code then you might opt to mock, say, the database connection.
Doing so risks having to write so much database logic — with all the potential for getting that code buggy as well — that it’s often better to avoid the mock and test the entire system, end-to-end.
This was an end-to-end rocket test.
The vehicle is designed to hold all that fuel, plus whatever payload it carries on top, but it's not designed to have heavy loads attached to it in any other way. Rockets are so intensely optimized for weight that sometimes they're barely strong enough to stand upright if you fuel them the wrong way: https://www.youtube.com/watch?v=imkdz63agHY.
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Isn’t that the point of the test fire? To find out if there’s a problem that will make it go boom
You don't need to fill it all the way up for that. If in flight your engines burn for 2 minutes, but your static fire is only a few seconds you can see why.