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Much to everyone's relief. The SpaceX Starship SN10 successfully completed its flight and landed.....

But, sometime later, It exploded! Starship SN10 Exploding

Starship SN10 Totaled

Why?

And did it have anything to do with the fire near the Raptor engines?

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    $\begingroup$ I noticed (with some grim sarcasm) that the official spacex.com video ends long before this RUI (rapid unintended ignition; I just made that up) event. $\endgroup$
    – Carl Witthoft
    Commented Mar 4, 2021 at 12:55
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    $\begingroup$ @CarlWitthoft it's the recorded webcast, which ended after the landing and before the explosion. They have a whole compilation of exploding rockets on their YouTube channel, they're not afraid of showing the messy side of rocket development. $\endgroup$
    – Christopher James Huff
    Commented Mar 4, 2021 at 16:53
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    $\begingroup$ @CarlWitthoft, the NASASpaceFlight livecast came up with a more precise term "burned off the excess propellant in a rapid fashion", very bottom. "Rapid excess propellant burn-off" sounds more to the point. :) I also liked how they added "Or not" after the last item of the sequence, which was "Vehicle safing" (upper left). They also noted that SN10 is the first SN to lift off twice, which is technically true. Guys were having all the fun! $\endgroup$
    – kkm mistrusts SE
    Commented Mar 5, 2021 at 4:14
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    $\begingroup$ they blew it up (or let it blow up) because 1) it's fun, 2) it would have had to have been disassembled and scrapped anyway, so why not do that rapidly? (humor) $\endgroup$
    – uhoh
    Commented Mar 5, 2021 at 4:37
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    $\begingroup$ Covered by Scott Manley. $\endgroup$
    – Peter Mortensen
    Commented Mar 5, 2021 at 6:24

5 Answers 5

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EDIT: Elon has revealed in multiple tweets (one, two, three, four) what went wrong, and although this doesn't tell us exactly what led to the explosion directly, it gives some insight to what went wrong. I will be updating this answer later...

The proper answer to questions like, "What went wrong with SpaceX's [insert mission here]?" is:

Unless SpaceX tells us what went wrong, we won't know, and they haven't told us anything yet.

Elon or SpaceX will probably tweet/eventually talk about what went wrong, so until then, all we can do is guess. That said though, one of the key events that led to the explosion seems to be that the landing legs didn't lock into their "deployed" position after being released. This is clearly visible in this video which compares a previous hopper to SN10's performance. Furthermore, from the video of the landing, it looks like the landing wasn't quite "soft" and there was an appreciable impact on the landing pad. In this picture you can see that there are no landing legs deployed and that the whole thing is leaning, which implies hull damage:

SN10 landed

In my (not-a-rocket-engineer) opinion, this sequence could've led to the explosion:

  1. Landing legs fail to deploy properly
  2. SN10 lands with slightly too much speed (I'm unsure if landing legs would've helped)
  3. The impact damages fuel tanks, raptor connections, hull integrity
  4. Fuel begins to leak and catches on a hot surface or a spark (this is the fire)
  5. As time passes, leaks grow (thermal changes, fire damage, embrittlement?)
  6. Eventually the pressure of the leftover propellant/oxidizer can't be held anymore and bursts out
  7. On a spark, fire, or something hot, the large leak catches fire resulting in the explosion

An unlikely alternative (although I think Elon would've tweeted if this were the case), is that they could've determined that they can't make SN10 safe to approach because de-tanking systems were damaged or whatever, so they decided to detonate it via abort system instead of waiting hours for it to maybe explode.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – called2voyage ♦
    Commented Mar 8, 2021 at 13:40
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Eric Berger, who writes extensively about space exploration for ArsTechnica and for other organizations, and sometimes appears on national TV wrote

SpaceX has yet to provide details about what happened and likely won't.

Eric has some speculations, based in part on "informed sources":

However, informed sources suggested the accident may have been caused by a leaking valve, likely methane fuel. It is notoriously difficult to operate fuel valves at cryogenic temperatures.

This of course is speculation. However, Eric's "informed sources" can be extremely well-informed. On the other hand, SpaceX can be notoriously tight-lipped with regard to technical details. Being tight-lipped is how SpaceX protects its intellectual property. (SpaceX tends to eschew patents.) The general public may never know why SN10 failed.

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  • $\begingroup$ Eric does tend towards gushing praise of SpaceX in his articles, but generally has a good handle on the science side. $\endgroup$
    – throx
    Commented Mar 4, 2021 at 23:40
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    $\begingroup$ @throx - Eric has been critical of SpaceX, multiple times. He is not a fanboi. He's definitely not a fan of SLS, in any way, shape, or form, and he has let that (well-deserved) bias show. $\endgroup$
    – David Hammen
    Commented Mar 4, 2021 at 23:42
  • $\begingroup$ For those who don't know about Eric Berger, I strongly suggest following or subscribing to his weekly Rocket Report which comes out on Fridays (with occasional weeks off). His most recent Rocket Report (26 Feb 2021 as of this comment) is arstechnica.com/science/2021/02/… $\endgroup$
    – David Hammen
    Commented Mar 4, 2021 at 23:45
  • $\begingroup$ @DavidHammen - There's a difference between "never critical" and "tending towards gushing praise". This is probably OT, so I'll let it lie. $\endgroup$
    – throx
    Commented Mar 5, 2021 at 0:25
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Something I noticed from a higher-resolution feed: in the half-second before the explosion, there was a very brief black plume that “broke out” from the area near the rear flap of the ship. Here are some screenshots in quick succession:

enter image description here

enter image description here

enter image description here

I would guess from this, that an internal structural member failed suddenly, possibly after having sustained damage from impact and weakened from the fires at the landing site. I don't know enough about the internal structure of the ship to guess any further, but I could imagine that if a significant structural member failed at this location, and with some remaining amount of fuel and O2, it might explain what we saw.

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  • $\begingroup$ Is that rupturing seam in the engine skirt area or the tank area? $\endgroup$
    – Dan Is Fiddling By Firelight
    Commented Mar 5, 2021 at 15:23
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    $\begingroup$ In that 3rd photo, it looks like the sudden upward acceleration from the explosion crumpled the nose. $\endgroup$
    – Jeff Wolski
    Commented Mar 6, 2021 at 0:17
  • $\begingroup$ @JeffWolski I think the nose is still there, but because it's frost covered it's faded into the cloudy background and hard to make out - especially if you;re only looking at the resized image as shown in the answer. $\endgroup$
    – Dan Is Fiddling By Firelight
    Commented Mar 6, 2021 at 18:07
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    $\begingroup$ @DanIsFiddlingByFirelight it's still there, but it's starting to buckle down around the area of the base of the forward fins. $\endgroup$
    – Christopher James Huff
    Commented Mar 6, 2021 at 20:21
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Alright, so I found an answer on YouTube.

This video explains it nicley: SpaceX Starship SN10 Test Flight

It starts to explain the reason for the explosion from this part: Reason for Explosion

Seemingly, the oxygen tank ruptured; According to Scott Manley, the oxygen tank was under pressure and it ruptured before any fire started which might have triggered the explosion

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Until SpaceX announces the cause, the best we can do is guess.

Obviously something was damaged during the flight1 or landing, which allowed fuel to leak in the area under the skirt and find an ignition source (likely a hot engine component).

It bounced on landing and had a noticeable lean afterward, so it's reasonable to assume that the damage occurred during landing. It could be a tank dome or fuel line broke or was punctured. They've also had issues with the Raptors themselves, and it could be one of the engines had a leak.

But again, this is all guessing. We'll have to wait for official word from SpaceX, if they decide to give it.

  1. They are flinging rapidly spinning cryogenic turbopumps around rather vigorously during the landing flip, which has to put all kinds of interesting stress on the engines. Also, one of the engines had a more yellowish exhaust on ascent and it looked like they were throwing out a bit more soot than the previous launches, although that may just be an artifact of camera angle and lighting.
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    $\begingroup$ I remember seeing the yellowish color from two angles (inside the engine bay and from a ground camera), so it's unlikely an artifact. But they changed the landing sequence to igniting all 3 engines before landing, then shutting down two, leaving the one for landing which performed "the best" during this test burn. I think it was unlikely that engine which won the landing contest—it should have read further off nominal than the other two if there were a persistent problem with it. $\endgroup$
    – kkm mistrusts SE
    Commented Mar 5, 2021 at 4:33
  • $\begingroup$ There's a separate question on the yellowish color here. $\endgroup$
    – WBT
    Commented Mar 7, 2021 at 23:40

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