Starship/Superheavy Flight Test

There are three photos of the SpaceX “Starship/Superheavy” vehicle taken during the recent test that terminated in an explosion.  They are very informative. 

In the first one at liftoff,  look at the color and character of the "smoke" cloud.  That's not smoke,  it is dust,  and not very fine-grained,  either,  or it would have billowed up a lot higher.  Combine that with the reports of concrete blocks coming down multiple city blocks away,  and sand coming down 6 or more miles away,  and you understand that what you are really looking at,  is the excavation debris being flung out by the rocket blast as the launch stand is being destroyed for lack of a flame deflector.  See Figure 1.

Figure 1 – A Photo Taken Right At Liftoff

The other two photos show two separate things quite clearly: 

(#1) Yes,  there was vented methane streaming down the side of the vehicle.  It caught fire and base-burned with wake air around the engines,  which plays merry hell with the control wiring and the plumbing on those engines!  That burning methane also entrained onto the engine plumes as subsonic flaming sheaths around the supersonic plumes.  You can tell by the bright yellow color and the wavy nature that this is a subsonic fuel-rich flame. 

(#2) There are supersonic plumes encased in subsonic flame sheaths that point straight aft (from the undamaged engines),  and there are some supersonic plumes sheathed in subsonic flame jetting out to the side,  well off-axis.  Those are coming from badly-damaged engines that are not shut down.  I can see at least 3 of these in the photos.  They represent forces that act to spin the vehicle end-over-end. 

See Figures 2 and 3.  And note:  there is a misalignment between vehicle axis and main plume direction,  indicating the vehicle is not aligned with the slipstream,  by something near 10 degrees.

Figure 2 – A Photo Taken In Flight Before The Vehicle Tumbled

Figure 3 – Another Photo Taken In Flight Before The Vehicle Tumbled

Shortly after these two in-flight photos were taken,  the vehicle went completely out of control,  tumbling end-over-end about 4 times before the self-destruct signal was sent.  In the video footage of the tumbling vehicle,  one can see that the vehicle is no longer straight,  it is bent right at the stage point,  by something near 5-10 degrees.

Informed speculations: 

(#1) Odds favor that some of the concrete block debris chunks hit and badly-damaged multiple engines at ignition and during liftoff,  as the rocket blast excavated that huge hole.  Loss of engines reduced vehicle thrust,  and (more importantly) those damaged engines shedding lateral streams added very large side forces at the rear,  which eventually overcame the thrust vectoring control of vehicle attitude.  Which is why it eventually spun end-over-end.

(#2) It's not yet bent at the staging joint in these views (the photos in Figures 2 and 3),  but I saw the two stages bent out of alignment by around 5-10 degrees in the video footage of the spinning vehicle.  Once the vehicle gets broadside-enough to the supersonic slipstream (about Mach 2 at about 100,000 feet),  the dynamic pressure is around 65 pounds per square foot.  That pressure acting on multiple thousands of square feet of broadside area is way more than enough to bend very thin stainless steel structures.  The weakest point is where the two stages are clamped together,  which is right where it bent out-of-line.

My own observations about this incident:

(#1) SpaceX already knows a lot more about what happened than they are saying in public.  Musk's public admission that they should have had a flame diverter is a hint of that.  This test flight would have gone a LOT BETTER had they had one,  and they know it.

(#2) SpaceX is very likely in trouble again with the FAA,  because the debris that was flung,  was flung much farther than the estimated debris risk distances in the environmental impact documents,  upon which their launch license depended.  That would not have happened if they had had a flame diverter,  and they (and now the FAA) know that,  too.

(#3) FAA will likely not grant another launch license,  until they are shown just how “bad top-level management decisions” (like launching such a giant rocket without a flame diverter) can be avoided within SpaceX.  I'm talking about Musk,  not Shotwell.  She knows better.  He apparently does not,  or else does not care what damage he might cause.  And the FAA now knows that,  too!

(#4) That should give SpaceX plenty of time to install and properly test a flame diverter.  Any few-seconds-long static test of the Superheavy booster can serve to test that flame diverter.  And thus show the suppression of unintended debris-flinging. They don't need a launch license to do that.  But until they do that (and get it right),  they should not fly again.  Why?  Because the collateral damage risk is unjustifiable,  and we have now all seen that.  And I think the FAA now understands that,  too.

Final remarks:

Don’t get me wrong.  I want to see this vehicle fly and SpaceX succeed.  They just need to do it right.  Public safety is at risk.  

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Update 7-7-2023:  I have since seen in some of the liftoff video footage,  chunks of concrete and steel flung up alongside the rocket,  appearing out of the dust cloud,  and moving at least halfway up toward the nose.  That is very suggestive that the inoperative engines (and maybe some operating engines) were damaged by flung debris chunks at ignition.  

It is also possible that there was damage to the end of the propellant tankage or plumbing,  causing a larger-than-usual amount of methane to be base-burning around the engines and sheathing the supersonic plumes in subsonic flame.  That plume appearance was very unusual,  to say the least.  Just more proof that launching without a deluge flame diverter was an extremely stupid decision. 

I think the 41 second delay between sending the destruct signal,  and the actual destruction of the tumbling vehicle,  is a substantial indication that the destruct system failed to function.  During those 41 seconds the tumbling vehicle was descending rather sharply into denser air,  where the wind load forces finally broke it up.  

I saw a low of out-of-control rockets destroyed in exactly that way in the 1960's,  along with a lot of others destroyed by the destruct systems.  You can pretty much presume that anything that explodes before it tumbles was a self-destruct for going off-course.  Anything that just suddenly tumbles and explodes,  you can pretty much presume broke up due to air loads before they could send the destruct signal.  

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