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When the Antares 130 rocket carrying the Cygnus Orb-3 mission experienced an explosion in one of its turbopumps, did that lead rapidly (before crashing / before RSO triggered flight termination) to a total loss of propulsion? If the Antares rocket was designed with engine-out capability (e.g. by adding a third engine so that it could complete its mission on any two engines), might it have been able to continue to orbit after the pump failure? (Alternatively, if it had dumped mass fast enough, could the single remaining engine have gotten the doomed rocket clear of the pad before flight termination and saved a lot of damage?)

Video:

It looks to me like no engine plume is present during the descent, and also it only takes seven or eight seconds to peak and then drop a distance that took fifteen seconds to ascend (though presumably accelerating at less than 1G the entire time of powered flight). However, I have not been able to find an authoritative claim as to the status of the second engine in between the failure of the first one and the termination of the flight. Was it disabled by the explosion? Was it damaged but not immediately disabled? Was it still operating? Was it commanded to shut down, either manually or automatically, prior to flight termination?

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The second engine definitely stopped at the time of the initial explosion. More accurately, its plume tapers off in 4 frames, or about 0.13 seconds, of the video. The reducing plume is straight and not discolored.

This is much too slow to be due to direct damage from the adjacent explosion, and the "neatness" of the shutdown implies that it was a commanded shutdown not fuel or oxidizer starvation nor catastrophic failure of any mechanism. I don't see any evidence of fuel or oxygen being vented through the engine as the rocket falls, but this could be masked by the ample fuel leaking from the adjacent engine.

The fall speed is consistent with unopposed freefall.

The most likely cause of shutdown of the second engine(Aerojet AJ26 # E16) is that the rocket detected catastrophic failure of one engine, and commanded immediate shutdown of the second engine. Very possibly due to non-instantly-lethal damage to this second engine from being next to a bomb. This shutdown appeared to be "normal", considering the circumstance.

Despite somewhat conflicting reports on the root cause, both NASA and Orbital report the failure to be due to mechanical friction/contact in the oxygen turbopump of engine E15 (the left engine, as seen in that video)

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  • $\begingroup$ Thanks! I'd still love to know if there's any authoritative explanation for the shutdown of E16, and whether that was by design - it seems very undesirable to lose all propulsion that low (I'm reminded of the N-1 being reprogrammed after a failure that destroyed its launch pad, such that it wasn't allowed to automatically shut down any engines until somewhat longer into flight and would no longer crash on the pad) - but I agree that your theory fits the observed data. $\endgroup$
    – CBHacking
    Oct 19 at 1:12
  • $\begingroup$ @CBHacking when you are taking off with a TWR of 1.2, and you lose HALF of your engines, you DO want to cut thrust on the second engine. Because that rocket is coming down, and keeping the second engine running will just drop the rocket a few meters further from the launch pad in some random direction, like maybe on the control center or the fuel farm. 2-engine Antares needs to be handled differently from googolplus-engined N1 $\endgroup$ Oct 19 at 4:01
  • $\begingroup$ Huh, I would think you'd want to use what power you have to try and get away from the pad and out to the beach/ocean, or at least delay impact while burning off / dumping propellant, but I suppose that does depend on how much control authority you have. The recent Astra and Firefly launches demonstrate remarkable capability after engine-out, despite neither one being able to complete their missions... though both were at least capable of about 1:1 TWR after the engine loss, and that does perhaps make a difference here. $\endgroup$
    – CBHacking
    Oct 19 at 4:08
  • $\begingroup$ @CBHacking because the Astra and Firefly rockets had FIVE (or four for firefly) engines. 1 out, on TWR of 1.2, leaves 1.0.. enough for that silly hover-slide. Lose 1 of TWO engines, and you are heading straight to the ground. $\endgroup$ Oct 19 at 4:32
  • $\begingroup$ Sure, you can't manage two minutes of flight with a TWR of 0.6 and only being ~180m up (assuming ~6 seconds of free fall to crash), but you could probably get clear of anything that'll be too expensive to repair/replace if you land on it (again, assuming you still have control authority). Maybe not out over the ocean, and certainly not very far out, but surely it's better to crash on the beach (already cleared, no valuable infrastructure) than on the pad (millions of dollars in repairs before it was usable again)? Also, wouldn't it be better to activate FTS rather than just crash? $\endgroup$
    – CBHacking
    Oct 19 at 5:05

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