While the WSJ headline sounds ominous: Congressional Investigators Warn of SpaceX Rocket Defects, Quartz's SpaceX needs to redesign its engine to ensure it is safe for human spaceflight seems to be a better description. Cracking in the blades seems to be known and not unusual, and has been taken into account in turbopump design. It seems SpaceX is already working on some improvements to address these concerns with regard to manned spaceflight.

Is the issue and concern that it increases the likelihood of an engine failure - especially 2nd stage when there is only one engine, or is it like throwing a piston rod - where stories claim it can come shooting out of the hood and damage anything else in its path, possibly a propellant tank or two?

Or are there other issues related to pump failure - burst lines, leaking propellants, etc?

Question: What are the issues and concerns related to turbopump blade cracks and manned spaceflight?

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    $\begingroup$ Can you please stop adding the word (actually) to every question you add? It's getting annoying. $\endgroup$ – Hobbes Feb 3 '17 at 9:23
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    $\begingroup$ @Hobbes actually it's "only" 10% of them, not "every question". I wasn't actually aware that I used actually that often, but it seems that I actually do! And if you ask me, I think that that's actually too frequent. I'll remove it here, and try to avoid it. Actually I have a hard time writing the actual titles to question, and happy to hear constructive criticism any time, as long as it's actually constructive! $\endgroup$ – uhoh Feb 3 '17 at 10:21
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    $\begingroup$ @Hobbes I'll definitely stop saying that word, It must be pretty annoying! I'm glad you pointed it out to me. $\endgroup$ – uhoh Feb 3 '17 at 10:30
  • $\begingroup$ @Hobbes I have to thank you - in the last 24 hours I have stopped myself from needlessly typing the 'a' word a half-dozen times in various places. $\endgroup$ – uhoh Feb 6 '17 at 16:11
  • $\begingroup$ I've also noticed @NathanTuggy has been quietly converting the occasional minus sign into the intended 'em' dash I shudder to think of how many of those I've got wrong. $\endgroup$ – uhoh Feb 6 '17 at 16:13

Turbo pumps have parts spinning at thousands of RPM, which means the blades in the pump have a great deal of energy. A turbine blade crack can lead to a fracture which will fling the failed turbine part into the pump. The best case would be for the pump to fail in a contained way, either by the piece jamming something or ripping bits of it apart, which would lead to a loss of power in the rocket which may or may not cause an abort. The worst case scenario (and more likely given the energies involved) is an uncontained failure of the pump which will perforate the rocket in multiple places, including other pumps, fuel lines and tanks, which will lead to a catastrophic explosion.

Turbine failures in rocket motors have happened. In the Space Shuttle program there were contained pump failures where after a failure in testing:

A post-test inspection revealed that a first-stage turbine blade had broken off and inflicted significant damage to both turbine stages. Figure 17 shows the damage to the first-stage wheel. The engine was shut down safely with no other engine damage. Two weeks later, on December 1, 1977, Test 901-147 on Engine 0103 experienced a similar failure at slightly above 80 percent power level. This time the damage was more severe. The turbine blade debris caused the rotor to seize up, resulting in the cessation of fuel flow and very LOX rich operation. Major burning throughout the hot gas system followed; but, although significant damage was sustained, it was contained within the engine with no external burnthrough.

More recently an Antares rocket exploded just above the pad when a turbine failed in flight:

The failure began in one of the Antares rocket’s two AJ26 engines, when a spinning rotor inside a liquid oxygen turbopump contacted another component inside the powerplant, triggering an explosion, according to engineers.

This resulted in: enter image description here

Once a rocket lifts off any kind of abort will require the activation of the launch escape system for the crew to survive, which is not a scenario to be taken lightly as there's a great deal of risk involved. If a satellite is destroyed on launch it's a shame but you can build an identical one, if a person is killed you don't have that option, which is why there's this scrutiny.

  • $\begingroup$ A turbopump blade doesn't sound like an easy part to replace during refurbishment for reuse. But is it "actually" reasonable to replace it after every flight? $\endgroup$ – LocalFluff Feb 3 '17 at 9:29
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    $\begingroup$ It's hard to say, it depends on the construction I suppose. If you look at jet engines the blades are designed to be removed and replaced, but that's a completely different scenario. I would imagine that the goal would be to come up with a design and material which would not require replacement, and would have a defined design life. $\endgroup$ – GdD Feb 3 '17 at 9:34
  • $\begingroup$ Thanks! I'm curious, is this all hypothetical, or are contained and even uncontained failures things that actually happen? $\endgroup$ – uhoh Feb 3 '17 at 10:34
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    $\begingroup$ They absolutely do @uhoh, please see my edits for details. $\endgroup$ – GdD Feb 3 '17 at 11:04
  • $\begingroup$ Blade inspections and replacements on the SSME added a lot to turnaround time in the early Shuttle program. Blade redesigns happened. Eventually the entire turbomachinery packages were replaced by a different firm. See the 'taxonomy of the SSME` part in my answer to this question: space.stackexchange.com/questions/16971/… $\endgroup$ – Organic Marble Feb 3 '17 at 14:13

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