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A significant minority of the users over at the /r/SpaceX Reddit community seem to be of the opinion that SpaceX will attempt to reuse the Falcon 9 CRS-5 first stage provided it lands on the downrange barge successfully. I disagree, and believe that it's likely SpaceX will thoroughly examine and analyze the returned stage, whether that be through destructive or nondestructive testing.

In particular, I am led to believe that they will put significant focus on the engines, the turbopumps, and the tankage structure. Elon Musk has mentioned on a previous launch abort where they didn't see expected thrust rampup that they took Falcon 9 down and "boroscoped" the engines.

My question is, what mechanisms and tests will SpaceX likely employ to understand the stresses and fatigues that the first stage undergoes? Will these tests be destructive? Does anyone have examples of tests commonly employed in the aerospace industry to check for fatigue, etc?

If the answer to the second question is a "no", would it be a good idea to look at reuse of the CRS-5 stage?

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  • $\begingroup$ @TildalWave, hah, yes. My question is assuming they reland successfully. The big 'if' in my opinion is the grid fins. $\endgroup$ – ReactingToAngularVues Nov 27 '14 at 23:39
  • $\begingroup$ According to Musk the fuel costs are only '0.3 percent of the total cost of a rocket'. Considering the rocket will have already paid for itself, launching it again is a tiny increase in cost - even with a dummy payload - with potentially huge research and PR benefits. $\endgroup$ – NPSF3000 Nov 28 '14 at 4:14
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A suggestion (unsourced, floating around the NSF forums) is that they most likely will NOT refly the first recovered stage. But will rather take it apart to examine it in great detail.

However, they may take parts that are otherwise redundant (Flight computers, electrical components, single engines) and reuse them on other flights.

That is, use parts whose failure is not mission critical by themselves, and gain more flight experience with them.

If you consider the center Merlin 1D, it has been fired:

  1. Acceptance test fire in McGregor as an engine. (Full duration? Not sure)
  2. Acceptance test fire in McGregor as a complete core. (Pretty sure full duration)
  3. Hot fire on the pad, pre-launch. (Just ignition, but that is the hard part)
  4. Full duration fire for launch
  5. Hypersonic retro-propulsion fire (Short duration, length unknown)
  6. Braking/Landing burn (Unclear if 1 or 2 burns, time will tell)

So that is at least 6 firings of that engine. Then if integrated into another vehicle as a non-center engine, will probably repeat steps 1-4, getting it up to 10 firings in the real world, which could be helpful in determining life span of the Merlin engine in the real world.

By reflying some of the other 9 engines, they can gain engine life data with minimal risk to payload since they can handle an engine out almost all the way to orbit. (Usually first few seconds no rocket can tolerate an engine out, but since they ignite and hold before launch, they usually can get past that initial launch time window).

Same idea for other things like avionics, which are triple redundant, get some real world flight time on a couple of units to understand how long they can last in a non-risky fashion.

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  • $\begingroup$ I don't know much of anything about rockets, but I don't get why avionics would have a significant failure rate. Obviously they can fail and they have to handle that, but at least on planes avionics don't fail as a result of hardware issues often $\endgroup$ – raptortech97 Jan 11 '15 at 2:42
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Elon Musk said during the recent MIT AeroAstro Centennial Symposium (link to the video) that for the upcoming launch (CRS 5) he gives it about 50% or less chance of landing the first stage successfully on also recently announced floating platform, but if they do that he figures they'd be able to refly it.

So the answer to your first question seems to be: no. They do destructive testing on the Grasshopper, which is SpaceX' development vehicle. Gwynne Shotwell (SpaceX President & CEO) said in one past interview (I don't remember which one, it might have been the one for Atlantic Council), that the production of booster engines (Merlin 1D) is quality tested to assure roughly 50-flight reuse (again, if I remember correctly, but the number was impressive, someone will correct me if I'm way off). They need to assure high reusability of their booster stage so they would destructively test production samples, say hot fire test engines in simulated full ascent profile till they fail, and in-flight test new technologies with their Grasshopper platform, but they don't destructively test flight-ready hardware and I don't expect them to, unless absolutely necessary. Such practice would be too expensive and clearly clash with their aggressive pricing scheme.

As for nondestructive testing (NDT), methods usually employed in aerospace industry are visual inspection with high resolution cameras or microscopy in various wavelengths (visual, near-IR, IR, sometimes UV if you're looking for residual patterns and similar), 2D X-ray and 3D X-ray CT (Computed Tomography) scanning for deep material fatigue, ultrasound, vibration analysis, and so on, and sometimes as simple as partially refueling the stage, or nitrogen purging, and checking for leaks with thermal imaging system. Different methods and techniques might be employed for different parts of the booster stage, the list of them is really long and SpaceX isn't really forthcoming about exact methodology employed for the purpose. I guess they'll reassure clients to the level needed, or simply offer cheaper flights with reused boosters (which is their long-term plan anyway).

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