SpaceX Dragon 2 crew capsule explodes

Discussion in 'Science and Technology' started by MarsWeeps, Apr 21, 2019.

  1. MarsWeeps

    MarsWeeps Fleet Captain Premium Member

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  2. Asbo Zaprudder

    Asbo Zaprudder Vice Admiral Admiral

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    Better to find problems during unmanned testing and then fix them than to risk exposing a crew to an untested system.
     
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  3. MarsWeeps

    MarsWeeps Fleet Captain Premium Member

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    Well, the escape system has been successfully tested before. I believe this was the same Dragon 2 that just came back from the successful docking with the space station. They were going to re-use it and test the abort system during an actual rocket launch. The previous test of the abort system was just the capsule, no rocket.

    I'm wondering if the exposure to salt water during the splash down could have contributed to the explosion. This setback will probably delay a crewed flight by a year.
     
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  4. Santaman

    Santaman Vice Admiral Admiral

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    The more problems they find now the better, doesn't matter if it's about cupholders not working or making sure that things won't go boom, as for salt water, you can use materials that are salt water resistant, I don't see a problem there.
     
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  5. YellowSubmarine

    YellowSubmarine Vice Admiral Admiral

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    I would normally say explosions during unmanned ground testing is good, as you gather more data and increase safety, and in testing you can exceed safe parameters by orders of magnitude to explore actual safety margins and I originally thought the Grasshopper explosion was good news, as you gathered more data. Now, that was FTS I believe, so not comparable, but in a perfect world the RUD events during CRS-7 and Amos-6 should have been caught during testing somehow, and they would have been good news.

    However, this is bad:
    1. It didn't happen during factory testing, but during testing coordinated with customer on flown capsule, which implies a) high likelihood it's an unknown failure mode, b) they were not going crazy with testing parameters.
    2. The LES shouldn't explode. Like ever. It's supposed to make things safer. Now, it's a good reminder that a mixture of CH₆N₂ and N₂O₄ is explosive (what good a propellant would be if it was inert), but if you're going to stay in a room whose wall can blow, ‘for your own safety’, you need assurances that this stuff is kept in check.

    It's worse than that. The LES is supposed to be a last ditch resort to save the lives of the crew in the unlikely event that the rocket blows, provided that the rocket has been already secured not to blow to the largest extend possible (not to mention that Elon has claimed that the CRS-7 RUD was escapable without SuperDraco if the software had been configured to do that). In that situation, any small chance for the LES itself to be a cause of a catastrophic explosion is fatal, as it greatly diminishes effectiveness and can pretty easily decrease overall safety, instead of the other way round. The margin for failure of something that is supposed to be used in a exception unlikely scenario is extremely low.

    Goddamn you Bayes, you are an asshole, you should have never invented the goddamn Bayes' theorem.

    Let's hope it was either the failure was a) not in the Dragon/SuperDraco, or b) they were exceeding safety parameters when that happened. Someone said the colour of the smoke suggested it was the N₂O₄, and overpressurisation may have caused its tanks to rupture, so that would make (a) unlikely, but hopefully they did overpressurize on purpose or something. I love them 3D printed tanks, looked really robust when Elon demoed them.

    Or were just the engines printed? The tanks looked unbreakable either way. (Famous Last Words)
     
    Last edited: Apr 22, 2019
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  6. Asbo Zaprudder

    Asbo Zaprudder Vice Admiral Admiral

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    Poor old Reverend Bayes -- the name of the theorem would have gone to Laplace, in that case.
     
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  7. XCV330

    XCV330 Premium Member

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    Problem now is that CST-100 is WAY behind and missing key milestones. I have no doubt that SpaceX will learn from what happened and continue on, but this is going to be a delay, and it will just continue to push commercial crew back.

    I really wish crewed Dreamchaser had had a chance.
     
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  8. publiusr

    publiusr Vice Admiral Admiral

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    Dreamchaser might get another chance after this.

    From around the web...

    The first abnormal frame of the video shows a fireball about two meters in diameter. This is only a small fraction of the energy released in the CX-40 explosion which released the energy stored in a large COPV. This and the proximity to ignition suggests to me that this was a hydrazine detonation triggered by decomposition in a sealed line and resultant adiabatic compression. Contamination in the line (perhaps due to salt water intrusion) would seem the most likely cause.
    https://forum.nasaspaceflight.com/index.php?topic=48003.msg1938880#msg1938880

    Then too:

    The highlighted above assumes that the issue is with salt water. Alternatives could be:

    -Damage caused by frozen fuel lines (as hinted at by the restricted flight profile DM-1 flew).
    -Heating damage coming in thru the Super-Draco ports since they are open in that direction during re-entry.
    -Parts that are fine for one flight but cannot withstand the rigors of flight in condition for reflight and need to be replaced first.

    If it were any of those, then the explosion could have occurred after re-entry while the system was pressurizing for the landing. If any of the above prove true then I personally think this should be the final nail in the propulsive landing coffin.


    Of note:

    Hydrazine Rapid/Adiabatic compression sensitivity may occur when hydrazine flows into initially empty (e.g. filled with gas) propellant distribution lines resulting in a temperature increasing collapsing bubble sufficient to initiate detonation.

    Others disagree--

    That paper is talking about hydrazine N2H4, which can self-decompose and release heat, especially as a vapour. SpaceX is using mono methyl hydrazine CH3N2H3, which I understand is much harder to self-decompose and releases less energy.

    Cut aways
    https://forum.nasaspaceflight.com/index.php?topic=48003.msg1938957#msg1938957

    Discussion:

    The shape of the pressure vessel and the fact dragon is supported from below would seem to suggest the blast from a ruptured COPV would be directed upwards and outwards, as seen. The location of the Draco cluster adjacent to the COPV could provide additional directivity. So the copv behind the dracos looks like the top candidate and potentially it was damaged by some undetected internal failure on the Draco test that is said to have occurred just prior to the anomaly.

    SuperDracos protected from re-entry?
    https://forum.nasaspaceflight.com/index.php?topic=48003.msg1939184#msg1939184

    Or could it have sealed after damage was done?

    More:
    https://forum.nasaspaceflight.com/index.php?topic=48003.440

    Hopper lines dealing with ice
    https://www.universetoday.com/14189...mation-in-the-cryogenic-propellant-prevalves/

    Bad week for aerospace
    http://up-ship.com/blog/?p=40536

    As for the capsule blast:

    There's talk it may have been a ZOT*; unburned props being sucked into a manifold then not fully flushed before another burn and igniting there. Usually happens on the ground, not in space.

    * Named for the sound made by the anteater in the BC comics.

    http://forum.cosmoquest.org/showthread.php?149827-SpaceX&p=2481205#post2481205
     
    Last edited: Apr 30, 2019
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  9. Trinity Gingerbread

    Trinity Gingerbread Time is the thief of life Premium Member

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    Well at least this is all happening during testing now lives lost. Best place to iron out the bugs.
     
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  10. XCV330

    XCV330 Premium Member

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    But that's a problem. Cargo Dreamchaser isn't the same vehicle as the one they proposed for the crew contract, and it would be years to be ready. A US crewed space vehicle hasn't flown now (not counting suborbital) since 2011. This is getting ridiculous.
     
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  11. Trinity Gingerbread

    Trinity Gingerbread Time is the thief of life Premium Member

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    We need to make space great again :)
     
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  12. publiusr

    publiusr Vice Admiral Admiral

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    We'll get there.
     
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  13. publiusr

    publiusr Vice Admiral Admiral

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    Something I just thought about

    Hypergolic tanks don't seem to be as flush with the outer surface of the wider Orion as they are in Dragon. Maybe that makes a difference?

    I'm fine with hypergolics or solids, pusher/tractor set ups--everything has its pluses and minuses.

    Falcon rockets never really had a failure in returning through the atmosphere (just sticking the landing early on--which is dialed in now)

    Dealing with cramped confines/payloads/upper stages--that's where all the bad bugs are for whatever reason. I had hopes that Bezos would go for the plug nozzle Big Onion route. Scale things up--and it seems things just get more resistant what with extra mass.

    Now here is a crazy suggestion

    When I first heard of the MOL Gemini with the hatch through the heat-shield (and its Soviet VA counterpart), I thought it was insane. But shuttle has had no real problems with the landing gear covers, and the long stem VA (what with retros/escape towers part of one structure) was actually very agile. Cosmos 881 and 882 came down less than a mile from each other after two of them was lofted by a single UR-500 Proton (in The Dream Machines, it is falsely depicted as belly to belly minispaceplanes)
    https://en.wikipedia.org/wiki/VA_spacecraft#Kosmos_881_and_Kosmos_882

    So I'm going to throw this out and see what people think of this.

    Place the docking hatch on the bottom of a capsule, not the nose. The spacecraft points its belly to a target, and thus the heat shield is not in the way of space debris. The hypergolic tank is toward the center, ringed by passengers--far from the wall of the capsule. Thus, only inert hatch mechanisms are near the heat shield, as opposed to tankage, plumbling, etc.

    You have the hypergolics feed upward--to an escape tower that has no solids--or is a hybrid.

    Thus you have a liquid fueled tractor system. No chance of salt water intrusion--because it is up and out of the way.

    A diving bell has its lower hatch off--and the water stays out of that "capsule" even with a big hole in the bottom--or should I say--because of it. Pull it out of the water by a hook on the tower, and guys come out of the bottom inside a ship.

    That's new isn't it?

    Discuss, please...
     
    Last edited: Apr 30, 2019
  14. MarsWeeps

    MarsWeeps Fleet Captain Premium Member

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    You had it right the first time.
     
  15. diankra

    diankra Rear Admiral Rear Admiral

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    A brutal but probably accurate comment from the Apollo team was that it was fortunate the Apollo 1 fire happened: without it, they'd probably have lost a crew in orbit, and never been able to find out for sure what had gone wrong.
     
  16. XCV330

    XCV330 Premium Member

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    The X-37s log months in orbit with those landing gear hatches, too.

    I'm a fan of Big Gemini type craft but with all the work going on with what is out there right now, I don't think there is going to be another capsule design come along to challenge Starliner/Orion/Dragon/Crew Dragon/New Shep etc, not to mention Dreamchaser. That's a lot of spaceships being built right now.
     
  17. publiusr

    publiusr Vice Admiral Admiral

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    I understand why you would be skeptical of my post 13 above.

    Then too, suppose I could blow the bottom of the capsule off. Heat-shield and all.

    Then the capsule only needs a lightweight drogue chute, and the astronaut bails out, straight out the bottom--with small personal parachutes.

    The capsule IS the escape tower, saving weight, and the hollow space fills with an air-bag, so it still floats.

    This is all wild thinking of course, hatch through a heat shield that can be blown off altogether--a hypergolic liquid escape tower stem. It is always good to try to imagine the
    [​IMG]
     
  18. XCV330

    XCV330 Premium Member

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    Post-landing leaks with the Blue Gemini weren't a problem with the aft-hatch because Gemini's landed on their sides. A bigger capsule using an Apollo or Corona type OML would not have that luxury. If thermal stresses cause leaks in a water landing, the capsule becomes a deep sea tomb.
     
  19. YellowSubmarine

    YellowSubmarine Vice Admiral Admiral

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    I'm betting the rocket in tomorrow's launch of the new capsule will explode. Wait for it.
     
  20. YellowSubmarine

    YellowSubmarine Vice Admiral Admiral

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    The crew lives in the end.