Diagnosing Falcon

Well, as I expected, that didn’t take long:

Engine pressure anomaly traced to turbopump valve. Replacing on engine 5 and verifying no common mode. #DragonLaunch

So it’s a good thing it shut down — it could have resulted in a catastrophic engine failure in flight, something that SpaceX has theoretically designed for (they claim to have engine-out capability from liftoff, and sufficient inter-engine blast shielding to prevent fratricide), but probably doesn’t want to test, at least this early in the program. Also, they had no performance margin on this mission, so it probably would have meant an abort to a low orbit, and perhaps an inability to get to the ISS.

[Update a while later]

Here’s the story over at Popular Mechanics.

74 thoughts on “Diagnosing Falcon”

        1. You are right that we don’t know yet. But that tweet came before they discovered the offending valve. Since it’s very likely the shut down saved the vehicle it might be a good idea to rethink and not change the parameters (or less than they might have otherwise.)

          If they had, had a larger than one second window I think there is a very large chance they would have adjusted the parameters. With that you have a good chance they would have been able to test their RUD mitigation which otherwise is a difficult proposition.

          I think they prefer to have saved this rocket and will probably choose to save those that come after. Missing a launch is not the worst outcome.

  1. How can you have “no performance margin” and “engine out capability from liftoff” at the same time. That does not make sense.

    1. They had no performance margin with regard to the mission. Engine out means they still get to orbit but without enough fuel on the dragon to meet all it’s objectives.

    2. Rand and friends ‘find you lack of faith disturbing’.

      This is Space X.

      You just have to believe.

        1. If you mean your apparent point that the Falcon 9 (with an engine out) could deliver the Dragon (Cargo Version) to an orbit unusable for rendezvous with its intended target (in this case the ISS), then yes I understand your point.

          It is, however, a distinction without a difference.

          Hypothetically assuming that to be true, what good does it do to deliver cargo (intended to supply the ISS) to an orbit where it cannot reach the ISS?

          1. In this particularly case there is no difference, except that it allows to get to a safe orbit where it can be brought back safely and in a controlled manner (were the cargo valuable). In general, and in the future, if there were a tug based at ISS, it could be sent out to retrieve the payload. For some, perhaps many missions, they would presumably not be at the payload limit, and thus have adequate propellant reserve to handle engine out and still get to the designated orbit.

    3. He means an engine-out might not result in total loss of mission, but it might result in failure of some mission objectives.

      As in, the rocket could still put the payload into an off-nominal orbit. In that orbit, Dragon could still achieve many objectives–testing power and heat rejection, comms, GPS, and reentry/recovery–but would have insufficient propellant for the “home run” objective: rendezvous, prox-ops and berthing with the ISS.

      1. I guess the good news is that unlike most of the competition, it could bring the payload back for another try, if there’s anything on board that would be valuable enough to re-use.

  2. At this morning’s Abort Press Conference Ms. Shotwell mentioned that the overpressure was likely from the engine not getting enough fuel. So the turbopump valve is great news. If this is the only cause of the overpressure I suspect they’ll make a go of it on Tuesday.

    Don’t forget the launch delay experienced by the last Atlas V launch… If I recall correctly, it was a bad valve. These things happen and the launch software reacted exactly as designed.

    I would think this test will build confidence in the LV’s signed customer base.

  3. Rand Simberg May 19, 2012 at 3:29 pm

    “In general, and in the future, if there were a tug based at ISS, it could be sent out to retrieve the payload.”

    In general and in the future if there were a highly reliable SSTO (I was a real Delta Clipper fan in the 1990s – even donated free time to work on it) we would not even be having this discussion, but I thought we were talking about right now.

    1. We were talking about SpaceX’s design philosophy. They plan for the future.

      And even with (especially with, because the off-nominal performance is so bad) an SSTO, you’d want a tug at the station to retrieve payloads at lower altitudes.

      1. But in our current reality, even hypothetically granting that the Falcon 9 could place a Dragon (cargo version) into orbit after an engine out; that orbit would not allow rendezvous with the ISS.

        Therefore the mission would not be a success.

        1. Since no one said that it would be a “success” under those circumstances, congratulations on knocking down that big bad straw man.

          But in fact, because it is a “test flight” (you do understand the meaning of that phrase, right?), there are several mission objectives that could still be achieved, as was pointed out. So it would be kind of stupid to dub it a “failure.” Any test flight from which you learn useful things is a success in that sense. The only failed test flight is one that doesn’t advance you at all.

          1. OK, last round for the evening.
            At least half the press are reporting this as if it were an operational mission and Space X has done nothing to dissuade them. If you now want to fall back on it is just a test, fine by me.

            However the two big components of that test (those tests – plural actually) were ISS Prox Ops and ISS Berthing. Under the circumstances we are discussing neither of those objectives would be achieved.

          2. Rand Simberg
            May 19, 2012 at 5:10 pm | #


            Well that settles that debate (don’t know why I didn’t think of saying something witty like that earlier).

            Good night.

          3. I call them the way I see them. How many links do I have to give you (we know you’re lazy about looking them up yourself) in which SpaceX has downplayed expectations about this flight?

            I stand by bullshit.

          4. Well that settles that debate (don’t know why I didn’t think of saying something witty like that earlier).

            I’m sure you had the brain power. You just didn’t have a reason. Merely saying something doesn’t make it so. For example, your response to Bill Miller about “You just have to believe.” was just stupid.

            As Ken Anthony pointed out, this particular mission just doesn’t have the performance margin to take advantage of engine out capability (and as Tom Cuddihy points out, even when you do have the performance margin, it matters when the engine out happens as to whether you can achieve the mission trajectory). One merely need study the Falcon 9’s technological capabilities to determine that.

            You didn’t do that and claimed instead that it was some fanboy reflex even though the capability and the slim performance margins (for this particular margin) both were well explained in the media. This sort of insulting and irrational nonsense, which you repeat throughout this thread, is why you get replies like “bullshit”.

            We don’t need some idiot who can’t be bothered to understand the background of the topic of discussion. Do your homework and bring something to the table. Or just get the hell out.

        2. Couldn’t reply downstream, so I’ll do so here, to your amazingly mendacious (or ignorant) comment that “SpaceX has done nothing to dissuade” the press that this is an operational mission.

          Clearly you didn’t watch yesterday’s press briefing, in which both NASA and SpaceX repeatedly emphasized that this was a test flight. Shotwell, in fact, very candidly predicted a 50/50 chance of launching Saturday morning.

          Which brings me back to my first paragraph: Are you lying, or merely ignorant?

          1. I think “Joe” must be an alias for “Andy Pasztor”. Figures.

            I don’t think even Gaetano Marano would say stuff like this.

        3. The engine out at liftoff capability of the Falcon 9 makes it especially useful for the eventual manned missions. If an Atlas V loses it’s RD-180 or if the engine on the Delta IV fails, you immediately have to go to the launch escape system and hope it works. The Stupid Launch System isn’t much more robust. With the Falcon 9, you have a lot more time. You might be able to abort to a low orbit, get settled, and then do a controlled reentry or you might choose to abort during flight. Those are powerful options that no other booster provides.

    2. In general and in the future if there were a highly reliable SSTO (I was a real Delta Clipper fan in the 1990s – even donated free time to work on it) we would not even be having this discussion, but I thought we were talking about right now.

      But it didn’t happen, Joe. In comparison, a space tug just isn’t hard to put together. Basically, an ion drive and some sort of grapple. We can do that far easier than the SSTO wish list. And you’ll need one down the road whether or not you have an SSTO.

      1. Ion tugs would be useful for some applications, but we’ll need chemical ones too, for more rapid response (particularly crew applications).

      2. “In comparison, a space tug just isn’t hard to put together.”

        And yet after all these decades it never has been and there is currently no funded project to do so.

        Space X job (as far as COTS is concerned) is to deliver cargo reliably to the ISS without wishful thinking about a nonexistent Space Tug.

        1. Space X job (as far as COTS is concerned) is to deliver cargo reliably to the ISS without wishful thinking about a nonexistent Space Tug.

          SpaceX has lots of jobs. They have a business plan.

          Are you being deliberately obtuse?

          1. You missed the “as far as COTS is concerned” I assume.

            Are you being deliberately obtuse?

            Good night.

        2. COTS only involves demonstration flights as I recall, nothing in there about cargo. They just added cargo because the goal of the mission is to berth and test all of the associated rendezvous, berthing and docking procedures.

          Cargo is CRS not COTS. COTS is very specifically development and test.

          Just FYI … joey

        3. “In comparison, a space tug just isn’t hard to put together.”

          And yet after all these decades it never has been and there is currently no funded project to do so.

          And when NASA does decide to make a tug (or perhaps buy an off-the-shelf one), it’s not going to take ten years of R&D and a large number of billions of dollars to crank it out. NASA (and the US) just doesn’t want it enough now. You conflate demand with difficulty.

        4. Space X job (as far as COTS is concerned) is to deliver cargo reliably to the ISS without wishful thinking about a nonexistent Space Tug.

          Just wanted to add a little more. Even if we view such things in this narrow context, why are you whining hypocritically about SSTO? It’s pretty nonexistent as well. If I don’t get to talk about space tugs, then you don’t get to talk about the far less feasible SSTO.

          For a modest increase in cost of COTS, they could add a space tug. They might even be able to squeeze it into the current COTS budget. Sure, they aren’t doing that, but the tug would be a natural extension within the scope of the program and it wouldn’t seriously threaten their budget.

          SSTO would require a lot more such as development of a wholly new launch vehicle.

  4. Didn’t Elon get the memo about the necessity of sacrificing a valve to the engine deities?

  5. I think it’s impressive that they can repair the engine on the pad in such a short time.

  6. It is great that they have the ability to assess performance on the pad and make go/nogo decisions in milliseconds. But they are lucky that this was engine 5 on stage 1 and not engine 1 on stage 2.

    Think of Falcon Heavy with 27 engines…

      1. Ok Rand, here is a question:

        How does he recover the current size stages with a big merlin? With the current stage, he only needs one small merlin to throttle dowm.

        You would almost have to have a smaller engine just for recovery, how could you possibly throttle the big merlin low enough without combustion instabilities in the dense lower atmosphere?

        1. That’s a good question. It’s not clear that the reusability is compatible with reducing number of engines, but maybe he thinks he can do deep throttling.

          1. Wouldn’t he have to throttle the big merlin below 5%? Is that possible in dense air?

          2. I would think he’d design the stage to use a mix of big Merlins and small Merlins, shutting down the big Merlins entirely during recovery and landing. That also simplifies the mounting for the big Merlins, since only the small Merlins would need to gimbal, restart, and throttle.

          3. George. The plans I have seen for Merlin 2 are it is so large it would have to be throttled-down at start on the Falcon Heavy. It is too powerful to launch at 100% thrust. I don’t see where you could put a regular Merlin on those stages as well.

            Remember, Merlin 2 is intended for Elon’s BFR primarily. It is his answer to the F-1 of yore.

  7. Reportedly a check valve failed on E-5. My experience with check valves in general is that they are notoriously unreliable!

      1. Best thing in the world to have on a sewer line. Shit is one thing you don’t want to be coming back up the toilet or sink!

    1. Wasn’t it a check valve that failed in an umbilical on the last F9 launch, causing the combustion in the strongback when the vehicle passed by?

    2. In this futuristic society of rocket men we’ve created, who checks the check valves, and who checks the check valve checkers?

      1. The check valve checker checkers are the check valves themselves.

        It’s called Democracy.

  8. Rand, you’re wrong that F9 can have an engine fail on liftoff and still make it to orbit Ken and Joe are also wrong. It’s not even a margin issue, F9 cannot have an engine fail until well into the flight or else it fails to reach or it. Read Ms. Shotwell’s previous public statements carefully. She is careful never to imply an engine could fail early in flight and F9 still make orbit. Elon’s a little less precise with his statements. Trust the steely-eyed missle woman though.

    1. Tom, you should provide a link but I’ll see if I can find Shotwell’s statement that supports your assertion. However, SpaceX says

      Falcon 9 has nine Merlin engines clustered together. This vehicle will be capable of sustaining an engine failure at any point in flight and still successfully completing its mission.

      Then goes on about the hold down system. Any point in flight doesn’t sound ambiguous to me. I do recall reading that with one engine out they just have to fire the others longer to achieve orbit. They can have two engines out (after 90secs I believe and still make it.)

      Do you have any explicit info that says otherwise? I will try to confirm those items from my swiss cheese memory.

      1. I heard her say in this morning’s press conference that the F9 needs all nine engines running at liftoff.

        Or maybe that’s just for this flight, since there’s no margin.

          1. That makes sense. Before the holds release, an abort is possible, with a chance to repair. After, you’re committed to launch. In many cases it makes sense to delay if you know you’re not going to be at 100% at liftoff. Of course it won’t look good if such delays become common.

          2. I don’t understand why this should be a common cause for a delay. If anything, I would expect that the engineers developing the Merlin engine are going to look at this particular valve that caused the problem with this launch attempt and look at trying to improve its reliability… now that there is something to target for improvement.

            This is precisely the kind of things you want to find during an R&D flight, and that it was found without a loss of vehicle or loss of mission (other than a slight delay) seems to reinforce that the standards being expected were valid parameters to look for.

            Engineers try very hard to avoid problems like this, but sometimes problems simply show up and have to be dealt with. This is precisely one of those occasions.

            If on the other hand there was a problem of inconsistent quality coming from the parts supplier, the inconsistency would be an issue that would be much harder to address. SpaceX makes most of their own parts explicitly because of this issue so precision and consistency of parts is much easier to control.

      2. The “will be capable of sustaining an engine failure” likely refers to the upgraded Merlin1D F9, what they’re now calling “Falcon 9 v1.1”. The current model with Merlin 1Cs (“now called F9 v1.0”) doesn’t have sufficient thrust to lift off the pad…except…very..slowly…if an engine fails at lift off. That increases gravity losses to the point where it cannot make orbit.

        That only matters for C2+ and CRS 1 and 2, after that all F9s are supposed to be V1.1. (source is Elon Musk twitter feed)

        Later in flight, it doesn’t matter so much, in fact shortly after max Q two engines are shut down to keep acceleration below 3 gees.

        I can’t find a link to a public statement laying out the failure mode for the current F9, but it is a fact that has been confirmed on NasaSpaceFlight L2 forums by both NASA and SpaceX engineers. They are very quick to correct unfactual assertions about F9 and Dragon capabilities.

        The weasel wording of both the statements you linked is probably confirmation enough.

        1. You could be right Tom. However, with the Merlin 1C they currently have 4.94MN for 333mt at sea level launch. Take out one engine and you’ve still got 4.39MN of thrust which is still significant. Either way, most of your velocity change comes in the second stage. In talking about reuse, Elon mentions that the payload weight penalty is 1:1 on the upper stage but 10:1 on the first stage (meaning he could add legs and heat shield without that great a penalty and still keep enough fuel to land. I’m sure he means with the upgraded Merlins though.)

          Max-Q happens at about 84 secs. So it’s pretty safe to say somewhere before the first minute they can handle one engine out. When I couldn’t say. I wish they were clearer about it.

          1. I do remember them touting it as a safety feature for crew but again that might just be with the upgraded Merlins. Thinking about it, if 8 of the upgraded Merlins provide as much thrust as 9 of the 1Cs that would pretty much close the question.

            Ok. 9xMerlin 2 is 7.6MN so 8x would be 6.75… way more than enough. You could drop this thing for a negative velocity and still make orbit with one engine out… and wouldn’t that be a ride? 🙂

    2. Shotwell’s statement to COMMITTEE ON SCIENCE, SPACE & TECHNOLOGY

      Falcon 9 is the first U.S. launch vehicle with engine-out capability after liftoff
      since Saturn V.

      Liftoff occurs when the hold downs are released. After liftoff might mean something else… still looking…

      1. I’ll be curious to see what you find. Methinks there will even be an effect as to which engine fails. If you lose #5, thrust is still symmetrical around the vehicle. A failure in any of the others requires shutdown of the opposing engine or a changed thrust vector which costs efficiency.

        1. a changed thrust vector which costs efficiency

          Minor point. This is only true (and to what extent I have no idea) while in an atmosphere. Either in or out of the atmosphere I believe you would gimble through the cg so in space it may look funny (not much if noticeable at all) but would have 100% of the remaining efficiency. I’m still looking but seem to be having some difficulty googling some of the interviews I know exist. I share your curiosity in seeing some exact quotes.

  9. Seems like Americans used to celebrate mavericks–the guys who defied the odds, the Davids who defeated the Goliaths with “pluck and courage” as they say.

    Obviously those days are long gone. Now it’s more fashionable to paint the successful maverick as a conman. What truly amazes me is the number of people in our little pro-space population who go after SpaceX in this way, and treat SpaceX enthusiasts or defenders with such contempt.

    Robert Heinlein’s ashes are making tight little whirlpools in the ocean.

    1. Don’t be dismayed by what may be little more than selection bias. People who write things that everybody agrees with get no response. People who write something ignorant get a correction, making the ignorant thread twice as large. People who write something wilfully ignorant can spawn endless back and forth arguments. This doesn’t mean that most people are wilfully ignorant, just that the exceptions tend to be louder.

      1. You make a good point except the willfully ignorant seem to be very much on display especially at the more popular venues and often get no correction at all.

        There seems to be a high correlation with register to comment sites as well.

    2. Seems like Americans used to celebrate mavericks–the guys who defied the odds, the Davids who defeated the Goliaths with “pluck and courage” as they say.

      Not if they are eating your lunch…

    3. Those being challenged and displaced by mavricks have always hated those mavricks. Do you think the blacksmiths, livery stable owners, buggy whip makers, etc. applauded those pioneers of the automobile? Does “get a horse” ring a bell?

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