Author Topic: Engine Out Emergency Landing  (Read 10611 times)

Offline dorkmo

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Engine Out Emergency Landing
« on: 04/11/2016 06:40 am »
If the first stage had an engine failure or two and would be unable to make orbit could the the entire rocket (w/ payload) land on the ASDS or RTLS.

I assume the weight on the legs would be the first obvious thing to consider.

Would the grid fins have less control?

Too top heavy?

Since they were able to program the dragon to survive a rare case, perhaps it'd be worth programming to save f9 in an engine out?
« Last Edit: 04/11/2016 06:43 am by dorkmo »

Online CameronD

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Re: Engine Out Emergency Landing
« Reply #1 on: 04/11/2016 07:19 am »
F9 is designed to continue it's mission with one engine out.
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline Stan-1967

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Re: Engine Out Emergency Landing
« Reply #2 on: 04/11/2016 07:20 am »
No, the entire rocket could not land on the ASDS or RLTS.  If failure was a certainty, maybe the S1 core could make it back for a RTLS or DPL landing, and if the payload was a Dragon V2, maybe it could land on the ASDS.  It would all depend on the trajectory and positioning of the ASDS. 

More than likely the flight software would still try to get the payload to orbit, even if it is a lower orbit than intended, and that would probably mean all propellant reserves would be used in that effort, not in ditching payload and trying to save the rocket.

You do realize customers would hate SpaceX if they dumped the payload to save the Falcon?

Wasn't there another famous Falcon that dumped it's cargo of spice at the first sight of trouble, and the owner of that spice, some nasty slug,  hunted down the captain and had him frozen in carbonite?

Offline Kaputnik

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Re: Engine Out Emergency Landing
« Reply #3 on: 04/11/2016 08:00 am »
The empty first stage and its legs almost certainly cannot handle the additional weight of a fully fuelled second stage and payload. As an absolute minimum you would need a second stage propellant dump capability. IMHO none of this is remotely likely for this generation of RLV.

I actually thought that this topic, from its title, might be speculating about performing a recovery of the first stage when the centre engine is lost. To which, admittedly unasked, question I would suggest- yes, it might just be within a whisker of the possible to switch to using two opposing engine instead and land with a more aggressive hoverslam. It all comes down to the minimum impulse and start/shutdown transients of the Merlins, none of which are public information.
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Offline The Amazing Catstronaut

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Re: Engine Out Emergency Landing
« Reply #4 on: 04/11/2016 08:06 am »
They have attempted aggressive three engine low altitude burns before. Two should be doable, but the chance of success goes down significantly.
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Offline R7

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Re: Engine Out Emergency Landing
« Reply #5 on: 04/11/2016 08:08 am »
If the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.
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Offline hamerad

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Re: Engine Out Emergency Landing
« Reply #6 on: 04/11/2016 08:27 am »
I would doubt the stability of the rocket on the barge with 2nd stage and payload attached, since AIUI the centre of gravity would be shifted much higher. So as others have said they'd probably just forgo recovery.

Offline su27k

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Re: Engine Out Emergency Landing
« Reply #7 on: 04/11/2016 12:20 pm »
If the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.

I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.

Offline Jim

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Re: Engine Out Emergency Landing
« Reply #8 on: 04/11/2016 01:44 pm »
If the first stage had an engine failure or two and would be unable to make orbit could the the entire rocket (w/ payload) land on the ASDS or RTLS.

I assume the weight on the legs would be the first obvious thing to consider.

Would the grid fins have less control?

Too top heavy?

Since they were able to program the dragon to survive a rare case, perhaps it'd be worth programming to save f9 in an engine out?

The ASDS doesn't have the capability to handle a loaded second stage.

The first stage likely can't handle the weight of the second stage during touchdown

The spacecraft can't handle the marine environment and it would be out of contact with its control center and would be in a hazardous state.

Offline Jim

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Re: Engine Out Emergency Landing
« Reply #9 on: 04/11/2016 01:45 pm »
If the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.

I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.

Save a $40 million stage vs a $200 million spacecraft.

Any ways the launch vehicle doesn't know it is doomed.
« Last Edit: 04/11/2016 01:46 pm by Jim »

Offline JamesH65

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Re: Engine Out Emergency Landing
« Reply #10 on: 04/11/2016 02:11 pm »
If the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.

I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.

Save a $40 million stage vs a $200 million spacecraft.

Any ways the launch vehicle doesn't know it is doomed.

It must know if all its engines are still running. If it knows that then it would know if there is enough thrust to make orbit. If there isn't, does it just just destruct, or could decide to stage itself, separate from the second stage, (if carrying Dragon, eject the Dragon as well for parachute landing - we know it can do that), try and land the first stage, crashing the second stage? I certainly cannot see any way of saving the second stage, but 1stage and Dragon might be possible.

Of course, reliability of the first stage and its redundant engines make this a very unusual circumstance.

Offline Jim

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Re: Engine Out Emergency Landing
« Reply #11 on: 04/11/2016 02:44 pm »
It must know if all its engines are still running. If it knows that then it would know if there is enough thrust to make orbit. If there isn't, does it just just destruct, or could decide to stage itself, separate from the second stage, (if carrying Dragon, eject the Dragon as well for parachute landing - we know it can do that), try and land the first stage, crashing the second stage? I certainly cannot see any way of saving the second stage, but 1stage and Dragon might be possible.

Of course, reliability of the first stage and its redundant engines make this a very unusual circumstance.

It doesn't use thrust, it uses acceleration.  Look at the Atlas V, it is didn't know it if was going to make it.  It just kept trying.  Destruct only happens if it goes off course.

Offline Kaputnik

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Re: Engine Out Emergency Landing
« Reply #12 on: 04/11/2016 02:55 pm »
If the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.

I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.

It seems pretty unlikely that a vehicle which had launched with sufficient reserves to attempt recovery suffered so many failures that it could not make orbit even using all of that margin, and yet was somehow still functional. You would need multiple independent engine failures that did not include the centre engine. Anybody versed in statistics care to work out the chances?
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Offline mme

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Re: Engine Out Emergency Landing
« Reply #13 on: 04/11/2016 02:58 pm »
If the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.

I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.

Save a $40 million stage vs a $200 million spacecraft.

Any ways the launch vehicle doesn't know it is doomed.

It must know if all its engines are still running. If it knows that then it would know if there is enough thrust to make orbit. If there isn't, does it just just destruct, or could decide to stage itself, separate from the second stage, (if carrying Dragon, eject the Dragon as well for parachute landing - we know it can do that), try and land the first stage, crashing the second stage? I certainly cannot see any way of saving the second stage, but 1stage and Dragon might be possible.

Of course, reliability of the first stage and its redundant engines make this a very unusual circumstance.
Propellent used for recovery, especially for RTLS, would provide enough fuel for a crazy long burn.  Depending when the engine loss occurred I suspect it could lose more than one engine and still eventually make up most the delta-v.
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Offline JamesH65

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Re: Engine Out Emergency Landing
« Reply #14 on: 04/11/2016 03:43 pm »
If the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.

I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.

Save a $40 million stage vs a $200 million spacecraft.

Any ways the launch vehicle doesn't know it is doomed.

It must know if all its engines are still running. If it knows that then it would know if there is enough thrust to make orbit. If there isn't, does it just just destruct, or could decide to stage itself, separate from the second stage, (if carrying Dragon, eject the Dragon as well for parachute landing - we know it can do that), try and land the first stage, crashing the second stage? I certainly cannot see any way of saving the second stage, but 1stage and Dragon might be possible.

Of course, reliability of the first stage and its redundant engines make this a very unusual circumstance.
Propellent used for recovery, especially for RTLS, would provide enough fuel for a crazy long burn.  Depending when the engine loss occurred I suspect it could lose more than one engine and still eventually make up most the delta-v.

That would be my assessment too tbh.

Offline sevenperforce

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Re: Engine Out Emergency Landing
« Reply #15 on: 04/11/2016 03:56 pm »
I actually thought that this topic, from its title, might be speculating about performing a recovery of the first stage when the centre engine is lost. To which, admittedly unasked, question I would suggest- yes, it might just be within a whisker of the possible to switch to using two opposing engine instead and land with a more aggressive hoverslam. It all comes down to the minimum impulse and start/shutdown transients of the Merlins, none of which are public information.
My thought as well.

One point is that a two-engine suicide burn conserves fuel far better than a single-engine burn without being nearly so aggressive as a three-engine landing. They'll need 2-3 engines for the high-velocity returns, so if they get those down to a science then I can see them using that arrangement for even low-velocity landings to save propellant and to extend the life of the central engine.

Offline sewebster

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Re: Engine Out Emergency Landing
« Reply #16 on: 04/11/2016 04:39 pm »
One point is that a two-engine suicide burn conserves fuel far better than a single-engine burn without being nearly so aggressive as a three-engine landing. They'll need 2-3 engines for the high-velocity returns, so if they get those down to a science then I can see them using that arrangement for even low-velocity landings to save propellant and to extend the life of the central engine.

I believe this has been discussed elsewhere, but there may be an issue with gimbal or throttle range if you don't use the centre engine.

Offline R7

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Re: Engine Out Emergency Landing
« Reply #17 on: 04/11/2016 04:45 pm »
I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.

IIRC SpaceX has advertized that Falcon 9 has single engine out capability from almost T-0 and twin engine out capability later in S1 flight. Don't know if this includes using the landing propellant reserve.

Anyway, it appears the really hairy situation where one might save only S1, if lucky, starts with 3+ engine out scenarios. The odds for such event are very low. Keep in mind that the odds aren't just any three simultaneous engine failures, but three benign engine failures. Making a lot of planning and guidance software tweaking for such unlikely event where the least worst possible outcome is to save 1/3 defunct S1 while S2 and non-Dragon payload is lost does not seem worth the effort.

Say you have three engine out event 15 second after liftoff. What now? You might not even make it to the barge. For RTLS you'd have to loiter somewhere to burn off the prop. Would Cape officials even allow attempting RTLS with crippled stage? Suppose you somehow manage to get rid off S2, payload and land the S1. You have a stage that is most likely a write-off anyway and unhappy customer. To me "rescued" S1 while the hundreds million comsat is at the bottom of the sea is just bad PR and salt to customer's wounds, leaving "would sacrificing S1 have saved the mission" doubts in everyone's minds.
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Offline Doesitfloat

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Re: Engine Out Emergency Landing
« Reply #18 on: 04/11/2016 04:48 pm »
For their engine out on landing procedure, I think we hear it in the audio of the landing. The FTS was safed after the rocket was on the ship.  IRRC they used to safe it soon after separation from the 2nd stage. 
Perhaps this give the rocket a chance to use the FTS in the event of bad landing burn. They would rather have falcon rain than falcon lawn dart.

Offline Rocket Science

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Re: Engine Out Emergency Landing
« Reply #19 on: 04/11/2016 05:49 pm »
For their engine out on landing procedure, I think we hear it in the audio of the landing. The FTS was safed after the rocket was on the ship.  IRRC they used to safe it soon after separation from the 2nd stage. 
Perhaps this give the rocket a chance to use the FTS in the event of bad landing burn. They would rather have falcon rain than falcon lawn dart.
Confirmed FTS was safed after landing. Which means destruct command is available, another member disagreed with me on previous "hole punch" landing attempt which could have minimized damage to the barge...
« Last Edit: 04/11/2016 06:18 pm by Rocket Science »
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Offline sevenperforce

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Re: Engine Out Emergency Landing
« Reply #20 on: 04/11/2016 07:20 pm »
One point is that a two-engine suicide burn conserves fuel far better than a single-engine burn without being nearly so aggressive as a three-engine landing. They'll need 2-3 engines for the high-velocity returns, so if they get those down to a science then I can see them using that arrangement for even low-velocity landings to save propellant and to extend the life of the central engine.

I believe this has been discussed elsewhere, but there may be an issue with gimbal or throttle range if you don't use the centre engine.
Do the SL-optimized Merlin 1Ds gimbal?

Definitely an issue with throttle range; a much hotter suicide burn.

Offline Kaputnik

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Re: Engine Out Emergency Landing
« Reply #21 on: 04/11/2016 07:42 pm »
One point is that a two-engine suicide burn conserves fuel far better than a single-engine burn without being nearly so aggressive as a three-engine landing. They'll need 2-3 engines for the high-velocity returns, so if they get those down to a science then I can see them using that arrangement for even low-velocity landings to save propellant and to extend the life of the central engine.

I believe this has been discussed elsewhere, but there may be an issue with gimbal or throttle range if you don't use the centre engine.
Do the SL-optimized Merlin 1Ds gimbal?

Definitely an issue with throttle range; a much hotter suicide burn.

Yes. That's how the first stage is controlled.
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Offline sevenperforce

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Re: Engine Out Emergency Landing
« Reply #22 on: 04/11/2016 08:10 pm »
Do the SL-optimized Merlin 1Ds gimbal?

Definitely an issue with throttle range; a much hotter suicide burn.

Yes. That's how the first stage is controlled.
I had assumed it was controlled with cold gas RCS.

Offline Kaputnik

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Re: Engine Out Emergency Landing
« Reply #23 on: 04/11/2016 09:24 pm »
Do the SL-optimized Merlin 1Ds gimbal?

Definitely an issue with throttle range; a much hotter suicide burn.

Yes. That's how the first stage is controlled.
I had assumed it was controlled with cold gas RCS.

No LV of the size of F9 would do that. Cold gas thrusters are pretty inefficient and puny compared to gimballing your engines.
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Offline RanulfC

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Re: Engine Out Emergency Landing
« Reply #24 on: 04/12/2016 09:12 pm »
Unless the other engines have extra starter-fluid tanks over and above the boost-back burn then no it can't recover with the center engine out. Unless they've changed the design significantly each engine has it's own tank and only the center engine has more than two 'starts' worth of fluid.

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Offline GabrielP

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Re: Engine Out Emergency Landing
« Reply #25 on: 04/12/2016 09:21 pm »
Unless the other engines have extra starter-fluid tanks over and above the boost-back burn then no it can't recover with the center engine out. Unless they've changed the design significantly each engine has it's own tank and only the center engine has more than two 'starts' worth of fluid.

Randy

Unless I'm missing something, aren't there at least 3 starts for the 3 engines that participate in the landing maneuvers?
1. liftoff
2. boostback
3. entry

Then a 4th for the center engine.

Offline Jcc

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Re: Engine Out Emergency Landing
« Reply #26 on: 04/16/2016 08:50 pm »
Unless the other engines have extra starter-fluid tanks over and above the boost-back burn then no it can't recover with the center engine out. Unless they've changed the design significantly each engine has it's own tank and only the center engine has more than two 'starts' worth of fluid.

Randy

SES9 did a 3-engine landing burn (not successfully). If the center engine is out, it seems plausible that a 2 engine landing could be possible. It would take modelling that scenario in the landing software, and maybe require a hardware mod. Probably a low priority since the Merlin 1D is proving to be quite reliable.

With any other engine out, the landing may still be forced to use less fuel, which could mean coming in hotter and using a 2-3 engine landing  burn.
« Last Edit: 04/16/2016 08:53 pm by Jcc »

Offline CorvusCorax

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Re: Engine Out Emergency Landing
« Reply #27 on: 04/16/2016 10:42 pm »
It stands to reason that with enough margins to land S1, even a multi engine failure on ascent can still make orbit at the expense of the landing ability - except if you loose so much thrust so early in ascent (basically just past T-0) that you end up with a thrust to lift ration < 1.0. In that case you definitely can't make orbit regardless of reserves.

But in that case, the rocket would also be doomed either way, it cannot land with insufficient thrust to overcome gravity and would just fall back down on the pad Atlas 1965 style.

Also, if you have a heavily damaged S1, why even try to save the S1 - especially if you can still at least attempt a last effort try to somehow reach orbit. The S1 is usually worth a lot less than the payload currently. (Although that might change in the mid to long term future if launch prices come down big time)

I see only one reason why you'd want the malfunctioning booster back in one piece: To be able to trouble shoot what went wrong based on actual hardware instead of a cloud of debris on the ocean floor. But the chance of that ever happening are so remotely slim, it wouldn't even be worth coding the fallback behaviour for it.

Then again, they also thought that about Dragon 1 parachute release after booster failure - before CRS-7


Let's say, if there really ever is a case where a booster failure leads to a situation where the payload was doomed, and the booster could have been saved, and they find out they really needed the booster to fix the issue that caused it, I guess it's then that they will start looking into ways to get it back if that happens again - but not before that unlikely case even materializes - or the ratio of booster to payload value changes drastically.


Offline RanulfC

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Re: Engine Out Emergency Landing
« Reply #28 on: 04/19/2016 08:04 pm »
SES9 did a 3-engine landing burn (not successfully).

Everything I saw said it was one engine for landing and not three, and what they did was "burp" the three engines to test the retro-burn sequence. I believe they now carry another charge for all three engines for the supersonic retro burn for RTLS but if the center engine fails at that point they will not be able to land because they still can't restart the other two engines for lack of starting charges. About the only scenario that would fit here is if they were going for RTLS and had a malfunction and had pre-planned and placed the barge "just-in-case". In that case you eliminate the boost back burn, (but you'll probably have to dump propellant to get down to the proper weight) and then you can use that charge to re-start the other two engines but I don't see how you'd control the landing properly.

I'd call this at least a semi-good reason to come up with another, more reusable ignition method though :)

Quote
If the center engine is out, it seems plausible that a 2 engine landing could be possible. It would take modelling that scenario in the landing software, and maybe require a hardware mod. Probably a low priority since the Merlin 1D is proving to be quite reliable.

"Plausible" is very far from possible or even viable :) Twice the minimum thrust, both axis of thrust slightly out of line with the center-line, double the propellant use, and VERY different landing dynamics to touchdown.

Quote
With any other engine out, the landing may still be forced to use less fuel, which could mean coming in hotter and using a 2-3 engine landing  burn.

More, not less propellant since you're running more engines. Any other engine out on launch won't be an issue, they only use three engines for everything after staging. Landing shouldn't be effected by any failure of an engine that are not the three used for boost-back, retro-burn and landing unless it damages those engines and then you're probably looking at a LOV situation rather than any attempt at landing.

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline envy887

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Re: Engine Out Emergency Landing
« Reply #29 on: 04/19/2016 10:33 pm »
More, not less propellant since you're running more engines. Any other engine out on launch won't be an issue, they only use three engines for everything after staging. Landing shouldn't be effected by any failure of an engine that are not the three used for boost-back, retro-burn and landing unless it damages those engines and then you're probably looking at a LOV situation rather than any attempt at landing.

Randy

The math is posted elsewhere in this sub-forum, but a 2 or 3 engine landing does use less fuel due to a much shorter burn time leading to lower gravity losses.

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