Author Topic: SpaceX: Merlin 1D thread  (Read 520690 times)

Offline mlindner

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Re: SpaceX: Merlin 1D thread
« Reply #620 on: 03/23/2013 01:40 am »
Better performance margin if you fly to depletion for the first stage... Otherwise, you're leaving some margin behind when you stage.

No reason to not fly to depletion, agreed. There is no reason that flying to depletion excludes having a closed loop system measuring acceleration and engine status and throttling as needed.
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Offline mlindner

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Re: SpaceX: Merlin 1D thread
« Reply #621 on: 03/23/2013 01:44 am »
All of which I thought was irrelevant: doesn't the Falcon just have one (redundant) control system on the 2nd stage controlling the whole vehicle?

First I've heard of this. I was under the impression they have a computer per stage. Each one is triply redundant (with each element having two computers each voting against each other) linux based embedded system.

At the very least we know they have a computer per stage in F9 v1.1.
« Last Edit: 03/23/2013 01:45 am by mlindner »
LEO is the ocean, not an island (let alone a continent). We create cruise liners to ride the oceans, not artificial islands in the middle of them. We need a physical place, which has physical resources, to make our future out there.

Online LouScheffer

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Re: SpaceX: Merlin 1D thread
« Reply #622 on: 03/23/2013 11:54 am »
Would 7 @ 112.5% be worth trying if there was reason to believe the engines could probably hack those conditions *once* and stay close enough to profile to prevent loss of mission? Think in terms of red lining a racing engine. You can probably get away with exceeding the red line once, but don't try it on a regular basis. All of this is modulo the question of how much can they overboost and what does the failure probability look like when doing so.
Of course this is worth trying if the alternative is certain doom.  As the accident report said where a pilot did not simply jam the throttles full forward, when redline thrust was not enough:  "Who was he trying to save the engines for?  The accident investigators?"

Online ugordan

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Re: SpaceX: Merlin 1D thread
« Reply #623 on: 03/23/2013 11:57 am »
At the very least we know they have a computer per stage in F9 v1.1.

We know this from where?

Online Silmfeanor

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Re: SpaceX: Merlin 1D thread
« Reply #624 on: 03/23/2013 12:00 pm »
At the very least we know they have a computer per stage in F9 v1.1.

We know this from where?


This follows from the fact that they'll try restarts on the frst stage, and the 2nd stage needs guidance aswell. So, a minimum of 1 computer per stage.

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Re: SpaceX: Merlin 1D thread
« Reply #625 on: 03/23/2013 12:07 pm »
For the restart tests, yes, they'll need guidance for the first stage, but it doesn't follow from that that every v1.1 has/will have 2 sets of computers. Certainly not 2 complete sets of triple string computers as mlindner is asserting. I would be surprised if the restart tests use anything more than single string on the 1st stage.

Offline baldusi

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Re: SpaceX: Merlin 1D thread
« Reply #626 on: 03/23/2013 01:38 pm »
8 1Ds at 112.5% thrust should be the same total thrust and propellant flow rate as 9 at 100%, so immediately throttling the remaining 8 up, if possible, after an engine out should avoid any performance loss. Or is this wrong?
What if the way to increase the thrust is to change the O/F ratio?

Not good if you are going to throttle a lot - you want oxidizer and fuel to be depleted at the same time.
That was my point. That even with increased thrust on an engine out situation you might not end with the same MECO point. You might be oxidizer limited, for example. I'm not stating one way or the other since I ignore who the Merlin 1D throttles. But I'm stating that flat out same situation might not happen.

Offline Robotbeat

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Re: SpaceX: Merlin 1D thread
« Reply #627 on: 03/23/2013 04:39 pm »
For the restart tests, yes, they'll need guidance for the first stage, but it doesn't follow from that that every v1.1 has/will have 2 sets of computers. Certainly not 2 complete sets of triple string computers as mlindner is asserting. I would be surprised if the restart tests use anything more than single string on the 1st stage.
Well, the first v1.1 will have two sets of computers (redundancy level really doesn't matter too much in this discussion), and they likely plan to do similar tests on later flights before going entirely to their future recovery plan. So why would you design multiple different types of v1.1, one with two computers another with one? The differences in avionics integration would make it not worth it, the differences in software, etc. The cost of the hardware itself wouldn't be that great compared to the cost of having multiple versions of the avionics set. Once it's designed for two computers, they wouldn't go back without a major change.
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Re: SpaceX: Merlin 1D thread
« Reply #628 on: 03/23/2013 04:48 pm »
That's like saying they put parachutes in the first F9 so why not keep putting them in all other vehicles as well, to avoid multiple configurations. Recovery systems had logic as well. 1st stage guidance and 2nd stage guidance shouldn't really be linked in a way that it counts as an integration problem if you *remove* 1st stage guidance when you don't need it. It's supposed to kick in only after staging and be completely inactive until then. At least that's what the customers would like, I'd think.

Offline meekGee

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Re: SpaceX: Merlin 1D thread
« Reply #629 on: 03/23/2013 05:12 pm »
Elon said they want to start recovering stages by 2015

Before they fly those, they'd want to experiment with re-entering standard F9 1.1 stages, as many times as possible.

If those were dedicated tests, then "possible" means "financially possible" and so maybe 2-3 times tops.

But if they can get those tests for free by making the standard 1.1 as close ot the F9R as possible, why not?

They might even collect some of the hardware to get a statistical picture of post-launch damage, and since they'll likely not be able to recover the first few experiments, I think the next year and a half worth of F9 launches will be mostly with recovery attempts.
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Offline meekGee

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Re: SpaceX: Merlin 1D thread
« Reply #630 on: 03/23/2013 05:31 pm »
That's like saying they put parachutes in the first F9 so why not keep putting them in all other vehicles as well, to avoid multiple configurations. Recovery systems had logic as well. 1st stage guidance and 2nd stage guidance shouldn't really be linked in a way that it counts as an integration problem if you *remove* 1st stage guidance when you don't need it. It's supposed to kick in only after staging and be completely inactive until then. At least that's what the customers would like, I'd think.

And actually, looking back about a couple of month, we had a fierce argument here where I argued that they should standardize the pitch-over/restart/avionics hardware on all 1.1s, to facilitate testing.

As always it was the case of "you don't know anything", "cool-aid", and "customers won't allow it" - since they hate configuration changes.

So we had a trade-off: SpaceX wants to experiment with reentry, customers want a stable configuration.

Now that we know (btw, was it ever corroborated?  I think it is still a single-source bit of knowledge) that the first flight will already carry all of the hardware, there's no longer a trade-off - everyone wants the same thing.

As for the first stage avionics, I wouldn't make them "turn on" after separation.  If they're not driving the combined stack, I'd at least make them fully awake, keeping track of all the data, and in independent communication with the ground - again, to get as much development done as early as possible, which is what SpaceX has always been doing.
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Offline joek

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Re: SpaceX: Merlin 1D thread
« Reply #631 on: 03/23/2013 05:49 pm »
So we had a trade-off: SpaceX wants to experiment with reentry, customers want a stable configuration.

Customers want to reduce risk.  A stable configuration is one way; greater margins is another way.

Offline cambrianera

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Re: SpaceX: Merlin 1D thread
« Reply #632 on: 03/23/2013 05:52 pm »
Off topic.
Please go on the right topic: http://forum.nasaspaceflight.com/index.php?topic=21923.0
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Offline russianhalo117

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Re: SpaceX: Merlin 1D thread
« Reply #633 on: 03/24/2013 12:47 am »
Thank you Chris for oversight on the thread. I lost my reading glasses a few days ago and am having difficulties with reading and writing.

Maybe a possible 1E will come out of the long wait of the 1D?

Even the "Is  Falcon 1E dead?" thread is dead.  (No, he's just resting.  Dead!  Dead, I tell you!)

There must be a bunch of Merlin 1C's around and they have the F1 launch erector and pad available from Kwaj which they could set up at CCAFS or VAFB, but SpaceX said they would not sell any Falcon 1 rockets.  I was disappointed.  They "built it" but "they did not come".   The Merlin 1D just makes it less likely. SpaceX is not going to the effort of creating a whole new rocket that is not on their main path.
F1 programme Merlin-1C's were transferred to the F9 programme quite a while ago, so the answer to the beginning of post is a confirmed no.

Offline llanitedave

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Re: SpaceX: Merlin 1D thread
« Reply #634 on: 03/24/2013 01:35 am »
Thank you Chris for oversight on the thread. I lost my reading glasses a few days ago and am having difficulties with reading and writing.

Maybe a possible 1E will come out of the long wait of the 1D?

Even the "Is  Falcon 1E dead?" thread is dead.  (No, he's just resting.  Dead!  Dead, I tell you!)

There must be a bunch of Merlin 1C's around and they have the F1 launch erector and pad available from Kwaj which they could set up at CCAFS or VAFB, but SpaceX said they would not sell any Falcon 1 rockets.  I was disappointed.  They "built it" but "they did not come".   The Merlin 1D just makes it less likely. SpaceX is not going to the effort of creating a whole new rocket that is not on their main path.
F1 programme Merlin-1C's were transferred to the F9 programme quite a while ago, so the answer to the beginning of post is a confirmed no.

I don't think the question was about the Falcon 1E, but about about a possible Merlin 1E, a hypothetical follow-on to the Merlin 1D.

I don't know if they're going to be happy with that engine and make it mainstream for a while, or if they have a continuous development program going on with it.
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Offline spectre9

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Re: SpaceX: Merlin 1D thread
« Reply #635 on: 03/24/2013 01:40 am »
Has a Merlin 1D ever failed (exploded) in testing?

If one did would SpaceX disclose it?


Offline meekGee

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Re: SpaceX: Merlin 1D thread
« Reply #636 on: 03/24/2013 02:18 am »
Has a Merlin 1D ever failed (exploded) in testing?

If one did would SpaceX disclose it?
"If engines are not exploding, you are not testing hard enough" ?
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Offline 8900

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Re: SpaceX: Merlin 1D thread
« Reply #637 on: 03/24/2013 02:50 am »
Thank you Chris for oversight on the thread. I lost my reading glasses a few days ago and am having difficulties with reading and writing.

Maybe a possible 1E will come out of the long wait of the 1D?

Even the "Is  Falcon 1E dead?" thread is dead.  (No, he's just resting.  Dead!  Dead, I tell you!)

There must be a bunch of Merlin 1C's around and they have the F1 launch erector and pad available from Kwaj which they could set up at CCAFS or VAFB, but SpaceX said they would not sell any Falcon 1 rockets.  I was disappointed.  They "built it" but "they did not come".   The Merlin 1D just makes it less likely. SpaceX is not going to the effort of creating a whole new rocket that is not on their main path.
F1 programme Merlin-1C's were transferred to the F9 programme quite a while ago, so the answer to the beginning of post is a confirmed no.

I don't think the question was about the Falcon 1E, but about about a possible Merlin 1E, a hypothetical follow-on to the Merlin 1D.

I don't know if they're going to be happy with that engine and make it mainstream for a while, or if they have a continuous development program going on with it.
As far as I know there is no plan of (Merlin) 1E, no one has talked about it so I assume it doesn't exist
There are talks of Elon abut Merlin 2 (large engine, one is enough to power the F9 first stage but the rocket will also lose engine out capability) and Raptor cryogenic upper stage, maybe what he means is Merlin 2 instead of 1E

Offline Okie_Steve

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Re: SpaceX: Merlin 1D thread
« Reply #638 on: 03/24/2013 02:57 am »
"If engines are not exploding, you are not testing hard enough" ?
Yep, failure tells you where the boundaries really are as opposed to where you *think* they are. I don't expect Spacex to tell us where those boundaries are either since current appearances to the contrary they might decide to iterate to a Merlin 1E at some point if it looks worth while enough. In any case they don't want to give away any competitive advantages. Which comes back to the question of how far might it be possible to push a kero-lox engine like the Merlin 1D in a do-or-die situation? Anyone have any guess based on prior art? If the answer is 1-2% vs 10-20% the number of useful scenerios changes greatly.

Offline meekGee

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Re: SpaceX: Merlin 1D thread
« Reply #639 on: 03/24/2013 03:05 am »
Regarding a hypothetical Merlin 1E, maybe someone remembers - were there any rumors about the 1D before it was revealed?  If yes, how long before?

I wouldn't be surprised if they iterated again, since a) re-usability is coming and they want engines to last many cycles and b) they will soon start having engines recovered after flight, and there will a lot to learn from them towards future iterations.

EDIT: D, not E.
« Last Edit: 03/24/2013 07:14 am by meekGee »
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