Author Topic: SpaceX: General Falcon and Dragon discussion (Thread 3)  (Read 761324 times)

Offline MP99

EDIT: I agree that SpaceX really needs to transition into operations mode.

Hell, yeah.

NB this was part of response to:-

While I'm glad there is a useful growth head in basic designs, I'm concerned that everything they do requires upgrades. Seems like a recipe for endless R&D spending spree without operations volume to back it up. If they started ramping Merlins up after launching 8 F-9s, it would seem more comfortable.

P.S. I'm also afraid that an endless procession of one-off rockets, each a little different, cannot be good for expected reliability and insurance premiums.

Offline baldusi

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #441 on: 03/20/2011 09:43 pm »
Why do they need to move turbopump prodution away from a mature and experienced producer to their own internal "start-up" to become "operational"? Save money, OK. Guaranteed to be just as reliable? Well, how many 1D flights do they need before they've proved that?
I don't really know, but I can speculate. The turbopumps have to supply enough extra fuel to achieve the increase in thrust. That would need upgraded turbopumps. To upgrade is to actually do a new turbopump. I don't know if the wholly designed it inhouse or licensed the BN one and then improved on that. But they still needed new ones. Don't forget that they already do a whole lot of inhouse production.
The truth is that high quality production is not that difficult to do. It's expensive and requires a very strict QA. In particular, you have to be very picky about the suppliers. Some times, might be even cheaper to do it yourself than to do all the necessary controls to your supplier.
In SpaceX case, they already have a world class factory and QA team. So adding a new piece might not be such a problem. And it helps them streamline their cashflow. They already have to pay for the machines, tooling, machinists and quality engineers. Once you have the design and specifications, you just need a good materials supplier (that they already must have) and the quality control equipment for such materials (which most probably already have).
So it's just an extra set of pieces to machine, control, assemble and test.

Offline Halidon

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #442 on: 03/20/2011 10:56 pm »
Just re-posting Nut's post from earlier in case it was buried before people could look at it:
How about a little history of the Merlin engine and its evolution.

First is the Merlin 1a, an all-ablative (that includes the combustion chamber, throat and nozzle), gas generator turbopump fed hydrocarbon engine with a pintle injector. It flew twice, failing on its first flight (F1 f1) due to a fuel leak and subsequent fire. The next flight (F1 f2) it performed nominally and was then retired. SpaceX had planned to add a higher performance turbopump, increasing overall thrust, for use on Falcon 9 launches. This is the Merlin 1b, but before it was ever used, SpaceX decided ablative was too much of a hassle, and switched to a regenerativley-cooled design. This is the Merlin 1c. It has a channel wall cooled combustion chamber and throat, and a tube wall cooled nozzle. It first flew on F1 f3, and was de-tuned to provide the same thrust  as a Merlin 1a (so as not require a redesign of the Falcon 1) and even though it performed nominally (and 19 Merlin1c since), the failure to account for the residual thrust inherent to its design doomed this mission as well. This new regen configuration allows for a higher chamber pressure (and therefore more thrust) but its early generation turbopump, manufactured by Barber-Nichols, under performs for this task.

Ever since the switch to regen, SpaceX's publicly announced plan was to eventually replace this tubopump with one optimized for the-now-regen cooled design, and to increase the diameters of propellant feedlines accordingly (but AFAIK no changes to tank sizes). They reffered to this as BLOCK II. BLOCK II is Merlin 1d, they only recently starting calling it such.

Now that there is some evidence that SpaceX has decided to bring turbopump design and production in-house, and that Max Vozhoff has stated that Merlin 1d will have "a lower part count" (read: simpler, optimized) perhaps this explains their decision to rename the Merlin 1c BLOCK II as Merlin 1d.

To add to the confusion, we have Falcon9 BLOCK II. To over simplify: Falcon9 + Merlin 1d = Falcon9 BLOCK II (again, AFAIK, no tank stretch)

And that is why Merlin 1d and Falcon 9 BLOCK II are the "low hanging fruit" on the SpaceX family tree, NOT Falcon 1e. Falcon 1e = Merlin 1d + new first stage + new fairing + needs better launch site.

Once SpaceX gets Falcon 9 BLOCK II, then they are that much closer to Falcon Heavy common core. That leaves the launch site, Vandenberg. Build it for Falcon Heavy but make it backward-compatible for Falcon 9 and even Falcon 1e, and then decide if the time is right to put F1e on the front burner again.

Anyone thinking "Falcon 1e is dead" or "Merlin 2 is alive" is staring at the tea leaves too hard...

Offline baldusi

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #443 on: 03/20/2011 11:02 pm »
There was a discussion by someone from SpaceX that stated that a pintle injector and an ablatively cooled chamber was a bad combination. Basically, the pintle injector creates a ring of high temperature that would need a lot more material to be ablatively cooled. It's easier to use a regen chamber. And once you go regen, it's easier go the whole way.

Offline Robotbeat

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #444 on: 03/21/2011 12:44 am »
...
The truth is that high quality production is not that difficult to do. It's expensive and requires a very strict QA. In particular, you have to be very picky about the suppliers. Some times, might be even cheaper to do it yourself than to do all the necessary controls to your supplier.
...
Not just cheaper, but sometimes faster, too, when it's a new design. From my experience architecting and integrating high-end embedded servers, if you have relatively strict requirements, it can be a real pain making sure your supplier integrates the product properly, with just the right components, etc. Especially with an upgraded product, you may know your requirements much more than your supplier does because you have the whole picture while your supplier doesn't. Thus, it may take a few tweaks to get it right. Usually, my company has our supplier integrate our servers, but actually we often have to reintegrate it ourselves, anyways, since we have stricter quality control and have to double-check all that they do.

I'd imagine that in the case of a rocket engine, vertical integration with the engine components makes a lot of sense, since the requirements are very inter-related. When you discover your supplier did something you didn't anticipate, it can be a real pain to have them drop-ship a replacement. With vertical integration, you can have a lot lower "latency" between the design and production sides... You don't have to wait for one to ship the product to the other, you can possibly go through multiple iterations in a day (depending on the complexity of the piece). If there's a mistake, you can correct it immediately.
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Offline telomerase99

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #445 on: 03/21/2011 02:12 am »
Amen to that. A lot of the trouble with LM and Orion was that Ares kept downgrading its performance. if LM had been doing Orion and Ares then they maybe could have mitigated the impact of such tweaks or atleast had more information up front about the limitations of the stick design.

The nice thing about a vertically integrated rocket designer is that the information you have about each piece of technology is better understood and there should be less bluffing about capability between departments under a single roof no?

Offline mlorrey

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #446 on: 03/21/2011 02:29 am »
Amen to that. A lot of the trouble with LM and Orion was that Ares kept downgrading its performance. if LM had been doing Orion and Ares then they maybe could have mitigated the impact of such tweaks or atleast had more information up front about the limitations of the stick design.

The nice thing about a vertically integrated rocket designer is that the information you have about each piece of technology is better understood and there should be less bluffing about capability between departments under a single roof no?

Well yes, you dont have sales people in between departments. However I do appreciate the concern by others at SpaceX aspiring to produce turbopumps to the same quality and reliability as a company thats been in the business for a long time, without a lengthy development period. That said, this is machinery, fluid dynamics, thermal dynamics and mechanical engineering, its not wizardry.
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Offline Antares

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #447 on: 03/21/2011 03:51 am »
P.S. I'm also afraid that an endless procession of one-off rockets, each a little different, cannot be good for expected reliability and insurance premiums.

Ding ding.

EDIT: I agree that SpaceX really needs to transition into operations mode.
The good thing is that since they are assuming at this point that COTS 2 & 3 are being combined, the Dragon/Falcon mission in a few months will likely be 95% the same vehicle/payload that flies for the next 2-3 years.

If that doesn't streamline production, SpaceX is in big trouble.

And what proof is there to expect it will be 95% the same?
If I like something on NSF, it's probably because I know it to be accurate.  Every once in a while, it's just something I agree with.  Facts generally receive the former.

Offline nooneofconsequence

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #448 on: 03/21/2011 04:57 am »
No surprise here. Your first few are always *unique*. Where I'd be scared is if successive contract missions aren't largely the same.

If they aren't, you can't accumulate meaningful flight history - it becomes meaningless.
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Offline beancounter

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #449 on: 03/21/2011 06:26 am »
No surprise here. Your first few are always *unique*. Where I'd be scared is if successive contract missions aren't largely the same.

If they aren't, you can't accumulate meaningful flight history - it becomes meaningless.

I think it all boils down to being a matter of degree. 

The Merlin engine currently has a pretty well defined upgrade path and flight history will be quickly built up on it since each flight requires 9 engines plus the intial test firings.  So first stage changes are all about engine upgrades to the best of my knowledge.  No vehicle changes have been mentioned.  2nd stage remains as is - no changes identified there, are there?

Dragon Cargo is a bit unknown but I would think that NASA would be pretty unhappy if the vehicle that flys Demo 3 isn't pretty much complete and that design and specification used as is for the duration of the CRS contract.  Isn't that what the COTS program is about, certifying a vehicle to transfer cargo to and from the ISS?  The CRS contract, as far as I know, is not a development contract but an operational one.
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Offline MP99

Ever since the switch to regen, SpaceX's publicly announced plan was to eventually replace this tubopump with one optimized for the-now-regen cooled design, and to increase the diameters of propellant feedlines accordingly (but AFAIK no changes to tank sizes). They reffered to this as BLOCK II. BLOCK II is Merlin 1d, they only recently starting calling it such.

Now that there is some evidence that SpaceX has decided to bring turbopump design and production in-house, and that Max Vozhoff has stated that Merlin 1d will have "a lower part count" (read: simpler, optimized) perhaps this explains their decision to rename the Merlin 1c BLOCK II as Merlin 1d.

Actually, this suggests that 1D is a new project to simplify the engine, and that it also includes the turbo-pump upgrades previously planned for block II.

It looks like they've dropped their previous plan to put an upgraded pump into essentially the same engine, which was "1C block II" (same "complex" design, just upgraded). I think it's useful to recognise this as a separate configuration that fell by the wayside in the same way that Falcon 5 did.

I do wonder if we'll ever see an F9 flight carrying 8x1C + 1x1D, and whether that would actually deliver any useful information, or really be any less risk than jumping straight to F9 block II.

cheers, Martin

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #451 on: 03/21/2011 08:14 am »
So first stage changes are all about engine upgrades to the best of my knowledge.  No vehicle changes have been mentioned.  2nd stage remains as is - no changes identified there, are there?

F9 User Guide mentions a weight reduction campaign as one of the things to be done in Block 1 -> Block 2 transition.

Oh, and, wasn't Merlin 1d sea level thrust targeted to be 125 klbf for years already - as per F9 page?
« Last Edit: 03/21/2011 10:48 am by ugordan »

Offline corrodedNut

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #452 on: 03/21/2011 02:37 pm »
Oh, and, wasn't Merlin 1d sea level thrust targeted to be 125 klbf for years already - as per F9 page?

And now, according to the AvWeek article, Shotwell is predicting 125,000-135,000 lbs performance for the M1d. Sounds like it will come in with at least 125,000, if not more.

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #453 on: 03/21/2011 02:39 pm »
Yeah, that's what I was asking about. Seemed like non-news, really that it would be 125+ klbf.

Offline baldusi

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #454 on: 03/21/2011 02:58 pm »
I was thinking, 600kN vs current 423kN is is almost 42% extra thrust. What would be the performance of a 7 Merlin 1D Falcon? Or just taking the center engine, that would give you almost the expected thrust of the 556kN nominal Merlin with just eight engines.
I don't think they can lengthen the first stage much. Much less widen it (because of transport issues). So what do you do with the extra trust? I mean, you could climb faster, but that would change the payload environment, the loads on the structure and the staging altitude, right? If so, just putting the new engines would mean a new completely different ride than the COTS 1. Would that invalidate some of the data?

Offline LegendCJS

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #455 on: 03/21/2011 03:03 pm »
No surprise here. Your first few are always *unique*. Where I'd be scared is if successive contract missions aren't largely the same.

If they aren't, you can't accumulate meaningful flight history - it becomes meaningless.

Given their stated goal to keep tweaking everything until they can recover an intact first stage, does it really surprise you that they are very open to tweaks and changes in other aspects of the rocket? I wouldn't expect them to think that development mode is over for the F9 until they can fly a recovered first stage. 

I guess its a question of how similar one flight needs to be to the next to "accumulate a meaningful flight history."  The desire to have such a flight history legacy can cause a pressure to freeze their designs/ vehicle configurations, but I don't think SpaceX will feel that pressure if even the small modifications flight to flight for stage recovery reasons invalidate that flight history accumulation profile.
Remember: if we want this whole space thing to work out we have to optimize for cost!

Offline starsilk

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #456 on: 03/21/2011 03:08 pm »
does it seem likely that there will be a new Merlin-1D based Merlin-Vacuum engine? or will they stick with the existing design?

I'd guess there would be pressure to move to a new engine, otherwise they will have to keep building more complex (and presumably more expensive), 1C based MVacs.

Offline Robotbeat

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #457 on: 03/21/2011 03:19 pm »
I was thinking, 600kN vs current 423kN is is almost 42% extra thrust. What would be the performance of a 7 Merlin 1D Falcon? Or just taking the center engine, that would give you almost the expected thrust of the 556kN nominal Merlin with just eight engines.
I don't think they can lengthen the first stage much. Much less widen it (because of transport issues). So what do you do with the extra trust? ...
I'm thinking this is how they get a usable, credible engine-out capability.

But why couldn't they stretch the first stage?
« Last Edit: 03/21/2011 03:39 pm by Robotbeat »
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Online ugordan

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #458 on: 03/21/2011 03:26 pm »
But why couldn't they stretch the first stage?

The VTS3 support structure seems to be sized for current tank height, as is the Cape hangar. Lengthening the stage more could provide road transportation problems as well.

I did a BOTE calculation based on the rough volume of the current stage and RP-1/LOX typical densities. I got about 270 t of propellant load with I'd guess lower than 10% uncertainty. That would mean the tank is already maxed out in propellant load.
« Last Edit: 03/21/2011 03:27 pm by ugordan »

Offline Robotbeat

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #459 on: 03/21/2011 03:42 pm »
But why couldn't they stretch the first stage?

The VTS3 support structure seems to be sized for current tank height, as is the Cape hangar. Lengthening the stage more could provide road transportation problems as well.

I did a BOTE calculation based on the rough volume of the current stage and RP-1/LOX typical densities. I got about 270 t of propellant load with I'd guess lower than 10% uncertainty. That would mean the tank is already maxed out in propellant load.
Ah, I see. Still, I don't see why they couldn't make another one. Lengthening the hanger by a few feet and extending the support structure seems like it'd be far less expensive than some of SpaceX's other projects.

Even so, with more thrust, they get lower gravity losses.
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To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

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