Author Topic: SpaceX: General Falcon and Dragon discussion (Thread 3)  (Read 566182 times)

Offline hop

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #40 on: 02/22/2011 08:16 pm »
Didn't an N1 fail that way, just kept on shutting down engines to balance it until it could no longer lift itself over the lithosphere?
AFAIK the shutting down too many engines was due an implementation error. It was supposed to just shut down the engine directly opposite (which would have been fine, there was plenty of thrust to continue), but instead was off by one or something like that.

The number of engines invites comparison F9H to the N1, but given programmatic problems in the N1 project, it's not clear how relevant it might be. Lots of engines didn't help, but the N1 project would have been seriously troubled in any case.

Offline Robotbeat

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #41 on: 02/22/2011 08:30 pm »
The extended-length boosters point a little toward cross-feed, IMHO (as complicated as that may be). However, they may just cut-out a bunch (3? 4?) of core engines soon after lift-off (probably a more likely scenario considering that I don't think cross-feed between actual cores has been done before).

Another way to look at it is that the initial T/W would be about the same for the Falcon 9 and the Falcon 9 Heavy this way... to do that you have to stretch something, and by stretching the boosters instead of the core, commonality with Falcon 9 (regular) is maintained to a greater extent than if you extended the core.

Still, this is just a single image without much behind it.
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Offline Jim

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #42 on: 02/22/2011 08:34 pm »

1.  I addresses propellant issues before - this is an optimization issue - one of the affects of losing an engine is less efficient use of propellant, and you need to allocate margin for it.


2.  And again - where is the counter-argument?  This is still the same pattern of discussion.  You're just shooting things down, but not bringing anything to the table to argue the other way.

1.  no, you haven't.  It does no good if one strapon runs out of propellant before the other.

2.  The onus is on you.  The vehicle is only design for nominal conditions (3 sigma), you have to prove that the vehicle has to survive the off nominal.

You have not shown that the angle of attack is similar.
« Last Edit: 02/22/2011 08:42 pm by Jim »

Offline baldusi

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #43 on: 02/22/2011 08:38 pm »
I don't know if this is important. But being the Merlin 1C a pintle engine, wouldn't it be possible that it's actually "throttlable" at factory. I.e., they can dial a thrust by moving the pintle position slightly, as long as it's less than Thrust Max? This could allow they to dial a bit back the core. Just a thought.

Offline baldusi

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #44 on: 02/22/2011 08:41 pm »
...The vehicle is only design for nominal conditions (3 sigma)...
Why do you  equate nominal to three standard deviations? Is this a standard? As an econometrist this seems like a lot of variance. Unless you mean 99.7% reliability.

Online ugordan

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #45 on: 02/22/2011 08:41 pm »
Merlin 1c was certainly downrated on the Falcon 1 flights.

Offline Robotbeat

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #46 on: 02/22/2011 08:49 pm »
Regarding the many-engines (with engine-out capability (EOC)) versus single engine...

There is considerable difficulty associated with making redundant solutions work (I know this from experience). You are adding a lot of complexity to an already very complex system. Like the N-1 shows, lots and lots of testing is required because of this added complexity and you will fail if you neglect this. This is probably why NASA considers EOC as not really adding to the overall reliability of a rocket... If EOC isn't implemented right (say, sensor failures leading to unnecessary shut-downs), it can end up causing the mission to fail unnecessarily (as almost happened on STS-51-F)... It must be remembered that EOC adds new failure modes.

However, if you are able to clear out the vast majority of system-level failures caused by poor design and implementation and are able to mature the system over many flights (so that you are mostly left with random manufacturing defects not implementation flaws), I think that is where EOC can actually shine and perhaps even start to eclipse the reliability of just going with a single engine. But this is only after very many flights. Commercial aviation sees multiple engines (with EOC) as superior to single-engine, but commercial aviation tests the living **** out of their aircraft.

SpaceX is shooting for ~10 Falcon 9 flights per year. That's quite unlikely any time soon, but if you grant them that flight rate, then after not too many years (and I would say, about 20-30 flights), they start to get to the point where the implementation flaws are matured out of the design and they are left with the random manufacturing flaws dominating.

Of course, in order for EOC to be useful, the EOC must be effective in the great majority of engine failures (which is what all the rapid unexpected disassembly (RUD) talk is all about...).
« Last Edit: 02/22/2011 09:26 pm by Robotbeat »
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Offline Nate_Trost

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #47 on: 02/22/2011 08:51 pm »
One thing I find a bit interesting that hasn't been discussed is that it would seem, if NASA does consent to combining COTS2 and COTS3 (and the combined mission succeeds), that it would save SpaceX a not insignificant amount of money. That could conceivably be in the range of $50-$100 million depending on the rather large unknown of what SpaceX's costs are. One wonders if that could be applicable to internal development, or just to defray losses from migrating Falcon 1 contracts or price differentials on early Falcon 9 customers. It would seem SpaceX would have to spend a significant amount of money to develop F9H if the government won't foot the bill (which doesn't seem likely) and it has to self-finance all of the development plus a test launch.

Online ugordan

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #48 on: 02/22/2011 08:55 pm »
I'm thinking cost savings is the single major driver from SpaceX for combining the 2 COTS flights and potentially moving the CRS schedule slightly to the left is just a bonus at which NASA will or will not bite - we'll see.

Offline spacejulien

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #49 on: 02/22/2011 09:58 pm »
...The vehicle is only design for nominal conditions (3 sigma)...
Why do you  equate nominal to three standard deviations? Is this a standard? As an econometrist this seems like a lot of variance. Unless you mean 99.7% reliability.

That means that to 99.7% you achieve the required orbit without running out of propellants. That is nominal industry standard and the performance data given in the Payload Planners Guide should be based on this. This is to account for all parameter variations, like winds, dispersions on filling, thrust variation, mixture ratio, etc...

Reliability in terms of nominal operation of all launch vehicle elements is a completely different topic, but generally the calculated overall reliability should be in a similar range. Or higher, if manned.

Then, when planning for a specific mission the launch provider and customer might negotiate a higher payload mass but in return accept a higher risk of ending up in a lower-than-required orbit. The payload would then need to cover the missing deltaV with it's own propulsion system.

Such a case-by-case approach was quite common for Ariane 4 at the end of the 90ies and after, to squeeze ever more massive payloads onto the launcher. For an example, see page 6 of http://www.capcomespace.net/dossiers/espace_europeen/ariane/annexes/V129launchkit.pdf
« Last Edit: 02/22/2011 10:06 pm by spacejulien »
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Offline MP99

I'm thinking cost savings is the single major driver from SpaceX for combining the 2 COTS flights and potentially moving the CRS schedule slightly to the left is just a bonus at which NASA will or will not bite - we'll see.

...since we're in speculation mode.

Maybe SpaceX is concerned about ramping up their flight rate?

If they can make a success of a combined COTS 2 & 3, they can add 50% to the delivery times for both the combined COTS & first CRS flights, and still be on time for their first CRS delivery. (50% being notional, but based on just preparing two flights instead of three).

cheer, Martin

Offline Nomadd

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #51 on: 02/22/2011 10:22 pm »
I'm thinking cost savings is the single major driver from SpaceX for combining the 2 COTS flights and potentially moving the CRS schedule slightly to the left is just a bonus at which NASA will or will not bite - we'll see.

 I would have thought accelerated revenue, if they get paid after every delivery. It's hard to believe that they'll get there so fast that cutting out several months of development time wouldn't be a great advantage. Even if NASA didn't want to shift the schedule, it would free them to get their other revenue producing projects moving.
 The company's total expenses probably don't have that much room to decline for a few years since they're mostly salaries in that outfit, but the revenue could definitely rise if they keep or beat the schedules.
« Last Edit: 02/22/2011 10:25 pm by Nomadd »
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Offline nooneofconsequence

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #52 on: 02/22/2011 10:57 pm »
Actually combing COTS changes the game politically. By taking more off the Shuttle dependence more quickly, one predicates a future where scaling up such capability becomes a viable path forward against the spectre of LV (or should I say HLV) uncertainty ...
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Offline RocketEconomist327

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #53 on: 02/23/2011 01:49 am »
<snip>

Maybe SpaceX is concerned about ramping up their flight rate?

<snip>

They are concerned...

VR
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Offline Comga

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #54 on: 02/23/2011 04:31 am »
Why such complex speculation on motives?  How about why WOULDN'T they combine COTS-2 and COTS-3?

COTS-2 is going to the vicinity of the ISS, 6 km away IIRC.  If they are successful, it will wind up in this stationkeeping position before it departs for reentry.  With the full orbital configuration, including solar arrays, they should not be life limited. 

Now if they add the grapple fixture and the berthing mechanism, they could in theory be allowed to complete the rendezvous and be berthed, meeting the COTS-3 milestones.  Then the COTS-3 flight becomes a CRS revenue flight.

How could they NOT go this route, so long as NASA isn't excluding the possibility up front?  (This may still happen due to things like ISS crew member training or something else.) Add the cost and time to install the grapple and berthing  mechanisms for what amounts to the chance at the revenue from the CRS-1 flight.  It would seem to be a lot lower risk than many that they have retired.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Comga

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #55 on: 02/23/2011 05:57 am »
* Warning: speculation ahead *

9+9+5 Merlin 1d engines should produce about 1230 tons liftoff thrust. So it could get off the ground, albeit slowly.

I believe that you are assuming less thrust than would be available from the Merlin 1d.  23 engines should produce 1438 tons of thrust and give a T/W of almost 1.4 using your mass estimate.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline baldusi

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #56 on: 02/23/2011 11:47 am »
Seeing how they are allowing Orbital to do it with one launch, and even paying them to do a risk reduction Taurus II launch, I don't see how merging missions would be unfair.

Offline Dave G

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #57 on: 02/23/2011 05:24 pm »
Elon already mentioned that they were looking at a cross-fed solution for multiple cores.  I believe that was in the interview just after the second F9 launch.

Assuming he means this for Falcon 9 Heavy, then there's no need to throttle down or leave out engines.

Also keep in mind that Falcon 9 Heavy will probably be migrating from 27 Merlin 1s to 3 Merlin 2s. 
« Last Edit: 02/23/2011 05:24 pm by Dave G »

Offline Aeroman

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #58 on: 02/23/2011 05:28 pm »
So, if they replace 9 Merlin 1's with 1 Merlin 2 it wouldn't be called a Falcon 9 anymore correct?

Just wondering.


Offline Nate_Trost

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Re: SpaceX: General Falcon and Dragon discussion (Thread 3)
« Reply #59 on: 02/23/2011 05:33 pm »
Also keep in mind that Falcon 9 Heavy will probably be migrating from 27 Merlin 1s to 3 Merlin 2s. 

There's no Merlin 2 without serious $$$ coming from somewhere.

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