Author Topic: SpaceX: General Falcon and Dragon discussion (Thread 7)  (Read 348775 times)

Offline R7

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Re: SpaceX: General Falcon and Dragon discussion (Thread 7)
« Reply #900 on: 03/16/2013 09:32 am »
Look at the "ball valve"

3-way valve may work in the central core but you need cutoff valves in the side boosters too. Otherwise they would blow all residuals upon the central core when separated.

Wouldn't the TPs require stable NPSH anyway, so different ullage pressures in side boosters and central core near separation event is given.

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Offline grythumn

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Re: SpaceX: General Falcon and Dragon discussion (Thread 7)
« Reply #901 on: 03/16/2013 12:16 pm »
ELV.  Delta IV and Atlas V are the only EELV's.  EELV's was a specific contract for the DOD.

Isn't that changing? IIRC, the Air Force is in the process of certifying F9 and F9H as EELVs under NEEP. Hmm... link:

http://www.spacex.com/press.php?page=20121205

Quote
These two missions will support the EELV certification process for both the Falcon 9 and Falcon Heavy. Falcon Heavy, the most powerful rocket in the world, is expected to take its first flight in the second half of 2013. Building on reliable flight proven architecture, the Falcon 9 and Falcon Heavy launch vehicles are designed for exceptional reliability, meeting the stringent U.S. Air Force requirements for the Evolved Expendable Launch Vehicle (EELV) program.

-R C

Offline Jim

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Re: SpaceX: General Falcon and Dragon discussion (Thread 7)
« Reply #902 on: 03/16/2013 12:53 pm »
No.  Air Force is not certifying F9 and F9H as EELV's, they are certifying that they meet the requirements of the EELV program.

The first "E" in EELV means Evolved.  Falcon 9 did not evolved from previous ELV's unlike Delta IV and Atlas V and was not developed under the EELV contract.  Falcon 9 is a EELV class vehicle but it is not an EELV.


Offline modemeagle

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Re: SpaceX: General Falcon and Dragon discussion (Thread 7)
« Reply #903 on: 03/16/2013 01:41 pm »
[quote author=MP99 link=topic=30385.msg1026742#msg1026742
The valving is interesting.  The pressure at the pump inlet is proportional to the liquid column height and to the acceleration.  When switching from the empty side core to the center core, pressure will increase. Also, until you close the path to the side core, fuel will try to flow back to it, to equalize the heights.


Just add gas  to side boosters to keep them above the core pressure,

A few issues:
1. It solves the back flow, but still requires instantaneous valving action.
2. That's a hell of a lot of has pressure and a hell of a lot of volume.
3. It applies high pressure to the top of the tank, whereas before the high pressure was only at the bottom of the tank.  I don't know if the structure is optimized around this gradient.
4. The buffer tank is also very useful for zero-g restarts.
Look at the "ball valve" :) I have drawn, you can rotate it slowly (1 second or even more) so there is no sudden pressure surge on turbopump inlet.

When you rotate it there is the period when the tanks are connected, so some liquid will flow into side boosters, that is no problem, you just switch off boosters 0.1 seconds later.

Do not look for solution (buffer tank???) if there is no problem! :)

A ball valve is not needed.  Think simpler!  If you have two tanks feeding a burner, one your adding pressure (side boosters) and the other your not (center core) then the flow will come from the side tanks and not the center tank.  When you need to switch to core flow you start to pressurize the center tank which will decrease flow from the sides to zero.  Now you close the QDs to the boosters without interrupting flow to the core engines.

The connections just have to be sized to flow the volume needed from each side booster.  No propellant from the side booster needs to travel up into the center tank.

Offline Jim

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Re: SpaceX: General Falcon and Dragon discussion (Thread 7)
« Reply #904 on: 03/16/2013 01:46 pm »
There was a thread on all this earlier.

http://forum.nasaspaceflight.com/index.php?topic=28424.0
« Last Edit: 03/16/2013 01:53 pm by Jim »

Online docmordrid

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Re: SpaceX: General Falcon and Dragon discussion (Thread 7)
« Reply #905 on: 03/16/2013 03:03 pm »
>
The first "E" in EELV means Evolved.  Falcon 9 did not evolved from previous ELV's unlike Delta IV and Atlas V and was not developed under the EELV contract.  Falcon 9 is a EELV class vehicle but it is not an EELV.

Hmmmm. That sounds like a distinction without a difference.
DM

Offline hrissan

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Re: SpaceX: General Falcon and Dragon discussion (Thread 7)
« Reply #906 on: 03/16/2013 03:27 pm »
Ok, lets say it is 15 meters, LOX with 1.1 g/ml and at acceleration of 5 g. This gives the pressure difference of 15*1.1*5 atm = 82 atm. This is the excess pressure in side buster tank which is required just to keep LOX from going backwards, from the core.
Wrong calculation. You forgot to multiply by 9.8 (g), multiply by 1000 (density is kg/m) and divide by 101000 (KiloPascals in atm).

Not 82, but around 8 atm.

82 atm (1200 psi) looks more like the pressure in the combustion chamber! :)

A ball valve is not needed.  Think simpler!  If you have two tanks feeding a burner, one your adding pressure (side boosters) and the other your not (center core) then the flow will come from the side tanks and not the center tank.  When you need to switch to core flow you start to pressurize the center tank which will decrease flow from the sides to zero.  Now you close the QDs to the boosters without interrupting flow to the core engines.
You will need a cut-off valves anyway. I do not know if it is easy to balance delicate pressure difference between tanks. Without 3-way valve the side boosters become also interconnected and can exchange fluid between them, so may be 3-way valve is simple enough to simplify control logic. We may learn what approach SpaceX selected closer to actual launch.

I'm sure Elon will take this opportunity to boast how unheavenly smart his team is!
« Last Edit: 03/16/2013 03:31 pm by hrissan »

Offline Jim

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Re: SpaceX: General Falcon and Dragon discussion (Thread 7)
« Reply #907 on: 03/16/2013 04:22 pm »
>
The first "E" in EELV means Evolved.  Falcon 9 did not evolved from previous ELV's unlike Delta IV and Atlas V and was not developed under the EELV contract.  Falcon 9 is a EELV class vehicle but it is not an EELV.

Hmmmm. That sounds like a distinction without a difference.

Far from it.   Thumb is a finger but not all fingers are thumbs
« Last Edit: 03/16/2013 04:28 pm by Jim »

Offline Nomadd

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Re: SpaceX: General Falcon and Dragon discussion (Thread 7)
« Reply #908 on: 03/16/2013 05:03 pm »
 You're not defining the rocket. You're defining the word. There might be a lot less difference between F9 1.0 and 1.1 than there is between the Atlas V and the previous model, but "evolved" is still a perfectly valid term. Maybe a better term for the F9, seeing how the Delta and Atlas are closer to entirely new rockets.
Those who danced were thought to be quite insane by those who couldn't hear the music.

Offline Jim

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Re: SpaceX: General Falcon and Dragon discussion (Thread 7)
« Reply #909 on: 03/16/2013 05:28 pm »
You're not defining the rocket. You're defining the word. There might be a lot less difference between F9 1.0 and 1.1 than there is between the Atlas V and the previous model, but "evolved" is still a perfectly valid term. Maybe a better term for the F9, seeing how the Delta and Atlas are closer to entirely new rockets.

It doesn't matter about the difference between F9 1.0 and 1.1.  F9 was not a contender for the intital EELV contracts and therefore is not an EELV, it is just a plain ELV.  EELV is specific title for some specific contracts.  No other vehicles were procured under those contracts and therefore the term is not applicable as a proper name to other vehicles.
« Last Edit: 03/16/2013 05:32 pm by Jim »

Online Chris Bergin

This was wandering all over the place again, with some really crap "LOLZ!" level posts - from members who really should know better. Trimmed, but you can see it's still shaky, so started a new thread.

http://forum.nasaspaceflight.com/index.php?topic=31402.0

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