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SpaceX Updates (Thread 4): F9, FH & Dragon


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#106 OP DocM

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Posted 11 January 2014 - 06:08

They will take what cost reduction schemes they can until R&D can catch up, but by then SpaceX will be flying theor next generation methane fueled launchers, the next-gen Dragon and deep space MCT spacecraft.

Using methane gives very close to liquid hydrogen performance without the need for the very expensive cryogenic hardware, and it doesn't have the boil-off problems that make fuel depots and long missions tough. This leaves toxic hypergolic fuels like the hydrazine famuly, which work but are inefficient and very hard to handle.

The SpaceX Raptor methane staged combustion engine (650,000 lbf thrust sea level / ~690,000 lbf vacuum) for the Saturn V-class superheavy most are calling "Falcon X" starts component testing at NASA Stennis in Mississippi early this year. Russia's RD-0162/0164 methane engine for Soyuz V is in develipment.

All we hear about methane engines elsewhere is a small one from XCOR, and they're focussed on their spaceplane and piston liquid hydrogen pumps for a ULA upper stage.

Otherwise, from the US and other nations/major companies it's <crickets>


#107 SarK0Y

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Posted 11 January 2014 - 21:06

DocM, where'd you ever see cost-efficient LH2 rockets? for example, hypergolics have comparatively low Isp, but their compactness & capability to throttle thrust up/down highly accurate & safely make possible to drop drag + gravity losses into bottoms. i very doubt Methane's advantages over RP-1 & Hypergolics.



#108 SarK0Y

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Posted 12 January 2014 - 02:32

 

Using methane gives very close to liquid hydrogen performance without the need for the very expensive cryogenic hardware, and it doesn't have the boil-off problems that make fuel depots and long missions tough. This leaves toxic hypergolic fuels like the hydrazine famuly, which work but are inefficient and very hard to handle.

completely incorrect: 

 

Methane has a boiling point of −161 °C (−257.8 °F) at a pressure of one atmosphere.
 
http://en.wikipedia.org/wiki/Methane

+ oxidizer out there is LOX, so there'll be gotten Just yet another cryogenic rocket. actually, only niche i can see is to use Methane for low-power upper stages. seems it has good odds to beat Hydrogen: LH2 is worst choice to gain powerful thrust because of problems to cool engines.



#109 OP DocM

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Posted 12 January 2014 - 03:56

Cryogenic begins at -150°C.

Liquid hydrogen:. −252.87 °C (−423.17 °F)
Liquid methane: −164 to −160 °C (−263 to −256 °F)

Liquid methane is barely cryogenic and liquid hydrogen is deeply so. Enough so that it presents storage issues liquid methane does not.

For in-space propulsion the really big deals are Specific Impulse (Isp) and storability.

Isp is a deal breaker, being similar to miles per gallon in a car, and even a few points matter a lot, Since we're talking hydrogen vs methand vs hypergolics here are their numbers,

Liquid Hydrogen+LOX: 455
Liquid Methane:+LOX: 380
MMH+NTO4: 336 (hypergolic)

(MMH: monomethyl hydrazine (toxic)
NTO4: nitrogen tetroxide (toxic)
LOX: liquid oxygen
Also, nitric acid (hypergolic, toxic)

Hydrogen is the clear Isp winner, with methane second. Both will deliver much more "mpg" than NTO4+MMH, which are also highly toxic - complicating ground operations, but with hydrogen there are storage issues.

First, liquid hydrogen is cryogenic so that takes expensive hardware and storage or it'll boil off easily. Second, it is a very tiny molecule that will infiltrate most materials it touches, degrading them over time. As a result special materials or coatings are required.

Bottom line: liquid hydrogen hardware dramatically ups costs.

Methane gives "good enough" Isp, much higher than hypergolics, and does not have near the storage issues of hydrogen.

The hypergolics low Isp is a problem, but toxicity alone is why most companies and nations are actively developing replacements for them. They greatly complicate ground opetations, and crashed hypergolic stages have killed civilians (China, mitric acid+hydrazine).

These advantages over hypergolics and hydrogen are enough that, in addition to SpaceX, Russia is now developing the RD-0162/0164 methane engines for the future Soyuz 5 launcher.

#110 flyingskippy

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Posted 12 January 2014 - 04:02

http://www.braeunig....pace/propel.htm

My understanding with methane propellent is that since the density is higher than hydrogen, it would require less storage volume in a fuel tank. A storage tank with less volume would mean a rocket with less mass.

#111 SarK0Y

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Posted 12 January 2014 - 04:06

Hypergolics are only choice for long-lasting missions, if to say of chemical propellants.



#112 OP DocM

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Posted 12 January 2014 - 04:11

You are truely clueless.

http://www.braeunig....pace/propel.htm

My understanding with methane propellent is that since the density is higher than hydrogen, it would require less storage volume in a fuel tank. A storage tank with less volume would mean a rocket with less mass.

That's known as bulk density and yes, methane is better than liquid hydrogen.

Methane: 801 kg/m^3
Hydrogen: 358 kg/m^3

and for SarK0Y's sake

MMH: 972 kg/m^3, but for long missions or fuel depots it'll freeze solid as a rock without heavy extra insulation heaters in the tank. Not to mention its highly toxic.

#113 SarK0Y

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Posted 12 January 2014 - 04:14

http://www.braeunig....pace/propel.htm

My understanding with methane propellent is that since the density is higher than hydrogen, it would require less storage volume in a fuel tank. A storage tank with less volume would mean a rocket with less mass.

 it'd be heavier than Hydrogen, but Methane looks better in terms of thrust because there needs less volume to cool engines. In short, at greater thrust, we could hope upon mass savings too.



#114 flyingskippy

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Posted 12 January 2014 - 04:17

You are truely clueless.


That's known as bulk density and yes, methane is better than liquid hydrogen.


I gave it my best shot! ;-)

#115 SarK0Y

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Posted 12 January 2014 - 04:19

 

You are truely clueless.

DocM, it's truly fascinating comment from you :) how long do you Hope to store Methane in the spacecraft at stable state?



#116 SarK0Y

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Posted 12 January 2014 - 04:20

I gave it my best shot! ;-)

relax, it was to me :)



#117 OP DocM

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Posted 12 January 2014 - 04:23

I gave it my best shot! ;-)


My first line was aimed at SarK0Y. Sorry for the friendly fire.

#118 OP DocM

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Posted 12 January 2014 - 04:26

DocM, it's truly fascinating comment from you :) how long do you Hope to store Methane in the spacecraft at stable state?


A lot longer than you can hydrogen, which requires active cooling and heavier insulation to prevent boil-off, then there is th problem of hydrogen infiltration damage which requires many expensive materials that methane doesn't need.

#119 flyingskippy

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Posted 12 January 2014 - 04:31

No sweat Doc.

#120 SarK0Y

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Posted 12 January 2014 - 04:36

this comparison has no ground because Hydrogen never has been used for long-lasting missions. if you want to store Methane for days/weeks/months/.., you need active cooling. where'd you mind to take energy for, DocM???





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