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  #1  
Old 10-20-2014, 06:39 PM
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Default Electron NZ SLV

Hello All,

The New Zealand firm Rocket Lab (see: www.rocketlabusa.com ), which has several years of experience with all-composite rocket vehicles (including the Atea sounding rocket), is developing a three-stage, all-composite, small satellite launch vehicle called Electron (see: http://www.b14643.de/Spacerockets_1...ption/Frame.htm ). This SLV is 18 m long and 1 m in diameter, and it is designed to inject a nominal 110 kg payload into a 500 km Sun-synchronous orbit.

Electron's first stage is powered by nine 13.3 kN thrust Rutherford pump-fed, regeneratively-cooled LOX/kerosene engines that develop an aggregate thrust of 27,000 pounds (120 kN) at launch (34,000 pounds [146 kN] in a vacuum), while the single second stage Rutherford engine (identical to the Stage 1 engines except for its vacuum-optimized nozzle) produces 4,000 pounds (18 kN) of thrust (the first stage's thrust is the same as that of the Vanguard launch vehicle). The third stage is a small solid propellant rocket motor, which appears to be spin-stabilized; the first and second stage engines are gimbaled to provide thrust vector control. Also:

Here is a link to articles about the Electron launch vehicle (see: https://www.google.com/search?hl=en...0.0.scL0ah91IPU ). Whoever said Kiwis can't fly? :-)
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Old 10-20-2014, 09:03 PM
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That's a huge difference in thrust for the vacuum optimized nozzle. 1,000 lbs doesn't seem like much until you realize that the 1st stage individual motors only put out 3,000 lbs each.
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Old 10-20-2014, 09:14 PM
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Quote:
Originally Posted by tbzep
That's a huge difference in thrust for the vacuum optimized nozzle. 1,000 lbs doesn't seem like much until you realize that the 1st stage individual motors only put out 3,000 lbs each.
I'd noticed that, too--either the vacuum Rutherford has a very efficient nozzle (it is a lot longer than the first stage engines' nozzles), or maybe the first stage engines' turbopumps run at a lower speed due to the atmospheric back-pressure at sea level?
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Old 10-20-2014, 09:27 PM
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Quote:
Originally Posted by blackshire
I'd noticed that, too--either the vacuum Rutherford has a very efficient nozzle (it is a lot longer than the first stage engines' nozzles), or maybe the first stage engines' turbopumps run at a lower speed due to the atmospheric back-pressure at sea level?

I know that rocket motors are supposed to be more efficient in a vacuum assuming they have been designed properly, but that's a huge chunk of performance there.

It makes me want to find out, but I doubt there's much information available for the engine. There's not much from the USA to compare it with either. The J-2 second stage was ignited at near vacuum so each engine should perform very close to the third stage J-2's numbers. However they are liquid hydrogen engines and it's really a double apples to oranges comparison. I can't really think of any identical 1st and 2nd stage kero/lox engines off the top of my head for a quick comparison. The original Atlas half stage engines were based off the Navajo engine design, but there were enough changes made to consider them different engines from the sustainer. I think they were both fed by a single pair turbopumps (split twin chamber, for lack of a better description). I don't recall any performance numbers of the sustainer at altitude anyway.
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Old 10-20-2014, 10:22 PM
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In "The Promise of Space," Arthur C. Clarke included a table of exhaust velocities for various propellant combinations; their vacuum values were higher, but by a less dramatic 10% - 15%, than their sea level values, so I believe the sea level vs. vacuum thrust figures (for the same given engines) would be similar. Also:

The only "common" engine (used on a second stage as well as on a first stage) that I can think of off the top of my head is the Merlin, which powers both stages of SpaceX's Falcon 9 (the Vacuum Merlin [MVAC] has a bigger nozzle than the Stage 1 Merlin engines, of course). (Comparing the engines of the Falcon 1 would be "apples and oranges," since the first stage used a [pump-fed] Merlin, while the second stage was powered by a different, pressure-fed engine called Kestrel.)
Quote:
Originally Posted by tbzep
I know that rocket motors are supposed to be more efficient in a vacuum assuming they have been designed properly, but that's a huge chunk of performance there.

It makes me want to find out, but I doubt there's much information available for the engine. There's not much from the USA to compare it with either. The J-2 second stage was ignited at near vacuum so each engine should perform very close to the third stage J-2's numbers. However they are liquid hydrogen engines and it's really a double apples to oranges comparison. I can't really think of any identical 1st and 2nd stage kero/lox engines off the top of my head for a quick comparison. The original Atlas half stage engines were based off the Navajo engine design, but there were enough changes made to consider them different engines from the sustainer. I think they were both fed by a single pair turbopumps (split twin chamber, for lack of a better description). I don't recall any performance numbers of the sustainer at altitude anyway.
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Old 10-20-2014, 11:15 PM
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Quote:
Originally Posted by tbzep
I can't really think of any identical 1st and 2nd stage kero/lox engines off the top of my head for a quick comparison.


Merlin? (as in SpaceX)

Oh, I see Jason beat me to it. That's what I get for skimming......
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Old 10-21-2014, 02:00 AM
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Quote:
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Merlin? (as in SpaceX)

Oh, I see Jason beat me to it. That's what I get for skimming......
As Marigold Heavenly Nostrils www.gocomics.com/heavenly-nostrils says, *Unicorn*! :-) But I don't know if the Merlin and Vacuum Merlin are absolutely identical except for their nozzles and the MVAC's roll control turbopump nozzle; it's possible that the MVAC (Vacuum Merlin) might have a slightly different fuel/oxidizer mix ratio (or perhaps a variable one, as the S-II J-2 engines on Skylab's Saturn V did).
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http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
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