Author Topic: ARCA Space Corporation  (Read 18189 times)

Online envy887

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Re: ARCA Space Corporation
« Reply #60 on: 04/21/2017 01:27 PM »
The article says "Between the engine and the fuels, Popescu says his engine is 30 percent more fuel efficient than today’s traditional engines."  Anyone have any idea how they justify that?

Maybe they meant impulse density? HTP/Kero can be have up to 15% greater impulse density than LOX/Kero.

I'm pretty sure they meant this:

Quote
A vehicle with an aerospike engine uses 25–30% less fuel at low altitudes, where most missions have the greatest need for thrust.

http://www.ijmetmr.com/olseptember2016/SudarsanGajula-KBabitha-KBharadwajan-225.pdf

Online Lars-J

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Re: ARCA Space Corporation
« Reply #61 on: 04/21/2017 05:24 PM »
The article says "Between the engine and the fuels, Popescu says his engine is 30 percent more fuel efficient than today’s traditional engines."  Anyone have any idea how they justify that?

Maybe they meant impulse density? HTP/Kero can be have up to 15% greater impulse density than LOX/Kero.

I'm pretty sure they meant this:

Quote
A vehicle with an aerospike engine uses 25–30% less fuel at low altitudes, where most missions have the greatest need for thrust.

http://www.ijmetmr.com/olseptember2016/SudarsanGajula-KBabitha-KBharadwajan-225.pdf

If that was true - and there weren't other tradeoffs to make - every launch vehicle would be using aerospike engines. And despite being tested off and on since the 60's, there has been exactly ZERO launch vehicles with aerospike engines.

« Last Edit: 04/21/2017 08:54 PM by Lars-J »

Online ChrisWilson68

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Re: ARCA Space Corporation
« Reply #62 on: 04/21/2017 06:10 PM »
The article says "Between the engine and the fuels, Popescu says his engine is 30 percent more fuel efficient than today’s traditional engines."  Anyone have any idea how they justify that?

Maybe they meant impulse density? HTP/Kero can be have up to 15% greater impulse density than LOX/Kero.

I'm pretty sure they meant this:

Quote
A vehicle with an aerospike engine uses 25–30% less fuel at low altitudes, where most missions have the greatest need for thrust.

http://www.ijmetmr.com/olseptember2016/SudarsanGajula-KBabitha-KBharadwajan-225.pdf

This paper doesn't explain that quote at all.  My best guess is that it means 25-30% less fuel compared with a vacuum-optimized engine with the same thrust.  After all, being able to use the same engine at sea level and vacuum is the one big advantage of an aerospike.

Of course, the way ARCA used the 30% figure in the quote in the article, it implied that they'll get some sort of 30% improvement compared with other launch vehicles, which is just silly because other launch vehicles aren't using a vacuum engine at sea level.

Online envy887

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Re: ARCA Space Corporation
« Reply #63 on: 04/21/2017 09:35 PM »
The article says "Between the engine and the fuels, Popescu says his engine is 30 percent more fuel efficient than today’s traditional engines."  Anyone have any idea how they justify that?

Maybe they meant impulse density? HTP/Kero can be have up to 15% greater impulse density than LOX/Kero.

I'm pretty sure they meant this:

Quote
A vehicle with an aerospike engine uses 25–30% less fuel at low altitudes, where most missions have the greatest need for thrust.

http://www.ijmetmr.com/olseptember2016/SudarsanGajula-KBabitha-KBharadwajan-225.pdf

This paper doesn't explain that quote at all.  My best guess is that it means 25-30% less fuel compared with a vacuum-optimized engine with the same thrust.  After all, being able to use the same engine at sea level and vacuum is the one big advantage of an aerospike.

Of course, the way ARCA used the 30% figure in the quote in the article, it implied that they'll get some sort of 30% improvement compared with other launch vehicles, which is just silly because other launch vehicles aren't using a vacuum engine at sea level.
ARCA probably got their information from the Wikipedia article on aerospikes, which has the exact same quote. I doubt they have a better answer in any context.

Offline as58

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Re: ARCA Space Corporation
« Reply #64 on: 04/22/2017 08:23 PM »
The article says "Between the engine and the fuels, Popescu says his engine is 30 percent more fuel efficient than today’s traditional engines."  Anyone have any idea how they justify that?

Maybe they meant impulse density? HTP/Kero can be have up to 15% greater impulse density than LOX/Kero.

I'm pretty sure they meant this:

Quote
A vehicle with an aerospike engine uses 25–30% less fuel at low altitudes, where most missions have the greatest need for thrust.

http://www.ijmetmr.com/olseptember2016/SudarsanGajula-KBabitha-KBharadwajan-225.pdf

This paper doesn't explain that quote at all.  My best guess is that it means 25-30% less fuel compared with a vacuum-optimized engine with the same thrust.  After all, being able to use the same engine at sea level and vacuum is the one big advantage of an aerospike.

Of course, the way ARCA used the 30% figure in the quote in the article, it implied that they'll get some sort of 30% improvement compared with other launch vehicles, which is just silly because other launch vehicles aren't using a vacuum engine at sea level.
ARCA probably got their information from the Wikipedia article on aerospikes, which has the exact same quote. I doubt they have a better answer in any context.

M.Tech Gajula and professors Babitha and Bharadwajan would be well advised to think carefully what plagiarism means. The whole intro of the paper has a bit too much similarity to the wikipedia article.

Offline meekGee

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Re: ARCA Space Corporation
« Reply #65 on: 04/24/2017 05:52 AM »
The focus on 5 minutes to orbit instead of 8 is also really bizarre -- as if that matters in any way whatsoever.

It helps a lot, since gravity losses are reduced, meaning less delta-V is required to reach orbit.

How many seconds of these 3 minutes are saved during the vertical portion of the flight?

But yes, for a hypothetical SSTO, every little bit matters a lot.
ABCD - Always Be Counting Down

Offline ringsider

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Re: ARCA Space Corporation
« Reply #66 on: 04/24/2017 06:23 AM »
M.Tech Gajula and professors Babitha and Bharadwajan would be well advised to think carefully what plagiarism means. The whole intro of the paper has a bit too much similarity to the wikipedia article.

Wow. Except for half a dozen words in one sentence, it is exactly the same.

https://en.wikipedia.org/wiki/Aerospike_engine

Offline Phil Stooke

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Re: ARCA Space Corporation
« Reply #67 on: 04/24/2017 01:51 PM »
Do we know which came first? 

Online LouScheffer

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Re: ARCA Space Corporation
« Reply #68 on: 04/24/2017 02:37 PM »
M.Tech Gajula and professors Babitha and Bharadwajan would be well advised to think carefully what plagiarism means. The whole intro of the paper has a bit too much similarity to the wikipedia article.

Indeed:  Here is the intro to their paper.  Words identical to Wikipedia are in bold.  Wikipedia text is in brackets.

The aerospike engine is a type of rocket engine that maintains its aerodynamic efficiency within [across] a wide range of altitudes. It is a member of the class of altitude that compensaties [compensating] nozzle engines. A vehicle with an aerospike engine uses 25–30% less fuel at low altitudes, where most missions have the greatest need for thrust. Aerospike engines have been studied for a number of years and are the baseline engines for many single-stage-to-orbit (SSTO) designs and were also a strong contender for the Space Shuttle Main Engine. However, no such engine is in commercial production, although some large-scale aerospike’s [ s] are in testing phases.

That's more than 100 words of extremely similar text.  The small differences that are present look like an attempt to avoid direct copying, since they do not improve the text but in fact make it worse by introducing spelling and punctuation errors.  This text was in Wikipedia as of 2012, while their article was in 2016, so almost surely their text was copied from Wikipedia and not vice versa.  Such a large stretch of uncredited identical text would constitute plagiarism in many academic contexts.

Wikipedia is *not* public domain.  You are free to use it, in any manner you like, but you need to give credit.   The license states:
Quote
You are free:

to Share—to copy, distribute and transmit the work, and
to Remix—to adapt the work
for any purpose, even commercially.

Under the following conditions:

Attribution—You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work.) [...]
I can't find any reference of any kind to Wikipedia in their article.

Offline JH

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Re: ARCA Space Corporation
« Reply #69 on: 04/24/2017 04:00 PM »
I know that plagiarism is rampant in less well known publications, but the editor(s) of the journal should be notified.

Online LouScheffer

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Re: ARCA Space Corporation
« Reply #70 on: 04/24/2017 07:39 PM »
OK, this is not funny.  On a hunch, I checked some of the following text.  Again, it almost exactly matched another publication, but this one is not WIkipedia, it's an uncredited academic paper.  Parts in bold are identical to words in
Design and Numerical Analysis of Aerospike Nozzleswith Different Plug Shapes to Compare theirPerformance with a Conventional Nozzle, by  Mehdi Nazarinia, Arash Naghib-Lahouti, and Elhaum Tolouei

Expansion and discharge of a gas in different propulsion systems, e.g. jet engines and rockets, is always accomplished by a nozzle. Thrust of available from a conventional fixed nozzle, discharging jet to [ in]atmosphere can be expressed by the following simple  relation:
F = ṁeVe - ṁoVo+ (PeAe - PatmAExt) (1)
For a nozzle designed to operate at constant Pe (also known as design exhaust pressure, Pdes), thrust is affected
due to altitude change with respect to operation [by change of altitude]. At the design altitude, where Patm = Pdes, the second term of the above relation (known as pressure thrust) is zero, and the nozzle is said to be working in “optimum condition”. At altitudes lower than the design altitude, where Patm>Pdes, pressure thrust assumes a negative value, and loss of thrust is inevitable. These conditions, which occur at altitudes ranging from ground level to the design altitude, are known as over-expansion conditions. Due to in-built thrust losses, [Besides the inherent loss of thrust] the conventional nozzle might suffer problems including shock waves, flow separation in divergent section; thrust oscillation; and flow asymmetry in over-expansion conditions.

From their results and discussion: (compare to results and discussion of cited paper above)

In this section, flow pattern of the ideal aerospike nozzle in different working conditions is compared to that of the truncated aerospike and conventional nozzles. [...] Exhaust flow of the aerospike nozzle is characterized by formation of a series of expansion waves, which originate from the upper lip of the convergent section. Since the exhaust flow is not bounded by a solid wall, these expansion waves can adjust their intensity and domain to match the exhaust flow with the external flow.  For the ideal aerospike, in over-expansion conditions, the domain covered by these waves ends before the end of the plug. At that station, flow properties are close to those of the optimum condition, which usually involve a higher Mach number and a lower pressure compared to the external flow. From this station onwards, flow encounters reflection of the expansion waves in form of a series of compression waves, which increase the pressure and reduce Mach number to a value close to that of the external flow. [..] But for the truncated aerospike nozzles, the situation is such that the expansion waves originated from the upper lip of the convergent section will face the truncated portion of the plug, while in the ideal case these expansion waves meet the plug surface. The flow facing the truncation first encounters a sharp expansion, then by continuing its way to the centre of the plug base a compression, stagnating exactly at the centre of the plug base. This phenomenon is due to the formation of two symmetric vortices in the base of the plug, which counteract the effect of each other at two locations, one of which is located at the centre of the plug base, where flow conditions change into the stagnation conditions. It should be pointed out that regardless of the amount of truncation and the extent of the plug base area, the flow parameter distribution pattern is the same. [..] The exhaust flow of a conventional nozzle, on contrary, does not have the chance to adapt itself to the condition prevailing outside the nozzle before leaving the nozzle. After leaving the nozzle, flow is compressed through a series of compression waves originating from the edge of the exhaust surface, which resemble converging shock waves. These compression waves contract the flow, and impose a radial velocity component, which contributes to loss of thrust in over-expansion conditions.

This goes on and on - the next paragraph matches as well.  I'm writing a letter to the editor.

Online LouScheffer

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Re: ARCA Space Corporation
« Reply #71 on: 04/24/2017 08:10 PM »
OK, this is not funny.  On a hunch, I checked some of the following text.  Again, it almost exactly matched another publication, but this one is not WIkipedia, it's an uncredited academic paper.  Parts in bold are identical to words in Design and Numerical Analysis of Aerospike Nozzleswith Different Plug Shapes to Compare their Performance with a Conventional Nozzle, by  Mehdi Nazarinia, Arash Naghib-Lahouti, and Elhaum Tolouei
[...]

This goes on and on - the next paragraph matches as well.  I'm writing a letter to the editor.
The editor wrote back, very quickly.  They will investigate, and (potentially) remove the article in whole or in part.  They will reply with their actions within 7 business days.  I'm glad they are treating this seriously.

Offline matthewkantar

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Re: ARCA Space Corporation
« Reply #72 on: 04/25/2017 10:05 PM »
This sort of thread reminds me of how great NSF can be. The (likely) ferreting out of a (likely) dastard plagiarist in real time.

Matthew

Offline savuporo

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Orion - the first and only manned not-too-deep-space craft

Online launchwatcher

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« Last Edit: 05/17/2017 12:37 AM by launchwatcher »

Offline CameronD

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Re: ARCA Space Corporation
« Reply #75 on: 05/16/2017 11:03 PM »
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.


Offline Craftyatom

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Re: ARCA Space Corporation
« Reply #77 on: 05/17/2017 01:42 AM »
Lol

https://twitter.com/arcaspace/status/864485699810058241

I tried to find some source on the picture they used there, since I couldn't quite tell if it was superb CGI or a mockup.  I now have no doubt that this is actually a real-life mockup that they built and put on a truck.  Two reasons: first, an example of their CGI is attached, which is pretty recognizable.  Second, they've built a mockup orbital launch vehicle before - back in 2012, when they were testing a standard de Laval nozzle that burned kerolox in a TSTO configuration.  Picture of that attached too.

At first I was running around trying to find hi-res versions of these pictures on Romanian news sites, but it turns out that ARCA's website still has the default index page set for their /images/ folder, so you can actually go through all of their images pretty easily: http://www.arcaspace.com/images/

But why spend time sifting through images when we could all be hopping on that sweet $5.3B gravy train?  ;D
All aboard the HSF hype train!  Choo Choo!

Offline GWH

Re: ARCA Space Corporation
« Reply #78 on: 05/17/2017 04:53 AM »
Lol

https://twitter.com/arcaspace/status/864485699810058241

I tried to find some source on the picture they used there, since I couldn't quite tell if it was superb CGI or a mockup.  I now have no doubt that this is actually a real-life mockup that they built and put on a truck.   

It is a real mock up, they posted a video of them ceremoniously offloading it into a hanger but then people made fun of them because is is obviously juat a painted tube and now its not on their twitter.
 
Edit: There it is, on their youtube:
« Last Edit: 05/17/2017 04:59 AM by GWH »

Offline savuporo

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Re: ARCA Space Corporation
« Reply #79 on: 05/17/2017 05:51 AM »
..It is a real mock up..
That's kind of their thing.
Orion - the first and only manned not-too-deep-space craft

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