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#360
by
acsawdey
on 09 Oct, 2015 15:56
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You are assuming standard~ish 150wh/kg or so, which is a fair guess. However, apparently one can do better these days
Don't forget that you need to reach a certain power density as well. The need for 1MW power output has come up in a couple quotes. Some of the higher energy density cells can't be discharged at a high enough rate to be drained in ~3 minutes.
Can we come up with an estimate of max discharge rate on Tesla's 18650 cells based on "ludicrous mode" in the model P90D? Power output is stated to be 762 hp == 568kW, and pack voltage is apparently 375V, giving current of at least 1515A to allow for losses. But, dividing the 90kWh by 568kW gives 9.5 minutes. We need 76% more power than that (1.76x) which gives 5.4 minutes, still almost 2x more than we need. Also this pack weighs 450kg but a lot of that is cooling and structure.
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#361
by
savuporo
on 09 Oct, 2015 16:32
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The main assumption here is the pump required power. For a 300 kw pump you'll need ~12 kw/h pack over 150 seconds. I'm not sure Electron is nearly big enough to require 300kw of pumping power though.
And discharge rates really are not the limiting issue here, if you don't care about battery longevity, which you don't for an expendable vehicle, you can draw crazy rates.
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#362
by
acsawdey
on 09 Oct, 2015 17:22
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The main assumption here is the pump required power. For a 300 kw pump you'll need ~12 kw/h pack over 150 seconds. I'm not sure Electron is nearly big enough to require 300kw of pumping power though.
And discharge rates really are not the limiting issue here, if you don't care about battery longevity, which you don't for an expendable vehicle, you can draw crazy rates.
In the video he says "50 horsepower" which is 37kW. Times 9 engines that's 333kW. Not clear whether this is just one pump or both. It's quite clear from the images that it has separate pumps and motors for fuel and oxidizer.
I see your point about the discharge rate. You could qualify the cells for a rate that allows a couple of tests, even. But you don't need to last hundreds of cycles.
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#363
by
baldusi
on 09 Oct, 2015 18:16
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I was wondering about the weight of the batteries to power the pumps, using the 342kw power demand for the 9 first stage engines and assuming a first stage burn of 150s, I get a required capacity of 500,000,000J, at 0.5mJ/kg that's a first stage battery weight of 100kg.
I'm sorry, but you probably meant 0.5MJ/kg, right? The above mentioned Panasonic cells have 0.84MJ/kg.
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#364
by
savuporo
on 09 Oct, 2015 18:37
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BTW, RocketLab is not the only one choosing an electric pump for a smallsat launcher. If you click through the builders on this thread :
http://forum.nasaspaceflight.com/index.php?topic=38583.0You'll find a few others. Ventions for example, who is prototyping for ALASA and also providing engineering services/components to some others
http://ventions.com/menu/I doubt that the electric pumps will scale well to big first stage engines, and the optimization would go towards as short engine burns as possible
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#365
by
Alf Fass
on 09 Oct, 2015 19:02
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I was wondering about the weight of the batteries to power the pumps, using the 342kw power demand for the 9 first stage engines and assuming a first stage burn of 150s, I get a required capacity of 500,000,000J, at 0.5mJ/kg that's a first stage battery weight of 100kg.
I'm sorry, but you probably meant 0.5MJ/kg, right? The above mentioned Panasonic cells have 0.84MJ/kg.
Yeah, and having a google, some claim just over 1MJ/kg for lithium–iron disulfide and lithium–manganese dioxide the latter suitable for high drain devices, so 50kg for 1st stage batteries, 5.5kg each motor.
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#366
by
acsawdey
on 09 Oct, 2015 19:11
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I doubt that the electric pumps will scale well to big first stage engines, and the optimization would go towards as short engine burns as possible
Yes, electric pumps are meant to solve the problem that the gas turbine driving a conventional turbopump doesn't scale down to smaller sizes well. Also the electric motor is significantly easier to design and build than a gas turbine.
Also, as the Rocketlabs guy said, this reduces throttle and mixture control to "a software problem". You could reduce the pump power needed by throttling back later in flight just to the point where you take full advantage of the nozzle's expansion ratio, which would maximise Isp. If the pump is more efficient with lower output pressure, this could reduce the overall energy requirement.
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#367
by
sdsds
on 09 Oct, 2015 19:33
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Did the R-1 suborbital vehicle they launched in 2009 use a pumped liquid propellant engine? How did that engine differ from the current "Rutherford" design? Was it pressure fed?
Also: don't 18 electric motors all spinning at 40,000 rpm as they go through max-q present some reliability challenges? Has RocketLab claimed the Electron would reach orbit if an engine went out?
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#368
by
savuporo
on 09 Oct, 2015 19:52
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Also: don't 18 electric motors all spinning at 40,000 rpm as they go through max-q present some reliability challenges? Has RocketLab claimed the Electron would reach orbit if an engine went out?
I wouldnt expect that. You get electric motors spinning at half a million RPM
For really high end of this kind of stuff, magnetic bearings and all see
http://www.celeroton.com/en/products/motors.htmlThats obviously at a different scale, and as motors get bigger they normally need to slow down. But 40k rpm at that size should not be a challenge
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#369
by
ChrisWilson68
on 09 Oct, 2015 20:52
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RocketLab started work in 2007 and that year is very interesting for many reasons. SpaceX started in 2006, BlueO 2005 so each company runs in their own timeline/path.
SpaceX was founded in 2002. Blue Origin was founded in 2000.
The first Falcon 1 launch attempt was in 2006 and the first Blue Origin flight was 2005, so maybe that's what's confusing you. Those first launch dates shouldn't be compared with the founding date of RocketLab. The first launch date for RocketLab hasn't even occurred yet.
BO is in testing.
SpaceX isn't launching anything, and the New F9 has never launched what's your point?
My point is that your post is at best misleading and at worst downright wrong.
If someone didn't already know the dates for SpaceX, RocketLab, and Blue Origin, they would think from your post that they all started within two years of one another. That is not correct. By listing a founding date for RocketLab and a first-flight date for SpaceX and Blue Origin, you're giving a misleading impression.
I was correcting your misleading post.
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#370
by
sdsds
on 09 Oct, 2015 21:37
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RocketLab has taken electron deposition and refined his custom 3D printer for his needs in house. The company has been built RockeLab around the 3D Printer, and not just added a 3D Printer as a tool like other firms. [...]
Is it your impression that a vehicle of this basic design
requires 3D printing, i.e. no other manufacturing technology could produce engines that would get the vehicle to orbit? Or is it "solely" a cost issue? (FWIW my impression is that the difficulty of printing a gas-driven turbopump brought them to the electric-driven design, which is the underlying design choice that makes the effort so interesting, rather than the 3D printing per se.)
Only concern is his launch software
Even before launch they should be able to demonstrate "fine control" of the engine thrust on a test stand, yes? Is there an expected date for that milestone?
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#371
by
Alf Fass
on 09 Oct, 2015 23:06
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RocketLab has taken electron deposition and refined his custom 3D printer for his needs in house. The company has been built RockeLab around the 3D Printer, and not just added a 3D Printer as a tool like other firms. [...]
Is it your impression that a vehicle of this basic design requires 3D printing, i.e. no other manufacturing technology could produce engines that would get the vehicle to orbit? Or is it "solely" a cost issue? (FWIW my impression is that the difficulty of printing a gas-driven turbopump brought them to the electric-driven design, which is the underlying design choice that makes the effort so interesting, rather than the 3D printing per se.)
They're claiming the main benefit is that they can print an engine in 3 days
Only concern is his launch software
Even before launch they should be able to demonstrate "fine control" of the engine thrust on a test stand, yes? Is there an expected date for that milestone?
They've had 300 test stand firings of the engine.
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#372
by
savuporo
on 09 Oct, 2015 23:43
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#373
by
sdsds
on 10 Oct, 2015 04:42
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Even before launch they should be able to demonstrate "fine control" of the engine thrust on a test stand, yes? Is there an expected date for that milestone?
They've had 300 test stand firings of the engine.
Can you disclose the thrust levels those test stand firings demonstrated? Were all of them at 100% of rated thrust?
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#374
by
Alf Fass
on 10 Oct, 2015 07:27
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Even before launch they should be able to demonstrate "fine control" of the engine thrust on a test stand, yes? Is there an expected date for that milestone?
They've had 300 test stand firings of the engine.
Can you disclose the thrust levels those test stand firings demonstrated? Were all of them at 100% of rated thrust?
I assume they did the tests to test the engine, and I'm betting that testing the engine involves putting it to the test.
Are you suspecting that they did tests that were at less than rated thrust so that the engine wouldn't fail the tests?
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#375
by
ChrisWilson68
on 10 Oct, 2015 07:40
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Even before launch they should be able to demonstrate "fine control" of the engine thrust on a test stand, yes? Is there an expected date for that milestone?
They've had 300 test stand firings of the engine.
Can you disclose the thrust levels those test stand firings demonstrated? Were all of them at 100% of rated thrust?
I assume they did the tests to test the engine, and I'm betting that testing the engine involves putting it to the test.
Are you suspecting that they did tests that were at less than rated thrust so that the engine wouldn't fail the tests?
There are reasons for testing at reduced thrust other than just for PR purposes to avoid failing.
They might have had a program where they started at low thrust, for example and gradually increased the thrust. So only the later tests might have been at full thrust.
Or they might not be done testing so they might not have hit full thrust yet.
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#376
by
Alf Fass
on 10 Oct, 2015 07:48
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Call me a starry eyed optimist, but as they've been testing the Rutherford engine since 2013 and are still talking about a launch end of 2015, I'm betting that they've run all of tests they consider necessary.
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#377
by
savuporo
on 10 Oct, 2015 17:24
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300 Engine tests says volumes when combined with 3D printing. See if your "iffy" in some area you can print out 5 different models to test. At this size the cost, and time involved minimal.
Try quoting a thrust chamber on DMLS machine with large enough working envelope
I wouldn't call either the cost or time involved exactly minimal - but yeah, it beats traditional methods.
Important to remember though that additive manufacturing techniques cant do all that you'd want - coatings and surface treatments and so on.
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#378
by
Prober
on 10 Oct, 2015 18:31
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300 Engine tests says volumes when combined with 3D printing. See if your "iffy" in some area you can print out 5 different models to test. At this size the cost, and time involved minimal.
Try quoting a thrust chamber on DMLS machine with large enough working envelope I wouldn't call either the cost or time involved exactly minimal - but yeah, it beats traditional methods.
Important to remember though that additive manufacturing techniques cant do all that you'd want - coatings and surface treatments and so on.
coatings & surface treatment costs are still there but are also needed in conventional processes (a wash cost wise). On the same hand some of these parts can't be built conventionally.
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#379
by
LouScheffer
on 13 Oct, 2015 03:48
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BTW, RocketLab is not the only one choosing an electric pump for a smallsat launcher. If you click through the builders on this thread :
http://forum.nasaspaceflight.com/index.php?topic=38583.0
You'll find a few others. Ventions for example, who is prototyping for ALASA and also providing engineering services/components to some others
http://ventions.com/menu/
I doubt that the electric pumps will scale well to big first stage engines, and the optimization would go towards as short engine burns as possible
Why would a short burn be better? You need to pump exactly the same amount of fuel (1 tank full) up the same pressure gradient. So it's the same number of joules in either case. And it might be easier to get the power out of the battery over a longer time interval, favoring longer burns.
I wouldn't call either the cost or time involved exactly minimal - but yeah, it beats traditional methods.