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#220
by
RanulfC
on 22 Apr, 2015 18:06
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Actually glass cockpits predate main stream tablets like the ipad by several decades first appearing in the early 1980s.
Heh, okay - I was just remembering that when Musk presented Dragon 2, it looked like the big screens on the inside were just large tablets. It seems like consumer tablet technology is currently evolving much faster than any glass cockpit systems created by aerospace people - but that's just the kinetics of a larger and more active market.
More accurately maybe; Tablets=No Cockpit?
(Imagine a capsule in orbit tumbling around as the "pilot" curses "Who the !@#%^ is playing KSP while hooked into the capsule WiFi?
"
)
Randy
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#221
by
RanulfC
on 22 Apr, 2015 18:13
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How's the comparison with something like decomposed H2O2 run through a turbopump and then into the combustion chamber similar to a staged combustion engine?
(Yes I have a specific engine in mind
)
Randy
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#222
by
Elmar Moelzer
on 22 Apr, 2015 18:33
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IIRC, hydrogen fuel cells have a higher power density than batteries as well
Don't think this is true.
A quick google search reveals a 8 to 10X energy density of fuel cells versus batteries.
You said power density not energy density, which are different things.
Yeah, sloppy writing there on my side.
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#223
by
Robotbeat
on 22 Apr, 2015 19:16
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That is a key difference. Fuel cells have much worse power density than LiPos. (A couple orders of magnitude difference, comparing a hobby LiPo to a typical aerospace fuel cell.)
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#224
by
ArbitraryConstant
on 22 Apr, 2015 21:12
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AFAICT, the only big improvements on lithium ion batteries in the last ten years have been increasing the safe charge & discharge rate by a factor of five or ten in LiPos with new anode & cathode chemistries. This has been basically irrelevant for battery life, and affects only high-power applications, and possibly but not definitely charging rates.
Disagree, lithium ion has an improvement rate of 5+ percent annually, doubling time is <15 years. When did the first 2 AH 18650 cell come out, after 2000? You can get over 4 AH now.
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#225
by
jongoff
on 22 Apr, 2015 21:55
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This might belong elsewhere, but I wanted to comment:
Expander is a great cycle. It is simple and efficient. There are some major drawbacks though. It has to use cryogenic propellant, either fuel or oxidizer. The colder the better which means LH2 has pretty much been the only one worth using this cycle for. The other drawback is limited thrust these engines can provide. As the thrust increases the heat exchange that drives the cycle becomes less effective.
While expander cycles typically run cryogenic, they don't theoretically have to. Typically you want to run the coolant at pressures high enough to be supercritical, and the critical pressure for kerosene is only 150psi. I remember hearing that someone (P&W I think) was doing work on a Kersosene expander using some of the techniques they had learned from scramjet research to avoid coking in the cooling channels. You probably couldn't bootstrap such a cycle like you could a more traditional cryogenic expander cycle engine, where latent heat in the engine provides enough energy to start the ball moving, but otherwise it might be perfectly workable. And since kerosene is like 10-12x higher density than LH2, it means that far less of your pump energy is going into pumping the fuel, so a kerosene expander should be able to go a lot higher thrust than a hydrogen expander, and there were already concepts for driving expander cycles closer to 60-100klbf.
All that said, I really like the electropump and agree for small sizes they look really interesting.
~Jon
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#226
by
ArbitraryConstant
on 23 Apr, 2015 03:38
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All that said, I really like the electropump and agree for small sizes they look really interesting.
It seems like a really good illustration of the principle that it's advantageous to use a technology that can be brought to market quickly with low cost.
There's a number of expanders (MB-60/RL-60, XCOR, Vinci) that have spent a long time in development and likely won't fly for years more, often stalling due to lack of funding, while it looks like Rutherford's development cycle was extremely quick on the strength of a few rounds of venture funding and we may see one in orbit this year.
It's true Rutherford is smaller than any of those, but it's pinned to technologies that improve themselves without any input from the space industry. I think the area of usefulness will tend to increase over time.
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#227
by
QuantumG
on 23 Apr, 2015 03:40
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It certainly doesn't make sense to spend a lot of money on tech development when you don't have the experience to cash in on it. Whether or not we'll see this engine fly is still a question.
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#228
by
ArbitraryConstant
on 23 Apr, 2015 04:56
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It certainly doesn't make sense to spend a lot of money on tech development when you don't have the experience to cash in on it.
Agreed, but the development on expander looks borderline unaffordable even for the incumbents.
These 10+ year development cycles are bad news. Things change. Assumptions that made sense at the outset can get invalidated by the time you're done, then some or all of the investment can get stranded. Constant payments over that long even if they're small can add up to a lot and could well have gotten better returns elsewhere, especially if the engine ends up getting canceled, as so many engines do. You can pay more to accelerate development but then the bill is due all at once, harder to fund it out of existing revenue streams.
Conversely a quick, cheap development cycle that starts providing returns sooner may well be the better investment, even if the performance isn't as good.
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#229
by
notsorandom
on 23 Apr, 2015 15:05
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This might belong elsewhere, but I wanted to comment:
Expander is a great cycle. It is simple and efficient. There are some major drawbacks though. It has to use cryogenic propellant, either fuel or oxidizer. The colder the better which means LH2 has pretty much been the only one worth using this cycle for. The other drawback is limited thrust these engines can provide. As the thrust increases the heat exchange that drives the cycle becomes less effective.
While expander cycles typically run cryogenic, they don't theoretically have to. Typically you want to run the coolant at pressures high enough to be supercritical, and the critical pressure for kerosene is only 150psi. I remember hearing that someone (P&W I think) was doing work on a Kersosene expander using some of the techniques they had learned from scramjet research to avoid coking in the cooling channels. You probably couldn't bootstrap such a cycle like you could a more traditional cryogenic expander cycle engine, where latent heat in the engine provides enough energy to start the ball moving, but otherwise it might be perfectly workable. And since kerosene is like 10-12x higher density than LH2, it means that far less of your pump energy is going into pumping the fuel, so a kerosene expander should be able to go a lot higher thrust than a hydrogen expander, and there were already concepts for driving expander cycles closer to 60-100klbf.
All that said, I really like the electropump and agree for small sizes they look really interesting.
~Jon
That is interesting that RP-1 can be used in an expander. If I remember right volume is what drive the power requirement on a turbo pump and not mass. So that using the same pump and power a higher density propellant would pump more mass. Does the phase change of RP-1 give less power than LH2? If so is that more than made up for by RP-1's higher density needing less power to pump? Also if one were designing an RP-1/LOX expander why not just use LOX?
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#230
by
simonbp
on 23 Apr, 2015 15:13
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It certainly doesn't make sense to spend a lot of money on tech development when you don't have the experience to cash in on it. Whether or not we'll see this engine fly is still a question.
Given RocketLab's history I'm sure it will fly at least once, the question is whether they will actually be able to fly paying customers.
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#231
by
R7
on 23 Apr, 2015 18:53
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Disagree, lithium ion has an improvement rate of 5+ percent annually, doubling time is <15 years. When did the first 2 AH 18650 cell come out, after 2000? You can get over 4 AH now.
A reference for genuine >4Ah 18650, please. Haven't seen anything above 3.4Ah Panasonic cell that isn't fake Chinese crap.
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#232
by
jongoff
on 23 Apr, 2015 20:54
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This might belong elsewhere, but I wanted to comment:
Expander is a great cycle. It is simple and efficient. There are some major drawbacks though. It has to use cryogenic propellant, either fuel or oxidizer. The colder the better which means LH2 has pretty much been the only one worth using this cycle for. The other drawback is limited thrust these engines can provide. As the thrust increases the heat exchange that drives the cycle becomes less effective.
While expander cycles typically run cryogenic, they don't theoretically have to. Typically you want to run the coolant at pressures high enough to be supercritical, and the critical pressure for kerosene is only 150psi. I remember hearing that someone (P&W I think) was doing work on a Kersosene expander using some of the techniques they had learned from scramjet research to avoid coking in the cooling channels. You probably couldn't bootstrap such a cycle like you could a more traditional cryogenic expander cycle engine, where latent heat in the engine provides enough energy to start the ball moving, but otherwise it might be perfectly workable. And since kerosene is like 10-12x higher density than LH2, it means that far less of your pump energy is going into pumping the fuel, so a kerosene expander should be able to go a lot higher thrust than a hydrogen expander, and there were already concepts for driving expander cycles closer to 60-100klbf.
All that said, I really like the electropump and agree for small sizes they look really interesting.
~Jon
That is interesting that RP-1 can be used in an expander. If I remember right volume is what drive the power requirement on a turbo pump and not mass. So that using the same pump and power a higher density propellant would pump more mass. Does the phase change of RP-1 give less power than LH2? If so is that more than made up for by RP-1's higher density needing less power to pump? Also if one were designing an RP-1/LOX expander why not just use LOX?
To be honest, I'm not much of turbopump guy or thermodynamicist. I just used to build rocket engines (pressure-fed ones).
~Jon
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#233
by
Robotbeat
on 24 Apr, 2015 00:00
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Disagree, lithium ion has an improvement rate of 5+ percent annually, doubling time is <15 years. When did the first 2 AH 18650 cell come out, after 2000? You can get over 4 AH now.
A reference for genuine >4Ah 18650, please. Haven't seen anything above 3.4Ah Panasonic cell that isn't fake Chinese crap.
Here's one for 3600mAh and is real:
http://lygte-info.dk/review/batteries2012/Orbtronic%2018650%203600mAh%20%28Black%29%20UK.htmlI believe the 4000mAh Panasonic ones are being sampled now, even if they haven't been officially released.
Anyway, the point is still valid: Battery energy density HAS been significantly increasing as time goes on and is likely to continue (although I don't think Li-Ion will /ever/ more than double again from the current state of the art, there are other battery chemistries that can continue the progress).
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#234
by
acsawdey
on 24 Apr, 2015 03:31
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You need much smaller cells than the 18650 to get the required power density. The panasonic 3400mAh cells are 2C discharge rate, or about 23W per cell. To get the megawatt needed for the Electron, that's 43252 cells which at a weight of 46g each gives a pack weight of 2000kg just for the cells. You can do better with the stuff I found on hobbyking (small 20C Li poly cells).
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#235
by
Robotbeat
on 24 Apr, 2015 03:36
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You need much smaller cells than the 18650 to get the required power density. The panasonic 3400mAh cells are 2C discharge rate, or about 23W per cell. To get the megawatt needed for the Electron, that's 43252 cells which at a weight of 46g each gives a pack weight of 2000kg just for the cells. You can do better with the stuff I found on hobbyking (small 20C Li poly cells).
Of course. You would use those 100-150C hobby LiPos.
I was merely countering the idea that battery specific
energy has not markedly improved over the introduction and widespread use of lithium ion batteries. Specific energy has about doubled and could possibly nearly double again (eventually), though my guess is that most of the new improvements will come from switching to another chemistry.
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#236
by
R7
on 24 Apr, 2015 03:45
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Disagree, lithium ion has an improvement rate of 5+ percent annually, doubling time is <15 years. When did the first 2 AH 18650 cell come out, after 2000? You can get over 4 AH now.
A reference for genuine >4Ah 18650, please. Haven't seen anything above 3.4Ah Panasonic cell that isn't fake Chinese crap.
Here's one for 3600mAh and is real:
http://lygte-info.dk/review/batteries2012/Orbtronic%2018650%203600mAh%20%28Black%29%20UK.html
I believe the 4000mAh Panasonic ones are being sampled now, even if they haven't been officially released.
Anyway, the point is still valid: Battery energy density HAS been significantly increasing as time goes on and is likely to continue (although I don't think Li-Ion will /ever/ more than double again from the current state of the art, there are other battery chemistries that can continue the progress).
Thanks! I was not countering the idea of battery improvements as surely even 3.4 was bigger number than 2 but was interested if even better cells are really available because might myself be interested in buying them if the price is right. Bought some 18650 and 26650 flashlights last winter and found the hard way that those cheap Ebay Chinese 8000mAh 18650s are cack. Wiser now, Korean 2600mAh cells had Wh/$ sweet spot.
What's the best specific energy primary battery chemistry today with adequate discharge rate? Just wondering what they use in second stage.
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#237
by
ArbitraryConstant
on 24 Apr, 2015 03:51
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I believe the 4000mAh Panasonic ones are being sampled now, even if they haven't been officially released.
Ah, thanks. I had seen 4120 mah for those. Also didn't realize they were sampling rather than being generally available. Mea culpa. ¯\_(ツ)_/¯
I was merely countering the idea that battery specific energy has not markedly improved over the introduction and widespread use of lithium ion batteries.
Yes. Picking a specific form factor is useful to track progress over time, and 18650 is perhaps the most common.
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#238
by
acsawdey
on 24 Apr, 2015 03:55
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You need much smaller cells than the 18650 to get the required power density. The panasonic 3400mAh cells are 2C discharge rate, or about 23W per cell. To get the megawatt needed for the Electron, that's 43252 cells which at a weight of 46g each gives a pack weight of 2000kg just for the cells. You can do better with the stuff I found on hobbyking (small 20C Li poly cells).
Of course. You would use those 100-150C hobby LiPos.
I was merely countering the idea that battery specific energy has not markedly improved over the introduction and widespread use of lithium ion batteries. Specific energy has about doubled and could possibly nearly double again (eventually), though my guess is that most of the new improvements will come from switching to another chemistry.
Completely agree. Li-ion theoretical limit is something like 406 Wh/kg, and those 18650's are at around 250. There are experimental cells that approach the limit, but only at very low discharge rates (0.1C). So, that's what will probably continue to improve, getting more power density without giving up energy density.
The competitive pressure to improve these things is intense, given how important they are to the performance/useability of smartphones, laptops, and EVs. And improving the capacity at high discharge rates really means lowering the internal resistance, which makes the cell more efficient for a lot of uses. So there is pressure to do that.
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#239
by
ArbitraryConstant
on 24 Apr, 2015 04:29
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What's the best specific energy primary battery chemistry today with adequate discharge rate? Just wondering what they use in second stage.
Linked earlier:
http://www.dima.uniroma1.it:8080/STAFF2/jpp12r3.pdfRelevant to your question is Figure 2 on page 33, it varies based on burn time, and as you suggest the longer burn time does change the optimal choice. I'd assume that graph changes over time as new battery technology becomes available and Rocket Lab will update as appropriate.
"