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#180
by
sanman
on 21 Apr, 2015 00:09
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Interesting technology but getting rid of the turbine makes "electric turbopump" an oxymoron.
Still applicable as the pump is likely a centrifugal turbopump even if it's driven by electricity.
The definition of tumbopump is that it has a turbine powering it.
And for a
turbopump too
(j/k)
But seriously, after just discovering this thread, I want to understand - is the central proposition of this rocket that it uses an electric motor-driven "turbopump" as a simpler substitute for a regular turbopump? And of course since it's battery-powered, then it's less efficient and can't be scaled up to higher thrust. But does it have other advantages in restartability and reliability? I just wanted to understand the pro's and cons better.
Even if it's kind of weak here on Earth, would it be better suited for the Moon? Could it be used in a lunar lander perhaps, to shuttle between the surface and lunar orbit?
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#181
by
QuantumG
on 21 Apr, 2015 00:15
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I think a turbopump at that scale would have similar thrust/weight. At least so far, anyway, Firefly might prove otherwise. Even then, RocketLab can expect the electric pump to be more reliable - everything else being equal - and it's certainly an easier way to start than building turbo machinery. As battery technology improves they could scale up.
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#182
by
sanman
on 21 Apr, 2015 00:58
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Since restartability and reliability are particularly nice things to have for upper stage or space-based engines, then could this "electric-turbopump" technology find itself a nice niche there?
Would this kind of rocket engine be useful for a space tug, perhaps?
(Gee, it also sounds like a Poor Man's ICBM)
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#183
by
Patchouli
on 21 Apr, 2015 01:14
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Since restartability and reliability are particularly nice things to have for upper stage or space-based engines, then could this "electric-turbopump" technology find itself a nice niche there?
Would this kind of rocket engine be useful for a space tug, perhaps?
(Gee, it also sounds like a Poor Man's ICBM)
One potential use I can think of is a lighter weight OMS system for orbital vehicles that already have an electrical system capable of charging the high amp battery bank needed for surge power to operate the pumps.
Ie poor man's OME for RLVs.
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#184
by
sanman
on 21 Apr, 2015 01:51
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Well, if this thing can lift 100kg to LEO, then it should be able to lift 6 times that on the Moon. And if it's reliable, restartable, and can be 3D-printed easily, then it sounds like it would be good to support lunar transportation.
A space tug is a reusable vehicle, and likewise so is a lunar shuttle traveling between surface and orbit.
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#185
by
Patchouli
on 21 Apr, 2015 02:52
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Well, if this thing can lift 100kg to LEO, then it should be able to lift 6 times that on the Moon. And if it's reliable, restartable, and can be 3D-printed easily, then it sounds like it would be good to support lunar transportation.
A space tug is a reusable vehicle, and likewise so is a lunar shuttle traveling between surface and orbit.
They use ten of them to put a payload in LEO nine in the first stage and one in the second.
A small lunar lander the size of the Apollo LEM would only need two or three of the engines.
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#186
by
sanman
on 21 Apr, 2015 03:13
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Maybe if composites or alloys could be developed that could function both as structure and as electrical energy storage, then you could make a big rocket stage that could also store lots of electrical energy too. For instance, graphene has very high molecular tensile strength suitable for composites, and yet graphene has also been used to create high-performance capacitors.
http://www.pv-magazine.com/news/details/beitrag/graphene-solar-could-be-a-game-changer_100018591/#axzz3Xua8PlE5Of course, you'd probably have to make sure to always launch in clear weather.
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#187
by
Robotbeat
on 21 Apr, 2015 03:46
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Call it a "super" pump, in analogy to the distinction between turbocharger and supercharger in an automobile.
Actually, that analogy works quite well and carries on to the thermodynamics as well (although a turbocharger kind of works the opposite from a full flow staged combustion turbopump... the turbocharger is powered by the exhaust fed from combustion "chamber" while turbopump often feeds into the combustion chamber). They operate on the same basic principles, they're both turn-y vane-y things.
I'm calling this kind of rocket pump a superpump. Because I can.
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#188
by
ArbitraryConstant
on 21 Apr, 2015 04:29
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But seriously, after just discovering this thread, I want to understand - is the central proposition of this rocket that it uses an electric motor-driven "turbopump" as a simpler substitute for a regular turbopump?
Sounds like it.
In an earlier interview, Beck said they elected to use a battery because it offered the best opportunity to reduce costs. “Unless you solve the turbopump problem, it’s really difficult to build a cost-effective system,” he said.
The battery-powered pump, he said, can be easily changed with software, making it far easier to modify. “It takes a really complex thermodynamic problem and turns it into software that’s infinitely tweakable,” he said
link: http://spacenews.com/rocket-lab-unveils-battery-powered-3d-printed-rocket-engine/
But does it have other advantages in restartability and reliability? I just wanted to understand the pro's and cons better.
Should do. A gas generator needs TEA/TEB or something like that to start, which is limited, but if the pumps are battery powered there's no need for anything like that. Electric ignition seems straightforward. So, yeah, extra restarts seems likely.
Even if it's kind of weak here on Earth, would it be better suited for the Moon? Could it be used in a lunar lander perhaps, to shuttle between the surface and lunar orbit?
I've had that thought. If it saves dry mass over pressure fed and gets high end hydrocarbon ISP that's an important improvement over Apollo.
Lunar descent/ascent was all pressure fed hypergols at 311s ISP, it looks like first stage Rutherford engines get 327s ISP in vac, which is extremely good for hydrocarbon, basically staged combustion territory. A larger nozzle should be able to improve that 20+ seconds. With that kind of performance it's not insane to contemplate a fully reusable lander that can do the round trip with one stage.
Combined Apollo descent stage and ascent stage delta-v is a touch less than 5 km/s, which isn't out of the question if you can credibly aspire to 350s.
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#189
by
TrevorMonty
on 21 Apr, 2015 04:54
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RP1 is not an ideal fuel lunar landers but the technology could just as easily applied to small methane or LH engines.
The critical thing is max single burn time for a an application, every minute of energy storage adds mass to batteries.
A lunar landers mission may need to be broken up to sections to allow batteries to recharge.
1) EML1 to LLO
2) Recharge batteries (hours/days?)
3) LLO lunar surface.
4) Recharge
5) Surface - LLO.
6) Recharge
7) LLO- EML1.
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#190
by
sanman
on 21 Apr, 2015 05:17
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Well, if it was an unmanned robot lander/shuttle, then maybe stopping in the middle to recharge like that is perfectly acceptable.
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#191
by
ChrisWilson68
on 21 Apr, 2015 06:04
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More informative article from Forbes.
110kg to 500km SSO
400kg to LEO
50hp from electric motor size of soda can. (Just what I need for the bike.)
http://www.forbes.com/sites/alexknapp/2015/04/14/rocket-lab-unveils-a-3d-printed-battery-powered-rocket-engine/
http://www.rocketlabusa.com/about-us/propulsion/rutherford/
4600 lbf thrust, 327s ISP :o
I assume this is the first stage version because 4600*9 is similar to the total thrust claimed for the vehicle, which means even though there's a mass penalty for the batteries, not having to divert any of the propellant flow means it gets expander/staged combustion-like ISP. This beats Merlin 1D by 16 seconds, so the vac version may get 350+ ISP. :o
Thoughts:
-battery contributes to dry mass but I bet it's better than doing the same job with COPV helium in a pressure fed engine, which also has dry mass penalty
-dry mass penalty compared to expander, but comparable ISP, simpler and cheaper to develop and build, and can work with prop combinations like kerolox that don't work with expander
This seems workable for a smallish first stage but it occurs to me this would probably work well for a high energy kick stage on a larger launcher. It could use non-toxic storables like N2O+Propane and outperform a solid kick stage, or it could use cryo propellants like kerolox/methalox and probably get into 350+/360+ territory.
It really doesn't make sense to compare Isp of a battery-pumped engine with that of a turbopumped engine. The energy source for the turbopump goes into the exhaust, tending to decrease the Isp. That makes it look bad compared to the battery-pumped engine if you just look at Isp. But really the turbopumped version is much better because the power source for the electric pump has to be carried all the way. It's kind of like saying we're going to capture the exhaust of a turbopump and keep it onboard -- the Isp number of the engine goes up, but performance goes down.
This also has to be factored in when comparing power density -- even if the battery can hold as much energy per kg as the propellant, the battery gives worse performance because you have to haul the whole battery mass along on the whole trip.
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#192
by
QuantumG
on 21 Apr, 2015 09:15
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even if the battery can hold as much energy per kg as the propellant, the battery gives worse performance because you have to haul the whole battery mass along on the whole trip.
That's irrelevant. It's the thrust/weight at lift-off that matters, not the thrust/weight at burnout - assuming any sensible trajectory. Creating a small turbopump with similar thrust/weight is a much harder proposition.
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#193
by
TrevorMonty
on 21 Apr, 2015 11:14
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I found this paper that compares electric, turbopump and pressure fed engines. Slow read but some very interesting conclusions.
http://www.dima.uniroma1.it:8080/STAFF2/jpp12r3.pdf1) Electric and turbopump powered LVs far superior to Pressure feed LVs.
2) Not much in it between electric and turbopump, with Turbopump just edging out electric in study.
3) Most surprising of all is that turbopump 1st stage is slightly better than electric, but electric has a superior 2nd stage performance even though batteries need to drive pump for longer.
4) Better engine control with electric as pump speed can be varied under electronic control. No surprise there.
As expected electric will gain from improvements in battery, electronic and motor technologies. This is by far one of the more important advantages, Rocketlab just need to sit back and wait for these improvements. Fitting lighter batteries every year would not cost a lot in R&D plus would be extremely low risk.
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#194
by
meekGee
on 21 Apr, 2015 14:53
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Call it a "super" pump, in analogy to the distinction between turbocharger and supercharger in an automobile.
Excellent name.
It looks to me like a good replacement for pressure fed engines.
Controllable, reliable, simple. Under some circumstances, even rechargeable.
Not scalable though, since the energy density is poor, and especially since in rockets, the thermal energy byproducts are actually used to good benefit (unlike in internal combustion engines)
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#195
by
ArbitraryConstant
on 21 Apr, 2015 15:38
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RP1 is not an ideal fuel lunar landers but the technology could just as easily applied to small methane or LH engines.
That may not work as well. Pump power goes linearly with volumetric flow rate, so hydrogen would increase battery mass significantly. So would methane, though less so. There's other choices like subcooled propane though.
Also with hydrogen it won't last as long. LOX and LOX-like temperatures are much more manageable.
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#196
by
acsawdey
on 21 Apr, 2015 15:42
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I found this paper that compares electric, turbopump and pressure fed engines. Slow read but some very interesting conclusions.
http://www.dima.uniroma1.it:8080/STAFF2/jpp12r3.pdf
1) Electric and turbopump powered LVs far superior to Pressure feed LVs.
2) Not much in it between electric and turbopump, with Turbopump just edging out electric in study.
3) Most surprising of all is that turbopump 1st stage is slightly better than electric, but electric has a superior 2nd stage performance even though batteries need to drive pump for longer.
4) Better engine control with electric as pump speed can be varied under electronic control. No surprise there.
As expected electric will gain from improvements in battery, electronic and motor technologies. This is by far one of the more important advantages, Rocketlab just need to sit back and wait for these improvements. Fitting lighter batteries every year would not cost a lot in R&D plus would be extremely low risk.
That is a really great article. A few comments:
I think the 1st stage vs 2nd stage difference is largely due to the fact that he switches to higher energy density batteries for longer burn times. If somebody developed a better battery (i.e. better combination of high power density and energy density), the 1st stage battery-electric pump lines might move down below the turbopump ones.
He may have artificially hobbled the turbopump. He's assuming a relatively unsophisticated turbopump that uses decomposition of MMH for it's gas source and further requires a cooling water supply that is injected to keep the turbine inlet temperatures in check. A gas generator running on LOX/RP-1 might do better, as might one that has higher temperature metallurgy.
The point for rocket hobbyists is: you can build a pump fed rocket that is within spitting distance of a turbopump system. This is clearly light years ahead of a pressure fed system.
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#197
by
GWH
on 21 Apr, 2015 17:03
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4) Better engine control with electric as pump speed can be varied under electronic control. No surprise there.
This stands out to me as opening up some interesting avenues, specifically crossfeed of multiple core rockets. Whether via standalone pumps or throttling and split lines I would expect the complexity and development cost of such a system would be greatly reduced when pump flow isn't tied in directly to the engine.
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#198
by
edkyle99
on 21 Apr, 2015 17:20
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I found this paper that compares electric, turbopump and pressure fed engines. Slow read but some very interesting conclusions.
http://www.dima.uniroma1.it:8080/STAFF2/jpp12r3.pdf
1) Electric and turbopump powered LVs far superior to Pressure feed LVs.
2) Not much in it between electric and turbopump, with Turbopump just edging out electric in study.
3) Most surprising of all is that turbopump 1st stage is slightly better than electric, but electric has a superior 2nd stage performance even though batteries need to drive pump for longer.
4) Better engine control with electric as pump speed can be varied under electronic control. No surprise there.
As expected electric will gain from improvements in battery, electronic and motor technologies. This is by far one of the more important advantages, Rocketlab just need to sit back and wait for these improvements. Fitting lighter batteries every year would not cost a lot in R&D plus would be extremely low risk.
Note that this is a comparison with gas generator turbopump engines, which lose several percentage points of efficiency by tossing the turbopump exhaust overboard. Staged combustion turbopump engines would likely outperform electric pump engines.
- Ed Kyle
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#199
by
acsawdey
on 21 Apr, 2015 17:46
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I found this paper that compares electric, turbopump and pressure fed engines. Slow read but some very interesting conclusions.
http://www.dima.uniroma1.it:8080/STAFF2/jpp12r3.pdf
1) Electric and turbopump powered LVs far superior to Pressure feed LVs.
2) Not much in it between electric and turbopump, with Turbopump just edging out electric in study.
3) Most surprising of all is that turbopump 1st stage is slightly better than electric, but electric has a superior 2nd stage performance even though batteries need to drive pump for longer.
4) Better engine control with electric as pump speed can be varied under electronic control. No surprise there.
As expected electric will gain from improvements in battery, electronic and motor technologies. This is by far one of the more important advantages, Rocketlab just need to sit back and wait for these improvements. Fitting lighter batteries every year would not cost a lot in R&D plus would be extremely low risk.
Note that this is a comparison with gas generator turbopump engines, which loose several percentage points of efficiency by tossing the turbopump exhaust overboard. Staged combustion turbopump engines would likely outperform electric pump engines.
- Ed Kyle
Compare the development cost of a staged combustion system vs just developing a pump an connecting it to a motor, battery pack, and electronics that you can nearly buy off the shelf. Yes, it gives up some performance. But not nearly so much as going pressure fed. It potentially turns this into another option for the cost and risk tradeoffs. What if it's cheaper to just increase the size of your vehicle by 20% instead of developing and building a staged combustion engine? Tanks and propellant are cheap.
The other thing that would be really interesting for this concept would be some kind of flow battery where the spent electrolytes could be dumped overboard.
I'm looking forward to seeing what happens when RocketLab actually flies this, i.e. will it work, and can they make the economics work.
(j/k)
