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#1020
by
TrevorMonty
on 14 Jun, 2017 10:31
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What is interesting to me is how much they can scale this up.
It should be technically possible to scale it to any size. From a practical standpoint however, I don't think electric pumps scale up very well, especially when compared to other closed cycle engines. For example, (depending on what installed energy density you assume) the battery pack mass for a full duration Centaur burn is on the order of 1 tonne. Electric pumps are theoretically simple, so I guess in the end it depends on how you trade simplicity vs performance.
While battery may weigh 1t, weight of fuel required to drive a RL10 turbopump for 8 minutes is not insignificant.
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#1021
by
Ictogan
on 14 Jun, 2017 10:52
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What is interesting to me is how much they can scale this up.
It should be technically possible to scale it to any size. From a practical standpoint however, I don't think electric pumps scale up very well, especially when compared to other closed cycle engines. For example, (depending on what installed energy density you assume) the battery pack mass for a full duration Centaur burn is on the order of 1 tonne. Electric pumps are theoretically simple, so I guess in the end it depends on how you trade simplicity vs performance.
While battery may weigh 1t, weight of fuel required to drive a RL10 turbopump for 8 minutes is not insignificant.
True, but that weight is gone by the end of the burn, so if the fuel mass needed over those 8 minutes for a turbopump would be the same as the battery mass needed for an electric pumo, the turbopump would still be preferable in terms of delta-V.
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#1022
by
envy887
on 14 Jun, 2017 12:32
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What is interesting to me is how much they can scale this up.
It should be technically possible to scale it to any size. From a practical standpoint however, I don't think electric pumps scale up very well, especially when compared to other closed cycle engines. For example, (depending on what installed energy density you assume) the battery pack mass for a full duration Centaur burn is on the order of 1 tonne. Electric pumps are theoretically simple, so I guess in the end it depends on how you trade simplicity vs performance.
While battery may weigh 1t, weight of fuel required to drive a RL10 turbopump for 8 minutes is not insignificant.
RL-10 is a closed expander cycle: the fuel is heated by the nozzle, used to drive the turbine, then sent to the main combustion chamber. None of it is dumped as in a gas generator.
I don't think batteries can beat an expander cycle on mass. But they definitely scale better and are cheaper.
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#1023
by
FutureSpaceTourist
on 14 Jun, 2017 13:00
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#1024
by
lrk
on 14 Jun, 2017 21:51
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What is interesting to me is how much they can scale this up.
It should be technically possible to scale it to any size. From a practical standpoint however, I don't think electric pumps scale up very well, especially when compared to other closed cycle engines. For example, (depending on what installed energy density you assume) the battery pack mass for a full duration Centaur burn is on the order of 1 tonne. Electric pumps are theoretically simple, so I guess in the end it depends on how you trade simplicity vs performance.
While battery may weigh 1t, weight of fuel required to drive a RL10 turbopump for 8 minutes is not insignificant.
True, but that weight is gone by the end of the burn, so if the fuel mass needed over those 8 minutes for a turbopump would be the same as the battery mass needed for an electric pumo, the turbopump would still be preferable in terms of delta-V.
I seem to recall that the Electron upper stage drops batteries as they are exhausted? I don't remember where I heard this, but it should be theoretically possible.
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#1025
by
FutureSpaceTourist
on 15 Jun, 2017 07:39
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#1026
by
Steven Pietrobon
on 15 Jun, 2017 08:50
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I seem to recall that the Electron upper stage drops batteries as they are exhausted? I don't remember where I heard this, but it should be theoretically possible.
The limitation is the battery discharge time. For the first stage which runs for 2.5 minutes, it is just within the technology. That means no batteries can be dropped off for the first stage. I don't know how long the second stage runs for, but should be at least 5 minutes. That means half the batteries could be dropped off during flight. I don't know if Rocket Lab does that though.
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#1027
by
edkyle99
on 15 Jun, 2017 16:29
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What is interesting to me is how much they can scale this up.
It should be technically possible to scale it to any size. From a practical standpoint however, I don't think electric pumps scale up very well, especially when compared to other closed cycle engines. For example, (depending on what installed energy density you assume) the battery pack mass for a full duration Centaur burn is on the order of 1 tonne. Electric pumps are theoretically simple, so I guess in the end it depends on how you trade simplicity vs performance.
Don't forget the mass of the electric motor versus the mass of the gas generator and of the turbopump itself. High torque electric motors can be quite heavy.
- Ed Kyle
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#1028
by
TrevorMonty
on 15 Jun, 2017 18:15
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With 3D printing a conventional turbopump can be built inhouse compared to buying expensive electric motors and batteries.
With RLV the motors and battery costs are probably not as important, especially if they are good for dozens of flights.
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#1029
by
savuporo
on 15 Jun, 2017 18:33
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What is interesting to me is how much they can scale this up.
It should be technically possible to scale it to any size. From a practical standpoint however, I don't think electric pumps scale up very well, especially when compared to other closed cycle engines. For example, (depending on what installed energy density you assume) the battery pack mass for a full duration Centaur burn is on the order of 1 tonne. Electric pumps are theoretically simple, so I guess in the end it depends on how you trade simplicity vs performance.
Don't forget the mass of the electric motor versus the mass of the gas generator and of the turbopump itself. High torque electric motors can be quite heavy.
- Ed Kyle
About 5kW/Kg at relatively low rpm. High RPM motors can do better. Over >20kW/Kg in next few years likely.
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#1030
by
HVM
on 15 Jun, 2017 18:42
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...The epoxy is lox tolerant...
Good to know, tell that also to this thread's author.
...I seem to recall that the Electron upper stage drops batteries as they are exhausted? I don't remember where I heard this, but it should be theoretically possible.
Here are images of the battery packs(?).
Early modeling vs. 2S testing
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#1031
by
LtWigglesworth
on 16 Jun, 2017 07:16
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What is interesting to me is how much they can scale this up.
It should be technically possible to scale it to any size. From a practical standpoint however, I don't think electric pumps scale up very well, especially when compared to other closed cycle engines. For example, (depending on what installed energy density you assume) the battery pack mass for a full duration Centaur burn is on the order of 1 tonne. Electric pumps are theoretically simple, so I guess in the end it depends on how you trade simplicity vs performance.
Don't forget the mass of the electric motor versus the mass of the gas generator and of the turbopump itself. High torque electric motors can be quite heavy.
- Ed Kyle
About 5kW/Kg at relatively low rpm. High RPM motors can do better. Over >20kW/Kg in next few years likely.
Apparently they operate at 40,000 rpm, and each is the size of a soda can
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#1032
by
calapine
on 16 Jun, 2017 21:57
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#1033
by
Lars-J
on 16 Jun, 2017 22:16
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Yes, a $1 billion valuation is clearly laughable at this point.
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#1034
by
Zingpc
on 16 Jun, 2017 22:19
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New article from Peter B. de Selding
Arianespace valuation, $500 million. Rocket Lab, $1 billion: New Space thinking
Arianespace are stuffed in the reusable medium range launch market. They will incur losses and/or substantial subsidies from their national owner.
This VC evaluation is a vote of confidence in the innovation that a kiwi can make to soar above the clouds. It is not the size, rather the frequency. When the size of the rocket enables reuse it will happen.
The French are having trouble coming to terms with new space. They are getting whacked from both sides (small and medium sized). Soon we will have super heavy that will kill medium.
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#1035
by
Zingpc
on 16 Jun, 2017 22:48
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Also don't make the mistake of VC evaluation being anything more than VC promotion of their stock. Look at all the unicorns in a recent list. Many are zero now. Link later.
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#1036
by
TrevorMonty
on 16 Jun, 2017 23:01
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Yes, a $1 billion valuation is clearly laughable at this point.
That is 200 launches. Definitely VC talking up price for cash out.
Even if RL start flying frequently say 20 a year, they will need to invest most profits back into R&D to keep ahead competition.
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#1037
by
Lars-J
on 16 Jun, 2017 23:20
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New article from Peter B. de Selding
Arianespace valuation, $500 million. Rocket Lab, $1 billion: New Space thinking
Arianespace are stuffed in the reusable medium range launch market. They will incur losses and/or substantial subsidies from their national owner.
Did I dispute the Arianespace valuation? No.
This VC evaluation is a vote of confidence in the innovation that a kiwi can make to soar above the clouds. It is not the size, rather the frequency. When the size of the rocket enables reuse it will happen.
That sounds more like a wishful thinking argument from you. The Rocketlab valuation is almost all hype at this point, built on a belief in a massive smallsat market that so far has failed to materialize.
The French are having trouble coming to terms with new space. They are getting whacked from both sides (small and medium sized). Soon we will have super heavy that will kill medium.
If super heavy will kill the medium market, what hope does small have against medium? Medium has been killing the smallsat market for a long time, I don't expect that to change significantly. Rocketlab may eke out a niche, but that is far from killing the medium market.
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#1038
by
Zingpc
on 17 Jun, 2017 00:39
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I don't know of any of the technology of RL that is wishful, it all works. Gremlins are not show stoppers.
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#1039
by
QuantumG
on 17 Jun, 2017 00:44
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I think the value proposition of RocketLab is that they may be the first to get to orbit with such a small investment (in the first round). In a post-SpaceX world that's not saying much, but it's better than pouring money down the drain, ala Rocketplane.