[AR] Re: [AR] Re: [AR] piston pumps and peroxide (was Re: [AR] “Transitioning...)
- From: George Herbert <george.herbert@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 8 Apr 2023 13:06:39 -0700
On Apr 8, 2023, at 12:00 PM, Ben Brockert <wikkit@xxxxxxxxx> wrote:
It isn’t that the performance gain is negligible, it’s that you can’t drain
a LiPo fast enough to get through two batteries in a first stage burn. Even a
single battery needs to be drained so fast that it can easily exceed current
and temperature ratings by the end of the burn.
I’ve modeled it and done related designs, and it looks like it’s not much help
to drop. But I don’t have the Electron detailed plans and models that
Rocketlab have so I may be mistaken for their particular case.
It’s something to keep in mind for people looking at alternative chemistries.
For first stage use, it doesn’t matter if the energy density of a new
chemistry is twice that of LiPo if it takes ten minutes to dump 80% of the
nominal capacity.
The old NiCd rechargeable batteries can short like lead acid to a welding arc
grade current (accidentally did that once). LiPo aren’t quite that
aggressive. What you need is current over time for the desired burn duration,
yes. The solution of maximum performance may even want something like
supercapacitors for power boost during the first 20 seconds or so. Constant
current isn’t always the best performance profile.
Battery cooling is a useful thing in some circumstances, but LiPo don’t like
running too cold either so you can’t dump them in a LOX tank. Nevermind the
exciting fire hazards. But the fuel tank for storable fuels may be of use, or
a loop of fuel as coolant. Or storable oxidizers like peroxide.
This is totally not a missiles proliferation problem, either. Groan.
-george
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