This is how Rocketlab pumps both stages of its Electron rocket. Rare Earth
permanent magnet motors with Lion batteries in which half the battery pack
it jettisoned during stage one boost. A Coke can sized motor generates 50
HP.
Pretty cool.
Ken
On Fri, Apr 7, 2023 at 11:30 AM Robert Steinke <robert.steinke@xxxxxxxxx>
wrote:
On Thu, Apr 6, 2023 at 10:54 AM Alexander Mikhailov <
alexander.mikhailov@xxxxxxxxx> wrote:
When you run the numbers the energy density of modern batteriescompares quite well to the kinetic energy extractable from decomposed
peroxide monoprop in a practical steam engine. I did a presentation about
this maybe 10 years ago at space access because when I looked at the
numbers I was floored by how good batteries are nowadays.
I'd definitely be very interested to look at that presentation.
My BOTE calculations for peroxide go like that: at ~50 atm liquid
output pressure amount of input peroxide to drive pumps is ~1/20 of
the total amount of peroxide, mass of pump hardware is negligible,
nothing to drop as too heavy.
What would be approximate numbers for electrical pumping system?
Alex
1 cubic meter of 85% H2O2 (1350 kg) pumped uphill against a dP of 5MPa
takes 5MJ of work. Here's a hobby battery with a "nominal" capacity of
1.8MJ
https://hobbyking.com/en_us/turnigy-high-capacity-battery-20000mah-6s-12c-drone-lipo-pack-xt90.html
Three of them weigh 7.9kg, 1/170 the mass of the peroxide.
Now, this is a back of the envelope assuming 100% efficiency and the
battery actually delivers its nominal capacity at a high discharge rate,
and not accounting for electric motor and pump hardware mass. But it's
still surprising that batteries are competitive with an H2O2 monoprop steam
engine.