Ben,
I think this turns into a great argument for a dynamo cycle - no power draw
rate limitations.
Now if we just had a use case for light, 1000 kN engines…
On Sat, Apr 8, 2023 at 3:00 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.
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.
In-space propulsion systems generally have the advantage of being able to
do longer burns without hurting system performance, especially in systems
like Rocket Lab’s where the second stage does much more than half of the
total delta-v.
On Saturday, April 8, 2023, George Herbert <george.herbert@xxxxxxxxx>
wrote:
On Apr 7, 2023, at 11:36 AM, roxanna Mason <rocketmaster.ken@xxxxxxxxx>
wrote:
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.
Minor detail; on Electron, it’s the upper stage that drops a first
battery pack before continuing to orbit on a second. The first stage has
too much upper stage above it to justify a swap and drop; Mf savings is
negligible there. For upper stage it’s significant.
-george