"electric starter" as an automobile starting motor? If so the power to
weight isn't as high as a rare earth permanent magnet motor,
as aforementioned a coke can sized motor delivers 50 HP plus they run at
turbop[ump RPM, i.e. 30-50K RPM direct drive, no gear box.
Ken
On Sat, Apr 8, 2023 at 6:56 AM JOHN HALPENNY <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
How about an electric starter for a turbopump? It should be comparable
to bottles of gas, and it can stay engaged to provide fine speed control
when the pump is running.
John
On Saturday, April 8, 2023 at 08:50:25 a.m. EDT, Matthew JL <
prmattjl@xxxxxxxxx> wrote:
Ben,
Inclined to agree on all counts wrt electric turbopumps - being able to
decouple the powerhead from the propulsion really trades favorably at small
scales.
I think there’s an evolutionary pathway you’ve missed though - using an
expander cycle to drive a dynamo that, in turn, directly powers electric
turbopumps. On paper, this would help decouple the powerhead from the rest
of the engine in the same way battery-driven turbos would, but it wouldn’t
be limited by the weight of the battery. Some time ago I estimated the
losses in a dynamo cycle and they looked acceptable/on par with
conventional cycles.
Plus, mixture and throttle control becomes a breeze when the pumps
themselves can be spun up or down directly, independent of one another.
And I think that opens the door for triprops at the ~300-1000 kN scale,
with a relatively low development floor.
Best,
-Matt L.
On Sat, Apr 8, 2023 at 8:13 AM Ben Brockert <wikkit@xxxxxxxxx> wrote:
It's notable that two different companies, on their own and
independent of each other, managed to to use electric pumped rockets
to launch things into orbit at relatively low program costs compared
to many of their competitors. As far as I know no company has
independently built an orbital rocket based on gas
generator/expander/staged combustion or other turbine cycles. SpaceX
and Virgin Orbit both had help from Barber Nichols, Orbital and
Firefly from ex-Soviet programs.
It's a relatively small data set, but it suggests that electric pumps
are the easiest pump-fed rocket to get working. I definitely found
them relatively easy to test, in that most parts can be run
independently at high fidelity. Also, when integrated they have
relatively little feedback in the system, whereas even the relatively
simple gas generator cycle typically has the outlet of the pump
plumbed to the inlet of the gas generator, a positive feedback loop
that has to be controlled.
The performance of pure electric pumping is not spectacular for things
like first stages, though it is better than pressure fed. There is an
opportunity to move electric pumps into more advanced cycles. For
instance if you did a gas generator with electric pumps feeding the GG
only, you could apply Rocket Lab's existing pumps to make a
100,000+lbf engine and have the advantage of decoupling the systems as
well as making starting and restarting much simpler. Or, for maximum
performance, a sort of middle ground between gas generator and staged
combustion where you use electric pumps to pump the outlet of the main
pump up to a higher pressure for the gas generator, such that the
turbine outlet pressure is above chamber pressure and you can dump it
into the chamber instead of losing performance by dumping it
overboard. You still gain very tight control over the turbine throttle
and mixture ratio from the electric pumps, as well as the ability to
start or restart the engine without the usual (nonrenewable,
expensive) helium spin start.
It will take some time because deep space programs are extremely
conservative, but eventually electric pumps will gain a lot of
traction there. In missions like moon landers where you have a few
large burns that are separated in time, electric pumped main
propulsion that is recharged by solar is much higher performance than
big pressure-fed tanks.