Hybrid Electric Rocket Has Arrived Thanks To Rocket Labs


While not a plug-in, we do occasionally pay tribute to clever hybrid electric vehicles and the Rocket Lab Electron rocket fits the bill.

The Electron fuel pumps make use of a DC electric motor and lithium battery in place of traditional pumps powered by hot gas.

Standing 17 meters in height and 1.2-meter diameter, this 2 stage rocket will focus on small satellite market of 225kg and less. Electron liftoff thrust is 162 kN with 192 kN peak thrust.

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The carbon fiber design includes payload fairing and fuel tanks capable of carrying liquid oxygen thus maximizing lightweight flight.

An optional apogee kick stage is designed for multiple burns allowing additional payloads to be deployed into different circularized orbits. The Electron is powered by Rocket Lab’s 3D printed liquid propellant achieving 120N of multiple burn thrust.

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Electron’s second stage is powered by a variant of a 3D printed Rutherford engine using an oxygen/kerosene pump-fed engine powered by high-performance electric pumps further reducing mass and replacing hardware with software.

Rocket Labs Electron HEV will begin launching commercial flights this year.

Check it out below:

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7 Comments on "Hybrid Electric Rocket Has Arrived Thanks To Rocket Labs"

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Cool! I wonder if they can scale the power upwards.

They can’t, really. Turbopumps require insanely high power throughput, and as rocket engines grow larger, the pumps themselves have to grow larger and consume more power still. Even if your batteries are single use – if you can literally wreck them in one single discharge cycle – you just cannot pull energy from them fast enough to drive larger turbopumps. It’s not about capacity, it’s about sheer discharge speed.

This is the reason nobody has flown electric turbopumps before. Even this rocket, on the very small end of the scale, can only pull it off by using nine small engines on the first stage instead of one or two larger ones.

Still, they did find a way to make it work for them. They solved the engineering issues, closed the business case, and now they can reap the rewards in the form of a cheap, easily-manufactured system that is more fuel efficient in flight than comparable engines. Electron will probably remain a unique breed of rocket for the foreseeable future, but it’s undeniably a very cool one.

When you scale a rocket engine, everything scales. That include the turbo pump, the electric motor driving the turbo pump and the battery feeding the electric motor driving the turbo pump.

Just like how Tesla made the Semi (of which many said not too long ago that it was insanely impossible).

“Electron’s second stage is powered by a variant of a 3D printed Rutherford engine using an oxygen/kerosene pump-fed engine powered by high-performance electric pumps further reducing mass and replacing hardware with software.”

Hard to believe that setup would reduce mass.

Then again, maybe the motor and battery don’t have to last more than few minutes…

One alternative is a full-flow or staged combustion engine with two turbopumps, two or three combustion chambers and lots of complicated seals and plumbing. Very efficient because all of the fuel and oxidizer flow through the rocket nozzle and produce thrust, but complicated, expensive and not super light. Think Space Shuttle Main Engine.
The other alternative is a gas generator engine, which is a whole lot cheaper and simpler, but still has a separate pre-combustion chamber to run the turbopumps. It then just dumps the exhaust from that chamber overboard without generating any thrust with it, so it’s also a bit less efficient. Think Spacex Merlin engine.
Running the fuel and oxidizer pumps with an electric motor doesn’t seem like it would be very light, but it must make sense in some way or they wouldn’t use it I guess. It is almost guaranteed to be significantly easier to develop though, since you don’t need to seal any moving parts against hot gases. I assume that this is the kind of thing that mostly makes sense on a small rocket. But if a larger rocket could be reused…

The way this saves mass is by using the fuel that would normally drive the pumps to propel the rocket instead. That means you need to load less fuel in the first place. And with typical rockets being something like 95% fuel by mass, that can be significant.

And even if it’s a wash in terms of mass, the electric turbopump is cheaper and easier to manufacture, and don’t have to endure high-pressure hot gas in flight, improving reliability.

Also, the upper stage actually jettisons half its batteries in the middle of its burn. They have four packs on board, and begin by emptying two of them, then switch over to the second pair and toss the empty ones overboard. You can see it happen in the launch broadcast.

And yes, the batteries only have to last a few minutes. They are driven at charge levels and discharge speeds at the limit of what’s physically possible, sacrificing all durabilitry – they wouldn’t be usable again after going through a launch even if they could somehow be recovered. This is the only way they can put out enough power to drive the pumps, and be light enough to make sense.

Great New Zealand company thinking outside the box.