The Rutherford Rocket Engine: The First Electric Rocket Engine

In the realm of small satellite launches, Rocket Lab stands out as a global leader. Founded in 2006 by New Zealand engineer Peter Beck, the private aerospace company has made significant strides in the field.

Operating from New Zealand with its headquarters based in California, Rocket Lab has captured the world’s attention with its groundbreaking Electron rocket, a two-stage orbital launch vehicle that effectively transports satellites to orbit.

Central to the Electron’s success is the revolutionary Rutherford rocket engine, the world’s first electric pump-fed orbital-class rocket engine.

Rutherford Rocket Engine Statistics

The Rutherford rocket engine is a liquid propellant rocket engine named after the renowned New Zealand-born scientist Ernest Rutherford. The engine is fueled by RP-1, a very refined kerosene fuel, weighing just 35 kilograms.

Rutherford is capable of delivering 25 kilonewtons of thrust at sea level and it has a thrust-to-weight ratio of 72.8 and a sea-level specific impulse of about 311 seconds.

The electron rocket uses a cluster of nine identical Rutherford engines on the first stage and one vacuum-optimized variant with a more extended nozzle on the second stage.

The vacuum-optimized version of the engine produces a thrust of 26 kilonewtons with a specific impulse of 343 seconds.

rutherford rocket engine with ceo peter beck
Credit: Rocket Lab

Rutherford Rocket Engine History

Rocket Lab began development on the Rutherford engine in 2013.

Within the same year, Rutherford was test-fired for the first time marking the beginning of a new generation in rocket propulsion.

According to Rocket Lab, the test was successful, and the engine demonstrated stable performance. After two years of tests, on April 14, 2015, at the 31st space symposium held in Colorado, Peter Beck unveiled the Rutherford engine.

He stated that the company had completed the development of the Rutherford engine after completing more than 200 engine hot fires as part of the qualification program.

On March 21, 2016, Rocket Lab announced that its Rutherford engine had been qualified for a flight test. Peter Beck then stated that the company is looking to manufacture the engine in quantity for both tests and commercial flights.

The first flight of the engine happened on May 25, 2017. The electron rocket carrying no payloads lifted off from Rocket Labs launch complex one in New Zealand.

The rocket successfully performed its first stage in fairing separations after reaching an altitude of around 224 kilometers. The rocket’s telemetry signal was lost, and the range safety officer destroyed the rocket.

rutherford rocket engine test fire
Credit: Rocket Lab

Later on January 21, 2018, the Rutherford engine successfully carried the electron rocket to orbit placing four Cube Sats into a low earth orbit.

On January 31, 2018, Rocket Lab announced that the engine had completed its 500th test fire in a test stand. The 500th Rutherford test fire burned for 100 seconds.

The milestone firing brought the Rutherford engine series to 19,000 seconds of cumulative firing time since the first hot fire test in December 2013.

On 8 July 2019, Rocket Lab announced that it had produced 100 flight-ready engines at its Huntington Beach headquarters and conducted more than 850 successful engine test fires. 

How the Rutherford Rocket Engine is Made: Electron Beam Melting

The thrust chamber injector turbopumps and main propellant valves in the engine are all made with the electron beam melting technique.

Electron beam melting is an advanced form of 3d printing where metal powder is completely fused layer by layer with an electron beam in a high vacuum.

In the electron beam melting process, the metal powder is first loaded into the machine.

The build chamber is then closed, and a vacuum is created to ensure a clean and controlled environment.

A powder layering system then evenly distributes a thin layer of powder on the build area.

A powerful electron beam heats the powder bed to an optimal temperature of around 1000 degrees Celsius. As each layer is completed, the build is lowered, and a fresh layer of build powder is raked over it.

The process repeats one layer at a time until the final product is ready. Rocket Lab uses Inconel and titanium powder as the raw material for 3d printing the engine’s primary components.

According to Peter Beck, Rocket Lab can print an engine within 24 hours, and they plan to launch a rocket every 72 hours. Rutherford has the most 3d printed components of any rocket engine in the world.

The Unique Pump Cycle

rutherford rocket engine turbopump system
Credit: Rocket Lab

Rutherford is the world’s first electric pump-fed rocket engine launched into space as most rocket engines rely on turbo pumps to supply fuel and oxidizer to the main combustion chamber.

For example, the SpaceX Raptor Engine which operates under a full-flow staged combustion cycle consisting of two turbo pumps to pressurize and inject the fuel and oxidizer into the combustion chamber.

In an electric pump-fed engine, instead of liquid propellant, the pumps are powered by electric motors with lithium polymer batteries.

An inverter converts the battery’s DC electricity to the AC needed by the motor. The motor then drives the oxygen and fuel turbo pumps which pressurize the propellant before pushing it into the combustion chamber.

Liquid Oxygen is delivered directly into the combustion chamber while fuel is circulated around the engine belt to remove the heat of combustion before being fed into the combustion chamber.

The Rutherford Engine uses dual brushless DC electric motors and a lithium polymer battery; the motors generate a power of 37 kilowatts while spinning at 42 000 rpm.

The first stage battery, which powers the pumps of nine engines simultaneously, can provide over one megawatt of electric power.

The Rutherford Rocket Engine vs a Traditional Engine

1. Advantages

Now let’s compare the Rutherford rocket engine with a traditional rocket engine. Rutherford cuts down on much of the complex turbo machinery and plumbing typically required for gas generator cycle engines and is simpler to build than a conventional engine.

The electric pump-fed system eliminates the need for extra tubes and valves which add weight to the engine and are frequently the source of engine failure in a traditional engine.

The pre-burner combustion must be timed with engine operation.

But the Rutherford engine follows a radically different approach where using brushless DC motors and lithium battery cells completely eliminates this thermodynamic problem

2. Disadvantages

With all these advantages, why are electric pump-fed engines not popular in the rocket industry?

The problem is that the energy density of the batteries was too low in the past.

According to Peter Beck, there have been enormous advancements in battery technology in recent years that have allowed him to go for electric turbopumps.

It is claimed that electric motors improve efficiency from 50 percent of the standard gas generator cycle to 95 percent. However, the battery pack raises the weight of the complete engine and poses an energy conversion challenge. 

Final Thoughts

So, what do you think about this non-conventional rocket engine?

Do you think it will be able to launch heavy satellites and astronauts in the future?

Let us know in the comments.

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