Rutherford

Rutherford is a small rocket engine built by Rocket Lab to lift its Electron rocket off the ground. It broke new ground by using battery-powered electric motors to feed its propellants, where almost every other rocket engine uses a turbine driven by burning fuel.

Quick facts

• Maker: Rocket Lab (USA / New Zealand)
• Fuel: liquid oxygen (LOX, oxygen chilled until it becomes a liquid) plus RP-1, a highly refined kerosene similar to jet fuel
• Cycle: electric-pump-fed, the first flight-ready engine of its kind
• Thrust at sea level: 24.9 kN (5,600 lbf) — “thrust” is the pushing force the engine makes
• Thrust in vacuum (with an extended nozzle): 25.8 kN (5,800 lbf)
• Weight: about 35 kg (77 lb)
• Diameter: about 0.25 m (9.8 in)
• First test-fire: 2013 · Maiden flight: 25 May 2017
• Production: more than 1,000 engines built

What it is and how it works

Like every liquid-fuel rocket engine, Rutherford pushes two liquids — oxygen and kerosene — into a combustion chamber, where they ignite. The blast of hot gas is squeezed out through a shaped opening called a nozzle, and that rushing exhaust pushes the rocket the other way, much as letting go of an inflated balloon sends it darting across a room.

The clever part is how Rutherford gets the propellants into the chamber. Most engines use a gas-generator turbopump, which burns a little of the fuel just to spin a turbine that drives the pumps. Rutherford instead uses two small, high-speed brushless DC electric motors per engine, powered by lithium-polymer batteries (the rechargeable kind found in phones and laptops). Each motor produces about 37 kW (50 hp) and spins at roughly 40,000 rpm. On Electron’s first stage, a single battery pack delivers over 1 megawatt to drive all nine engines at once.

Removing the hot-gas turbine makes the engine simpler. Rocket Lab says the electric pump-drive runs at about 95% efficiency, compared with roughly 50% for a typical gas-generator cycle — that figure refers to how the pumps are driven, not the engine’s overall performance. The chamber is regeneratively cooled, meaning propellant flows around it to carry heat away before being burned. And nearly all the major hardware — chamber, injector, pumps, and valves — is 3D-printed from metal powder using a laser, a process called Direct Metal Laser Solidification, rather than machined or cast. The primary parts can be printed in about 24 hours.

Why it matters

For years, electric-pump-fed propulsion was thought impractical for reaching orbit because batteries are heavy. Rutherford proved it could work. Pairing that approach with heavy use of metal 3D printing lets Rocket Lab build engines fast and cheaply enough to cluster many in one rocket and offer dedicated launches for small satellites — rather than treating them as add-on passengers on a bigger mission. That helped open the dedicated small-launch market. With more than 1,000 units built, Rutherford is one of the most-manufactured rocket engines on Earth, and Rocket Lab has worked toward recovering and re-flying Electron’s first stage, including flying a previously used Rutherford engine.

There is a trade-off. The batteries are dead weight the rocket must carry, and on the first stage they are partly drained and jettisoned. That weight limits how well the design would scale to very large engines, but it works well at Electron’s small size.

Where it is used and notable examples

• Rocket Lab Electron — the two-stage small-satellite rocket Rutherford was built for: nine sea-level engines power the first stage, and one vacuum-optimized engine powers the second.
• Electron “It’s a Test” (25 May 2017) — Rutherford’s maiden flight. It reached space but not orbit; the test was ended early by a ground-equipment glitch. Electron first reached orbit on its second flight, “Still Testing,” in January 2018.
• Pre-flown engine reuse (announced 2023) — Rocket Lab flew a recovered and refurbished Rutherford as a step toward first-stage reusability.
• Smithsonian National Air and Space Museum — holds a Rutherford in its collection as a notable example of 3D-printed, electric-pump-fed propulsion.
• NASA and commercial smallsat missions — Electron, powered entirely by Rutherford engines, has flown dozens of missions delivering small satellites to orbit.

The engine is named after Ernest Rutherford, the Nobel-winning, New Zealand-born physicist.