Smaller and Smarter: The Electron Rocket Takes Flight

On January 21st, 2018 at 1:43 GMT, Rocket Lab’s Electron rocket lifted off from New Zealand’s Mahia Peninsula. Roughly eight minutes later ground control received confirmation that the vehicle entered into a good orbit, followed shortly by the successful deployment of the payload. On only their second attempt, Rocket Lab had become the latest private company to put a payload into orbit. An impressive accomplishment, but even more so when you realize that the Electron is like no other rocket that’s ever flown before.

Not that you could tell from the outside. If anything, the external appearance of the Electron might be called boring. Perhaps even derivative, if you’re feeling less generous. It has the same fin-less blunted cylinder shape of most modern rockets, a wholly sensible (if visually unexciting) design. The vehicle’s nine first stage engines would have been noteworthy 15 years ago, but today only serve to draw comparisons with SpaceX’s wildly successful Falcon 9.

But while the Electron’s outward appearance is about as unassuming as they come, under that jet-black outer skin is some of the most revolutionary rocket technology seen since the V-2 first proved practical liquid fueled rockets were possible. As impressive as its been watching SpaceX teach a rocket to fly backwards and land on its tail, their core technology is still largely the same as what took humanity to the Moon in the 1960’s.

Vehicles that fundimentally change the established rules of spaceflight are, as you might expect, fairly rare. They often have a tendency to go up in a ball of flames; figuratively if not always literally. Now that the Electron has reached space and delivered its first payload, there’s no longer a question if the technology is viable or not. But whether anyone but Rocket Lab will embrace all the changes introduced with Electron may end up getting decided by the free market.

A Tiny Rocket for a Growing Market

The first thing to understand about Electron is that it’s incredibly small and light for an orbital rocket. To put it into perspective, the Space Shuttle could have carried two fully fueled Electron rockets in its cargo bay without breaking a sweat. Accordingly, the Electron has an extremely low cargo capacity, topping out at around 500 lb. Compared to the Falcon 9’s maximum capacity of roughly 50,000 lb, one might wonder what the point is.

Rocket Lab CEO Peter Beck poses with Electron

The point, of course, is the cost. A launch on Falcon 9 costs the customer around $62 M, while a trip to space on Electron is less than $6 M. If you’ve got a payload light enough to hitch a ride on an Electron, the choice is obvious. As satellites get smaller and lighter, more and more payloads will be able to fit into this category. In fact, Rocket Lab hopes to be launching as many as 100 Electron rockets per year to meet the anticipated demand.

Pound-for-pound, it’s actually much cheaper to fly on Falcon 9. But a lightweight payload on Falcon 9 will be relegated to secondary cargo. The realities of this arrangement were demonstrated in 2012, when one of the Falcon 9’s engines failed on ascent. This only left enough power to accomplish the primary mission, delivering supplies and cargo to the International Space Station. The secondary payload, a satellite from communications provider Orbcomm, had to be left behind. At only 379 lb, Orbcomm’s satellite could have been a perfect fit for a dedicated Electron launch.

A New(er) Way To Build Rockets

Electron isn’t cheap just because it’s small, the price is also driven down by the state-of-the-art construction techniques being used throughout the vehicle. The combustion chamber, injectors, pumps, and valves of each of the Electron’s ten Rutherford engines is 3D printed via electron-beam melting in as little as 24 hours. This is a first in rocketry, and beats NASA and SpaceX to the punch by years. SpaceX won’t be flying their 3D printed engine until their “Dragon 2” capsule flies later this year, and NASA is still in the early stages of their research.

In another first, Rocket Lab has built nearly the entire rocket out of a carbon composite. This gives the rocket its deep black color, but more importantly, a dry weight that Rocket Lab’s CEO Peter Beck says is “less than a Mini Cooper. Critically, even the fuel and oxidizer tanks are made of carbon composite instead of the traditional aluminum. Electron is the first rocket to successfully fly with carbon composite tanks, but it certainly isn’t the first one to try.

In 2001, NASA famously canceled the Lockheed Martin X-33 spaceplane, a potential replacement for the Space Shuttle, in large part because they determined that its composite propellant tanks were simply beyond the technology of the time.

The Battery Powered Rocket

But the crowning achievement of the Electron isn’t how small it is, or how fast its engines can be 3D printed. Those are impressive feats in their own right, but arguably just extensions of work that’s been going on for years. They were eventualities that Rocket Lab were able to capitalize on, at least in part, because they have such a tiny vehicle.

A simplified liquid fuel rocket engine with preburner. Credit: Duk

The true revolution is the fact that Rocket Lab has completely done away with the complicated preburner and turbine traditionally used in liquid fuel rockets. Rocket engines consume an immense amount of fuel and oxidizer, and powerful pumps are required to get the propellants injected into the combustion chamber at the necessary pressure. To power these pumps, most engines have a turbine which is spun by what’s known as a preburner. In some cases the preburner uses the same fuel as the rocket engine itself, but can have its own fuel supply with associated plumbing and tanks.

The preburner, turbine, and pumps make up a powerful and complicated system that in some ways is just as difficult to master as the rocket engine itself. Consider that the turbine in each one of the F-1 engines used in the Saturn V developed 55,000 horsepower alone.

In the Rutherford engine, this entire system is replaced with two 50 horsepower brushless motors powered by a bank of lithium polymer batteries. These motors power the pumps directly, and give a level of control over engine operation that would be difficult to match with traditional techniques. With a turbine, spin-up time is directly correlated to throttle response and the engine startup sequence. But by using electrically driven pumps, Electron’s engines are able to respond faster and more accurately to commands from the flight computer.

The downside is that batteries are heavy, and unlike liquid fuel, don’t get consumed while being used. A dead lithium battery is just as heavy as a fully charged one. To combat this, the Electron actually dumps the dead batteries overboard as the vehicle climbs.

This Changes Everything, Right?

The engineering that Rocket Lab has done on Electron and the fact they made orbit on only their second attempt with such a wildly unconventional vehicle is an incredible achievement. There’s no question the Electron itself will be looked back on as a milestone in the history of rocketry.

But while 3D-printed engines and carbon composite propellant tanks are pretty much a sure bet for future generations of rockets, Electron’s engine technology might be looking at a much shorter life. There’s simply no getting around the fact that liquid fuels have a much greater energy density than batteries. While Rocket Lab has managed to find a workable combination of battery weight versus payload capacity in this specific vehicle, the equation just doesn’t work as you scale up the design. At some point, the weight of the batteries simply becomes too great to remain viable.

If Rocket Lab is right, and there’s a huge market for lightweight payloads, then we may see other small rockets adopt a similar engine. But if the market is content getting to space in the second or third class seats of larger rockets like Falcon 9, this innovative technology may end up taking the back seat itself for economic reasons.

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