Electron: Rocket Lab shrinks the space launch vehicle

Rocket Labs infographic: click the image to see the full size version.

Rocket Labs infographic: click the image to see the full size version.

Rocket Lab is revolutionising the global space industry with the creation of a light-weight, cost-effective rocket, making it easier for companies to launch small satellites into orbit. Peter Beck, chief executive of the New Zealand-headquartered aerospace company, speaks with New Zealand Engineering News Editor Romy Udanga about how they shrunk the space launch vehicle in the Electron, a reusable launch vehicle that is about 30 percent the average size and 10 percent the average weight of current models.

One of the fundamental challenges of building any rocket is mass, or weight. Of course there is the performance of the rocket engine, which counters the effect of mass, but rocket builders go to extraordinary lengths to minimise mass. Mr Beck says the three major components that contribute the most to the mass factor are the vehicle’s body, the rocket engine and the electronics.

“The whole launch vehicle is designed on CAD using Solid Works. We need to track mass very carefully, so we need to draw everything down to the last nut and bolt and screw and wire to account for every gram that is in it,” he says.

All carbon composite material

Historically, all of Rocket Lab’s launch vehicles have been built in carbon composites. It is one of the key fundamental decisions that Mr Beck made very early on “because composites offer greater stiffness and greater strength for lower mass”. So the company knows the material very well. But there are a lot of challenges with building an all-composite launch vehicle, and Rocket Lab is building the first one in history for a liquid fuel rocket.

“There are certainly attractive aspects of composites from a thermal standpoint, but there are also negatives,” Mr Beck says. “They can not get hot – at all. You have to keep that in mind because when you are building a rocket it gets hot, so there are certainly some challenges there.”

Usually composites are stayed away from when liquid oxygen, which is a very strong oxidising agent and a cryogenic fluid that has to be maintained at -187 degrees C, is involved. There are well documented issues, like micro cracking, at cryogenic temperatures.

“Cryogens are difficult materials to work with in fluids at the best of times let alone trying to do it in a plastic tube. That has been a huge challenge for us, but we solved a lot of the related issues, and we feel we are leading the world in that area,” Mr Beck says.

The engineering that is being done at Rocket Lab is, well, really rocket science. On one hand is a rocket motor running at over 2500 degrees C, and on the other hand, separated by a millimetre or two of steel, is the cryogenic fuel running at -187 degrees C at very high pressures and under a lot of stress – all at a safety factor of 1.2 or less.

Leading to the present, Rocket Lab has invested heavily in the development of carbon composite flight structures, especially propellant tanks, in the last five years beginning with its Atea-1 vehicle in 2009.

“We kicked off a big testing program. We developed new liner materials for the tanks but more so, really understanding of the material and what happens to the material when you cycle it and expose it to cryogenic temperatures. That drove things like laminate design and all that,” Mr Beck says.
Electron, whose dry mass is less than that of a Mini Cooper, takes full advantage of the low mass and high strength offered by carbon composites to achieve an exceptional mass efficiency. A low structural mass fraction is a crucial performance indicator for orbital launch vehicles.

“Traditionally, a low mass fraction is hard to achieve for smaller rockets in Electron’s class,” Mr Beck says. “Designing Electron as a fully carbon-fibre vehicle has allowed us to meet our mass fraction targets without compromising structural integrity. Unlike traditional metal flight structures, carbon composites can be designed to provide for strength and stiffness in the required directions only, so that every gram is working as hard as it can. This directly translates to larger payloads for our customers.”

While the composite tubes are made by a contractor all the designs, including the composition and lay up of the fibres come from Rocket Lab. “We spent quite some effort in getting the carbon fibre right and to get it tailored to the environment that it will be operating in,” Mr Beck says.

Electronics don’t scale down

When you shrink a rocket, not everything scales down. And this is the second engineering challenge Rocket Lab has to contend with.

“When mass is your prime objective, it is actually challenging to have to deal with things that are fixed,” Mr Beck says. “Take pressure transducers. They weigh around 50g each and is the size of a matchbox. When you have something the size of a Space Shuttle, this is not a big issue. But when you have something the size of Electron, that is a big deal. Unfortunately pressure transducers or, for that matter, the whole avionics system do not scale down.”

The avionics are responsible for control and monitoring of the rocket engines, launch sequencing, trajectory planning, guidance, navigation and control from the beginning of the countdown all the way to orbit. In the original Space Shuttle, the avionics system weighed approximately 4500kg, excluding cabling. Electron’s weighs just 8.6kg.

So what did Rocket Lab do with Electron’s electronics?

“We started from scratch,” Mr Beck says. “We built all our own flight computers, all our own avionics, all our own control systems simply because if you were to go and buy some of those from US aerospace contractors they actually weigh more than our payload. There is just no way that we could use that sort of stuff.”

Rocket Lab does absolutely everything in-house – all the electronic design and testing. It specifies some items from various contractors around town who manufacture things like circuit boards and populates them and run testing programs. It is a ground up approach, and the only way Rocket Lab can achieve what it set out to achieve.

In the end, Electron’s flight computer was reduced down to 200g. To put things into context, the Space Shuttle has 7,500kg of computers and wires.

“It is taking that clean sheet approach and really starting fresh and saying, ‘Okay, this is what we need to do. How do we go about doing it?” Mr Beck says.

“There were many challenges in the design phase because mass is king. Every component we have got in there has to justify its own weight, its own existence in mass, whether it is a fitting or a pressure transducer or even just a bracket for a pressure transducer. We do not just make a bracket and screw it on. The bracket goes through a full finite element analysis to look at that bracket and make sure we have every single gram we can out of that bracket. We run full simulations on that because a gram here and a gram there and you have a kilo! And in the launch business that is the difference.”

Rocket engine

Rocket Lab is yet to schedule a flight test for the Electron but once or twice a week it performs rocket motor, tank, structure, vibration, environmental and a whole lot of other tests. “This is not in a CAD model; this is real hardware undergoing major testing,” Mr Beck says.

Rocket Labs rocket engine, which it has daubed Rutherford to honour New Zealand-born physicist Ernest Rutherford, is a regeneratively cooled LOX/Kerosene engine, developed in-house. There are nine Rutherford engines on the first and one on the second stage of the Electron.

“World-first pump technologies and manufacturing methods make Rutherford the world’s most advanced engine yet,” claims Mr Beck.

The Electron, with its high-performance miniature avionics and flight computer systems, uses a distributed computing architecture with a focus on common hardware and modularity across each rocket stage and function.

A single Rutherford engine pumps rocket-grade kerosene and liquid oxygen from the low pressure tanks into the combustion chamber producing 13.3kN of thrust at lift-off. Electron uses two variants of the Rutherford engine, a sea level and a vacuum engine. The vacuum variant differs only in nozzle shape, which is tailored to suit the vacuum conditions outside Earth’s atmosphere.

“The duplicate engine design for both stages shrinks our development time and costs, which are essential steps for achieving high-frequency and low-cost launches. It also makes Electron highly optimised for mass production,” Mr Beck says.

Creating a space company in NZ

Rocket Lab has in the past launched out of privately owned islands in New Zealand. It is now evaluating new sites in the country.

“New Zealand has an ideal launch elevation,” Mr Beck says. “We can launch sun-synchronous or out of 46 degrees. Also we are a small island nation in the middle of nowhere so there is nothing to hit. It is just the sea and the sea is not busy and neither are the airways. If you take a map of New Zealand and plot all the airpaths, there is just a few lines coming into it. If you take the USA and plot all the airpaths and where they are flying you cannot even see the country beneath it for all the lines.”

Mr Beck says he is creating a space company in New Zealand – a country that has no space heritage. And the government is backing him up with a $25 million grant, spread over five years.

“Globally, Rocket Lab is the third private company to attempt to build an orbital launch vehicle. SpaceX and Orbital Sciences Corp are both in America, and Rocket Lab in New Zealand. That is three companies in the entire world that have actually tried to achieve this. The New Zealand Government, certainly see the value of this for the economic development for the country,” Mr Beck says.

At the moment, Mr Beck is recruiting engineers – mechanical, electrical and to work with him on the orbital launch vehicle.

“If you look at countries that have created indigenous launch capabilities, actually created their own launch system, historically it is always a government and it is a nation and it is a decade or more minimum. If you look at who have created those capabilities it is the superpowers,” Mr Beck says.

“Rocket Lab is trying to do in two years what typically takes a nation and a government a decade to do. Space is not just somebody else’s domain. It can be New Zealand’s.