2020 marks the start of a new decade of space exploration and innovation, in which nickel-containing alloys play an important role in many applications, including rocket, wheel and catalyst manufacturing.
SpaceX, a company dedicated to aerospace equipment manufacturing and repeatable space transportation, uses a nickel-containing 304 (S30400) stainless steel to manufacture Starships and super-heavy rockets.
The cost is lower compared to carbon fiber, which costs more than 60 times more per kilogram. It's also much more heat resistant than carbon fiber or other metals, so it requires far less, or possibly even, insulation.
Meanwhile, NASA is exploring another potential application for nickel-containing materials in probe wheels. Rubber wheels are impractical on the moon or Mars, so the original Apollo lunar rover wheels were made of spring steel, but the spring steel wheels on large and heavy wheels designed for use on Mars would deform. To solve this problem, NASA is developing a metal mesh tire made of nickel-titanium alloy, which has shape memory properties and can cope with 30 times the deformation of a spring steel wheel.
Equipped with a Raptor rocket engine, the SpaceX Starship is one of the first Starships powered by liquid methane and liquid oxygen and is designed to last 1,000 uses. Methane was chosen to make rocket fuel on Mars for the return journey. Methane can be produced by using carbon dioxide and hydrogen through the Chabatier reaction, in which hydrogen reacts with carbon dioxide through a catalyst at high temperature (optimal temperature is 300-400 °C) and high pressure to generate methane and water. One such catalyst that can be used is nickel.
The Martian atmosphere is 95 percent carbon dioxide, and NASA has confirmed the presence of water on Mars, the raw materials needed to generate methane and oxygen for rocket boosters and oxygen for astronauts to breathe. Nickel-containing materials are also required by the red planet's lower ambient temperature and the low temperatures required to generate liquefied methane, hydrogen and oxygen.
Nickel-copper alloy K-500 (N05500) has excellent ductility at low temperatures and is flame resistant in pure oxygen. This makes it the preferred choice for an oxygen booster pump that supplies oxygen to rocket engines.
With its high strength and toughness, Alloy 718 (N07718) is a precipitation hardenable nickel-chromium alloy used in aircraft turbojets, rocket engines and pressure vessels, and can handle low temperatures down to -250°C Liquefy gas and achieve boost. But the properties of alloy 718 make it more difficult to machine and form than other materials. Investment casting processes can be problematic because Alloy 718 is susceptible to porosity, segregation, and extremely coarse grain size, necessitating subsequent processing steps.
What is the solution? 3D printing can more efficiently utilize nickel-based alloys such as 718 alloys in high-performance applications with complex designs.
3D printing makes it easier to process alloy 718 and retains the material properties well. The process avoids welding and machining, thus greatly reducing material waste. The benefits of this fabrication method were demonstrated by 3D printing a prototype of a 718 alloy rocket engine. The prototype was designed entirely through artificial intelligence and developed by Hyperganic Software in Germany.
Unlike conventional rocket engines, which consist of individually designed and assembled components, the 3D-printed prototype is a continuous whole. It contains the combustion chamber where fuel and oxidant burn, and surface channels that circulate the fuel to cool the combustion chamber and avoid overheating. The monolithic construction method guarantees the lightest weight and the most efficient cooling for the best performance of a given rocket. The Vulcan II rocket project at the University of California, San Diego, also uses 3D printing to make the Ignus II 718 alloy rocket engine. For every new application in the future, nickel will help space exploration go further.
