STAR-3D™ HYBRID ROCKET ENGINES
Rocket Crafters is currently developing, testing, and prototyping the most advanced Hybrid Rocket Engine ever produced, providing smoother thrust and more consistent performance than any previous hybrid engine ever fired. Known as STAR-3D™ hybrid engines, Rocket Crafters’ proprietary engine design is Safe, Throttleable, Affordable, Reliable, and 3D Printed.
Mechanically Simple. Operationally Powerful.
Hybrid rocket engines combine the best elements of both liquid-fueled and solid-fueled rockets, using either a liquid oxidizer and a solid fuel or vice versa. STAR-3D™ hybrid rocket engines use liquid Nitrous Oxide as the oxidizer and solid ABS (Acrylonitrile-Butadiene-Styrene) thermoplastic (a common consumer-grade plastic) as the fuel and combustion chamber. Using a solid fuel allows for greater energy density like that found in a solid rocket motor. A liquid oxidizer allows the engine to be throttled by increasing or decreasing the flow of oxidizer into the combustion chamber, providing the control usually found in a liquid motor. Added to that, hybrid rocket engines are mechanically simple, needing only a handful of moving parts to operate. In short, Rocket Crafters is building a simple rocket engine burning Laughing Gas and Legos.
The Problem with Hybrids and How We’ve Solved it
Hybrid Rockets are not a new technology; they have been around for over seventy years. However, despite their innate advantages, they are not commonly used in large-scale rocketry. There are three major reasons for this: combustion instability, inconsistent performance, and low thrust.
The traditional approach to address these issues has been to:
- add a pre-burner to the oxidizer to help atomize it and convert it to a gas before it reaches the fuel and to
- add multiple ports to the fuel grain, increasing the exposed fuel surface area for combustion.
The biggest problem with these solutions is that they increase the complexity and decrease the efficiency of the engines.
In 2008, Rocket Crafters began working with Utah State University to conduct some of the first studies comparing 3D printed ABS Plastic Hybrid Rocket Engines to the more traditionally cast HTPB (Hydroxyl-terminated polybutadiene) fuel grain. This compared the combustion efficiency and reliability of rubber-based HTPB vs the more rigid ABS plastic. This study showed that not only does it maintain similar combustion efficiencies and regression rates, it also burned smoother and more consistently.
The use of ABS Plastic as a fuel also solves another issue – production time. Using 3D printing, solid fuel grains are produced in hours, vs. the weeks or months it can take using traditional cast molding methods.
Advancing Burn Efficiency with STAR-3D™ Hybrid Rocket Motors
Rocket Crafters has taken this data in conjunction with data gathered from over 30 tests using a 250 lbf (~1 kN) small scale engine to further advance the technology in the STAR-3D™ engine. This data has been incorporated into the new 2.5 kN (~500 lbf) thrust Cyclone Engine that is undergoing development and testing. This test engine uses a new patent-pending Vortex Flow Field Injector that produces a self-sustaining vortex flow path in the engine like that of a hurricane. By inducing a vortex flow, the fuel has more time to burn in the engine which increases the efficiency and thrust.
The end result of this testing and analysis is Rocket Crafters’ STAR-3D™ hybrid engine design:
Hybrids traditionally keep the fuel and oxidizer in two different matter states, which prevents them mixing except under specifically controlled conditions. With Rocket Crafters’ STAR-3D™ design, both fuel and oxidizer are non-hazardous and can be handled at room temperature. This eliminates the risk of accidental detonation found in both solid and liquid rocket engines, making them significantly safer than their other two counterparts. The fuel for the engines is so safe in fact that some of Rocket Crafters’ staff have taken the fuel with them on airplanes as carry-on luggage without issue.
The STAR-3D™ engines are so mechanically simple that they include only two moving parts, a main on/off valve and the throttle valve. The engines use differential pressure to maintain pressure in the oxidizer tanks: high-pressure Helium pushes the Nitrous into the engine; just like squeezing a tube of toothpaste. The engines can then be throttled by regulating the amount of oxidizer entering the engine, allowing thrust to be adjusted as needed.
Unlike Liquid Bi-propellent engines, the fuel in the STAR-3D™ engine serves as the main combustion chamber and there are no complicated expensive turbo-pumps and extensive plumbing lines. As a result, there are significantly fewer components necessary in the engine making the cost of production significantly lower. Because the engine itself is just plastic the total cost of materials is also less expensive.
The unprecedented safety of the hybrid motors also contributes to significant cost savings, from cheaper transport and handling to significantly fewer parts to monitor during launch – and thus, fewer potential fail points.
The simplicity of STAR-3D™ engines prevents complications where moving parts could fail or not perform properly. With only two moving parts, our engine avoids failures associated with mechanically complex engines.
In addition, because the fuel is 3D printed, the engines are nearly identical to each other; meaning that each one will perform the same as the next.
In addition to our revolutionary injection system, Rocket Crafters is producing fuel grains using our patent-pending, horizontal 3D printing method which reduces production time for orbital-class fuel grains to a matter of hours in a single section. Contrast this to the weeks or months required to produce traditional rocket engines.
Through the synergistic relationship of plastic and metal 3D printing with the simplicity of the STAR-3D™ design, Rocket Crafters is capable of developing and manufacturing new engines of almost any size and scale in a matter of weeks instead of the years required for the more complicated Liquid Bi-propellent Engines or more dangerous Solid Rocket Motors