The use of additive manufacturing technologies in aerospace applications has presented both opportunities and challenges. The ability to produce parts and components using additive manufacturing holds promise in both metals and plastics, whereas traditional subtractive manufacturing can be restrictive in design development and material selection.

Figure 1. The AMPS-H Motor is a fully functional additive manufactured rocket motor system.
The Additive Manufactured Pro pulsion System – Hybrid (AMPS-H) motor is the first known functional additive manufactured rocket motor system (see Figure 1). It was designed specifically for the small satellite market as a multi-start thruster that could deliver significant deltaV to a small cubesat spacecraft while maintaining a 10 cm3 form factor.

First, the AMPS-H motor was designed with the combustion chamber located inside the oxidizer tank (see Figure 2). This is only possible if the motor is additively manufactured. Additive manufacturing allows for the internal cavities and channels to be produced inside the part, maintaining a single component, unlike traditional manufacturing processes that require the part to be produced in multiple sections and fused together. The objective was to eliminate as many components as possible and incorporate them into a single part. By utilizing additive manufacturing, a 3D CAD model is designed on the computer, then printed in 3D.

The next step was to find a material that could meet the rigid mechanical properties required for space applications. A variety of additive technologies could produce the design, but the material properties available proved too weak and led to inconsistent density of the fused structure.

A strong, highly functional alternative material called Windform™ XT 2.0 was chosen. Specifically designed for the additive manufacturing laser sintering technology, it exhibited high tensile strength and could be fully fused, creating a solid structure that could hold high pressure. The material was suited to design the oxidizer tank and combustion chamber as a single part for the AMPS-H motor. It also was used as the fuel core to the hybrid motor.

Figure 2. An Internal Side View of AMPS. The motor was designed with the combustion chamber located inside the oxidizer tank; this is only possible if the motor is additively manufactured.
Utilizing additive manufacturing technology, the material provided no leak paths due to joints or voids from casting in a fuel. The combustion chamber port geometry was built directly into the fuel, and the design could be changed without tooling changes. The forward and aft combustion chambers were integrated as a single piece with the fuel grain. Internal oxidizer feed lines, igniter port, injector port, nozzle port, nozzle retaining ring groove, and pressure transducer ports all were incorporated and part of the single additive-manufactured part.

The motor was hydro pressure tested to insure that a margin of safety >2.0 had been met. Next, the motor was integrated on a test stand for cold flow testing where the injector and the high-pressure oxidizer tank would undergo thermodynamic cycling and flow rate calibration. After test stand integration was complete, several safety measures were taken to make the test stand ready for live firing. The final part was tested at a peak thrust level of 6.2 lbf for a duration of 16 seconds. The AMPS system is currently being integrated into several concepts for integrated boosters in cube satellites.

This article was contributed by CRP USA. For more information, Click Here .

NASA Tech Briefs Magazine

This article first appeared in the August, 2013 issue of NASA Tech Briefs Magazine.

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