Additively Manufactured, Thermally Stable Telescope Mirror Substrates

This proposal is to demonstrate the feasibility of using selective laser melting (SLM) to develop the material composition and the additive manufacturing fabrication process of silicon carbide (SiC) reinforced AlSi10Mg matrix composite (SiC-AMC). ASTS will also demonstrate feasibility that we can customize the coefficient of thermal expansion (CTE) in the substrate material based upon increasing the percent SiC by weight in the AlSi10Mg base substrate. As we are able to select a specific SiC-to-AlSi10Mg ratio that has a CTE closest to an electrolytic nickel-plating CTE, we can reduce the risk of mirror degradation over time due to CTE mismatch-based stresses. For both beryllium and pure silicon carbide as a mirror substrate, the cost factor and risk is quite high from a schedule perspective due to both these materials being very hard and brittle. Therefore, machining anomalies is a much higher risk than other metal mirror substrate materials. Our additive manufacturing development of SiC-AMC could be a game changer in reducing the fabrication cost and schedule risk for a mirror substrate. Another key technical risk to address is the problem of smoothly and consistently applying the metal powderbed over the SLM build plate. We will demonstrate that we can eliminate practically all voids and porosity in the SiC-AMC by teaming with Plasma Processes, Inc. to create a spheroid SiC powder. By this company developing the technique to produce a SiC-AMC powder product, which will allow ASTS to manage the SiC-to-AlSi10Mg ratio, we can assure a uniform SiC distribution within the aluminum base. Through this demonstration, great confidence can be obtained to continue material development in Phase II, establish additional SiC-AMC material properties at higher ratios of SiC, and develop weight efficient mirror substrate designs that meet NASA?s mission requirements.

We recognize that NASA, even as leaders in the application of AM across the aerospace industry, is likely to take a conservative approach to adopting flight-rated SLM components. However, we do believe there are several near-term applications. For example, additive manufactured mirrors using the techniques we will develop in Phase 1, can be directly applied to relatively small aperture mirrors that are launched on sounding rockets or on balloon missions. Our current capabilities using the Concept Laser M2 are a direct fit for further development of mirror substrates to be used in infrared, ultraviolet, or optical applications. A good example is the optical lens associated with missions in NASA?s Medium Class Explorers (MIDEX) TESS mission or the Gondola for High Altitude Planetary Science (GHAPS). In addition, continued mirror development and mounting schemes, we can see the development of larger segmented mirror development for launch on the future Space Launch System.

ASTS plans to develop processes and techniques using SLM on materials such as SS316L, Inconel 718, Ti6Al4V, and copper-based materials such as GrCop84 for use in rocket combustion devices. In addition, we see the potential in the use of aluminum silicon based alloys, to be used as a structural casing/jacket over a combustion device. By developing this material to have a near zero coefficient of thermal expansion (CTE) or target a CTE to further augment the structural bond with a copper based combustion chamber operating at very high temperatures, we will also revolutionize the development of rocket engine technology to reduce cost for not only NASA, but also the DOD. Not only that, but applications for optical in infrared mirrors could be developed as a low cost solution for utilization in unmanned aerial vehicles (UAV) for a variety of functions such as in the agriculture industry for climate and soil moisture monitoring, and in the transportation industry for delivery products or packages to residential addresses. Technological advances in mirror integration have developed in performance over traditional optical camera lenses. Our development in SLM for mirror substrate fabrication should reduce the cost in mirror fabrication for such applications.

This is early/mid-stage (TRL 5) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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