Year

2024

Season

Spring

Paper Type

Master's Thesis

College

College of Computing, Engineering & Construction

Degree Name

Master of Science in Mechanical Engineering (MSME)

Department

Engineering

NACO controlled Corporate Body

University of North Florida. School of Engineering

First Advisor

Dr. Stephen Stagon

Second Advisor

Dr. Jutima Simsiriwong

Third Advisor

Dr. Paul Eason

College Dean

Dr. Alan Harris

Abstract

Nickel Titanium (NiTi) is a shape memory alloy (SMA) that is capable of being deformed and subsequently returned to the original shape through heating. This unique property makes NiTi a prime material for potential applications in the aerospace industry. As manufacturing capabilities advance, the ability to produce and implement advanced materials, such as shape memory alloys like NiTi, becomes more feasible. One such application being studied is deployable mirrors for imaging satellites. Reflector and mirror surfaces for imaging in the visible and infra-red range of the light spectrum require low surface roughness across the largest allowable area for the collection of photons. Monolithic, single piece, mirrors and reflector surfaces for in-space imaging are overly heavy and occupy too much volume in the launch vehicle, as they cannot be folded or separated for stowage. The prospect of deployable mirrors made of polished sheets of SMA offers the possibly of significant weight and volume saving for future imaging satellites. Unlike monolithic mirrors, mirrors composed of SMA may be folded to reduce size while in transit and returned to shape once deployed in space. Imaging surfaces require high specular reflectivity to direct photons towards a central detector. Specular reflectivity of a metallic surface is achieved through creating a surface of appropriate surface roughness. This thesis presents a method of sequential grinding, polishing, shape setting, and vapor deposition coating to produce a NiTi SMA sheet with a surface roughness, Sa, of < 50 nm to achieve 95% reflectivity for the range of 1000-1500 nm. The surface roughness metric is established through the optical convention of wavelength divided by 20. The purpose is to determine if a sheet of shape memory NiTi with a reflective coating can be a viable alternative to current conventional monolithic and multi-piece satellite imaging reflectors. A polishing procedure was developed for an industrial computer numerical control (CNC) milling machine to smooth the surface and minimize the surface roughness. To achieved the reflectivity parameters, a thin film of reflective metal, aluminum, was deposited onto the surface with magnetron sputtering physical vapor deposition (PVD). The samples were characterized using laser scanning microscopy and an integrating sphere equipped ultra-violet, visible, infrared spectrometer device. The samples were characterized as fabricated, and then after introducing a deformation with a radius of curvature of 2 cm, exceeding that estimated 3 cm for a stowed imaging mirror. The resulting data showed that the coated NiTi SMA samples meet the proposed performance requirements, thus demonstrating the capability of NiTi as a viable alternative to current satellite mirror materials.

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