Hayden Spoelstra
Field Test Engineer
I’m a Field Test Engineer who loves turning ideas into real projects, from apps and engineering builds to writing a children’s book about the Mars rovers.
Projects
Per Diem Tracker
Apple & Android
Per Diem Tracker is a mobile app I built to solve a common frustration in flight-test and government travel: keeping track of daily per diem amounts while on the road. The app calculates remaining daily allowances, handles “per diem except” days, and logs expenses with receipt photos for easy voucher creation.It’s built with React Native/Expo and currently in TestFlight with real beta users. Android support is underway. The app focuses on speed, clarity, and offline-friendly functionality, no complex menus, just the tools travelers actually need.I built this from scratch: UI/UX, code, backend integration, and analytics. It’s been incredibly rewarding to watch other engineers adopt it into their travel workflow.
Mighty mars rovers
Children's Book
Mighty Mars Rovers is an illustrated children’s book I’m creating for my daughter, Zoey. The story introduces NASA’s Mars rovers — Sojourner, Spirit, Opportunity, Curiosity, Perseverance, Zhurong, Ingenuity, and even Pathfinder, through expressive characters, watercolor-style artwork, and simple engineering concepts.The goal is to inspire curiosity about space exploration while staying accurate to the real rovers. Each rover has its own personality, visual style, and emotion-based expressions, all while preserving their real structure. Every page blends science, engineering, and storytelling in a format kids can enjoy.It’s an ongoing passion project, and I’m designing every illustration, character, and layout from scratch.
About
I’m Hayden Spoelstra, a Systems & Field Test Engineer with a passion for building things that solve real problems and spark curiosity.I earned my Bachelor of Science in Engineering from the University of Arizona in 2020 (GO Wildcats!), where I sharpened my analytical skills, learned to tackle complex systems, and developed a foundation in problem-solving that I rely on every day.Professionally, I work in the defense industry, where I help evaluate and test critical systems, work with cross-functional teams, and ensure solutions perform reliably in real-world conditions. I work as a Field Test Engineer, where solving problems, troubleshooting systems, and adapting on the fly is part of the job.But engineering isn’t just a day job for me, it’s the lens through which I explore the world. Outside of work, I build tools like the Per Diem Tracker app, which helps travelers manage daily allowances with simplicity and clarity. I also enjoy hands-on garage projects that challenge me to think differently and push my skills further.I’m driven by a simple philosophy: ideas are worth creating when they move from thought to reality. Whether I’m writing code, sketching a story, or designing a mechanical build, I enjoy every step of the creative process.Explore my projects below, or reach out anytime. I love talking engineering, creativity, or collaboration.
Contact
Got a question, want to collaborate, or just want to say hello?Send me a message, I'll get back to you as soon as I can.
Per diem Tracker - Privacy Policy
Effective Date: February 2026Per Diem Tracker does not collect, store, transmit, or share any personal information.All trip data, expense entries, and backups are stored locally on the user’s device. The app does not require account creation and does not use third-party analytics, advertising services, or tracking technologies.No financial information, location data, contact information, or personal identifiers are collected by the app.Users may optionally create manual backup files, which are stored locally and controlled entirely by the user.If you have questions about this policy, please contact:[email protected]