Sebastian grew up in the Bay Area and followed a path that, on paper, looks like the archetype of “aerospace wunderkind.”

He went to MIT for undergrad, spending his early years in planetary science with internships at NASA and Lockheed Martin. His work spanned deep‑tech research and classic aerospace problems—exactly the kind of environments where you’re staring at Mars data one day and spacecraft constraints the next.

Halfway through MIT, his focus shifted. Instead of imagining a PhD track and a life publishing papers, he found himself more drawn to building things: real products, real systems, solving real use cases.

That led him to Amazon Prime Air, the company’s drone‑delivery effort promising “click to delivery in 30 minutes or less.”

His job quickly crystallized into a core discipline that would define his career: systems engineering.

In aerospace, a systems engineer sits at the center of a highly complex web:

You’re the person doing the “…technical coordination between these technical disciplines.”

When propulsion wants more mass, avionics wants more power, and operations wants more range, the systems engineer is the one brokering the tradeoffs and making the whole thing work.

Sebastian got very good at that.

After Prime Air, he stepped away from industry to deepen both his technical and business toolkits, completing a dual Master of Science and MBA at Harvard.

He briefly returned to Amazon, then followed a mentor to Cruise, the self‑driving car company, where he spent two intense years in San Francisco. Cruise was a proving ground for his skill set: complex, safety‑critical systems with massive technical and regulatory surface area.

Then, in April 2025, Cruise shut down.

For Sebastian, that forced a harder question:

Growing up in the Bay, startups had always been front of mind. But like many would‑be founders, he’d had excuses: timing, risk, comfort. The shutdown stripped those away.

So he made the leap.

He started solo—mapping the aerospace landscape, asking:

The answer became Wardstone.

Sebastian didn’t build Wardstone alone for long.

His co‑founder is his brother, Tobias—a mechanical engineer who studied at Cornell and worked at Astronus, a space company in San Francisco.

Sebastian worked on Wardstone for a few months solo, then asked Tobias a simple question:

He did.

Tobias joined right before they applied to YC, and the two brothers became co‑founders. Working with family is very different from just seeing each other at holidays—now they were solving hard problems together, learning each other’s working styles, and building a company with real stakes.

Wardstone builds satellites for missile defense, with a specific focus on a new and pressing threat: hypersonic missiles.

Hypersonic weapons—developed by U.S. adversaries—are not just “faster missiles.” They’re harder to detect, track, and intercept. The uncomfortable truth:

Existing U.S. missile defense systems don’t work very well against them.

The U.S. government knows this. Congress has committed substantial funding through what Sebastian calls “the big, beautiful bill” toward a new missile defense architecture known as the Golden Dome.

The Golden Dome is envisioned as a next‑generation shield—an integrated system designed, in large part, to handle the hypersonic threat.

Wardstone is building key pieces of that stack.

They’re not a PowerPoint company. They’re not pitching vaporware. Sebastian is adamant about that. On their website and in their outreach, they lean into real content and real hardware—demonstrating what they’ve already built, even as a two‑person team.

At its core, Wardstone’s job is to answer a simple but high‑stakes question for the United States:

Missile defense today is built around threats that look very different from modern hypersonic weapons. Traditional systems were optimized for ballistic trajectories and more predictable flight paths.

Hypersonic missiles:

Result: Current U.S. defensive systems aren’t built to reliably handle them.

At the same time, the government is making major, long‑term bets—funding, programs, and policy—on a new defensive layer: the Golden Dome.

But the Golden Dome is not a single monolithic product. It’s a complex ecosystem of technologies, systems, and vendors.

Wardstone is one of the companies tasked with building the enabling technologies for that ecosystem—specifically, satellites for missile defense that can serve this new threat environment.

Wardstone develops satellites and supporting technology that plug directly into this hypersonic defense mission. The shape of their work is clear:

They’re not trying to boil the ocean with generic “space platforms.” They’re building systems for a single, urgent use case: missile defense against hypersonics.

As Sebastian puts it, they’re essentially part of the technology development force‑multiplying the Golden Dome’s promise.

Wardstone’s customer is the U.S. government—but practically speaking, that doesn’t mean “one customer.”

They sell into:

Inside those organizations are multiple:

While it’s all “the government,” there’s no single point of failure. Different programs and offices have authority to evaluate, fund, and adopt new technologies.

Wardstone’s satellites and related technologies show up wherever the government is:

Their value isn’t just “we build satellites.” It’s that they’re building mission‑specific space systems for a threat profile the U.S. is urgently trying to close.

Selling to the U.S. government doesn’t look anything like selling SaaS.

You can’t just spin up a landing page, push some performance marketing, and watch Stripe ping as self‑serve accounts roll in.

Wardstone’s go‑to‑market is fundamentally relationship‑driven:

At the same time, Sebastian and Tobias are leveraging programs designed specifically for companies like theirs:

These programs provide non‑dilutive funding for early‑stage research and development—allowing Wardstone to move quickly on critical technologies without immediately giving up large chunks of equity.

In other words, Wardstone’s GTM playbook is:

Wardstone is fresh out of the gate—but moving fast.

They’re closing their seed round and immediately putting that capital to work. The plan for 2026:

Sebastian is clear that Y Combinator has been pivotal, especially as a first‑time founder.

YC’s impact shows up in a few ways:

That urgency has shaped how Wardstone operates: hardware shipped early, visible proof of progress, and a bias toward doing rather than theorizing.

Spending time with Sebastian, a few clear patterns emerge:

Most founders in defense and aerospace come either from pure research or pure business. Sebastian is a systems engineer at heart—trained to juggle constraints, arbitrate tradeoffs, and make complex technical programs converge.

At Amazon Prime Air, Cruise, and now Wardstone, he’s been the person responsible for aligning:

That mindset maps almost perfectly onto early‑stage company building. A startup is, in many ways, a systems engineering problem.

Each of these environments is high‑stakes, heavily regulated, and deeply interdisciplinary. That background matters when you switch to missile defense: you’ve already seen how small technical decisions echo across real‑world systems.

Wardstone isn’t another developer tool or marketing SaaS. It’s a company pointed straight at one of the U.S. government’s most pressing defense gaps.

The problem is hard, the buyers are sophisticated, and the mission is national‑level important. Sebastian chose that on purpose.

From the website to how he talks about Wardstone, there’s a clear throughline: ship real hardware early.

Even as a two‑person team, they’re focused on building and showcasing tangible engineering progress. That posture resonates in a defense ecosystem used to lofty roadmaps with little to show in the near term.

Defense and aerospace aren’t the classic YC domains—but Sebastian is importing YC’s best instincts:

He’s blending that with the long‑horizon reality of defense procurement, which is rare and valuable.

Sebastian isn’t trying to uproot the entire U.S. defense architecture or declare space‑based systems a cure‑all.

He’s doing something more targeted and more practical:

Focusing on the response and kinetic interception of the hypersonic missiles

Wardstone is a critical layer in a much bigger stack—one that lets the Golden Dome vision move from bill text and slideware into reality.

Behind the scenes: https://youtu.be/umZSR_tMN4o

After years as a systems engineer across Amazon Prime Air and Cruise, and armed with a dual MS/MBA from Harvard, YC founder Sebastian Fischer is now building Wardstone, a satellite company focused on missile defense against hypersonic missiles.

Backed by YC and closing its seed round, Wardstone is relocating to El Segundo to tap into Southern California’s aerospace ecosystem, stand up a lab, grow a team, and ship real hardware into one of the U.S. government’s highest‑priority initiatives: the Golden Dome.

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