One builds weapons in hopes that they are not used. Thus goes the central premise of deterrence theory, which says it is the credible threat of aggression — not the use of aggression — that will ensure states avoid war.This theory has dominated much of America’s strategic thinking over the past 50-plus years, but new technologies and new adversaries threaten to upend the status quo. For the first time, China has started to outpace the U.S. in critical weapons programs — the country developed a new type of weapon called a Hypersonic Glide Vehicle as early as 2014, which can strike Taipei and the Taiwan Strait in about 20 minutes from the country’s strategic bases in the South China Sea. America’s comparative sluggishness to develop such tech could result in the U.S. falling catastrophically behind its adversaries.The founders of Castelion, a startup that emerged from stealth this week, cut straight to the point: “Simply put — this cannot be allowed to happen.”The 11-month-old Defense startup wants to completely rethink defense hardware development for complex systems, starting with long-range strike hypersonic weapons, a capability that Castelion co-founder and CEO Bryon Hargis called “a national, strategic-level non-nuclear deterrent.”“China is going faster than us in basically every area,” he said. “They pass the U.S. in some areas, but if you give them enough time, they’re going to pass us in all areas if we don’t do something different. It’s, in my opinion, existential. We grew up in an era of fairly good security and I don’t know necessarily that our children are to have that opportunity if somebody doesn’t do something about it.”Castelion was founded by a trio of ex-SpaceXers, Bryon Hargis, Sean Pitt and Andrew Kreitz, in November 2022. The company is part of a wave of new defense tech startups that have little faith in large American primes and their ability to ensure the country retains its dominant position in the global asymmetry of military power.In a blog post announcing Castelion, the trio say as much, writing that conditions in the defense industrial base, like consolidation, production delays and ballooning program costs, “have left our nation in a worse position to protect democracy and confront our adversaries around the world.”The startup wants to do things differently: move faster, design hardware to be produced at scale, and vertically integrate to cut costs. Pitt said that long-range strike weapons were a clear opportunity for an agile hardware development approach.Its thesis has caught investor support, with the company closing a $14.2 million initial funding round co-led by Andreessen Horowitz and Lavrock Ventures, with participation from First In, BlueYard Capital and Champion Hill Ventures.Castelion’s founding team is notable for their individual success in the aerospace industry. Hargis, a mechanical engineer by training, joined SpaceX in 2017 and eventually became a senior director of government sales, essentially building out an entire government sales team and that enormous line of business for the company; Pitt was the original salesperson for SpaceX’s hugely successful ride-share program and eventually became director of launch and human spaceflight sales for the European continent; and Kreitz was a senior investment banker at Goldman Sachs before joining SpaceX as senior finance manager.Hargis and Pitt worked alongside each other at SpaceX’s D.C. office, and Hargis and Kreitz worked directly together regarding finance matters. The three would talk on the evenings and weekends, Pitt said, and the thesis for the company started forming. It was clear that they would have to leave SpaceX if they wanted to focus on defense hardware: SpaceX is not a defense company, even if its technologies do much to serve the national interest.“SpaceX is fundamentally a Mars company,” Kreitz said. “It will do great defense work if it’s along that development path, but [it] isn’t core, and that’s what precipitated us leaving.”Hargis echoed these comments: “I think we did some amazing work at SpaceX for national security that will continue to pay dividends for the country for probably multiple decades to come. But I really wanted to be more focused on defense than SpaceX wanted to be.”Castelion is kicking off its focus on hypersonic missile systems. The U.S. wants to procure these capabilities for a handful of reasons, many of which have to do with the particulars of the Western Pacific theater. These systems offer a big boost in range without a commensurate energy cost, which is critical for safely covering the roughly 1,800 miles between the U.S. territory of Guam and the coast of China. As two officials from the U.S. Department of Defense put it in a recent op-ed, all of the missiles in America’s arsenal “appropriate for the Western Pacific theater” will need to fly at Mach speeds.Hypersonic missiles are also highly maneuverable, which makes it difficult to predict where they will strike. But perhaps most importantly, they offer a non-nuclear deterrence option — a way for both the United States and China to avoid a severely catastrophic outcome that both countries have vowed to avoid via the adoption of no-first use policies.Of course, Castelion can’t simply turn up on Uncle Sam’s doorstep one day with a fully finished hypersonic weapon and a bill. Instead, the El Segundo, California–based startup is taking time to build its credibility with missile subsystems: solid rocket motors, low-cost avionics and ultra-high temperature ceramic matrix composite (CMC) materials. The idea is to first become a supplier to a prime working on an existing hypersonic missile program, before eventually building complete missile systems all in-house.Image credit: CastelionImage credit: CastelionBecause rapid design-build-test cycles are built into the company’s strategic mission, the company is also focused on building a hypersonic test platform both for customers looking to test and for in-house testing.Castelion’s primary engineering efforts, which include developing the avionics and manufacturing the high-temperature CMCs, are taking place in El Segundo. Castelion also has a special use permit for outside of Naval Air Station Fallon in Nevada to do rocket motor production and testing. Looking ahead, the company plans on conducting its first full flight test of its solid motors using a single-stage rocket later this year, and the company plans on scaling its materials testing, starting with a subscale hypersonic glide vehicle shell to demonstrate that it can make complex shapes using the CMC material.Next year, the 15-person company is planning on making a two-stage test vehicle. It also plans on executing out its three government contracts (the details of which the company couldn’t disclose) and to continue building out its team. It’s more than a little ambitious.“We’re fairly used to being called crazy,” Hargis joked. “I could see it from the outside, being slightly skeptical, but I think that after you’ve done several crazy things successfully, you realize it’s not crazy to dream big.”