It began as so many tiffs have in 2017—on Twitter. SpaceX had just completed a near-perfect first half of the year. Ten launches. Two re-flights. Zero accidents. Speaking to his 11 million followers, Elon Musk couldn’t resist taking a dig at his long-time rival in the US launch industry, United Launch Alliance.

“Worth noting that Boeing/Lockheed get a billion dollar annual subsidy even if they launch nothing. SpaceX does not,” Musk tweeted. Comparatively, this may not seem too incendiary for the social media platform. But within the stately rocket world, Musk had just trash-talked ULA, the joint launch venture between Boeing and Lockheed Martin.

Subsidy is a trigger word brandished often by Musk in this fight, implying that ULA cannot compete without government help. So it didn’t take long for ULA’s chief executive, Tory Bruno, to reply with his own tweet: “Sorry. That is simply not true. There is no ‘billion dollar subsidy’. Amazing that this myth persists.” (This myth may persist because it is, at least in part, true.)

This public exchange between the chief executives of two multi-billion-dollar rocket companies highlights the extraordinary competition that has unfolded in the US launch industry during the last dozen years. Unlike the space race of the 1960s, this clash has involved corporations, not countries. They’ve fought in Congress, the courts, and on the launch pad and, in doing so, they’ve revolutionized the aerospace industry.

A decade ago the smart money was on United Launch Alliance and its owners, Lockheed Martin and Boeing, the federal government’s two largest contractors. In 2015 alone, these two behemoths performed $50 billion in work for American taxpayers. They'd built America's rockets for decades. In the other corner stood some computer guy from Silicon Valley who partied with mariachi bands and dreamed about colonizing Mars.

At times, the competition has been bizarre. About a year ago, after SpaceX lost its Falcon 9 rocket during a launch pad test, there were murky allegations of a sniper on the roof of a nearby ULA facility when the booster exploded. SpaceX denied making such an accusation.

Even though it had nothing to do with the accident, ULA still sought to capitalize on the misstep. Just three months after SpaceX’s catastrophic explosion, ULA launched a new website, the “Rocket Builder.” It touted the reliability of ULA’s boosters compared to those of a certain company that kept blowing stuff up.

Despite the accidents and long odds, to a large extent Musk has prevailed against the two titans of US aerospace. Today, his Falcon 9 rocket is cheaper, and it regularly bests ULA’s fleet in bids for commercial and government satellite launches. Musk has continued to innovate, and, if SpaceX succeeds with commercializing reusable spaceflight, he stands poised to dominate the global launch market.

None of this means the war has ended, however. Large federal awards are presently on offer to develop new launch systems, and Bruno has been pushing ULA to be as competitive as possible, slashing jobs and pushing new technology. If anything, the future rocket wars are likely to only get more interesting from here.