Hurrying to stay ahead of Hurricane Irma, on Thursday rocket startup SpaceX launched one of the U.S. Air Force’s mysterious X-37B robotic space shuttles into low orbit—roughly 200 miles up—for a secretive and potentially record-breaking mission that has profound implications for the military... and for SpaceX founder Elon Musk.

The partially reusable Falcon 9 rocket carrying the X-37B lifted off from Launch Complex 39A at NASA’s Kennedy Space Center in Florida at 10 a.m. Two hours later, the Falcon 9’s first stage descended back toward Florida and safely landed at Kennedy Space Center.

While SpaceX has launched satellites and other spacecraft on behalf of NASA and private customers, the X-37B launch was its first strictly military mission. In May, SpaceX launched a satellite on behalf of the secretive National Reconnaissance Office, which supports military operations. Tech billionaire Musk founded SpaceX in 2002 with the goal of driving down the cost of space exploration.

The monopolistic United Launch Alliance, a consortium of mega-firms Boeing and Lockheed Martin, handled all previous X-37B launches. Air Force Secretary Heather Wilson reportedly barred ULA from even bidding on the current X-37B mission and, citing the potential cost savings, awarded SpaceX the launch contract without competition.

SpaceX typically charges less than $100 million to boost a spacecraft the size of the X-37B into orbit on a reusable Falcon 9 rocket. SpaceX claims that reusing portions of each rocket helps to keep down the price. The Atlas rocket that ULA has used for X-37B launches costs at least $109 million—and that price doesn’t necessarily include the full cost of launching the rocket. As recently as 2014, it cost the military an average of $420 million per launch to put a satellite into orbit on a ULA rocket.

After several years of explosive growth, SpaceX is on track to capture no less than 40 percent of the global commercial space-launch market, valued at around $6 billion annually, according to the Federal Aviation Administration. A recent, $1.6 billion NASA contract helped SpaceX get into the global government launch market. And now with the X-37B, the company is cementing its foothold in the prestigious national-security segment of the government market, which is worth as much as $70 billion through 2030.

SpaceX’s rapid growth underscores Musk’s power to shape markets and drive technological change. In addition to disrupting the rocket-launch industry, Musk is transforming the transportation economy... on Earth. Tesla, his electric-car company, is helping to force the gasoline-powered car toward possible, eventual extinction. Musk’s Hyperloop, a high-speed-train-in-a-tube concept, could displace existing highways, railways, and even air routes.

ULA, for one, refuses to surrender quietly. The consortium and SpaceX have been bitter rivals on the launch pad and in Washington, D.C. In 2016, Brett Tobey, then ULA’s vice president for engineering, was caught on tape accusing Musk of orchestrating congressional restrictions on the Russian-made engines that ULA uses on its heaviest rockets.

“He was able to get legislation through that basically got our number of engines down that we could use,” Tobey said.

ULA has argued that its rockets, with or without Russian engines, are more reliable than SpaceX’s are. ULA has launched more than 100 satellites for the U.S. government—and lost none to rocket failures—since its founding in 2006.

SpaceX, by contrast, has suffered some dramatic and costly accidents. In 2015, a Falcon 9 carrying supplies for the International Space Station exploded shortly after launch, costing SpaceX hundreds of millions of dollars. In September 2016, a Falcon 9 exploded on the ground during a test. The blast destroyed an Israeli communications satellite. SpaceX halted all launches for four months following the accident.

To minimize the risk to the X-37B ahead of Thursday’s launch, SpaceX reportedly waited until after ground testing to fit the Air Force spacecraft to the Falcon rocket.

Thursday’s launch was the fifth of an X-37B since the Air Force unveiled the 29-foot-long spacecraft in 2010. Like the manned Space Shuttle, which flew its last mission in 2011, the two Boeing-built X-37Bs—which the Air Force refers to as Orbital Test Vehicles, or OTVs—feature wings and payload bay, and can carry satellites and other equipment into orbit.

Unlike the Space Shuttle, the X-37B isn’t limited by the endurance of its human crew. Where the longest Space Shuttle mission lasted just 18 days, the longest X-37B mission—the type’s fourth—ended in May after a startling 717 days.

As the Air Force continues to refine the X-37B’s operations, it’s possible the current mission could last even longer. “The fifth OTV mission continues to advance the X-37B’s performance and flexibility as a space technology demonstrator and host platform for experimental payloads,” the Air Force stated.

The Air Force is still figuring out what the X-37B is capable of. But one thing is clear. “It sips power and fuel like a Prius,” in the words of one government space insider who spoke on the condition of anonymity.

The X-37B that launched Thursday is carrying a so-called Advanced Structurally Embedded Thermal Spreader built by the Air Force Research Laboratory.

According to the Air Force, the spreader will help to “test experimental electronics and oscillating heat pipe technologies in the long-duration space environment.” The X-37B itself, with its longer and longer missions, is driving demand in the United States for spacecraft components that can survive for years at a time in orbit.

In the past, the Air Force was cagey about exactly which payloads the X-37B carried into orbit—and that encouraged wide-ranging speculation by space experts. “You can put sensors in there, satellites in there,” Eric Sterner, from the George C. Marshall Institute in Virginia, said of the X-37B. “You could stick munitions in there, provided they exist.”

The Air Force denies that the X-37B has ever carried weapons—and there’s no evidence that the military has even developed weaponry that’s compatible with the mini-shuttle. Overtly arming a spacecraft would be a violation of the 1967 Outer Space Treaty.

But it would be perfectly legal, and unsurprising, for the X-37B to function as a kind of reusable spy satellite—and it could do so without necessarily jeopardizing its other, scientific missions.

Indeed, the Air Force acknowledged that testing the heat-spreader isn’t the X-37B’s only task on its fifth mission. The reusable spacecraft is also pioneering new orbital pathways for the type. “The fifth OTV mission will also be launched into, and landed from, a higher inclination orbit than prior missions to further expand the X-37B’s orbital envelope,” the Air Force explained.

A spacecraft’s orbital inclination is equal to the highest north-south latitude it passes over. The X-37B previously flew between 37 and 43 degrees, according to Brian Weeden, a former Air Force space operator who is currently an expert with the Secure World Foundation in Colorado. Amateur skywatchers can track the X-37B using commercially available telescopes.

Expanding the X-37B’s inclination changes “what it can collect information on, assuming that’s its mission,” Weeden told The Daily Beast. Notably, almost all of Russia lies north of the X-37B’s previous inclination range. The latest X-37B mission could send the spacecraft over significant swaths of Russian territory for the first time—a potential boon for U.S. intelligence-gathering.

But for Musk, the X-37B launch likely represents something more symbolic: another milestone in his wide-reaching effort to transform the way we move people and things from point A to point B, on Earth and in space.