10:20am ET Update: SpaceX made it. Beneath partly cloudy skies along the eastern coast of Florida, the rocket company launched the X-37B space plane near the beginning of the launch window. The spacecraft made it safely into orbit—how high was unspecified, due to the secretive nature of the mission—and the Falcon 9 rocket's first stage returned safely to a landing zone along the coast.

Now the rocket company, and the rest of Kennedy Space Center, Cape Canaveral Air Force Station, and other space companies along the coast, must make their final preparations for the effects of Hurricane Irma this weekend.

Original post: Florida has a lot to worry about right now with the imminent arrival of Hurricane Irma, but before the storm arrives this weekend, SpaceX is trying to squeeze out one more launch. And it's a big one. The company's Falcon 9 rocket will launch the US Air Force’s X-37B Orbital Test Vehicle on its fifth mission.

Few details are available about this secretive mission, but the primary launch window opens on Thursday 9:50am ET and closes at 2:55pm ET. Weather conditions Thursday are about 50 percent favorable for launch. A backup window is available on Friday, although this is uncertain due to the need for Floridians to prepare for Irma.

For the first four missions, the Boeing-developed X-37B space plane has launched on top of an Atlas V rocket, the military's go-to vehicle manufactured by United Launch Alliance. However, earlier this year, Air Force Secretary Heather Wilson told Congress that the emergence of the commercial space industry has proven a boon for the US military and that the military felt comfortable launching the X-37B on a SpaceX rocket.

"The benefit we're seeing now is competition," Wilson said in June. "There are some very exciting things happening in commercial space that bring the opportunity for assured access to space at a very competitive price."

The US military has not said what the X-37B has been doing up in space for years at a time, beyond furthering "operations development for reusable space vehicle technologies." In addition to testing surveillance technology, some experts think the Air Force may be working on equipment that could be incorporated into a human-rated version of the vehicle that could carry a flight crew. Among the applications contemplated for the X-37B would be the recovery of satellites for repair on Earth.