Since earning certification from the Air Force to launch national security payloads—typically spy satellites and military communications satellites—SpaceX has flown two military missions. It launched a classified payload for the National Reconnaissance Office in May and an Air Force space plane in September.

On Thursday, SpaceX will attempt to launch its third and most secretive payload for the military. The mission was not even made public until a launch license was released a month ago, and the company didn’t acknowledge the launch until this last week. The payload was developed by Northrup Grumman, and has the mysterious name “Zuma,” which sounds similar to a carbonated, alcoholic beverage briefly popular in the 1990s, Zima. There are few clues in the launch’s mission patch.