The spacecraft completed "all mission objectives," according to USAF Rapid Capabilities Office director Randy Walden. Just what those are isn't clear, though. X-37B payloads are still classified, and officials have typically provided only vague hints of what was aboard. One was a thermal spreader that helped test "experimental electronics" and heat pipe cooling in long-term spaceflight, while another project may have tested a Hall-effect ion thruster. Walden did acknowledge that the space plane deployed "small satellites."

This definitely isn't the end for the X-37B when a sixth flight is due to take off from Cape Canaveral in 2020. It does, however, raise the bar for future trips. If the USAF is going to continue bragging about long durations in orbit, it will have to fly the space plane for substantially more than two years -- that appears feasible, but it's considerably more challenging than it was this time around.