Astronauts aboard the U.S. space shuttle Endeavour are headed toward a middle-of-the-night landing early Wednesday in Florida.

Commander Mark Kelly and his crew circled 320 kilometers above the Earth, aiming to touch down at 2:35 a.m., local time, Wednesday at Kennedy Space Center. It will be the 25th time the U.S. space agency, NASA, has landed a space shuttle in darkness, about a fifth of all missions.

Flight director Tony Ceccacci says the weather looks “very promising” for the landing.

Endeavour has spent more than two weeks in space, delivering a $2 billion cosmic ray detector and spare parts to the International Space Station. Kelly said the shuttle had performed “really, really well.”

Wednesday's landing will end Endeavour's 19-year space career and mark the second of three U.S. shuttles to be retired. NASA, says Endeavour flew a total of 198 million kilometers in its 25 missions.

The shuttle Atlantis is scheduled to blast into space in July, in the last mission of the 30-year U.S. shuttle program.

With the shuttle program ending, NASA will have to depend on space vehicles owned by other countries or by private industry to deliver supplies and crew to the International Space Station.

In addition to Mark Kelly, the six-member Endeavour crew includes Italian astronaut Roberto Vittori.

Kelly's wife, U.S. Congresswoman Gabrielle Giffords, is recovering from wounds suffered during a shooting in Arizona in January.