PERTH, Australia (AP) — A robotic submarine has finished its sixth trip to the bottom of the Indian Ocean in the hunt for wreckage from the missing Malaysia Airlines plane, six weeks after the aircraft mysteriously disappeared, the search coordination center said Saturday.

The Bluefin 21 sub has covered around 133 square kilometers (51 square miles) since it began diving into the depths earlier this week to scan the seabed with sonar. The latest data are being analyzed, and a seventh mission is already underway, it said. So far, no debris has been spotted.