The first launch of NASA's Space Launch System (SLS), a heavy rocket that could one day bring humans to Mars, has been pushed back to 2019. It was last said to be headed for a late 2018 launch. It'll be quite a few years before a flight to Mars takes place.
When the first launch occurs, NASA will test the SLS and the Orion capsule. Independent analysis found last year that the Orion program was behind schedule and could go over budget. That delay has contributed to this change in the rocket's launch schedule.
NASA confirmed this timeline change in a letter attached to a Government Accountability Office report.