A NASA spacecraft chasing a rare metal asteroid swings past Mars this week for a gravity boost, snapping thousands of pictures as practice for the main encounter in 2029. Named Psyche like the asteroid it’s after, the robotic explorer will slingshot past the red planet at 12,333 mph (19,848 kph) on Friday. It will be an especially close flyby, with Psyche passing within 2,800 miles (4,500 kilometers) of Mars, equivalent to the distance between the U.S. east and west coasts. Then it will barrel toward the asteroid belt between Mars and Jupiter that is home to its enticing target. All of the spacecraft’s science instruments will be on for the Mars pass. NASA’s two Mars rovers along with a small fleet of U.S. and European orbiters will make surface and atmospheric observations at the same time for comparison. Psyche's cameras already are photographing Mars, appearing as a crescent on approach and a nearly full sphere once it’s in the rearview mirror.…