The Air Force expects to complete its assessment of last September's SpaceX launch failure in April, but the service said this week that based on preliminary findings, it concurs with the company's conclusion that the explosion was caused by a problem with the launcher's oxygen tank. A SpaceX Falcon 9 launch vehicle exploded while being fueled for a test fire right before a September launch -- destroying the attached payload and causing damage to the launch pad at Cape Canaveral...