The US has postponed a missile-destroying laser test for a third time, due to an unspecified problem with a tracking camera’s cooling system, the Pentagon‘s Missile Defense Agency has said.

An airborne, chemical oxygen iodine laser, fired from aboard a converted Boeing 747 aircraft, was to shoot down a mock ballistic missile 100-plus miles away, according to Reuters.

The Missile Defense Agency expects to conduct the delayed test on 22 August, said agency spokeswoman Debra Christman.