He cut to a different view, zoomed way out, showing a trajectory that started at the top of New Guinea and arced toward the Arafura Sea. The boundary of the stratosphere was helpfully delineated. The shell soared well above that, passed through apogee, and began to arc downward again as it approached the southern coast of the island. Its trail then straightened, leveled off, and became a thickening plume of yellow gas drawn southward across the airspace between New Guinea and Australia. "The burn phase," T.R. explained. Having been through all this at Pina2bo Willem understood that this was the part of the shell’s flight when the molten sulfur was burned to make thrust, extending the duration of the flight.