听力原文： Astronaut Steve Robinson is going where no one has ever gone in orbit--to a shuttle's underside, which is covered with thousands of fragile ceramic tiles as a barrier to the scorching heat caused by high-speed friction with the atmosphere. Slivers of heat-resistant fabric filling the thin gaps between the tiles have popped up a couple of centimeters in two places. Engineers worry that the protrusions might change the aerodynamics of Discovery's reentry Monday and make some parts of the orbiter a few hundred degrees hotter than normal. They do not know if the shuttle can with stand the extra heat. So astronaut Robinson's task is to stand on the end of the robot arm mounted on the International Space Station, where Discovery is docked, and either pull out or trim the gap filler. He must be very careful not to strike and damage the delicate tiles with his space suit or tools, as he explained to reporters. What is the problem with the space shuttle?