Which of the following statements is true?

The US space agency NASA says it has discovered another problem with the space shuttle Discovery and astronauts may need to repair the spacecraft before it can safely return to earth.
    Mission controllers say they are comfortable that Discovery’s protective heat tiles are in good shape for landing but they remain concerned about the gap filler, a material between and underneath the tiles’ that seals them and reduces friction, protecting the orbiter from the searing heat of reentry into earth’s atmosphere. The gap filler is protruding in some areas and shuttle lead flight director Paul Hill says engineers are trying to come up with some answers. There are a team of engineers that are working aggressively at options to go and make that gap filler safe if it is decided that it’s an issue and there is another team of engineers that are off looking at the aero-heating and the effects of leaving those gap fillers in place and protruding. Final results are expected to be obtained on aero-heating and a decision on whether anything needs to be done about the gap fillers on Monday. Meanwhile NASA spokesman Rob Navias says the space shuttle Atlantis is standing by to perform a rescue mission if necessary.