The National Aeronautics and Space Administration said lengthy repairs on the shuttle Challenger's heat-shield tile system and unfinished paper work will delay its scheduled launch this month by about a week. Charles Redmond of NASA said an official launch date will be announced late this week or early next. "The best guess was (Feb.) 27-28, and I suspect that will probably hold," he said. "It would certainly be no earlier than the 27th." Challenger was scheduled to take off Feb. 20 with a crew of seven, including Sen. Jake Garn (R-Utah), on a four-day mission to launch two communications satellites and retrieve a space experiment.