The board investigating the loss of the space shuttle Columbia has come one step closer to figuring out why the craft broke apart, officials said this week. Scientists fired a chunk of foam insulation into a shuttle wing panel to see whether debris that broke away and hit Columbias left wing on liftoff could have caused a fatal crack. The one-pound piece of foam was shot out of a cannon at 525 mph, and left a crack a tenth of an inch wide. The test bolstered the theory that superheated gases got into the wing and incinerated it. You would not take a piece that is this damaged into space, said Scott Hubbard, a NASA executive. The board will conduct more tests, and issue a report in July.