Stock Photo - 05/12/1999 ___ At Launch Pad 36B, two holes caused by hail on Space Shuttle Discovery´s external tank ET are visible. Left of the tank is one of the solid rocket boosters. Workers are investigating the damage and potential problems for launch posed by ice forming in the holes, which may number as many as 150 over the entire tank. The average size of the holes is one_half inch in diameter and one_tenth inch deep. The external tank contains the liquid hydrogen fuel and liquid oxygen oxidizer and supplies them under pressure to the three space shuttle main engines in the orbiter during liftoff and ascent. The ET thermal protection system consists of sprayed_on foam insulation. The Shuttle Discovery is targeted for launch of mission STS_96 on May 20 at 9:32 a.m