Columbia will have to be rolled back to the hangar next week so NASA can repair a hydrogen leak, a move that leaves the shuttle's astronomy mission up in the air and disrupts the year's flight plans. ``Safety's the first priority, and we've got an item here which we absolutely have got to put to bed and we're going to do that,'' launch director Bob Sieck said Wednesday. The leak had forced NASA to scrub last week's launch of the shuttle with the $150 million Astro observatory. On Wednesday, a test in which super-cold liquid hydrogen was pumped into Columbia's big external fuel tank confirmed the leak is in a tight cavity between two metal plates that connect the orbiter and the tank, Sieck said. To fix the leak, the orbiter will have to be separated from the tank in the hangar, he said. Even then, it will be hard to pinpoint the leak because it seems to occur under extremely cold conditions only, Sieck said. Sieck declined to estimate when Columbia might be able to lift off. NASA officials have said it will take about a month to return the shuttle to the hangar and perform repairs. The move will take place sometime next week. The Astro mission is one of six remaining shuttle flights scheduled for 1990. It's virtually certain now one of the missions will be pushed into next year or later because of Columbia's problems. But Sieck said preparations for Atlantis' secret military flight in July will continue. Shuttles have been moved from the launch pad back to the hangar twice because of mechanical failures and once because of payload problems. When last week's launch attempt was scrubbed, Columbia's mission already was two weeks late because of cooling system repairs. ``It's always disappointing when the hardware is bad to you, and that looks like what we've got here,'' Sieck said. ``But we're reminded it's a complex system and things don't always go for the plan.'' Astro, an on-board observatory consisting of three ultraviolet telescopes and one X-ray telescope, was to have gone up in 1986. But the Challenger explosion postponed the mission, depriving NASA of the chance to see Halley's Comet. Comet Austin, discovered last year, is on its way out of the solar system, and the chances of seeing it grow slimmer every day.
