Shuttle Countdown Begins for Late Wednesday Liftoff : Space: Replacement of a data transmitter ends NASA’s latest snag. Delays have kept the Astro observatory grounded since 1986.
NASA engineers Sunday morning replaced the electronic component that caused the latest delay for Columbia and the $150-million Astro observatory, clearing the way for a launch as early as 10:20 p.m. PDT Wednesday.
Engineers had encountered some initial problems testing the new component, but by 2 p.m. Sunday, NASA spokesman Dick Young said the problem had been corrected and a new countdown would begin at 10 p.m.
The latest problem to afflict the star-crossed Astro observatory, which has been delayed since 1986, occurred late Wednesday. Just after engineers closed the payload bay doors on Columbia, technicians in the control room lost contact with one of the observatory’s four telescopes.
That instrument, the Broad Band X-ray Telescope, is cooled by liquid argon at a pressure and temperature that must be monitored for safety. The failed component was the one that converts temperature and pressure data from the telescope into a form that can be sent to the control room via telephone lines while the shuttle is on the pad.
Engineers had hoped to make a quick fix by using a specially prepared cable to route the signal through a redundant unit, a course that would have allowed for launch Tuesday evening. But the patch did not work and the component had to be replaced, necessitating an extra day’s delay.
Initial tests of the replacement unit showed that it would work on the ground, but not necessarily in space. That problem was found to be in the software, and was readily corrected.
Engineers will have a “window” of two hours and four minutes in which to launch the mission Wednesday night.
During the nine or 10 days in space, Columbia’s crew of seven will work around the clock with the four telescopes to observe the universe in ultraviolet and X-ray wavelengths, which are absorbed by the Earth’s atmosphere and so are inaccessible to ground-based telescopes.
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