NASA Postpones Shuttle Launch

Still Worries Fuel Tank May Shed Damaging Ice Or Foam On Liftoff

(CBS/AP)  Other problems facing the launch team:

• One of four hydrogen depletion sensors inside the external tank did not operate properly during a tanking test April 14. Engineers initially a wiring problem was to blame, but so far no such problems have been found. The sensor is critical and flight rules require all four to be operational for launch. To replace the sensor, if that is required, engineers would need to remove insulation, open an access hatch and enter the hydrogen tank.
  
  
• A pressurization relief valve operated, or cycled, more often than expected during the tanking test. Engineers are not yet sure if this is an actual problem or not, but they are looking into it.
  
  
• Hydraulic fluid was blown onto one of the shuttle's aft rocket pods during high winds, contaminating nearly 20 insulation blankets. Engineers want to replace the blankets because of concerns about normal ascent heating and the possibility some of the residual fluid could actually ignite.

A launch delay to July allows NASA to roll Discovery back to the Vehicle Assembly Building where engineers would have much better access and a controlled environment for any repairs or upgrades, including installation of a new external tank heater and replacement of the insulation blankets.

NASA managers have said for months they are not being driven by the launch schedule and a delay to July would appear to be in keeping with that post-Columbia philosophy. But some senior managers, sources say, argue against giving up the May-June launch window unless it's absolutely necessary.

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CBS News Space Consultant William Harwood has covered America's space program full time for nearly 20 years, focusing on space shuttle operations, planetary exploration and astronomy. Based at the Kennedy Space Center in Florida, Harwood provides up-to-the-minute space reports for CBS News and regularly contributes to Spaceflight Now and The Washington Post.