Shuttle to try launch again

After scrubs, Atlantis set for liftoff today

September 09, 2006|By Michael Cabbage | Michael Cabbage,Orlando Sentinel

CAPE CANAVERAL, Fla. -- NASA will get one more chance this morning to launch space shuttle Atlantis before the mission is delayed for at least three weeks.

The latest in a series of launch scrubs happened yesterday because of a faulty sensor in the shuttle's external fuel tank. The problem occurred as the tank was being fueled.

NASA will make another launch attempt at 11:14 a.m. today using guidelines developed when the same issue cropped up during a 2005 launch.

The decision to scrub came after a lengthy debate among mission managers. Many favored proceeding with launch. Astronauts representing Atlantis' crew did not.

"There were many points of view," said Wayne Hale, NASA's shuttle program manager. "At the end of the day, we decided that staying with the plan that we established ... was the prudent thing to do."

The fuel sensor issue has dogged NASA for more than a year.

The shuttle's flight computers are designed to cut off the three main engines when the orbiter is going fast enough to reach its planned orbit. If there is a problem, however, the sensors are part of a backup system that shuts down the engines before the tank's liquid oxygen and liquid hydrogen supplies run dry. Running the engines on empty could trigger a catastrophe.

Early yesterday, one of four cutoff sensors inside the tank's liquid hydrogen reservoir mistakenly gave a "wet" indication when it was commanded to indicate "dry." A similar failure happened in July 2005 during the countdown to launch shuttle Discovery. Three months earlier, two other sensors had malfunctioned during a fueling test of another tank.

After Discovery's scrub last year, mission managers developed a rationale under which they could launch if three of the four sensors were working properly. The plan calls for delaying liftoff for a day and testing the sensors again when the tank is fueled for another launch attempt.

If no problems are seen other than the same failure on the same sensor, engineers would have confidence that the issue is isolated.

The sensor problem is the latest setback frustrating efforts to get Atlantis off the ground.

A lightning strike at Atlantis' launch pad scrubbed an earlier pair of launch attempts in late August. Then, Tropical Storm Ernesto forced NASA managers to roll Atlantis halfway to shelter before the storm lost strength and the shuttle was returned to the launch pad. Finally, a problem with one of Atlantis' three power-producing fuel cells canceled launch attempts Wednesday and Thursday while engineers studied the problem.

Michael Cabbage writes for the Orlando Sentinel.

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