With only hours remaining before liftoff, NASA on Sunday declared space shuttle Endeavour's engines safe to fly despite lingering uncertainty over two fuel pump seals.
The announcement kept Endeavour on track for a 12:47 p.m. launch this afternoon for an Earth-mapping mission. Thick clouds, however, still could force a delay.
Shuttle managers ordered an exhaustive review of seals in Endeavour's fuel turbopumps late last week after a defective seal turned up in one of Discovery's main engines.
The bad seal should have been thrown away as a factory reject, but instead was installed in a fuel pump that flew on Discovery six weeks ago. It also flew on Discovery in October 1998 _ the flight that returned John Glenn to orbit _ and on Endeavour earlier that year.
NASA was able to determine, through documents, that 16 of 18 seal segments on Endeavour's three fuel pumps are certified and good. The paperwork on the two remaining seals is missing, but shuttle managers concluded Sunday that Endeavour's engines are safe and voted unanimously to proceed with the launch.
Shuttle program manager Ron Dittemore said the likelihood of another defective seal turning up on one of Endeavour's three engines is "very, very, very low."
Dittemore said NASA will continue to search for the paperwork detailing the history of the two seals. NASA also will review the paperwork for seals in all its other fuel pumps before clearing any more shuttle engines to fly, he said.
The nickel-plated seals, each made of six segments, help direct hot gas into the turbine blades to increase engine performance. If a seal should fail, an engine could shut down during launch and force an emergency landing.
On Endeavour's 11-day mission, scientists hope to gather data to create a high-resolution, three-dimensional map covering at least 72 percent of Earth's land surface. The digital data will be a quantum leap over current topographic maps, a patchwork quilt of observations from aircraft and satellites. In fact, thanks to interplanetary probes, better global topographic maps exist of Venus and Mars than Earth.
Most of Earth's maps were created from elevation measurements taken more than six-tenths of a mile apart. The distance between data points recorded by the shuttle will be reduced to the length of a football field.
The resulting information is expected to fill 13,500 compact disks and could take up to two years to process.
Potential uses include elevation maps that could make air travel safer, more accurate flood maps and better placement of cellular phone towers.
_ Information from the Orlando Sentinel was used in this report.