NASA Begins 2nd Columbia Countdown

NASA started a second countdown for Columbia’s medical research mission Tuesday after checking out the space shuttle’s new computer parts and fuel temperature sensors.

The countdown for the Saturday morning launch began at 6 p.m. PDT. Earlier, workers did a final sweep of the ship’s cramped engine compartment, where they replaced bad parts.

“All the work is done, and we’re ready to go,” said Lisa Malone, a spokeswoman for the National Aeronautics and Space Administration.

NASA halted the previous countdown May 21, the day before Columbia was supposed to lift off with seven astronauts, 30 white rats and 2,478 baby jellyfish.

A report on a leaky fuel temperature sensor pulled from Columbia in September raised doubts about the ship’s remaining sensors. The final analysis, issued May 20, revealed dangerous cracks in the steel that could have caused the part to snap off. That could have caused main engine failure and, possibly, an explosion.

Tests have since uncovered cracks in the steel welds of five other sensors--one from Columbia and two each from Discovery and Atlantis. None of these is as badly damaged or as threatening as the one taken last fall from Columbia, NASA’s oldest shuttle, said NASA spokesman James Hartsfield.

In addition to the sensor problems, a unit in Columbia’s engine compartment that processes computer signals malfunctioned, and one of five main computers in the crew cabin failed. Both items were replaced with spares.