Engineers Work to Solve Malfunction on Shuttle

Technicians installed work platforms around Columbia’s engine section Friday so that they could examine a faulty rocket-steering unit that halted the countdown 15 seconds before liftoff and delayed the flight until Jan. 4.

Jim Ball, a spokesman for the National Aeronautics and Space Administration, said some in-place testing would be done before the unit is removed today in the efforts to find the source of the problem.

He said a replacement unit would be installed late today, and would be tested thoroughly on Sunday.

The breadbox-sized device is part of one of the two solid-fuel rocket boosters that help propel the shuttle into orbit. It supplies hydraulic pressure to push and pull two actuators that move the booster nozzles steering the rocket during the first two minutes of flight.

The shuttle’s huge, apricot-colored external tank was drained of its half-million-gallon load of fuel overnight Thursday, so that NASA could reopen the launch pad and give workers access to the solid-rocket booster on Columbia’s right side.

A computer stopped the countdown Thursday when it detected the power unit’s turbine spinning at about 86,000 rpm, about 7,000 rpm faster than the safety red-line rate. Normal speed is about 72,000 rpm.

Larry Mulloy, a NASA rocket expert, said the speed could have resulted from sluggish fuel flow, a bad control valve or a false reading caused by a defective sensor.

There is a redundant unit in each of the two rocket motors, but mission rules dictate that liftoff may not occur unless both are working. If there was only one unit functioning on launch, and it failed, the shuttle would cartwheel out of control and the crew probably would be killed.

Robert Sieck, director of shuttle launch operations at the Kennedy Space Center, said after Thursday’s aborted countdown that Columbia probably could be ready for launching by Dec. 30 or 31, but officials decided to let thousands of shuttle workers enjoy the holiday vacations they had been promised. So engineers will take Christmas off, and only a skeleton crew will be on duty at the launch pad until after New Year’s Day, Sieck said.

Columbia’s crewmen plan to fly back here Jan. 1 for the start of their second countdown on Jan. 2. Blastoff is scheduled for the morning of Jan. 4.

On board will be the commander, Robert L. Gibson, pilot Charles F. Bolden, Franklin R. Chang-Diaz, Steven A. Hawley, George D. Nelson, RCA engineer Robert J. Cenker and Rep. Bill Nelson (D-Fla.), who chairs the House subcommittee on space science and applications.