Space shuttle technicians closed up the engine compartment Wednesday as the countdown advanced smoothly toward Thursday's scheduled launch of Atlantis with five astronauts.

NASA spokeswoman Lisa Malone said the launch team completed certification of two replacement parts in the fuel system and other components and reinstalled access panels on the engine compartment.Also under way Wednesday was a check of the shuttle communications system.

"We're humming right along," she said.

"This time we're going to see if we can get it right," astronaut David Walker, who will command the flight, said Tuesday. Four days earlier, a launch attempt was called off just 31 seconds before the planned liftoff.

"Looks like the vehicle's been turned around real well," Walker told reporters. "We're extremely pleased the folks here at the cape were able to do such a good and quick job getting it ready to go again."

The other crew members are pilot Ronald Grabe and mission specialists Mary Cleave, Mark Lee and Norman Thagard.

Liftoff is scheduled for 11:48 a.m. MST Thursday.

"There are no major issues in sight," Robert Crippen, NASA's deputy director of operations, said after a mission management meeting Tuesday. "We're pressing on."

Shuttle weather forecasters said there was a 70 percent chance conditions would be favorable. The only concern was a threat of crosswinds greater than 17 mph that could be dangerous if the shuttle had to make an emergency landing on a runway near the launch pad.

Atlantis will carry into space the $550 million Magellan probe, which the astronauts are to dispatch on a 15-month journey to Venus. The probe is to orbit the planet and map its cloud-shrouded surface with a high resolution radar system.

The launch attempt was halted on Friday because of a short circuit in a fuel pump.

Technicians working around the clock replaced the pump and a suspect fuel line in half the time expected.

Engineers thought there was a leak in the fuel line, but tests turned up nothing. They believe a vapor cloud seen spewing from the line, thought to be gas, might have been trapped air.