While a faulty valve delayed last week's original launch date, NASA test director Steve Payne said that all repairs have been made and the shuttle was ready to begin the new countdown Sunday night, the Houston Chronicle reported.
"All our systems are in very good shape right now. The countdown work is on schedule," Payne said.
The shuttle's crew returned to Florida's Cape Canaveral on Friday, including former teacher Barbara Morgan and crew commander Scott Kelly.
If the shuttle is able to launch on Wednesday as scheduled, it will begin the first step of adding the newest addition to the growing international space station.
The shuttle is carrying an $11 million extension that its crew will add to the station's solar power system, along with additional supplies for the station's crew.
Endeavour's power system was recently modified to allow it to gain additional electrical power from the space station while docked, the Chronicle said.
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