The launch was scrubbed twice during the weekend because of bad weather and then on Sunday night, engineers discovered a pencil-sized crack in the foam insulation on the spacecraft's external fuel tank.
However, by Monday night, Associate Administrator William Gerstenmaier told reporters the cracked foam wouldn't affect the launch.
The crew is now aboard the orbiter ready for the shuttle's scheduled launch time of 2:38 p.m. ET, according to the brother of Discovery's pilot, astronaut Mark Kelly.
"They were feeling great, they feel ready to go and are encouraged about the weather forecast this morning," Scott Kelly told CNN.
A faulty circuit breaker was discovered on the shuttle Tuesday morning but NASA officials have said it would fixed in time for liftoff.