EL PASO, Texas -- It's flight day three for Space Shuttle Discovery and Astronaut Danny Olivas, and Sunday is one of the most important days of the mission as they tried and successfully docked with the International Space Station.

Sunday's docking at the International Space Station became just a little more difficult with one of the first technical problems of the mission.

"We had a thruster failure, one of the small, what we call vernier thrusters failed," said LeRoy Cain with the NASA Mission Management Team.

Cain said docking with the space station was slightly more challenging, because the crew has to use the main thrusters.

"The crew is very well trained for this particular failure mode, they've trained various times in their preparations for flight, and so we don't have any concerns for that," said Cain.

At about 600 feet below the International Space Station, Discovery made a back flip so that astronauts on the space station can take photos of the heat shield, before flying 400 feet directly in front of the station for docking -- a docking that successfully happened just after seven o'clock tonight.

Of course the other concern of the first few days of the mission is damage to Discovery's heat shield during launch.

"The level one assessment is complete, which is to say that there are no significant areas of concern that they've seen in anything in level one, where they do sort of a broad look," said Cain.

While NASA will have to wait for more photos and analysis, Cain is happy with what he's seen so far.

"Overall, very clean ascent, very clean vehicle, the crew is doing great on orbit," he said.

All of this happened on the 25th birthday of Space Shuttle Discovery. As for Danny Olivas, he'll start to get ready for his space walk which is on flight day five on Tuesday.