He says the end of the program after 30 years will help push the frontiers of space exploration and human space flight.
He said jokingly, "I was just dialing out for pizza, and I didn't expect to end up in space."
The day didn't start off well for the astronauts. They had to fix another failed computer that went offline on Thursday.
Over the weekend, a different main computer failed, but it was successfully restarted.
Computer failures like this are extremely rare in orbit, said lead flight director Kwatsi Alibaruho. The two problems appear to be quite different, he noted. The first was caused by a bad switch throw; the second possibly by cosmic radiation.
Atlantis and its crew are due back to Earth late next week.
The Associated Press contributed to this report.