NASA flew more than 130 space shuttle missions since the vehicle went into orbital use in the early 1980s, and today the agency wowed many in D.C. with a landing at Dulles International Airport. (Yes, they are making poor Discovery commute in to the city from Dulles). Together, the shuttles have spent more than 1,300 days in flight.
This chart shows their total time in orbital flights. Discovery spent about a year in the air, more than its sister shuttles:
And their total flights during those missions:
Data source: Wikipedia