BWI is  ~22 miles away from NASA GSFC's Visitor Center but the most direct route to the center. 

Getting to and From BWI

DCA is   ~19 miles away from NASA GSFC's Visitor Center but will likely take you much longer to get to GSFC's Visitor Center. Metro access is available from DCA to either New Carrolton (orange line) or Greenbelt (green line).  

Washington Metropolitan Area Transit Authority (WMATA) * Access trip planner, information about metro & buses, etc.*

Getting to and From DCA