With the successful landing of the space shuttle Endeavour Sunday night, the International Space Station is on the verge of completion after $100 billion and 11 years of construction. NASA plans just four more missions to wrap up its few remaining station deliveries.

For Endeavour, in particular, Sunday's shuttle landing marked the beginning of the end. The spacecraft is the youngest of NASA's three aging space shuttles and engineers quickly began working to prepare it to launch one final spaceflight in July.

"We'll go into that with our heads held high," shuttle launch director Mike Leinbach said after the landing. "It's a little bit [of a] sad note, but a great ending to a great mission and we're looking forward to the next one."