NASA

Space shuttle Endeavour has spent 19 years pushing boundaries, and its final mission will allow that legacy to live on.

Among Endeavour’s missions was the first to include four spacewalks, and then the first to include five. Its STS-67 mission set a length record almost two full days longer than any shuttle mission before it. Its airlock is the only one to have seen three spacewalkers exit through it for a single spacewalk. And in its cargo bay, the first two pieces of the International Space Station were joined together.

0 like Space Shuttle Launch: How to Watch the Discovery Liftoff Live with Your Kids

Ladies and gentlemen, start your engine!

The 3-hour process of fueling the space shuttle Discovery began this morning at 7:25 a.m. EST by NASA technicians in preparation for this afternoon’s 4:50 p.m. scheduled launch.

This will be the last flight for Discovery before it is retired by NASA. This particular mission has been three months in the making — the original launch was scheduled for November 1st, but due to bad weather and some mechanical problems, it was delayed. The purpose of this mission is to supply the International Space Station with food and various other supplies and equipment.