It will be nearly a month after its initial launch date, but Endeavour finally has the date for when it will lift off for its final trip into space.

NASA announced in a press conference that it has pegged May 16, 8:56 a.m, as the definitive launch date and time for Endeavour. Originally, the space shuttle was supposed to launch on April 19 but was delayed 10 days because of a scheduling conflict with a Russian spacecraft. Following that delay, it was pushed back indefinitely hours before the April 29 launch because of a problem with the heating auxiliary power unit-1 (APU-1).

As a result of Endeavour's launch on the 15th, NASA's final space shuttle mission, SMS-135, on the Atlantis is be pushed to early July the agency said. They have not determined an exact date, but said July 4 is unlikely.

NASA said the Load Control Assembly-2 (LCA-2) box in the orbiter's aft compartment, where the heating unit was located, was fixed and tested over the weekend. The agency ran the heaters for up to 30 minutes to verify they are working properly and completed retesting of the other systems powered by the switchbox. The team will begin close out the aft compartment and begin launch countdown preps today.

SMS-134 will cap a nice career for Endeavour. Since its first mission, Endeavour has traveled 116,372,930 miles, spent 283 days in space and has had a total of 4,423 orbits. Over the years, it has housed many of space related milestones.

It was the first to include four spacewalks, and then the first to include five.  One of its first missions, STS-67, 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 is where the International Space Station first started to be constructed.

During the 14-day mission, Endeavour and its crew will deliver the Alpha Magnetic Spectrometer (AMS) and spare parts including two S-band communications antennas, a high-pressure gas tank and additional spare parts for Dextre. After it finishes up, NASA will conclude the space shuttle program with the Atlantis. Following that, the three remaining space shuttles and a fourth prototype will head to museums across the country.

A NASA official told, the cost of the delay would be at least $500,000, if not more. This is mainly due to the cost of de-tanking, where the fuel propellant is drained for an external tank.

Along with being the final trip for Endeavour, the mission also features commander Mark Kelly, husband of congresswoman Gabrielle Giffords, who was nearly shot to death earlier this year.  President Barack Obama was in Florida on the 29th for the proposed launch and met with Commander Kelly and his team. He also met with Giffords.

Follow Gabriel Perna on Twitter at @GabrielSPerna