Space Shuttle Endeavour, which is one of the last two remaining operational orbiters in the Space Shuttle fleet of NASA, made its final launch today. 

A few months ago, NASA's space shuttle Discovery made its final flight from Cape Canaveral, Florida after 30 years of space travel. Space shuttle's Endeavour and Atlantis are the remaining two operational orbiters in the Space Shuttle fleet of NASA, but now, Endeavour has started the first leg of its final mission. 

Space shuttle Endeavour began construction in 1987 at a price of $2.2 billion. It was completed in May 1991, and embarked on its first space venture in May 1992. In total, space shuttle Endeavour has spent 280 days in space, carried 148 astronauts, and traveled 166,003,247 km at this point. It has completed 24 missions total -- its 25th mission will be its last. 

The Endeavour's commander will be Cmdr. Mark Kelly. Kelly's wife, U.S. Rep. Gabrielle Giffords, who suffered a gunshot wound to the head in the Tuscon, Arizona mass shooting three months ago, will be in attendance today.

Kelly's crew consists of pilot Gregory H. Johnson, mission specialists Michael Fincke, Andrew Feustel and Greg Chamitoff, and European Space Agency astronaut Roberto Vittori. 

The Endeavour will embark on a 15-day journey through space. Four spacewalks are planned, where experiments will be retrieved, new ones will be placed, parts will be lubricated and tanks will be refilled at the International Space Station.  

In addition, the Endeavour is carrying the Alpha Magnetic Spectrometer, which is a $1.5 billion piece of equipment that captures space particles like dark matter so that scientists can learn more about it. Space walkers will place the Alpha Magnetic Spectrometer outside of the International Space Station so it can gather these particles and contribute to our knowledge of our universe. 

Kelly noted that today will be a very emotional day for him, as he fears that it could possibly be his last flight into space.  

"Flying in space is a very difficult thing to give up," said Kelly. "I remember after my last flight thinking, 'Well, maybe this is the last time I'm going to do this.' And you know, you go a couple of months out and you're like, 'Oh, I really hope this is not the end of my flying career.'"

With two of NASA's Space Shuttle fleet orbiters in retirement, and the third expected to make its final launch later this summer, U.S. astronauts are going to have a difficult time going into space unless they utilize Russian rockets.  

"I'll be thinking the same thing, I can't really give this up," said Kelly. "I've got to figure out a way to get back into space."

Space shuttle Endeavour lifted off the launchpad at 8:56 a.m. ET. It was originally supposed to launch on April 29, but a "broken set of heaters" prevented the launch from taking place.