Endeavour blasted off on the next-to-last shuttle flight Monday morning under the command of Mark Kelly, the husband of Rep. Gabrielle Giffords. The wounded congresswoman watched the launch in private from Kennedy Space Center.

Shuttle Endeavour Poised for Last Launch

As many as 45,000 guests jammed NASA's launch site. The crowd outside the gates was estimated to be in the tens of thousands, if not more.

It was the second launch attempt. Late last month, an electrical problem halted the countdown.

Endeavour and its six astronauts will arrive at the International Space Station on Wednesday. They are delivering a $2 billion particle physics experiment. The mission will last 16 days.

Only one other shuttle trip remains.

Shuttle Endeavour

The six astronauts of Endeavour's STS-134 mission - the final flight of NASA's youngest orbiter - depart the Operations & Checkout building at NASA's Kennedy Space Center in Cape Canaveral, Fla. on May 16. The astronauts boarded the "Astro Van" at 5:11 a.m. EDT to journey to Endeavour's seaside Launch Pad 39A

Space Shuttle Endeavour Glistens in the Sun

Space shuttle Endeavour glistens in the sun on Launch Pad 39A at NASA's Kennedy Space Center in Florida. The shuttle is launching on its final mission, STS-134, on May 16, 2011.

Lightning Strikes Over Shuttle Endeavour

The space shuttle Endeavour is seen on launch pad 39a as a storm passes by prior to the rollback of the Rotating Service Structure (RSS), Thursday, April 28, 2011, at Kennedy Space Center in Cape Canaveral, Fla.

You Are Not Spock

This shuttle mission (STS-134) can't go wrong with a poster parodying a movie reboot of the 1960s cult hit "Star Trek."