NASA's Space Shuttle Discovery is scheduled to make its last trip into low Earth orbit. Discovery will be traveling to the International Space Station, carrying a large module packed with supplies and critical spare parts, as well as a robotic assistant named Robonaut 2. With the entire Space Shuttle program scheduled for mandatory retirement this year, Discovery is the most-flown spacecraft in history, traveling 143 million miles (230 million kilometers) over the course of its 39 missions since 1984, and spending nearly a full year in orbit. Gathered here are images of Discovery, its crew, and support staff from the past several months, while the spacecraft was being prepared for today's launch. This mission, STS-133, is scheduled for liftoff at 4:50 p.m Eastern Time. Robonaut 2 waits inside the electromagnetic interference chamber at Johnson Space Center following tests that ensure the robot's electronic systems won't cause problems for other important systems at the International Space Station. R2 will be journeying to the space station onboard Discovery during the STS-133 mission. At NASA's Kennedy Space Center in Florida, shuttle Discovery pauses in between Orbiter Processing Facility-3 and the Vehicle Assembly Building (VAB) during a move called "rollover" on September 9th, 2010. Once inside the VAB, the shuttle will be joined to its solid rocket boosters and external fuel tank. Later, Discovery was scheduled to "rollout" to Launch Pad 39A for its launch to the International Space Station on the STS-133 mission. Spectators watch as space shuttle Discovery lifts off from the Kennedy Space Center in Cape Canaveral, Florida, February 24, 2011. Six astronauts are aboard on a mission to the International Space Station.