Liftoff of the 134th shuttle mission is scheduled for 3:47 p.m. EDT from the Kennedy Space Center in Florida.
The all-veteran crew is led by Mark Kelly, husband of Arizona Democratic Representative Gabrielle Giffords, who is recovering from a January 8 shooting that killed six people and injured 12 others.
Pending approval from her doctors, Giffords, who has not been seen publicly since the attack outside a Tucson, Arizona, grocery store, plans to attend the launch, Kelly has said.
The primary purpose of the flight is to deliver the $2 billion Alpha Magnetic Spectrometer, or AMS, particle detector, an instrument designed to detect dark matter, antimatter and other exotic phenomena.
"It has the potential of returning really Earth-shattering science," said NASA's Bill Gerstenmaier.
A team of 600 scientists from 16 nations, including China and Taiwan, are partners in the project.
After installing AMS the Endeavour astronauts will turn their attention to four spacewalks and other tasks to help get the space station ready for operations without shuttle support. The station is a $100 billion project of the United States, Russia, Europe, Japan and Canada that has been under construction since 1998, 220 miles above Earth.
After one final shuttle flight in June to deliver a year's worth of supplies, the station will depend on smaller cargo ships from Russia, Europe and Japan.
Endeavour, which will be making its 25th and final space mission, is expected to stay in orbit up to 16 days.
Sister ship Discovery completed its last mission on March 9. The shuttle Atlantis is targeted for launch on June 28 to complete the 30-year-old shuttle program. The fleet is being retired due to high operating costs and to free up funds to develop new spacecraft.