KENNEDY SPACE CENTER, FLA. -- STS-101 Mission Specialist Susan J. Helms adjusts her helmet after climbing into her seat inside Space Shuttle Atlantis for a simulated launch countdown. The countdown is part of Terminal Countdown Demonstration Test (TCDT) activities that also include emergency egress training and familiarization with the payload. Other crew members taking part are Commander James D. Halsell Jr., Pilot Scott J. "Doc" Horowitz and Mission Specialists Mary Ellen Weber, James Voss, Jeffrey N. Williams, and Yury Usachev of Russia. During their mission to the International Space Station, the STS-101 crew will be delivering logistics and supplies, plus preparing the Station for the arrival of the Zvezda Service Module, expected to be launched by Russia in July 2000. Also, the crew will conduct one space walk to perform maintenance on the Space Station. This will be the third assembly flight for the Space Station. STS-101 is scheduled to launch April 24 at 4:15 p.m. from Launch Pad 39A KSC00pp0473

The Space Shuttle program was the United States government's manned launch vehicle program from 1981 to 2011, administered by NASA and officially beginning in 1972. The Space Shuttle system—composed of an orbiter launched with two reusable solid rocket boosters and a disposable external fuel tank— carried up to eight astronauts and up to 50,000 lb (23,000 kg) of payload into low Earth orbit (LEO). When its mission was complete, the orbiter would re-enter the Earth's atmosphere and lands as a glider. Although the concept had been explored since the late 1960s, the program formally commenced in 1972 and was the focus of NASA's manned operations after the final Apollo and Skylab flights in the mid-1970s. It started with the launch of the first shuttle Columbia on April 12, 1981, on STS-1. and finished with its last mission, STS-135 flown by Atlantis, in July 2011.

Space Shuttle Atlantis was a space shuttle that was operated by NASA as part of the Space Shuttle program. It was the fourth operational shuttle built, and the last one to be built before the program was retired in 2011. Atlantis was named after the first research vessel operated by the Woods Hole Oceanographic Institution, and it made its first flight in October 1985. Over the course of its career, Atlantis completed 33 missions and spent a total of 307 days in space. Its last mission was STS-135, which was the final mission of the Space Shuttle program. Atlantis is now on display at the Kennedy Space Center Visitor Complex in Florida. Space Shuttle Atlantis (Orbiter Vehicle Designation: OV-104) was one of the four first operational orbiters in the Space Shuttle fleet of NASA, the space agency of the United States. (The other two are Discovery and Endeavour.) Atlantis was the fourth operational shuttle built. Atlantis is named after a two-masted sailing ship that operated from 1930 to 1966 for the Woods Hole Oceanographic Institute. Atlantis performed well in 25 years of service, flying 33 missions.