Apollo 8 astronaut William Anders, Lunar Module (LM) pilot, is suited up for the Apollo 8 mission countdown demonstration test. The first manned Apollo mission launched aboard the Saturn V and first manned Apollo craft to enter lunar orbit, the SA-503, Apollo 8 mission lift off occurred on December 21, 1968 and returned safely to Earth on December 27, 1968. Aboard were Anders and fellow astronauts James Lovell, Command Module (CM) pilot; and Frank Borman, commander. The mission achieved operational experience and tested the Apollo command module systems, including communications, tracking, and life-support, in cis-lunar space and lunar orbit, and allowed evaluation of crew performance on a lunar orbiting mission. The crew photographed the lunar surface, both far side and near side, obtaining information on topography and landmarks as well as other scientific information necessary for future Apollo landings. All systems operated within allowable parameters and all objectives of the mission were achieved.

S69-56596 (28 Oct. 1969) --- A nighttime, ground-level view of Pad A, Launch Complex 39, Kennedy Space Center (KSC) showing the Apollo 12 (Spacecraft 108/Lunar Module 6/Saturn 507) space vehicle, during the terminal phase of a Countdown Demonstration Test (CDDT). The crew of the National Aeronautics and Space Administration's (NASA) second lunar landing mission will be astronauts Charles Conrad Jr., commander; Richard F. Gordon Jr., command module pilot; and Alan L. Bean, lunar module pilot. The Apollo 12 launch has been scheduled for 11:22 a.m. (EST) on Nov. 14, 1969.

Apollo XI Launch Vehicle AS-506 and Spacecraft 107, Launch Pad 39A for CDDT (Countdown Demonstration Test), includes MSS (Mobile Service Structure) pullback, KSC. 1. APOLLO XI - PRELAUNCH KENNEDY SPACE CENTER, FL

Apollo 11 crew member Michael Collins appears calm after suiting up activities for his participation in the countdown demonstration test aboard the Apollo 11 space craft along with astronauts Aldrin and Armstrong. The Apollo 11 mission, the first lunar landing mission, launched from the Kennedy Space Center (KSC) in Florida via the Marshall Space Flight Center (MSFC) developed Saturn V launch vehicle on July 16, 1969 and safely returned to Earth on July 24, 1969. Aboard the space craft were astronauts Neil A. Armstrong, commander; Michael Collins, Command Module (CM) pilot; and Edwin E. (Buzz) Aldrin Jr., Lunar Module (LM) pilot. The CM, “Columbia”, piloted by Collins, remained in a parking orbit around the Moon while the LM, “Eagle’’, carrying astronauts Armstrong and Aldrin, landed on the Moon. On July 20, 1969, Armstrong was the first human to ever stand on the lunar surface, followed by Aldrin. During 2½ hours of surface exploration, the crew collected 47 pounds of lunar surface material for analysis back on Earth. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

S69-34333 (13 May 1969) --- The three Apollo 10 astronauts suit up for a Countdown Demonstration Test at the Kennedy Space Center during preparations for their scheduled lunar orbit mission. From front to rear, are Thomas P. Stafford, commander; John W. Young, command module pilot; and Eugene A. Cernan, lunar module pilot.

S69-34330 (13 May 1969) --- Astronaut Thomas P. Stafford, Apollo 9 commander, is suited up at the Kennedy Space Center for a Countdown Demonstration Test during preparations for the scheduled Apollo 10 lunar orbit mission. The other two crewmembers are astronauts John W. Young, command module pilot; and Eugene A. Cernan, lunar module pilot.

S69-25488 (23 Feb. 1969) --- Interior view of the White Room at Pad A, Launch Complex 39, Kennedy Space Center (KSC), during an Apollo 9 Countdown Demonstration Test (CDDT). Astronauts James A. McDivitt, commander; David R. Scott, command module pilot; and Russell L. Schweickart, lunar module pilot, were participating in a dress rehearsal in preparation for their scheduled 10-day Earth-orbital space mission.

S73-25696 (15 May 1973) --- An overall view of Pad B, Launch Complex 39, Kennedy Space Center, Florida, showing the Skylab 2/Saturn 1B space vehicle during a Countdown Demonstration Test (CDDT). This is the launch vehicle for the first manned Skylab mission. The vapor being emitted from the vehicle is the venting of cryogenic propellants. Photo credit: NASA

Apollo 11 crew members (left to right) Michael Collins, Edwin Aldrin (foreground), and Neil Armstrong, wearing space suits, leave the Apollo 11 space craft after participation in the countdown demonstration test for the upcoming mission. The Apollo 11 mission, the first lunar landing mission, launched from the Kennedy Space Center (KSC) in Florida via the Marshall Space Flight Center (MSFC) developed Saturn V launch vehicle on July 16, 1969 and safely returned to Earth on July 24, 1969. The CM, “Columbia”, piloted by Collins, remained in a parking orbit around the Moon while the LM, “Eagle’’, carrying astronauts Armstrong and Aldrin, landed on the Moon. On July 20, 1969, Armstrong was the first human to ever stand on the lunar surface, followed Aldrin. During 2½ hours of surface exploration, the crew collected 47 pounds of lunar surface material for analysis back on Earth. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

Seriousness exudes from launch official Miles Ross (left) of Kennedy Space Flight Center (KSC) and Major General E.F. O’Conner, director of program management of the Marshall Space Flight Center (MSFC), as they participate in the Apollo 11 countdown demonstration test. The Apollo 11 mission, the first lunar landing mission, launched from the KSC in Florida via the MSFC developed Saturn V launch vehicle on July 16, 1969 and safely returned to Earth on July 24, 1969. Aboard the space craft were astronauts Neil A. Armstrong, commander; Michael Collins, Command Module (CM) pilot; and Edwin E. (Buzz) Aldrin Jr., Lunar Module (LM) pilot. The CM, “Columbia”, piloted by Collins, remained in a parking orbit around the Moon while the LM, “Eagle’’, carrying astronauts Armstrong and Aldrin, landed on the Moon. On July 20, 1969, Armstrong was the first human to ever stand on the lunar surface, followed by Aldrin. During 2½ hours of surface exploration, the crew collected 47 pounds of lunar surface material for analysis back on Earth. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

Apollo 11 crew members (rear to front) Neil Armstrong, Edwin Aldrin, and Michael Collins, wearing space suits, ride the van to the launch pad to participate in the countdown demonstration test for the upcoming Apollo 11 mission. The Apollo 11 mission, the first lunar landing mission, launched from the Kennedy Space Center (KSC) in Florida via the Marshall Space Flight Center (MSFC) developed Saturn V launch vehicle on July 16, 1969 and safely returned to Earth on July 24, 1969. Aboard the space craft were astronauts Neil A. Armstrong, commander; Michael Collins, Command Module (CM) pilot; and Edwin E. (Buzz) Aldrin Jr., Lunar Module (LM) pilot. The CM, “Columbia”, piloted by Collins, remained in a parking orbit around the Moon while the LM, “Eagle’’, carrying astronauts Armstrong and Aldrin, landed on the Moon. On July 20, 1969, Armstrong was the first human to ever stand on the lunar surface, followed by Aldrin. During 2½ hours of surface exploration, the crew collected 47 pounds of lunar surface material for analysis back on Earth. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

Apollo 11 crew members (left to right) Neil Armstrong, Edwin Aldrin, and Michael Collins, wearing space suits, leave the elevator after descending from the top of the launch tower. The three had just completed participation in the countdown demonstration test for the upcoming Apollo 11 mission. The Apollo 11 mission, the first lunar landing mission, launched from the Kennedy Space Center (KSC) in Florida via the Marshall Space Flight Center (MSFC) developed Saturn V launch vehicle on July 16, 1969 and safely returned to Earth on July 24, 1969. Aboard the space craft were astronauts Neil A. Armstrong, commander; Michael Collins, Command Module (CM) pilot; and Edwin E. (Buzz) Aldrin Jr., Lunar Module (LM) pilot. The CM, “Columbia”, piloted by Collins, remained in a parking orbit around the Moon while the LM, “Eagle’’, carrying astronauts Armstrong and Aldrin, landed on the Moon. On July 20, 1969, Armstrong was the first human to ever stand on the lunar surface, followed by Aldrin. During 2½ hours of surface exploration, the crew collected 47 pounds of lunar surface material for analysis back on Earth. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

S89-41093 (9 Aug 1989) --- STS-28 Columbia, Orbiter Vehicle (OV) 102, mission specialist David C. Leestma relaxes in chair after donning launch and entry suit (LES) and launch and entry helmet (LEH). Technician in the background monitors LES systems. Leestma, along with fellow crewmembers, is participating in the terminal countdown demonstration test (TCDT) at the Kennedy Space Center (KSC) Operations and Checkout (O&C) Building. View provided by KSC with alternate number KSC-89PC-673.

S88-53244 (14 Nov 1988) --- The crewmembers for STS-27 leave the operations and checkout (O&C) building en route to a transfer van that will take them to Launch Pad 39B for their terminal countdown demonstration test. From the front to the rear are astronauts Robert L. Gibson, Guy S. Gardner, William M. Shepherd, Richard M. (Mike) Mullane and Jerry L. Ross.

S69-33853 (4 May 1969) --- Ground-level view of the Apollo 10 (Spacecraft 106/Lunar Module 4/Saturn 505) space vehicle on Pad B, Launch Complex 39, Kennedy Space Center, Florida. This photograph of the 363-feet tall Apollo/Saturn V stack was taken during Countdown Demonstration Test (CDDT) activity. The Apollo 10 crew will be astronauts Thomas P. Stafford, commander; John W. Young, command module pilot; and Eugene A. Cernan, lunar module pilot.

S69-25884 (23 Feb. 1969) --- Interior view of the white room atop Pad A, Launch Complex 39, Kennedy Space Center, during Apollo 9 Countdown Demonstration Test activity. Standing next to spacecraft hatch is astronaut James A. McDivitt, commander. Also, taking part in the training exercise were astronauts David R. Scott, command module pilot; and Russell L. Schweickart, lunar module pilot. The Apollo 9 mission will evaluate spacecraft lunar module systems performance during manned Earth-orbital flight. Apollo 9 will be the second manned Saturn V mission.

S88-53086 (17 Nov 1988) --- STS-27 Atlantis, Orbiter Vehicle (OV) 104, crewmembers participate in the terminal countdown demonstration test (TCDT) at the Kennedy Space Center (KSC). Standing in front of the M113 tracked rescue vehicle (armored personnel carrier (APC)) are left to right Mission Specialist (MS) William M. Shepherd, Pilot Guy S. Gardner, Commander Robert L. Gibson, MS Richard M. Mullane, and MS Jerry L. Ross. Crewmembers are wearing orange partial pressure or launch and entry suits (LES).

Lee B. James (left), manager of the Saturn Program at the Marshall Space flight Center (MSFC), talks with Isom Pigell in the firing room 1 of the Kennedy Space Center (KSC) control center during the countdown demonstration test for the Apollo 11 mission. The Apollo 11 mission, the first lunar landing mission, launched from the KSC in Florida via the MSFC developed Saturn V launch vehicle on July 16, 1969 and safely returned to Earth on July 24, 1969. Aboard the space craft were astronauts Neil A. Armstrong, commander; Michael Collins, Command Module (CM) pilot; and Edwin E. (Buzz) Aldrin Jr., Lunar Module (LM) pilot. The CM, “Columbia”, piloted by Collins, remained in a parking orbit around the Moon while the LM, “Eagle’’, carrying astronauts Armstrong and Aldrin, landed on the Moon. On July 20, 1969, Armstrong was the first human to ever stand on the lunar surface, followed by Aldrin. During 2½ hours of surface exploration, the crew collected 47 pounds of lunar surface material for analysis back on Earth. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

Lee B. James (left), manager of the Saturn Program at the Marshall Space flight Center (MSFC), talks with Isom Pigell in the firing room 1 of the Kennedy Space Center (KSC) control center during the countdown demonstration test for the Apollo 11 mission. At left is Dr. Hans C. Gruen of KSC. The Apollo 11 mission, the first lunar landing mission, launched from the KSC in Florida via the MSFC developed Saturn V launch vehicle on July 16, 1969 and safely returned to Earth on July 24, 1969. Aboard the space craft were astronauts Neil A. Armstrong, commander; Michael Collins, Command Module (CM) pilot; and Edwin E. (Buzz) Aldrin Jr., Lunar Module (LM) pilot. The CM, “Columbia”, piloted by Collins, remained in a parking orbit around the Moon while the LM, “Eagle’’, carrying astronauts Armstrong and Aldrin, landed on the Moon. On July 20, 1969, Armstrong was the first human to ever stand on the lunar surface, followed by Aldrin. During 2½ hours of surface exploration, the crew collected 47 pounds of lunar surface material for analysis back on Earth. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

Dr. Kurt Debus, director of the Kennedy Space Flight Center (KSC), participated in the countdown demonstration test for the Apollo 11 mission in firing room 1 of the KSC control center. The Apollo 11 mission, the first lunar landing mission, launched from KSC in Florida via the Marshall Space Flight Center (MSFC) developed Saturn V launch vehicle on July 16, 1969 and safely returned to Earth on July 24, 1969. Aboard the space craft were astronauts Neil A. Armstrong, commander; Michael Collins, Command Module (CM) pilot; and Edwin E. (Buzz) Aldrin Jr., Lunar Module (LM) pilot. The CM, “Columbia”, piloted by Collins, remained in a parking orbit around the Moon while the LM, “Eagle’’, carrying astronauts Armstrong and Aldrin, landed on the Moon. On July 20, 1969, Armstrong was the first human to ever stand on the lunar surface, followed by Aldrin. During 2½ hours of surface exploration, the crew collected 47 pounds of lunar surface material for analysis back on Earth. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

KENNEDY SPACE CENTER, FLA. - STS-79 Commander William F. Readdy arrives at KSC's Shuttle Landing Facility with five fellow astronauts, ready to participate in the Terminal Countdown Demonstration Test (TCDT). The TCDT is a dress rehearsal for launch for the flight crew and launch team. Over the next several days, the astronauts will take part in training exercises at the launch pad that will culminate in a simulated launch countdown. The Space Shuttle Atlantis is being prepared for liftoff on STS-79 around Sept. 12.

STS-82 Terminal Countdown Demonstration Test (TCDT

STS-82 crew arrival for Terminal Countdown Demonstration Test (TCDT

STS-82 crew arrival for Terminal Countdown Demonstration Test (TCDT

STS-82 crew arrival for Terminal Countdown Demonstration Test (TCDT

STS-83 crew M113 driver training during Terminal Countdown Demonstration Test (TCDT

STS-83 crew M113 driver training during Terminal Countdown Demonstration Test (TCDT

The STS-87 crew participates in Terminal Countdown Demonstration Test activities at Launch Complex 39B

The STS-87 crew participates in Terminal Countdown Demonstration Test activities at Launch Complex 39B

The STS-87 crew participates in Terminal Countdown Demonstration Test activities at Launch Complex 39B

STS-83 crew M113 driver training during Terminal Countdown Demonstration Test (TCDT

The STS-87 crew participates in Terminal Countdown Demonstration Test activities at Launch Complex 39B

STS-83 crew M113 driver training during Terminal Countdown Demonstration Test (TCDT

The STS-87 crew participates in Terminal Countdown Demonstration Test activities at Launch Complex 39B

KENNEDY SPACE CENTER, FLA. - Apollo 11 crew "suiting up" for Countdown Demonstration Test.

STS-83 crew M113 driver training during Terminal Countdown Demonstration Test (TCDT

The STS-87 crew participates in Terminal Countdown Demonstration Test activities at Launch Complex 39B

The STS-87 crew participates in Terminal Countdown Demonstration Test activities at Launch Complex 39B

The STS-87 crew participates in Terminal Countdown Demonstration Test activities at Launch Complex 39B

The STS-87 crew participates in Terminal Countdown Demonstration Test activities at Launch Complex 39B

CAPE CANAVERAL, Fla. – Space shuttle Endeavour's STS-127 mission crew members greet the media after arriving at NASA's Kennedy Space Center in Florida for the Terminal Countdown Demonstration Test, or TCDT. Seen here is Mission Specialist Julie Payette, who represents the Canadian Space Agency. The astronauts will be taking part in Terminal Countdown Demonstration Test activities that include equipment familiarization and emergency egress training, and culminates in a simulated launch countdown aboard Endeavour. The STS-127 mission is the final of three flights dedicated to the assembly of the Japanese Kibo laboratory complex. Launch is targeted for June 13. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Space shuttle Endeavour's STS-127 mission crew members greet the media after arriving at NASA's Kennedy Space Center in Florida for the Terminal Countdown Demonstration Test, or TCDT. Seen here is Mission Specialist Tim Kopra. The astronauts will be taking part in Terminal Countdown Demonstration Test activities that include equipment familiarization and emergency egress training, and culminates in a simulated launch countdown aboard Endeavour. The STS-127 mission is the final of three flights dedicated to the assembly of the Japanese Kibo laboratory complex. Launch is targeted for June 13. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Space shuttle Endeavour's STS-127 mission crew members greet the media after arriving at NASA's Kennedy Space Center in Florida for the Terminal Countdown Demonstration Test, or TCDT. Seen here is Mission Specialist Chris Cassidy. The astronauts will be taking part in Terminal Countdown Demonstration Test activities that include equipment familiarization and emergency egress training, and culminates in a simulated launch countdown aboard Endeavour. The STS-127 mission is the final of three flights dedicated to the assembly of the Japanese Kibo laboratory complex. Launch is targeted for June 13. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Space shuttle Endeavour's STS-127 mission crew members greet the media after arriving at NASA's Kennedy Space Center in Florida for the Terminal Countdown Demonstration Test, or TCDT. Seen here is Mission Specialist Tom Marshburn. The astronauts will be taking part in Terminal Countdown Demonstration Test activities that include equipment familiarization and emergency egress training, and culminates in a simulated launch countdown aboard Endeavour. The STS-127 mission is the final of three flights dedicated to the assembly of the Japanese Kibo laboratory complex. Launch is targeted for June 13. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Space shuttle Endeavour's STS-127 mission crew members greet the media after arriving at NASA's Kennedy Space Center in Florida for the Terminal Countdown Demonstration Test, or TCDT. Seen here is Mission Specialist Dave Wolf. The astronauts will be taking part in Terminal Countdown Demonstration Test activities that include equipment familiarization and emergency egress training, and culminates in a simulated launch countdown aboard Endeavour. The STS-127 mission is the final of three flights dedicated to the assembly of the Japanese Kibo laboratory complex. Launch is targeted for June 13. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Space shuttle Endeavour's STS-127 mission crew members greet the media after arriving at NASA's Kennedy Space Center in Florida for the Terminal Countdown Demonstration Test, or TCDT. Seen here is Pilot Doug Hurley. The astronauts will be taking part in Terminal Countdown Demonstration Test activities that include equipment familiarization and emergency egress training, and culminates in a simulated launch countdown aboard Endeavour. The STS-127 mission is the final of three flights dedicated to the assembly of the Japanese Kibo laboratory complex. Launch is targeted for June 13. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Space shuttle Endeavour's STS-127 mission crew members greet the media after arriving at NASA's Kennedy Space Center in Florida. Seen here is Commander Mark Polansky, who explained they were at Kennedy for the Terminal Countdown Demonstration Test, or TCDT. The astronauts will be taking part in Terminal Countdown Demonstration Test activities that include equipment familiarization and emergency egress training, and culminates in a simulated launch countdown aboard Endeavour. The STS-127 mission is the final of three flights dedicated to the assembly of the Japanese Kibo laboratory complex. Launch is targeted for June 13. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. - STS-114 Commander Eileen Collins places a mission patch on an M-113 armored personnel carrier during Terminal Countdown Demonstration Test (TCDT) activities. Looking on are Mission Specialists Andrew Thomas, Stephen Robinson and Soichi Noguchi, who is with the Japan Aerospace Exploration Agency.. The crew is at KSC for Terminal Countdown Demonstration Test (TCDT) activities. The TCDT is held at KSC prior to each Space Shuttle flight. It provides the crew of each mission an opportunity to participate in simulated countdown activities. The test ends with a mock launch countdown culminating in a simulated main engine cutoff. The crew also spends time undergoing emergency egress training exercises at the launch pad. STS-114 is designated the first Return to Flight mission, with a launch window extending from July 13 to July 31.

CAPE CANAVERAL, Fla. - STS-125 Mission Specialist Megan McArthur is ready to enter the hatch into space shuttle Atlantis for a simulated launch countdown. The countdown is the culmination of terminal countdown demonstration test, or TCDT, activities as preparation before launch. TCDT provides astronauts and ground crews with an opportunity to participate in various launch activities, including equipment familiarization, emergency training and the countdown. Atlantis’ STS-125 mission to service NASA’s Hubble Space Telescope is targeted for launch Oct. 14. Photo credit: NASA/Amanda Diller

CAPE CANAVERAL, Fla. - STS-125 Mission Specialist Andrew Feustel is ready to enter the hatch into space shuttle Atlantis for a simulated launch countdown. The countdown is the culmination of terminal countdown demonstration test, or TCDT, activities as preparation before launch. TCDT provides astronauts and ground crews with an opportunity to participate in various launch activities, including equipment familiarization, emergency training and the countdown. Atlantis’ STS-125 mission to service NASA’s Hubble Space Telescope is targeted for launch Oct. 14. Photo credit: NASA/Amanda Diller

Astronauts Thomas K. Mattingly, II., right, and Henry Hartsfield, Jr. pose for news photographers in front of the Space Shuttle vehicle during break in the countdown demonstration test (CDDT) for STS-4.

Astronaut Harrison H. Schmitt, Apollo 17 Lunar Module Pilot, suits up in the Astronaut Quarters in the Manned Spacecraft Operations Building in preparation for the Countdown Demonstration Test which was successfully completed here today.

The STS-83 crew departs the Operations and Checkout Building on their way to Launch Complex 39A during the crew's <a href="http://www-pao.ksc.nasa.gov/kscpao/release/1997/40-97.htm">Terminal Countdown Demonstration Test (TCDT).</a

Personnel atop the 402-ft. Mobile Service Structure look back at the Apollo 11 spacecraft as the tower is moved away during a Countdown Demonstration Test. Photo filed 11 July 1969.

KENNEDY SPACE CENTER, FLA. --Apollo 10 astronaut Thomas P. Stafford is assisted in being suited up prior to the Countdown Demonstration Test, a full dress rehearsal.

STS-83 Pilot Susan L. Still talks to the media at Launch Complex 39A during the crew's <a href="http://www-pao.ksc.nasa.gov/kscpao/release/1997/40-97.htm">Terminal Countdown Demonstration Test (TCDT).</a

Members of the STS-83 crew receive instruction at Launch Complex 39A during the crew's <a href="http://www-pao.ksc.nasa.gov/kscpao/release/1997/40-97.htm">Terminal Countdown Demonstration Test (TCDT).</a

Apollo 17 Astronauts, front to rear, Eugene A. Cernan, Ronald E. Evans and Harrison H. Schmitt walk to the transfer van at start of brief ride to launch pad during countdown Demonstration test activities.

Apollo Spacecraft 009 atop the Saturn 1B launch vehicle is seen at Launch Complex 34 during the Saturn 1B countdown demonstration. Preparations are continuing for the Apollo Saturn 201 Test Flight. CAPE KENNEDY, FL CN

CAPE CANAVERAL, Fla. – On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-127 crew members make a hasty exit from space shuttle Endeavour to practice their emergency exit training. From left are Mission Specialists Christopher Cassidy, Julie Payette, Tom Marshburn, Tim Kopra and Dave Wolf. The crew is at Kennedy for the terminal countdown demonstration test, which concluded with a simulated launch countdown. The crew is at Kennedy for the terminal countdown demonstration test, which concluded with a simulated launch countdown. Endeavour's STS-127 mission is the final of three flights dedicated to the assembly of the Japanese Kibo laboratory complex on the International Space Station. Endeavour's launch is scheduled for June 13 at 7:17 a.m. EDT. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- ASTP asstronauts Donald slayton, Vance Brand and Thomas Stafford leave the transfer van at Complex 39's Pad B and enter the pad elevator during the Countdown Demonstration Test. The test, a step-by-step dress rehearsal for the July 15 launch, simulates the actual countdown but without the propellants in the Saturn IB launch vehicle's fuel tanks. The fueled portion of the test was conducted yesterday.

NASA Launch Director Charlie Blackwell-Thompson stands next to her console in Firing Room 1 at the Kennedy Space Center's Launch Control Center during a terminal countdown demonstration for Exploration Mission 1, or EM-1. The launch will be the first integrated test of the Space Launch System rocket and Orion spacecraft that will eventually take astronauts beyond low-Earth orbit to destinations such as the Moon and Mars. Taking place on Dec. 14, 2018, the countdown demonstration was intended to validate the launch team's capability to perform an EM-1 countdown and respond to challenges put into the system for practice.

KENNEDY SPACE CENTER, FLA. -- STS-85 Payload Commander N. Jan Davis (left) and Mission Specialist Robert L. Curbeam, Jr., go through countdown procedures aboard the Space Shuttle orbiter Discovery during Terminal Countdown Demonstration Test (TCDT) activities for that mission. The TCDT includes a simulation of the final launch countdown. The primary payload aboard the Space Shuttle orbiter Discovery is the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere-2 (CRISTA-SPAS-2). Other STS-85 payloads include the Manipulator Flight Demonstration (MFD), and Technology Applications and Science-1 (TAS-1) and International Extreme Ultraviolet Hitchhiker-2 (IEH-2) experiments

NASA Launch Director Charlie Blackwell-Thompson makes notes at her console in Firing Room 1 at the Kennedy Space Center's Launch Control Center during a terminal countdown demonstration for Exploration Mission 1, or EM-1. The launch will be the first integrated test of the Space Launch System rocket and Orion spacecraft that will eventually take astronauts beyond low-Earth orbit to destinations such as the Moon and Mars. Taking place on Dec. 14, 2018, the countdown demonstration was intended to validate the launch team's capability to perform an EM-1 countdown and respond to challenges put into the system for practice.

KENNEDY SPACE CENTER, FLA. -- STS-85 Pilot Kent V. Rominger goes through countdown procedures on the flight deck aboard the Space Shuttle orbiter Discovery during Terminal Countdown Demonstration Test (TCDT) activities for that mission. The TCDT includes a simulation of the final launch countdown. The primary payload aboard the Space Shuttle orbiter Discovery is the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere-2 (CRISTA-SPAS-2). Other STS-85 payloads include the Manipulator Flight Demonstration (MFD), and Technology Applications and Science-1 (TAS-1) and International Extreme Ultraviolet Hitchhiker-2 (IEH-2) experiments

NASA Launch Director Charlie Blackwell-Thompson looks out over Firing Room 1 in the Launch Control Center at NASA’s Kennedy Space Center in Florida during a terminal countdown demonstration for Exploration Mission 1, or EM-1, on Dec. 14, 2018. The launch will be the first integrated test of the Space Launch System rocket and Orion spacecraft that will eventually take astronauts beyond low-Earth orbit to destinations such as the Moon and Mars. The countdown demonstration was intended to validate the launch team's capability to perform an EM-1 countdown and respond to challenges put into the system for practice.

An overall view of Firing Room 1 at the Kennedy Space Center's Launch Control Center shows the launch team at work during a terminal countdown demonstration for Exploration Mission 1, or EM-1. The launch will be the first integrated test of the Space Launch System rocket and Orion spacecraft that will eventually take astronauts beyond low-Earth orbit to destinations such as the Moon and Mars. Taking place on Dec. 14, 2018, the countdown demonstration was intended to validate the launch team's capability to perform an EM-1 countdown and respond to challenges put into the system for practice.

NASA Launch Director Charlie Blackwell-Thompson stands next to her console in Firing Room 1 at the Kennedy Space Center's Launch Control Center during a terminal countdown demonstration for Exploration Mission 1, or EM-1. The launch will be the first integrated test of the Space Launch System rocket and Orion spacecraft that will eventually take astronauts beyond low-Earth orbit to destinations such as the Moon and Mars. Taking place on Dec. 14, 2018, the countdown demonstration was intended to validate the launch team's capability to perform an EM-1 countdown and respond to challenges put into the system for practice.

KENNEDY SPACE CENTER, FLA. -- STS-85 Commander Curtis L. Brown, Jr., goes through countdown procedures on the flight deck aboard the Space Shuttle orbiter Discovery during Terminal Countdown Demonstration Test (TCDT) activities for that mission. The TCDT includes a simulation of the final launch countdown. The primary payload aboard the Space Shuttle orbiter Discovery is the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere-2 (CRISTA-SPAS-2). Other STS-85 payloads include the Manipulator Flight Demonstration (MFD), and Technology Applications and Science-1 (TAS-1) and International Extreme Ultraviolet Hitchhiker-2 (IEH-2) experiments

Michael Guzman, an umbilical engineer, monitors his console in Firing Room 1 in the Launch Control Center at NASA’s Kennedy Space Center in Florida, during a terminal countdown demonstration for Exploration Mission 1, or EM-1, on Dec. 14, 2018. The launch will be the first integrated test of the Space Launch System rocket and Orion spacecraft that will eventually take astronauts beyond low-Earth orbit to destinations such as the Moon and Mars. The countdown demonstration was intended to validate the launch team's capability to perform an EM-1 countdown and respond to challenges put into the system for practice.

KENNEDY SPACE CENTER, FLA. -- STS-85 Payload Specialist Bjarni V. Tryggvason and Mission Specialist Stephen K. Robinson go through countdown procedures aboard the Space Shuttle orbiter Discovery during Terminal Countdown Demonstration Test (TCDT) activities for that mission. The TCDT includes a simulation of the final launch countdown. The primary payload aboard the Space Shuttle orbiter Discovery is the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere-2 (CRISTA-SPAS- 2). Other STS-85 payloads include the Manipulator Flight Demonstration (MFD), and Technology Applications and Science-1 (TAS-1) and International Extreme Ultraviolet Hitchhiker-2 (IEH-2) experiments

Mark Tripp, center, monitors his console in Firing Room 1 in the Launch Control Center at NASA’s Kennedy Space Center in Florida, during a terminal countdown demonstration for Exploration Mission 1, or EM-1, on Dec. 14, 2018. The launch will be the first integrated test of the Space Launch System rocket and Orion spacecraft that will eventually take astronauts beyond low-Earth orbit to destinations such as the Moon and Mars. The countdown demonstration was intended to validate the launch team's capability to perform an EM-1 countdown and respond to challenges put into the system for practice.

KENNEDY SPACE CENTER, FLA. - The Apollo 15 Saturn V Space Vehicle is seen from a camera located at the mobile launcher's 360-foot level at Launch Pad 39A during venting of the liquid oxygen during the 'wet' portion of the Countdown Demonstration Test today. Astronauts David R. Scott, Commander; James B. Irwin, Lunar Module Pilot; and Alfred M. Worden, Jr., Command Module Pilot, will participate tomorrow in the 'dry' portion of the Countdown Demonstration Test (CDDT), as a final dress rehearsal for the launch to the Moon, scheduled for no earlier than July 26, 1971.

CAPE CANAVERAL, Fla. – On the Shuttle Landing Facility at NASA's Kennedy Space Center in Florida, STS-119 Mission Specialist Richard Arnold is greeted by Shuttle Launch Director Mike Leinbach. Next to Leinbach is Jerry Ross, chief of the Vehicle Integration Test Office. The crew flew to Kennedy to take part in terminal countdown demonstration test activities, which include equipment familiarization and emergency exit training and culminate in a simulated launch countdown. Photo credit: NASA/Kim Shiflett

S82-28454 (19 Feb. 1982) --- Astronaut Jack R. Lousma, right, STS-3 commander, and C. Gordon Fullerton, pilot, carry portable spacesuit air controllers as they walk from a transport van to Launch Pad 39A to participate in a simulated countdown and launch. This countdown demonstration test (CDDT) is part of the preparations for NASA?s third orbital flight test in the space shuttle Columbia. The two are scheduled to spend a week orbiting Earth in Columbia this spring. Photo credit: NASA

CAPE CANAVERAL, Fla. – Space shuttle Endeavour's STS-127 mission crew members greet the media after arriving at NASA's Kennedy Space Center in Florida. At the microphone is Commander Mark Polansky, who explained they were at Kennedy for the Terminal Countdown Demonstration Test, or TCDT. The other crew members behind Polansky are, from left, Mission Specialist Tim Kopra, Pilot Doug Hurley, and Mission Specialists Tom Marshburn, Julie Payette, Dave Wolf and Christopher Cassidy. Payette represents the Canadian Space Agency. The astronauts will be taking part in Terminal Countdown Demonstration Test activities that include equipment familiarization and emergency egress training, and culminates in a simulated launch countdown aboard Endeavour. The STS-127 mission is the final of three flights dedicated to the assembly of the Japanese Kibo laboratory complex. Launch is targeted for June 13. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- At NASA Kennedy Space Center's Launch Pad 39A, the pilot of space shuttle Endeavour's STS-123 mission, Gregory H. Johnson, answers a question from the media during a break from emergency egress training. The crew is at Kennedy for a full launch dress rehearsal, known as the terminal countdown demonstration test or TCDT. The terminal countdown demonstration test provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on a 16-day mission to the International Space Station. On the mission, Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- At NASA Kennedy Space Center's Launch Pad 39A, the crew for space shuttle Endeavour's STS-123 mission receives instruction on the operation of an M-133 armored personnel carrier during emergency egress training. The crew is at Kennedy for a full launch dress rehearsal, known as the terminal countdown demonstration test or TCDT. The terminal countdown demonstration test provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on a 16-day mission to the International Space Station. On the mission, Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 speak to the media following their arrival at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. From left are Mission Specialists Daniel Tani, Paolo Nespoli, Doug Wheelock, Stephanie Wilson, Scott Parazynski; Pilot George Zamka and Commander Pam Melroy. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. Commander Pam Melroy, seen here, will be making her third shuttle flight. She is the second woman to command a shuttle mission. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. Commander Pam Melroy, who will be making her third shuttle flight, prepares to exit the plane. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- At NASA Kennedy Space Center's Launch Pad 39A, a mission specialist on space shuttle Endeavour's STS-123 mission, Mike Foreman, prepares to take questions from the media during a break from emergency egress training. The crew is at Kennedy for a full launch dress rehearsal, known as the terminal countdown demonstration test or TCDT. The terminal countdown demonstration test provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on a 16-day mission to the International Space Station. On the mission, Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. Mission Specialist Paolo Nespoli, representing the European Space Agency on his first shuttle flight, is seen here with the space shuttle mate-demate device in the background. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA_Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- In NASA Kennedy Space Center's News Room, STS-123 Mission Specialist Takao Doi, of the Japan Aerospace Exploration Agency, shows his enthusiasm for his upcoming flight during an interview. The crew for space shuttle Endeavour's STS-123 mission is at Kennedy for a full launch dress rehearsal, known as the terminal countdown demonstration test or TCDT. The terminal countdown demonstration test provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on a 16-day mission to the International Space Station. On the mission, Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Amanda Diller

KENNEDY SPACE CENTER, FLA. -- At NASA Kennedy Space Center's Launch Pad 39A, the crew for space shuttle Endeavour's STS-123 mission receives instruction on the operation of a slidewire basket during emergency egress training. In the basket are Mission Specialists Takao Doi of the Japan Aerospace Exploration Agency, Garrett Reisman and Rick Linnehan. The crew is at Kennedy for a full launch dress rehearsal, known as the terminal countdown demonstration test or TCDT. The terminal countdown demonstration test provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on a 16-day mission to the International Space Station. On the mission, Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. Mission Specialist Paolo Nespoli, representing the European Space Agency on his first shuttle flight, prepares to exit the plane. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- At NASA Kennedy Space Center's Launch Pad 39A, the crew for space shuttle Endeavour's STS-123 mission receives instruction on the slidewire basket system at the landing site for the baskets at the base of the pad during emergency egress training. The crew is at Kennedy for a full launch dress rehearsal, known as the terminal countdown demonstration test or TCDT. The terminal countdown demonstration test provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on a 16-day mission to the International Space Station. On the mission, Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. Mission Specialist Daniel Tani, shown here, will be making his second shuttle flight and remain on the International Space Station as a member of the Expedition 16 crew. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. Mission Specialist Doug Wheelock, who will be making his first shuttle flight, is welcomed by Shuttle Launch Director Michael Leinbach, at right. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- At NASA Kennedy Space Center's Launch Pad 39A, a mission specialist on space shuttle Endeavour's STS-123 mission, Robert L. Behnken, answers a question from the media during a break from emergency egress training. The crew is at Kennedy for a full launch dress rehearsal, known as the terminal countdown demonstration test or TCDT. The terminal countdown demonstration test provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on a 16-day mission to the International Space Station. On the mission, Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- At NASA Kennedy Space Center's Launch Pad 39A, a mission specialist on space shuttle Endeavour's STS-123 mission, Takao Doi of the Japan Aerospace Exploration Agency, prepares to take questions from the media during a break from emergency egress training. The crew is at Kennedy for a full launch dress rehearsal, known as the terminal countdown demonstration test or TCDT. The terminal countdown demonstration test provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on a 16-day mission to the International Space Station. On the mission, Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. Shuttle Launch Director Michael Leinbach shakes hands with Mission Specialist Stephanie Wilson, who will be making her second shuttle flight, as Commander Pam Melroy, at left, looks on. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- At NASA Kennedy Space Center's Launch Pad 39A, the crew for space shuttle Endeavour's STS-123 mission views the landing site at the base of the pad for the slidewire baskets during emergency egress training. The crew is at Kennedy for a full launch dress rehearsal, known as the terminal countdown demonstration test or TCDT. The terminal countdown demonstration test provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on a 16-day mission to the International Space Station. On the mission, Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. The T-38 jet aircraft on which Mission Specialist Doug Wheelock arrived is shown here. Wheelock will be making his first shuttle flight and will perform three spacewalks during the STS-120 mission. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- At NASA Kennedy Space Center's Launch Pad 39A, a mission specialist on space shuttle Endeavour's STS-123 mission, Rick Linnehan, prepares to take questions from the media during a break from emergency egress training. The crew is at Kennedy for a full launch dress rehearsal, known as the terminal countdown demonstration test or TCDT. The terminal countdown demonstration test provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on a 16-day mission to the International Space Station. On the mission, Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- At NASA Kennedy Space Center's Launch Pad 39A, the commander of space shuttle Endeavour's STS-123 mission, Dominic Gorie, answers a question from the media during a break from emergency egress training. The crew is at Kennedy for a full launch dress rehearsal, known as the terminal countdown demonstration test or TCDT. The terminal countdown demonstration test provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on a 16-day mission to the International Space Station. On the mission, Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. Mission Specialist Stephanie Wilson, seen here, will be making her second shuttle flight. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. Mission Specialist Doug Wheelock, seen here, will be making his first shuttle flight. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. Pilot George Zamka, who will be making his first shuttle flight, prepares to exit the plane. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- The crew members of mission STS-120 arrive at NASA's Kennedy Space Center Shuttle Landing Facility aboard T-38 jet aircraft to take part in terminal countdown demonstration test activities. Mission Specialist Scott Parazynski, who will be making his fifth shuttle flight, waves to those on hand to greet him. The terminal countdown demonstration test provides astronauts and ground crews an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Launch of Discovery on mission STS-120 is targeted for Oct. 23 at 11:38 a.m. EDT on a 14-day mission to the International Space Station. Photo credit: NASA/Kim Shiflett