CAPE CANAVERAL, Fla. – Seated in space shuttle Discovery on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 Pilot Tony Antonelli checks a mirror as he prepares for a simulated launch countdown as part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Following the simulated launch countdown on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 Commander Lee Archambault and Pilot Tony Antonelli take seats in the slidewire basket used for emergency egress from the pad. The practice egress is part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Seated in space shuttle Discovery on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 Pilot Tony Antonelli checks a mirror as he prepares for a simulated launch countdown as part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Following the simulated launch countdown on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 crew members are in the slidewire basket they would use during an emergency egress. The slidewire basket could propel them to a landing area below, if needed. The practice egress is part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Following the simulated launch countdown on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 crew members practice an emergency egress from the 195-foot level of the fixed service structure as part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 Mission Specialist John Phillips is seated in space shuttle Discovery for a simulated launch countdown as part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Following the simulated launch countdown on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 crew members practice an emergency egress from the 195-foot level of the fixed service structure as part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 Mission Specialists John Phillips, Koichi Wakata and Richard Arnold are seated in space shuttle Discovery for a simulated launch countdown as part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 Mission Specialist Koichi Wakata is seated in space shuttle Discovery for a simulated launch countdown as part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Following the simulated launch countdown on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 crew members are in the slidewire basket they would use during an emergency egress. The slidewire basket could propel them to a landing area below, if needed. The practice egress is part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 Mission Specialist Richard Arnold is seated in space shuttle Discovery for a simulated launch countdown as part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Following the simulated launch countdown on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 Mission Specialists Joseph Acaba (left) and Richard Arnold practice emergency egress from the pad. They are seated in a slidewire basket that could propel them to a landing area below. The countdown and emergency egress are part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Following the simulated launch countdown on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 Mission Specialists Joseph Acaba (left) and Richard Arnold are seated in a slidewire basket that could propel them to a landing area below. The slidewire basket is used for emergency egress from the pad. In the background at left are Mission Specialists Richard Arnold and Koichi Wakata. The countdown and emergency egress are part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Following the simulated launch countdown on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 crew members are in the slidewire basket they would use during an emergency egress. The slidewire basket could propel them to a landing area below, if needed. From left are Mission Specialists John Phillips, Richard Arnold and Koichi Wakata. The practice egress is part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – After practicing emergency egress from the pad, the STS-119 crew members pose on the 225-foot level for a crew photo. From left are Mission Specialists Richard Arnold and Steve Swanson, Pilot Tony Antonelli, Commander Lee Archambault, and Mission Specialists Koichi Wakata, John Phillips and Joseph Acaba. The crew also took part in a simulated launch countdown, part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 Mission Specialists Koichi Wakata and John Phillips complete emergency egress training from the pad. Practicing emergency egress is part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 crew members gather around the slidewire baskets used for emergency egress from the pad. From left are Mission Specialist Steve Swanson, Pilot Tony Antonelli, Mission Specialist Koichi Wakata, Commander Lee Archambault and Mission Specialist John Phillips. Practicing emergency egress is part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Kim Shiflett

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.

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.

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).

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

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

KENNEDY SPACE CENTER, FLA. - STS-79 Mission Specialist John E. Blaha 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 around Sept. 12 on STS-79, the fourth docking between the U.S. Shuttle and Russian Space Station Mir. During the approximately nine-day flight, Blaha will change places with fellow spaceflight veteran Shannon Lucid, who is wrapping up a record-setting stay on Mir. Blaha will remain aboard the Station for about four months, returning to Earth in January 1997 withthe crew of Shuttle Mission STS-81.

KENNEDY SPACE CENTER, FLA. - After the conclusion of Terminal Countdown Demonstration Test (TCDT) activities at NASA’s Kennedy Space Center, STS-114 Commander Eileen Collins briefly talks to media about the importance of the TCDT as pre-launch training. The TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

STS-87 Commander Kevin Kregel holds the crew patch in front of Columbia’s entry hatch at Launch Pad 39B during Terminal Countdown Demonstration Test (TCDT) activities. The crew of the STS-87 mission is scheduled for launch Nov. 19 aboard the Space Shuttle Columbia. The TCDT is held at KSC prior to each Space Shuttle flight providing the crew of each mission opportunities to participate in simulated countdown activities. The TCDT ends with a mock launch countdown culminating in a simulated main engine cut-off. The crew also spends time undergoing emergency egress training exercises at the pad and has an opportunity to view and inspect the payloads in the orbiter's payload bay

STS-83 crew M113 driver training during 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

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

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

CAPE CANAVERAL, Fla. - After taking part in a simulated launch countdown aboard space shuttle Atlantis, the STS-125 crew members practice an emergency escape from the shuttle. They are heading for the slidewire baskets that will speed them away from Kennedy Space Center’s Launch Pad 39A. 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/Kim Shiflett

CAPE CANAVERAL, Fla. - The STS-125 crew is taking part in a simulated launch countdown aboard space shuttle Atlantis at NASA's Kennedy Space Center in Florida. Seen in their seats in the mid-deck are Mission Specialists Andrew Feustel (left) and Mike Massimino. 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/Kim Shiflett

CAPE CANAVERAL, Fla. - The STS-125 crew is taking part in a simulated launch countdown aboard space shuttle Atlantis at NASA's Kennedy Space Center in Florida. Seen in his seat in the cockpit is Commander Scott Altman. 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/Kim Shiflett

CAPE CANAVERAL, Fla. - After taking part in a simulated launch countdown aboard space shuttle Atlantis, the STS-125 crew members practice an emergency escape from the shuttle. Here they are ready to release the slidewire basket that will speed them away from Kennedy Space Center’s Launch Pad 39A. 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/Kim Shiflett

CAPE CANAVERAL, Fla. - The STS-125 crew is taking part in a simulated launch countdown aboard space shuttle Atlantis at NASA's Kennedy Space Center in Florida. Seen in her seat in the mid-deck is Mission Specialist Megan McArthur. 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/Kim Shiflett

CAPE CANAVERAL, Fla. - STS-125 Mission Specialist John Grunsfeld is helped donning a harness over his launch and entry suit before entering 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, FIa. -- After taking part in a simulated launch countdown aboard space shuttle Atlantis, the STS-125 crew members practice an emergency escape from the shuttle. They are heading for the slidewire baskets that will speed them away from Kennedy Space Center’s Launch Pad 39A. 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/Kim Shiflett

CAPE CANAVERAL, Fla. - The STS-125 crew is taking part in a simulated launch countdown aboard space shuttle Atlantis at NASA's Kennedy Space Center in Florida. Seen in his seat in the mid-deck is Mission Specialist John Grunsfeld. 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/Kim Shiflett

CAPE CANAVERAL, Fla. - The STS-125 crew is taking part in a simulated launch countdown aboard space shuttle Atlantis at NASA's Kennedy Space Center in Florida. Seen in their seats in the mid-deck are (front to back) Mission Specialists Andrew Feustel, Mike Massimino and John Grunsfeld. 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/Kim Shiflett

CAPE CANAVERAL, Fla. - STS-125 Mission Specialist Andrew Feustel is helped by suit technicians to don a harness over his launch and entry suit before entering 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. - After taking part in a simulated launch countdown aboard space shuttle Atlantis, the STS-125 crew members practice an emergency escape from the shuttle. Here they are ready to release the slidewire basket that will speed them away from Kennedy Space Center’s Launch Pad 39A. 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/Kim Shiflett

CAPE CANAVERAL, Fla. - After taking part in a simulated launch countdown aboard space shuttle Atlantis, the STS-125 crew members practice an emergency escape from the shuttle. They are heading for the slidewire baskets that on the fixed service structure that will speed them away from Kennedy Space Center’s Launch Pad 39A. 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/Kim Shiflett

CAPE CANAVERAL, Fla. - STS-125 Mission Specialist Michael Good is helped by suit technicians to don a harness over his launch and entry suit before entering 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 Mike Massimino s helped by a suit technician to don a harness over his launch and entry suit before entering 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 Commander Scott Altman is helped by a suit technician to don a harness over his launch and entry suit before entering 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

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.

KENNEDY SPACE CENTER, FLA. - After the conclusion of Terminal Countdown Demonstration Test (TCDT) activities at NASA’s Kennedy Space Center, STS-114 Commander Eileen Collins briefly talks to media about the importance of the TCDT as pre-launch training. At left is NASA Public Information Officer Bruce Buckingham, who moderated. The TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - After the conclusion of Terminal Countdown Demonstration Test (TCDT) activities at NASA’s Kennedy Space Center, STS-114 Mission Specialist Soichi Noguchi speaks to the media about his experiences in his first TCDT. Noguchi is with the Japan Aerospace Exploration Agency. The TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

STS-90 Commander Richard Searfoss addresses the media at KSC's Launch Pad 39B, where the crew are participating in Terminal Countdown Demonstration Test (TCDT) activities. The TCDT is held at KSC prior to each Space Shuttle flight to provide crews with the opportunity to participate in simulated countdown activities. Columbia is targeted for launch of STS-90 on April 16 at 2:19 p.m. EDT and will be the second mission of 1998. The mission is scheduled to last nearly 17 days

KENNEDY SPACE CENTER, FLA. - After a three-day series of Terminal Countdown Demonstration Test (TCDT) activities, the crew of mission STS-121 are leaving NASA's Kennedy Space Center to return to Houston. Waving on her way to the plane at the Shuttle Landing Facility is Mission Specialist Stephanie Wilson. The TCDT includes equipment familiarization, emergency egress training and a simulated launch countdown. Mission STS-121 is scheduled to launch July 1. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. - After a three-day series of Terminal Countdown Demonstration Test (TCDT) activities, the crew of mission STS-121 are leaving NASA's Kennedy Space Center to return to Houston. Boarding the plane at the Shuttle Landing Facility are Mission Specialists Piers Sellers and Stephanie Wilson. The TCDT includes equipment familiarization, emergency egress training and a simulated launch countdown. Mission STS-121 is scheduled to launch July 1. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. - After a three-day series of Terminal Countdown Demonstration Test (TCDT) activities, the crew of mission STS-121 are leaving NASA's Kennedy Space Center to return to Houston. Waving on his way to the plane at the Shuttle Landing Facility is Thomas Reiter of Germany, who represents the European Space Agency. The TCDT includes equipment familiarization, emergency egress training and a simulated launch countdown. Mission STS-121 is scheduled to launch July 1. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. - After a three-day series of Terminal Countdown Demonstration Test (TCDT) activities, the crew of mission STS-121 are leaving NASA's Kennedy Space Center to return to Houston. Walking toward the plane at the Shuttle Landing Facility are Mission Specialists Lisa Nowak and Piers Sellers. The TCDT includes equipment familiarization, emergency egress training and a simulated launch countdown. Mission STS-121 is scheduled to launch July 1. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- STS-120 Pamela Melroy (front) is ready for training on the M-113 armored personnel carrier, part of emergency egress training. The training is part of terminal countdown demonstration test, or TCDT, activities the crew is undertaking at NASA's Kennedy Space Center. The TCDT also includes equipment familiarization and a simulated launch countdown. Mission STS-120, which will carry the Italian-built U.S. Node 2 to the International Space Station, is targeted for launch on Oct. 23. Photo credit: NASA/Kim Shiflett

The crew of STS-90 participate in Terminal Countdown Demonstration Test (TCDT) activities at KSC's Launch Pad 39B. The TCDT is held at KSC prior to each Space Shuttle flight to provide crews with the opportunity to participate in simulated countdown activities. Here, Payload Specialist Jay Buckey, M.D., is assisted with his orange launch and re-entry suit by a USA technician. Columbia is targeted for launch of STS-90 on April 16 at 2:19 p.m. EDT and will be the second mission of 1998. The mission is scheduled to last nearly 17 days

STS-90 Mission Specialist Kathryn (Kay) Hire participates in Terminal Countdown Demonstration Test (TCDT) activities at KSC's Launch Pad 39B. The TCDT is held at KSC prior to each Space Shuttle flight to provide crews with the opportunity to participate in simulated countdown activities. Columbia is targeted for launch of STS-90 on April 16 at 2:19 p.m. EDT and will be the second mission of 1998. The mission is scheduled to last nearly 17 days

KENNEDY SPACE CENTER, FLA. -- STS-120 Mission Specialist Doug Wheelock tries on his launch and entry suit to prepare for launch. The fitting is part of terminal countdown demonstration test, or TCDT, activities the crew is undertaking at NASA's Kennedy Space Center. The TCDT also includes emergency egress procedures, equipment familiarization and a simulated launch countdown. Mission STS-120, which will carry the Italian-built U.S. Node 2 to the International Space Station, is targeted for launch on Oct. 23. Photo credit: NASA/Kim Shiflett

STS-90 Mission Specialists Dafydd (Dave) Williams with the Canadian Space Agency and Kathryn (Kay) Hire participate in Terminal Countdown Demonstration Test (TCDT) activities at KSC's Launch Pad 39B. The TCDT is held at KSC prior to each Space Shuttle flight to provide crews with the opportunity to participate in simulated countdown activities. The Space Shuttle Columbia is targeted for launch of STS-90 on April 16 at 2:19 p.m. EDT and will be the second mission of 1998. The mission is scheduled to last nearly 17 days

S97-00252 (15 Dec. 1996) --- Astronaut Brent W. Jett Jr., STS-81 pilot, arrives in a NASA T-38 jet trainer at the Kennedy Space Center's Shuttle Landing Facility for the Terminal Countdown Demonstration Test (TCDT). The TCDT represents a simulated final countdown until just before main engine ignition, now scheduled for Jan. 12, 1997.

KENNEDY SPACE CENTER, FLA. - The plane carrying the crew of mission STS-121 taxis onto the Shuttle Landing Facility at NASA's Kennedy Space Center. The crew was at the Center for a three-day series of Terminal Countdown Demonstration Test (TCDT) activities. The TCDT includes equipment familiarization, emergency egress training and a simulated launch countdown. Mission STS-121 is scheduled to launch July 1. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. -- STS-120 Mission Specialist Stephanie Wilson tries on her launch and entry suit, preparing for launch. The fitting is part of terminal countdown demonstration test, or TCDT, activities the crew is undertaking at NASA's Kennedy Space Center. The TCDT also includes emergency egress procedures, equipment familiarization and a simulated launch countdown. Mission STS-120, which will carry the Italian-built U.S. Node 2 to the International Space Station, is targeted for launch on Oct. 23. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. - After a three-day series of Terminal Countdown Demonstration Test (TCDT) activities, the crew of mission STS-121 are leaving NASA's Kennedy Space Center to return to Houston. Walking to the plane at the Shuttle Landing Facility are Commander Steven Lindsey (left) and Mission Specialist Michael Fossum. The TCDT includes equipment familiarization, emergency egress training and a simulated launch countdown. Mission STS-121 is scheduled to launch July 1. Photo credit: NASA/Kim Shiflett

S97-00248 (15 Dec. 1996) --- Astronaut Marsha S. Ivins, STS-81 mission specialist, arrives in a NASA T-38 jet trainer at the Kennedy Space Center's Shuttle Landing Facility for the Terminal Countdown Demonstration Test (TCDT). The TCDT represents a simulated final countdown until just before main engine ignition, now scheduled for Jan. 12, 1997.

KENNEDY SPACE CENTER, FLA. - Following the mock countdown and emergency egress practice from the Fixed Service Structure on Launch Pad 39B, STS-114 crew members stop at the 225-foot level for a unique view. Seen here is Pilot James Kelly. This culminates the pre-launch training known as Terminal Countdown Demonstration Test (TCDT) activities. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - Following the mock countdown on Launch Pad 39B, STS-114 Commander Eileen Collins (center) adjusts her glove before climbing into a slidewire basket used for emergency egress from the Fixed Service Structure at the pad. This is part of the pre-launch training included in Terminal Countdown Demonstration Test (TCDT) activities. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

CAPE CANAVERAL, Fla. - On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-125 Mission Specialist Andrew Feustel waits for a question from the media about his role in the mission. The crew is at Kennedy to take part in terminal countdown demonstration test, or TCDT, activities before launching on space shuttle Atlantis’ mission to service NASA’s Hubble Space Telescope. TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization, emergency training and a simulated launch countdown. Atlantis is targeted to launch Oct. 10. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. - Following the mock countdown on Launch Pad 39B, STS-114 Mission Specialists Soichi Noguchi (left) and Stephen Robinson climb into a slidewire basket used for emergency egress from the Fixed Service Structure at the pad. This is part of the pre-launch training included in Terminal Countdown Demonstration Test (TCDT) activities. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - As part of pre-pack and fit check for Terminal Countdown Demonstration Test (TCDT) activities, STS-114 Mission Specialist Stephen Robinson signals okay for his launch suit check. 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 the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

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

CAPE CANAVERAL, Fla. - On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-125 Mission Specialist Megan McArthur is ready to talk to the media about her role in the mission. The crew is at Kennedy to take part in terminal countdown demonstration test, or TCDT, activities before launching on space shuttle Atlantis’ mission to service NASA’s Hubble Space Telescope. TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization, emergency training and a simulated launch countdown. Atlantis is targeted to launch Oct. 10. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. - STS-125 crew members are ready to practice climbing out of the slidewire baskets used during emergency escape procedures from the shuttle and pad. From left are Mission Specialists John Grunsfeld, Mike Massimino and Andrew Feustel. The crew is at Kennedy to take part in terminal countdown demonstration test, or TCDT, activities before launching on space shuttle Atlantis’ mission to service NASA’s Hubble Space Telescope. TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization, emergency training and a simulated launch countdown. Atlantis is targeted to launch Oct. 10. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. - Following the mock countdown on Launch Pad 39B, STS-114 Pilot James Kelly adjusts his glove before climbing into a slidewire basket used for emergency egress from the Fixed Service Structure at the pad. This is part of the pre-launch training included in Terminal Countdown Demonstration Test (TCDT) activities. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - STS-114 crew members take part in a mock countdown as pre-launch training included in Terminal Countdown Demonstration Test (TCDT) activities. Seen here in their seats in the mid-deck of Space Shuttle Discovery are (left to right), Mission Specialists Charles Camarda, Wendy Lawrence and Andrew Thomas. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - Following the mock countdown and emergency egress practice from the Fixed Service Structure on Launch Pad 39B, STS-114 crew members stop at the 225-foot level for a unique view. Seen here is Mission Specialist Wendy Lawrence. This culminates the pre-launch training known as Terminal Countdown Demonstration Test (TCDT) activities. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

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

KENNEDY SPACE CENTER, FLA. - Following the mock countdown on Launch Pad 39B, STS-114 Mission Specialist Charles Camarda reaches for the release of the slidewire basket, used for emergency egress from the Fixed Service Structure. Behind him are Mission Specialists Andrew Thomas and Wendy Lawrence. This is part of the pre-launch training included in Terminal Countdown Demonstration Test (TCDT) activities. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

CAPE CANAVERAL, Fla. - On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-125 Pilot Gregory C. Johnson discusses his role in the mission for the media. The crew is at Kennedy to take part in terminal countdown demonstration test, or TCDT, activities before launching on space shuttle Atlantis’ mission to service NASA’s Hubble Space Telescope. TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization, emergency training and a simulated launch countdown. Atlantis is targeted to launch Oct. 10. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. - On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-125 Mission Specialist John Grunsfeld discusses his role in the mission for the media. The crew is at Kennedy to take part in terminal countdown demonstration test, or TCDT, activities before launching on space shuttle Atlantis’ mission to service NASA’s Hubble Space Telescope. TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization, emergency training and a simulated launch countdown. Atlantis is targeted to launch Oct. 10. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. - Following the mock countdown on Launch Pad 39B, STS-114 Commander Eileen Collins talks to Pilot James Kelly at the slidewire basket area used for emergency egress from the Fixed Service Structure at the pad. This is part of the pre-launch training included in Terminal Countdown Demonstration Test (TCDT) activities. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - Following the mock countdown on Launch Pad 39B, STS-114 Mission Specialist Stephen Robinson (left) and Soichi Noguchi talk at the slidewire basket area used for emergency egress from the Fixed Service Structure at the pad. This is part of the pre-launch training included in Terminal Countdown Demonstration Test (TCDT) activities. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - In the White Room on Launch Pad 39B, STS-121 Mission Specialist Stephanie Wilson waits for final adjustments to her launch suit before entering Space Shuttle Discovery. The crew is taking part in a full dress rehearsal for launch, including countdown and culminating in main engine cutoff. The rehearsal is the final part of Terminal Countdown Demonstration Test (TCDT) activities that the crew has been involved in for two days. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. Mission STS-121 is scheduled to be launched July 1. Photo credit: NASA/Amanda Diller

KENNEDY SPACE CENTER, FLA. - STS-114 crew members take part in a mock countdown as pre-launch training included in Terminal Countdown Demonstration Test (TCDT) activities. Seen here in their seats on the flight deck are Commander Eileen Collins (left) and Pilot James Kelly (right). TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - As part of pre-pack and fit check for Terminal Countdown Demonstration Test (TCDT) activities, STS-114 Mission Specialist Charles Camarda has his launch suit checked for fit. 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 the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - Following the mock countdown on Launch Pad 39B, STS-114 Mission Specialists Soichi Noguchi (left) and Stephen Robinson make a speedy exit on the 195-foot level of the Fixed Service Structure. Emergency egress is part of the pre-launch training included in Terminal Countdown Demonstration Test (TCDT) activities. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - As part of pre-pack and fit check for Terminal Countdown Demonstration Test (TCDT) activities, STS-114 Mission Specialist Soichi Noguchi tries on his helmet. 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 the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

CAPE CANAVERAL, Fla. - On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-125 Commander Scott Altman introduces his crew to the media and discusses his role in the mission. The crew is at Kennedy to take part in terminal countdown demonstration test, or TCDT, activities before launching on space shuttle Atlantis’ mission to service NASA’s Hubble Space Telescope. TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization, emergency training and a simulated launch countdown. Atlantis is targeted to launch Oct. 10. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. - Following the mock countdown on Launch Pad 39B, STS-114 Commander Eileen Collins (left) climbs into a slidewire basket used for emergency egress from the Fixed Service Structure at the pad. This is part of the pre-launch training included in Terminal Countdown Demonstration Test (TCDT) activities. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - As part of pre-pack and fit check for Terminal Countdown Demonstration Test (TCDT) activities, STS-114 Mission Specialist Wendy Lawrence tries on her helmet. 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 the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - As part of pre-pack and fit check for Terminal Countdown Demonstration Test (TCDT) activities, STS-114 Commander Eileen Collins examines glasses that will be on the flight. 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 the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

KENNEDY SPACE CENTER, FLA. - As part of pre-pack and fit check for Terminal Countdown Demonstration Test (TCDT) activities, STS-114 Pilot Jim Kelly looks at equipment that will be on the flight. 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 the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

CAPE CANAVERAL, Fla. - On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-125 Mission Specialist Michael Good discusses his role in the mission for the media. The crew is at Kennedy to take part in terminal countdown demonstration test, or TCDT, activities before launching on space shuttle Atlantis’ mission to service NASA’s Hubble Space Telescope. TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization, emergency training and a simulated launch countdown. Atlantis is targeted to launch Oct. 10. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. - As part of pre-pack and fit check for Terminal Countdown Demonstration Test (TCDT) activities, STS-114 Mission Specialist Wendy Lawrence has her boot checked. 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 the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

CAPE CANAVERAL, Fla. - On Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-125 Mission Specialist Mike Massimino discusses his role in the mission for the media. The crew is at Kennedy to take part in terminal countdown demonstration test, or TCDT, activities before launching on space shuttle Atlantis’ mission to service NASA’s Hubble Space Telescope. TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization, emergency training and a simulated launch countdown. Atlantis is targeted to launch Oct. 10. Photo credit: NASA/Kim Shiflett

KENNEDY SPACE CENTER, FLA. - Following the mock countdown on Launch Pad 39B, STS-114 Mission Specialist Wendy Lawrence arrives at the slidewire basket area used for emergency egress from the Fixed Service Structure at the pad. This is part of the pre-launch training included in Terminal Countdown Demonstration Test (TCDT) activities. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. STS-114 is the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.

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

KENNEDY SPACE CENTER, FLA. - As part of pre-pack and fit check for Terminal Countdown Demonstration Test (TCDT) activities, STS-114 Mission Specialist Soichi Noguchi tries on his helmet. 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 the first Return to Flight mission to the International Space Station. The launch window extends July 13 through July 31.