First Three-Person Spacewalk: STS-49 (Endeavour)
On May 13, 1992, during the first mission of the space shuttle Endeavour, a trio of astronauts conducted the first spacewalk to involve more than two spacewalkers at once.
STS-49 mission specialists Pierre Thuot, Richard Hieb, and Thomas Akers conducted the extravehicular activity (EVA) to capture and repair the broken Intelsat VI-F3 satellite. The communications satellite had been stranded in the wrong orbit since its launch two years earlier in March 1990.
The astronauts successfully attached a new second stage rocket to boost the spacecraft into its intended geosynchronous orbit.
Fixing Hubble: STS-61 (Endeavour)
Three years after Hubble launched into space with faulty optics, NASA launched the shuttle Endeavour on the STS-61 mission on Dec. 2, 1993. The mission came about after engineers completed a set of corrective optics to fix the problem, allowing NASA to launch seven astronauts on the first Hubble servicing mission.
The crew, led by commander Richard Covey spent 10 days performing five spacewalks to install the new hardware. The new optics proved to correct the blurring, and STS-61 was pronounced a triumphant success, opening the door for Hubble to revolutionize our understanding of the universe. [Spectacular Photos From The Revamped Hubble Telescope]
STS-61 would be followed by four more servicing missions to upgrade Hubble over the years.
Space Shuttle Docks at Russia's Mir: STS-71 (Atlantis)
While the United States and Russia began the space race as competitors, they evolved into collaborators. One of the brightest moments of the partnership came on June 27, 1995 when a U.S. space shuttle docked to the Russian space station Mir.
Atlantis' STS-71 mission delivered two Russian cosmonauts to the station to begin their months-long stay on Mir. The mission also picked up a NASA astronaut and two other cosmonauts – who had been serving on the Mir crew – to give them a ride home.
Shuttle Launches Oldest Astronaut: STS-95 (Discovery)
Shuttle Discovery carried the oldest person to space to date on Oct. 29, 1998 when it lifted off with Mercury astronaut and United States Senator John Glenn aboard. [Photos: Shuttle Discovery Sets Sail On Final Voyage]
The 77-year old Glenn was making his second spaceflight, after launching on Friendship 7 on Feb. 20, 1962. Glenn was one of the original Mercury 7, the first group of United States astronauts ever selected. He was the fifth person in space and the first American to orbit the Earth.
Shuttle's First International Space Station Trek: STS-88 (Endeavour)
The now-complete International Space Station has been called one of the space shuttle's crowning achievements, because many of its large components were only possible to haul to space inside the shuttle's roomy cargo bay. But in 1998, construction of the space station was just getting under way.
NASA's first shuttle to visit the space station was Endeavour, which launched on the STS-88 mission on Dec. 4, 1998 and carried the first American module, the Unity node to the station. Unity was connected to the first space station segment, the Russian Zarya module, which Russia had launched less than a month earlier on a Russian Proton rocket.
Columbia is Lost: STS-107 (Columbia)
The tragic loss of space shuttle Columbia – NASA's first shuttle to fly – on Feb. 1, 2003, dealt a withering blow to the space shuttle program. The seven-member crew, led by commander Rick Husband, launched on Jan. 16 of that year and was returning home after a successful 16-day mission filled with microgravity and Earth science experiments when the orbiter broke up during re-entry to Earth.
The cause was eventually traced to a piece of foam insulation on the shuttle's external tank, which had flaked off during launch and impacted the orbiter's left wing. Though no one knew it at the time, subsequent analysis showed the debris likely punched a plate-sized hole in the wing, causing the vehicle to fail to withstand the strains of reentry.
NASA Shuttles Resume Spaceflights: STS-114 (Discovery)
On July 26, 2005, the space shuttle fleet once again resumed spaceflights following a fatal accident. Discovery's STS-114 mission came two years of investigation into the Columbia accident to identify improvements to enhance safety for the spaceflight program.
Like the first return-to-flight mission, after Challenger, this voyage was flown by shuttle Discovery.
The 13-day mission, led by commander Eileen Collins, tested out the new safety techniques that had been developed post-Columbia, including using a sensor system attached to a long pole to scan the orbiter after launch to make sure no catastrophic debris strikes have taken place. Discovery's crew also tested heat shield repair techniques during several spacewalks.
Since then, heat shield inspections have become a standard part of every shuttle mission since the Columbia accident.
The Last Shuttle Mission: STS-135 (Atlantis)
In 2011, the space shuttle program flew its last flights. The final mission, slated to be flown by the shuttle Atlantis on June 28, 2011, will carry four astronauts and a cargo bay packed to the brim with spare supplies to the International Space Station.
The shuttle Discovery launched on its last mission Feb. 24, 2011. The orbiter delivered the final major U.S. contribution to the space station – the Permanent Multipurpose Module Leonardo – effectively completing the American portion of the orbiting lab.
The shuttle Endeavour is scheduled to lift off on its last space voyage June 29 to bring a cosmic ray-hunting astrophysics experiment and a load of extra hardware to the space station.
After the final space shuttle flights, NASA's three orbiters are to be retired to American museums.
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Clara Moskowitz is a science and space writer who joined the Space.com team in 2008 and served as Assistant Managing Editor from 2011 to 2013. Clara has a bachelor's degree in astronomy and physics from Wesleyan University, and a graduate certificate in science writing from the University of California, Santa Cruz. She covers everything from astronomy to human spaceflight and once aced a NASTAR suborbital spaceflight training program for space missions. Clara is currently Associate Editor of Scientific American. To see her latest project is, follow Clara on Twitter.