On April 12, 1981, NASA's premiere space shuttle Columbia launched into orbit with astronauts John Young and Robert Crippen at the helm, inaugurating the U.S. shuttle era.

After 25 years of spaceflight, NASA's orbiter fleet has sent planetary probes on their way to Venus and Jupiter, helped astronauts retrieve and repair satellites, launched the Hubble Space Telescope and plays a crucial role in the ongoing construction of the International Space Station.

But the road has not been smooth. Two shuttles and 14 astronauts have been lost during NASA's 1986 Challenger accident and the 2003 Columbia disaster. NASA's three remaining orbiters are now marked for a 2010 retirement to make way for a capsule-based vehicle, heralding the end of the U.S. space plane fleet.

The following is SPACE.com's coverage of NASA's space shuttle silver anniversary.

Image Gallery: NASA's First Shuttle Flight VIDEO: STS-1 Commander John Young Remembers Columbia's Debut The Ultimate Test Flight: NASA's Shuttle Fleet at 25 Two astronauts, one space plane and NASA's shuttle era began today in 1981 as the Columbia orbiter launched into the morning skies above Cape Canaveral, Florida. Looking Ahead: NASA's Push from STS-1 to CEV As NASA marks 25 years of shuttle flight this week, the space agency is looking ahead to its next spaceship to reach for the orbit and the Moon: The Crew Exploration Vehicle. Cast of Thousands: Shuttle Workers, Astronauts Remember Columbia's First Flight Twenty-five years ago this week, NASA launched two astronauts into orbit aboard the first flight of the Columbia space shuttle.

Columbia's White External Fuel Tanks Many SPACE.com readers have written letters asking about the white external fuel tanks that fed NASA's first two orbiter test flights and whether the paint job added any additional protection against the type of foam shedding that led to the 2003 Columbia accident. John Chapman, NASA's external tank project manager at the Marshall Space Flight Center (MSFC) in Huntsville, Alabama, explains.

Florida Today: NASA's Space Shuttle - Cheers to 25 Years from a Veteran Space Reporter CAPE CANAVERAL - Columbia blasted off 25 years ago today on NASA's first space shuttle mission. Seems like a good time to roll out my own personal list of shuttle program superlatives.

Florida Today: Columbia's First Launch Pushed Crew, Workers and Technology CAPE CANAVERAL - No one really expected the first space shuttle to fly on April 12, 25 years ago. It was only the second countdown for Columbia. A computer glitch scrubbed the first attempt two days earlier. After struggling through the ship's creation, workers and astronauts alike were sure several more counts were in the works. Then it got down to the last minute.

NASA Patchwork: The Shuttle's First Crew Emblem When John Young and Robert Crippen boarded Space Shuttle Columbia for its first launch on April 12, 1981, they were both clad in modified pressure suits originally designed for the U.S. Air Force's SR-71 high-altitude reconnaissance aircraft. Among the outfit's additions, albeit a minor one, was a 4-inch (10-centimeter) embroidered emblem with their names, their spacecraft's name, and a design that represented their soon-to- be record mission.

45 Years Ago: Mankind's First Crewed Spaceflight As NASA celebrates the silver anniversary of its first shuttle launch, the overall effort of human spaceflight hits its own landmark today.

More About the Space Shuttle from SPACE.com For more on NASA's next space shuttle flight: STS-121 Shuttle Commander Confident in July Launch Target NASA Set for Shuttle Fuel Tank Repair Return to Flight: NASA's Road to STS-121 SPACE.com's Collection of Launch and Mission Archives Enjoy these Space Shuttle themed image galleries: Discovery Launch Day! Discovery: Debris, Scuffs, and Shuttle Damage Views from Space: Imagery from Past Shuttle Missions NASA's 100 Spacewalks Space Shuttle: 100 Flights The Space Shuttle: NASA's Workhorse Visit SPACE.com's Image Gallery Archive

Image Gallery: Hail Columbia! Image Gallery: Crew Photos from Columbia's Final Flight