At its inception, NASA's Space Shuttle program promised to usher in a new era of exploration, keeping astronauts space-bound with a reusable and relatively inexpensive ride to orbit. It was a project that forever changed the course of spaceflight with its triumphs - and its tragic failures.
Considered an 'engineering marvel', the first of five winged orbiters - the space shuttle Columbia - made its maiden flight in 1981.
Twenty-two years and 28 space voyages later, the same shuttle broke apart during its final return to Earth, killing all seven crew members on board.
The tragedy marked the end of the U.S. space agency's transformative shuttle program. And the memory of this system continues to reverberate through the halls of NASA to this day, leaving a lasting mark on safety concerns.
"Human history teaches us that in exploration, after accidents like this occur, we can learn from them and further reduce risks, although we must honestly admit that risks can never be eliminated," he said. - NASA Administrator Sean O'Keefe, who led the agency from 2001 to 2004, in a speech to members of Congress shortly after the Columbia disaster.
After the shuttle program was halted, no American astronaut would travel to space on an American-made rocket for nearly a decade.
Reimagining rockets
The Space Shuttle project was born in the optimism of NASA's Apollo program, which landed 12 astronauts on the moon's surface and defeated America's Soviet rivals during the Cold War.
However, Apollo was extremely expensive: NASA spent $25.8 billion (or more than $200 billion adjusted for inflation) - according to a cost analysis by space policy expert Casey Dreier of the nonprofit Planetary Society.
Facing financial constraints, engineers within NASA built an entirely new means of space transportation in the mid-1970s.
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Apollo used towering rockets and small capsules - intended to be flown only once - that would dive home from space and parachute to an ocean landing.
The space shuttle concept was a remarkable pivot: Reusable, winged orbiters would lift off, tethered to rockets, cruise through Earth's orbit and glide to an airplane-like runway. From there, the shuttle could be refurbished and flown again, theoretically reducing the cost of each mission.
The legacy of Shuttle
Over the course of three decades, NASA's fleet of space shuttles has performed 135 missions: launching and repairing satellites, building permanent home for astronauts with the International Space Station and deploying the revolutionary Hubble Space Telescope.
But the shuttle program, which ended in 2011, never lived up to the U.S. space agency's original vision.
Each shuttle launch cost an average of about $1.5 billion, according to a 2018 paper by a researcher at NASA's Ames Research Center. That's hundreds of millions of dollars more than the space agency had hoped for at the start of the program, even after adjusting for inflation. Long delays and technical setbacks also bedeviled his missions.
"Every mission I was there for was scrapped, rescheduled, postponed because something wasn't quite right," O'Keefe, the former NASA administrator, said in a new CNN documentary series, "Space Shuttle Columbia: The Final Flight. "
And two disasters - the Challenger explosion in 1986 and the loss of Columbia in 2003 - claimed the lives of fourteen astronauts.
The Columbia Disaster: Looking Back
On the morning of February 1, 2003, the Columbia orbiter was on its way home from a 16-day mission to space.
The crew of seven on board had conducted dozens of scientific experiments while in orbit, and the astronauts were scheduled to land in Florida at 9:16 a.m. ET.
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NASA engineers knew that during the Jan. 16 launch, a piece of foam - used to insulate the shuttle's large, orange fuel tank - had broken off and struck the Columbia orbiter.
However, the space agency's position was that the lightweight insulation material was unlikely to cause significant damage. During previous missions, some foam had broken off and caused minor damage, but this was considered an "accepted flight risk" according to the official Columbia accident investigation report.
However, it was later revealed that concerns about the foam's impact were swept under the rug by NASA management, according to previous reports and "Space Shuttle Columbia: The Final Flight."
"I was very upset, angry and disappointed with my engineering organizations, from top to bottom," says Rodney Rocha, NASA's chief shuttle engineer, in the new series.
The astronauts even received an email from mission control alerting them to the foam attack on the eighth day of their mission, reassuring them that there was no cause for alarm, according to NASA.
But the assumption was wrong.
Investigations later revealed that the dislodged foam had struck Columbia's left wing during launch, damaging the spacecraft's thermal protection system.
The problem did not affect the crew members while they spent more than two weeks in space.
But heat protection is crucial for the dangerous return home. As with any mission returning from Earth orbit, the vehicle had to dive back into Earth's atmosphere while still traveling at over 17,000 miles per hour (27,359 kilometers per hour). The pressure and friction on a spacecraft can heat its exterior up to 3,000 degrees Fahrenheit (1,649 degrees Celsius).
The return proved too much for the damaged Columbia shuttle. As the vehicle neared its destination, via New Mexico to Texas, the orbiter began to break apart, leaving visible chunks of debris.
At 8:59 a.m. ET, ground controllers lost contact with the crew.
The last message came from mission commander Rick Husband, who said, "Roger, uh," before being cut off.
At 9 a.m., spectators watched Columbia explode over East Texas and watched in horror as the area was engulfed in debris.
The reality of risk
Twenty years later, the Columbia tragedy and the broader shuttle program provide a crucial perspective on the dangers and triumphs of space travel.
NASA entered the era confidently, expecting that the odds of a shuttle being destroyed in flight were about 1 in 100,000.
The space agency reevaluated that risk and estimated after the Challenger disaster that the shuttle had a 1 in 100 chance of disaster.
Sign up for CNN's Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific developments and more."If someone says to me, 'Hey, you can go on a roller coaster ride, and there's a 1 in 100 chance you'll die.' Well, there's not a chance in the world - not a chance in hell - I would do that," U.S. Senator Mark Kelly, a former NASA space shuttle astronaut, told the documentary makers of "The Final Flight."
"But I also think people generally think it won't be them," Kelly added.
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