Space Exploration takes courage, tenacity, and innovation. Tragically, it has also claimed the lives of three brave crews.

In this Mission Monday, we are going to look back at these missions and the heroic astronauts who made the ultimate sacrifice for space exploration.

Apollo 1 – Jan. 27, 1967

Gus Grissom, Ed White and Roger Chaffee all perished when a spark ignited the oxygen inside the Apollo 1 capsule they were testing. Grissom was the second American in space when he flew on Liberty Bell 7 as part of the Mercury Program. White was the first American to walk in space during Gemini IV. Chaffee was a naval aviator and aeronautical engineer; Apollo 1 was to be his first mission as an astronaut.

Their sacrifice was devastating and threatened to end the nation’s young space program. Instead, it galvanized everyone in the Apollo program. It drove them to create safer solutions, ensuring that Grissom, White and Chaffee would be part of humanity’s greatest achievement.

Challenger – Jan. 28, 1986

On Jan. 28, 1986, NASA lost astronauts Dick Scobee, Michael Smith, Ronald McNair, Ellison Onizuka, Judy Resnik, Gregory Jarvis and Christa McAuliffe as part of the space shuttle Challenger disaster.

Just 73 seconds after launch, a booster engine failed and caused Challenger to break apart, taking the lives of all seven crew members. The cause of explosion was determined to be an o-ring failure in the right solid rocket booster. Cold weather was determined to be a contributing factor.

This mission was meant to mark a milestone in spaceflight: the first orbital voyage of an American teacher. McAuliffe, a social studies teacher at Concord High School in New Hampshire, was NASA’s choice for the honor.

Columbia – Feb. 1, 2003

The seven-member crew of the STS-107 mission was just 16 minutes from landing on the morning of Feb. 1, 2003, when Mission Control lost contact with the shuttle Columbia.

A piece of foam, falling from the external tank during launch, had opened a hole in one of the shuttle’s wings, leading to the breakup of the orbiter upon re-entry.

This fatal accident claimed the lives of Rick Husband, William McCool, Michael Anderson, Kalpana Chawla, David Brown, Laurel Clark and Ilan Ramon as they returned from their mission.

Addressing the nation, President Bush said, “mankind is led into the darkness beyond our world by the inspiration of discovery and the longing to understand. Our journey into space will go on.”

NASA remembers all of these brave souls every year as part of their Day of Remembrance. Ceremonies take place in different ways at all of the NASA facilities. At NASA Johnson Space Center, there is a Memorial Grove of trees planted in memory of fallen astronauts and mission control personnel.

The legacy of those we have lost is present every day in our work and inspires generations of new space explorers. With each new challenge we overcome and every discovery we make, we honor these remarkable men and women.