This week marks a somber time for NASA, with the anniversaries of three U.S. spaceflight disasters recalling the memories of those astronauts who made the ultimate sacrifice in the pursuit of space exploration.

On Friday (Feb. 1), NASA will pause to honor the memories of the three astronauts killed in the Apollo 1 fire of 1967, the seven astronauts killed in the Challenger shuttle disaster in 1986, and the seven astronauts who died when the space shuttle Columbia broke apart during re-entry on Feb. 1, 2003. This year's Day of Remembrance ceremony is especially poignant it will mark the 10th anniversary of the Columbia disaster that led to the end of the space shuttle program.

"NASA's Day of Remembrance honors members of the NASA family who lost their lives while furthering the cause of exploration and discovery," NASA officials wrote in an announcement. "Flags across the agency will be flown at half-staff in their memory."

NASA will hold a televised ceremony on Friday at the Kennedy Space Center's Space Mirror, a memorial to astronauts who died during spaceflight. The service, hosted by the Astronaut Memorial Foundation, will begin at 10 a.m. EST (1500 GMT) and be webcast live via NASA TV. SPACE.com will carry the NASA video stream live.

NASA chief Charles Bolden a former space shuttle commander will pay tribute with other NASA officials during an observance at the astronaut memorial at Arlington National Cemetery in Virginia. [Columbia Shuttle Disaster: Share Your Thoughts]

NASA's spaceflight tragedies

On Jan. 27, 1967, Apollo 1 astronauts Gus Grissom, Ed White and Roger Chaffee were killed when a fire broke out in their crew capsule during a ground test a month before their planned launch. It was NASA's first mission-related tragedy and led to a safety investigation into the Apollo spacecraft. Two years later, in July 1969, the agency's Apollo 11 mission landed the first astronauts on the moon.

On Jan. 28, 1986, 19 years and a day after the Apollo 1 fire, NASA's space shuttle Challenger broke apart 73 seconds after liftoff due to an O-ring failure in one of the orbiter's twin solid rocket boosters. The malfunction allowed hot gas to escape the rocket booster, ultimately causing the shuttle's external fuel tank to explode. [NASA's Fallen Astronauts: A Photo Memorial]

Killed in the explosion were astronauts Francis "Dick" Scobee, Ronald McNair, Mike Smith, Ellison Onizuka, Judy Resnik, Greg Jarvis and Connecticut teacher Christa McAuliffe. McAuliffe was slated to become the first teacher in space during the mission, boosting national attention on the spaceflight. It would take NASA three years to resume flying the shuttle.

Today, the nonprofit StoryCorps released a video to honor the memory of Ronald McNair, the second African-American in space. The video commemorates McNair's childhood in Lake City, S.C., and his path to space.

Read the original here:

For NASA, a Somber Week of Space Disaster Anniversaries