Today marks 35 years since the Challenger explosion.
In 1986, the space shuttle Challenger broke apart 73 seconds into flight.
Seven crew members were killed including Christa McAuliffe, who would have been the first teacher in space.
Today is also NASA's Day of Remembrance.
The entire agency is set to commemorate space missions that ended in tragedy.
They will honor the crews of Apollo One, space shuttle Columbia, and Challenger.
