 Complete the following phrase:  The Space Shuttle Challenger Memorial was dedicated on May 20, 1986, in memory of the crew of flight STS-51-L, who died during launch on January 28, 1986. Transcribed on the back of the stone is the text of the John Gillespie Magee, Jr. poem High Flight, which was quoted by then President Ronald Reagan when he addressed the disaster. Although many remains were identified and returned to the families for private burial, some were not, and were laid to rest under the marker. Two crew members, Dick Scobee and Michael Smith, are buried in Arlington. On February 1, 2004, NASA Administrator Sean OKeefe dedicated a similar memorial to those who died when the Shuttle Columbia 