Glenn orbited Earth three times, while Carpenter was a backup pilot for the Mercury-Atlas 6 mission as part of the Mercury Project.
Glenn and Carpenter are the only astronauts of the original Mercury Project still alive. Gus Grissom died in 1967 when his spacecraft was engulfed in flames on the launch pad. Deke Slayton died of cancer in 1993, while Alan Shepard died of leukemia in 1998, Gordon Cooper died of heart failure in 2004, and Wally Schirra died of a heart attack in 2007.
The Kennedy Space Center was set to launch an unmanned spacecraft Friday, but weather forced a postponement, The Miami Herald reported.
"Welcome to the space program," joked Glenn, who suffered through 11 postponements before his first blast into space.
Glenn spoke on reinvigorating the manned space program, saying it never recovered from President George W. Bush's 2004 decision to replace shuttle flights with a program to reach the moon and Mars -- "but without the funding.''
He said there is a need to "galvanize public support" and "re-energize our thinking."