Her husband Mark Kelly, a retired astronaut and commander of the space shuttle Endeavour's final mission, was the night's featured speaker and said he was honoured to be sitting between two of his own heroes, Armstrong and Glenn. He brought the audience a message from Giffords: "Be passionate. Be courageous. Be strong. Be your best."
Glenn urged the audience to support research and education and shared the lessons he learned when he was among the top military test pilots presented in 1959 as the Mercury Seven. The only other surviving Mercury astronaut is Scott Carpenter, who called out the memorable line "Godspeed John Glenn" moments before the rocket ignited for Glenn's space flight.
"With a lot of work and a lot of people organised, you can do almost anything," Glenn said.
Earlier Monday, Nasa had surprised Glenn with the kind of anniversary gift only a space agency can give, enabling him to speak live with the International Space Station from a stage at Ohio State University.
Sitting on stage with Nasa Administrator Charles Bolden, he chatted with three space station crew members about space research and Nasa's future. Commander Dan Burbank appeared by video link, flanked by two flight engineers floating in the zero-gravity environment, and said the crew was delighted to help commemorate Glenn's momentous trip.
"Fifty years ago today, Friendship 7 was orbiting planet Earth, and that helped in a very big way, paved the way for America to become a space power, and to go to the moon, and to do the things that we're doing right now on the International Space Station," Burbank said.
Glenn had a light-hearted but educational exchange with the crew, asking them about the types and number of experiments on board – more than 100, they said – and explaining to his gravity-bound audience of more than 200 people that, for example, a candle burns differently in space than on Earth.
When Bolden asked the astronauts which experiment they'd like to hand off to Glenn if he could join them, Burbank suggested research on the "regenerative environmental control systems" on spacecraft.
"That's a fancy word for our lavatory," flight engineer Don Pettit added. "So he wants to put Sen. Glenn busy fixing the plumbing up here."
Mr Glenn took the humour in stride, replying: "That's exactly what I thought I was going to get assigned to."
Bolden joked that Glenn sometimes bugs him about making a trip to the space station. Glenn became the oldest person to fly in space in 1998, at age 77.