John Glenn is marking the 50th anniversary of his historic space flight with a series of events, including a chat with the International Space Station.
The astronaut became the first American to orbit the Earth on February 20, 1962, helping to lead the nation into space. The trip helped the United States catch up to the former Soviet Union's accomplishments, and Mr Glenn said he thinks it was a turning point for the national psyche.
"It's amazing to me to look back 50 years and think that it's been 50 years," he said last month.
He and Nasa administrator Charles Bolden were expected to speak with the space station to kick off a Nasa forum about the agency's future and its role in advancing fields such as science, technology and the economy.
Mr Glenn and Annie, his wife of almost seven decades, will attend a gala featuring a keynote speech by former astronaut Mark Kelly, the commander of the space shuttle Endeavour's final mission.
Mr Glenn 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 "God-speed John Glenn" moments before the rocket ignited for his space flight.
In 1998, when he was 77, Mr Glenn returned to space, becoming the oldest person to fly there.