CAPE CANAVERAL, Florida (CNN) -- After a brief delay, the shuttle Discovery blasted off Thursday carrying 77-year-old John Glenn and six other astronauts into space on the most publicized shuttle mission in years.

President Clinton and dozens of congressmen were among the approximately 250,000 people and 3,000 members of the media who watched Discovery lift off into a bright blue sky above Kennedy Space Center.

With the launch Glenn becomes the oldest person to go into space, surpassing U.S. astronaut Story Musgrave, who was 61 when he made his last shuttle flight two years ago.

NASA officials say the mission will be a "very busy" one, with the crew expected to perform 83 experiments in the eight days and 20 hours they are aloft.

But Clinton, the media throng and the large crowd were there not to applaud the crew's workload, but to witness Glenn's historic flight. So great was attention to the event that NASA armed its security guards at the space center with semi-automatic weapons.

The guns -- which are not usually present at shuttle launches -- were "a common sense precaution," NASA officials said, given the publicity and public interest surrounding the mission.

10 experiments for Glenn

Glenn was the first American to orbit the Earth, circling the planet three times aboard the Friendship 7 Mercury capsule on February 20, 1962. But he was forbidden by President John F. Kennedy from returning to space, lest the country lose a hero at a time when the space race was the focal point of the Cold War.

He eventually left NASA and in January will conclude his fourth and final term as a U.S. senator representing Ohio.

It was as a senator with a strong interest in aging and the plight of the elderly that Glenn campaigned successfully for his return to space. He is to participate in 10 experiments aboard Discovery, nearly all of them related to the effects of weightlessness on the human body.


STS-95 Crew members are briefed on the flight deck of a crew compartment trainer in April

The effects are similar to the symptoms of aging that many people suffer on Earth, and the hope is that the research will lead to new treatments for the elderly and for astronauts making extended stays in space.

Critics say the mission is scientifically invalid because NASA has no plans to fly other elderly astronauts and create a better picture of how the aging process and space travel intersect. But Glenn has said he hopes this is just the beginning of such studies.

Hubble parts to be tested

The astronauts are also planning to deploy the Spartan satellite to study the sun's corona, test some hardware that will be installed on the Hubble Space Telescope on a future mission, and perform dozens of other experiments.

The mission is scheduled to end with a landing at 11:50 a.m. EST at Kennedy Space Center on Saturday, November 7.