In this story:

• 'It's only a matter of time'
• Space program 'needs smarts'
• A celebration of heroism
• In pursuit of a high purpose
• Related stories and sites

CAPE CANAVERAL, Florida (CNN) -- John Glenn's fellow Mercury astronauts say they think his return to space will give the space program a needed boost, but not necessarily in the direction of Mars.

"If we use the old antiquated systems we've got now, a Mars landing won't happen in my lifetime," said 71-year old Gordon Cooper.

	COUNTDOWN: Mission News CNN Video Archive Panoramic Photos Tour Mission Control FLASHBACK: Whither the Mecury 7? Shuttle Milestones Gallery: Then and Now LAUNCHPAD: Message Boards Space Chat Glenn-Gram e-mail GAMES: Match the Mission Mission Quiz Crossword Puzzle Crew members Brown Duque Glenn Lindsey Mukai Parazynski Robinson

A Mars mission using present technology, Cooper estimated, "would take about three years if you want to spend any time there, but renewed research and effort could shorten that by a great deal."

The atmosphere on Mars is almost livable, Cooper said, "but you would need a little help." Cooper said he hoped "John's return to space would whip up enough public enthusiasm for a manned Mars mission."

He added, "I have every intention of being around when we send a crew to Mars and I'd like to be on it."

Scott Carpenter, who was Glenn's backup for his historic Friendship 7 flight and later spent more than four hours in orbit himself, says Mars is "only a matter of time."

"What we need is someone who will tell us we should go to Mars," said the 73-year-old Carpenter, recalling President John F. Kennedy's call to send a man to the moon by the end of the 1960s.

Space program 'needs smarts'

The fourth surviving Mercury astronaut, Wally Schirra, also is dubious about a manned mission to Mars happening any time soon.

"I don't see it happening before the year 2030," Schirra said. "That's a long trip. We need more propulsion, we need more data. We don't know if people can tolerate going to Mars and back."

He said the "sad part is that those who have been in space for a long time, four, five or six months, come back as basket cases. What good is it if we send them all the way to Mars and they can't tell us anything?"

The whole program, he suggested, "needs some smarts. We've got to spend more time at that international space station to learn how to take care of them physiologically."

The three space pioneers were gathered at a reception in their honor Wednesday at the Astronaut Hall of Fame, a non-profit museum and foundation. Of the original seven Mercury astronauts, Gus Grissom died in the Apollo 1 fire and Alan Shepard and Deke Slayton died of leukemia and cancer, respectively.

Glenn is the only one still directly involved with the space program, and that has been only since the retiring U.S. senator from Ohio was named to a shuttle crew earlier this year.

"John's going to get some unbelievable surprises," predicted Schirra, who flew in the Mercury, Gemini and Apollo missions and has the most flight time of the surviving astronauts. "Some people get quite sick in space and it's quite normal. It's not a macho thing -- it's something that can happen."

A celebration of heroism

Still "Jolly Wally," renowned for his quips and practical jokes, the 75-year-old Schirra said he is "delighted that John is going up, instead of me. He needs the flying time, I don't. I even gave up my pilot's license. Can't afford it."

Schirra celebrated the 30th anniversary of his final journey into space as commander of Apollo 7 by autographing copies of his book, "Schirra's Space."

The outspoken Schirra is less fondly remembered around NASA for criticizing scientists who inflicted "Mickey Mouse tasks" on his three-man Apollo crew.

Buzz Aldrin, the second man on the moon after Neil Armstrong, said he did not regard Glenn's mission as "genuine science," although there will be experiments on aging. "But that's not why all you members of the media are down here."

Glenn's return to space, he mused, "is a typical American story. We have a hero who accomplished something in the past and now at the culmination of his service to the nation is being given one last chance to revisit a great achievement."

Aldrin said "patriotism and celebration of heroism" were more at the heart of the flight than pure science. "But if John Glenn can go back into space at age 77," he added, "why can't the average citizen? That's what I've been promoting in the last several years."

In pursuit of a high purpose

He advocates a public lottery to choose further space voyagers. "We can't have space for just test pilots and scientists or wealthy people as we begin to move into tourism," he said.

As for heading to Mars, Aldrin said the American space program concentrated on beating the Russians to the moon rather than "taking advantage of what we put together in that Saturn 5 rocket. If we had chosen to put wings on that Saturn, we might have been on the way. But then the Russians might have got to the moon first."

Asked about the risk undertaken by the 77-year-old Glenn, the former Mercury astronauts echoed sentiments expressed by astronauts since the original seven were chosen in 1958.

"What people don't fully realize is that we view ourselves as expendable in the pursuit of a high purpose," Carpenter said. "If he or anyone else should perish, that's okay. We've recovered from it before and we will again."

Schirra put his own spin on things, noting that "This morning I drove the back roads to our Mercury launch pad, Complex Fourteen. There was a plaque with all our names on it. Now anyone who is happy to see his name engraved in marble really has something to worry about."

The Associated Press and Reuters contributed to this report.