Buzz Aldrin says he would be first in the queue for a spacewalk to carry out repairs if he was among the crew of the space shuttle Discovery.
The 75-year-old former astronaut, who in 1969 was the second man to walk on the moon, is closely following events aboard Discovery.
He believes the shuttle will make it back safely.
"I have confidence that the condition of Discovery is very good right now and that we shouldn't have that much concern about re-entry," he said from his Los Angeles home.
NASA managers say two protruding bits of material known as "gap fillers" could overheat as Discovery plunges back into Earth's atmosphere, raising fears of a recurrence of the Columbia disaster.
The Columbia shuttle broke up on re-entry in 2003. A chunk of foam insulation broke off the ship's fuel tank during launch and smashed into the wing, damaging its heat shielding.
Yesterday NASA officials decided astronauts would carry out repairs during a spacewalk.
Dr Aldrin said whoever did the job would probably never forget the "exhilaration" of floating outside the spacecraft travelling at more than 25,000km/h.
But the shuttle programme's days are numbered.
"Most everybody agrees we're overdue for a transition to go beyond Earth's low orbit and resume exploration," Dr Aldrin said.
"I think we're headed towards Mars although I'm not sure I'll be around to see that happen."
He does not believe criticism of the shuttle programme, with questions raised why the problems with debris weren't fixed, is justified.
"There are always people who want to get attention for criticising what's going on. There were people saying we were going to sink 50 feet into the dust of the moon when we tried to land," he said.
