CAPE CANAVERAL, Florida – Astronauts can become as weak as 80-year-olds after six months at the International Space Station, according to a new study that raises serious health concerns as NASA contemplates prolonged trips to asteroids and Mars.Marquette University biologist Robert Fitts, who led the study, stresses that the accelerated space aging is temporary: Astronauts’ muscles recover after a few months back on Earth.But what if a crew needed to make an emergency landing here on the home planet and rush from a burning spacecraft? “I’d be concerned,” Fitts said this week in an interview with The Associated Press. (AP)