John Glenn's got this space stuff down cold.

The 76-year-old U.S. senator donned rappelling gear and an orange flight suit Monday to practice exiting the space shuttle in the event of emergency. Though there's never been a need for one, every shuttle crew prepares just in case. Glenn completed the exercise without a hitch.The Ohio Democrat will become the oldest man in space when he flies on a nine-day mission this fall to help NASA learn more about aging in space.

Glenn and his six fellow crew members took turns popping out the hatch of a life-size shuttle mockup and lowering themselves down the side of the spacecraft. The exercise simulates how the astronauts would exit the shuttle if there were an emergency while the vehicle was on the ground.

Glenn called the training a challenge, but said preparing to become the first American to orbit the Earth in the early '60s was no cakewalk.

"Back then, we were just trying to find out, `Could you do this?' " Glenn said. "People were predicting eyeballs would change shape and you'd have uncontrollable vertigo and nausea and all that. Now it's gotten to where this is a science machine."