Too loud for comfort - In space, no one can hear above the din

CAPE CANAVERAL, Fla. -- The image is one of quiet serenity: Astronauts on a space station gliding effortlessly around Earth, removed from worldly clamor.

Here's the shrill reality: The fans and pumps are so loud up on the international space station that astronauts who spent nearly six months on board consider noise one of the top habitability issues.

"It's always there," says NASA astronaut Jim Voss.

"It's sort of like being in maybe a factory," he adds. "Not a factory where they're stamping steel, but a normal production facility where there's constant noise in the background all the time from machinery that's running."

Even though he wore ear plugs every night while he slept, Voss suffered a partial hearing loss during his space station stint. He says his ability to hear higher frequencies decreased, but, thankfully, was almost normal after his return to the relative quiet of Earth in August.

Things that go bump

Voss and Russian commander Yuri Usachev slept in the Russian service module, which contains the toilet, galley, treadmill and a multitude of life-control systems, many of which go bump and not just in the night. The biggest offenders, Voss says, were fans for cooling equipment and circulating air.

Because the doors to their sleeping compartments were removed for better ventilation, Voss and Usachev had to put up with even more racket than intended.

Crewmate Susan Helms, on the other hand, did not lose any hearing because she slept in the quieter U.S. laboratory. Even so, she occasionally wore noise-muffling headsets while she slept.

Helms says she was able to converse with Voss and Usachev in normal voice tones as long as they were close to one another and their ears were not plugged. Still, they found themselves saying, "What?" a lot.

Noisy Russian half

Russia's half of the space station -- the noisier half -- has long been a concern.

The two Russian core modules exceeded the safety limits of the National Aeronautics and Space Administration for noise even before they were launched in 1998 and 2000. Because they were patterned after existing Mir designs, the modules had higher noise limits than U.S. standards.

By the time NASA got all the acoustic data on Russia's Mir space station, it was too late. The agreement was struck, and NASA was stuck.

"We were in a dilemma, and it was very difficult to convince anyone at the time that we were going to have these kinds of problems," recalls Jerry Goodman, a NASA engineer who got involved in the space station acoustics three or four years ago. "We got into a difficult political situation."

Anxious to get something in orbit after years of delay, space station officials accepted the noisy Russian modules with the understanding that mufflers would be added later.

Mufflers have been added, and more are on the way. But the overall noise level remains "pretty high," Goodman says.

In fact, only two of the six space station rooms meet the desired limit of 60 decibels. (The limit originally was 58 but crept up to 60 to account for payload noise.)

The service module is the loudest room with a constant decibel level in the high 60s to low 70s, roughly equivalent to a busy highway. The crescendo rises to 78 decibels in a few spots.

The American-made Destiny laboratory registers 60 to 63 decibels, with periodic spikes in the 70s when equipment kicks in.

Repeating themselves

Earplugs or headsets are not the answer.

"You try to wear those 24 hours a day," Goodman says. "They're very uncomfortable, and the crew won't tolerate them."

Besides health, crew safety could be at stake.

"The crew has to repeat what they say quite often, and there's a possibility for mistakes," Goodman says. "If you don't hear the numbers correctly, you put in the wrong thing, it could have bad repercussions."