People who listen to loud rock music may lose some of their hearing. Astronauts are worried about the same thing, because there?s such a racket inside the International Space Station (ISS), you can hardly hear yourself think.
Fans, compressors, motors, transformers and pumps create a deafening cacophony that is hazardous to the health and well-being of the space crew. The noise situation has been rated as "bad"--and it's getting worse, as more equipment goes up.
Space station designers knew that noise could be a problem, but their attention was focused on more serious problems. "Noise was one of those issues that never seemed to get much respect," says NASA acoustics engineer Jerry Goodman.
The Russians paid even less attention to the noise issue. "Our primary concern is the Russian service module,? says Michael E. Engle, the acoustics integration manager for the ISS. The Russians are under severe financial constraints, so they didn?t give a high priority to the sound problem. Even the Mir space station was incredibly noisy?and also smelly, since there was mold growing in it.
?The continuous noise levels (in the Russian module) are in the 70- to 72-decibel range," says Engle. This is like standing next to a highway. By comparison, U.S. Navy standards mandate that continuous exposure to shipboard noise above 60 decibels must be limited, to prevent ear damage. In order to protect their ears, astronauts have been working less than two hours at a stretch in the Russian module.
In the U.S. lab module, at the other end of the ISS, sound levels have been measured between 55 and 62 decibels. The U.S. end may be "the only relatively quiet work place," according to an internal NASA report. But noise levels are creeping up there, too. In April the arrival of one device "about doubled the acoustic energy," the report says. Engle says that hearing loss among the crew members is a big concern.
They have been told that they are not in any danger of permanent hearing loss, just a temporary reduction, but this hasn?t reassured anyone. Of four U.S. astronauts who have served on long-term missions, one lost some hearing but recovered it later.
It?s even hard for crew members to talk with one another up there. Crew members "recalled saying 'What?' a lot to each other," Engle says. One American complained that the hazard alarms weren?t loud enough to be noticed against all the background noise.
In a January meeting in Houston to discuss noise issues, Boeing official Charles R. DuSold said the use of noise-canceling and noise-reducing headsets was "not acceptable," since they would be too uncomfortable for the astronauts to wear over long periods of time. Also, noise can be reduced in some areas, but only at the expense of increasing it elsewhere. Everyone doubts the practicality of retrofitting equipment that is already in orbit. Add-on mufflers and acoustic mats could damage equipment or block air cooling, leading to overheated components.
NASA is now encouraging builders to design quieter hardware from the start. Other equipment is being redesigned before it goes up. A Russian depressurization pump initially produced 100 decibels of sound, but was returned to Earth and retrofitted with four isolation mounts at $13.95 each to make it generate only 60 decibels. Engle says, "It would have been nice to fix this problem before we flew."
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