And with the ISS on the verge of becoming habitable, prolonged periods in space will soon be routine for U.S. astronauts. Facing this, scientists are scrambling to dampen all the potentially damaging clatter.
The dirt on noise
Enter J. Adin Mann III, an acoustics expert from Iowa State University who has shared with NASA some of his experience in quieting the Dirt Devil -- a Royal Appliance consumer product.
"It's immensely loud up there," Mann said. "Astronauts come back after 10-day missions with temporary hearing loss. Your ears recover, but if you're up on the space station for three months, then that temporary loss can become permanent."
Working with scientists at NASA's Glenn Research Center, Mann helped find simple solutions to sound problems that, in some cases, simply hadn't been given much previous thought. Mann said weight and cost considerations have long made acoustic engineering a back-burner issue at NASA and other space agencies. And even on piloted flights where there are decibel limits, waivers are often granted to allow more noise than most human ears would appreciate.
The problem has led to concerns that the space station could be dangerous for those who live 225 miles above the home planet.
As far back as 1997, according to an April report in New Scientist magazine, Russian researchers warned that the Zarya module -- a power control and fuel storage module launched a year ago -- could subject astronauts to a perceived noise level of 72.5 decibels. While NASA officials say the noise problem will be under control prior to habitation, New Scientist uncovered NASA documents in April indicating that acoustic mufflers installed as a countermeasure will be "minimally effective."
The apparent noise level for Zarya, though debated, exceeds NASA's limit of 58 decibels for working areas, and experts say it would require astronauts to raise their voice for normal communications and could make it difficult to hear important warning signals.
(Scientists know that the human ear can be damaged by long-term exposure to sound above about 85 to 90 decibels, and by short-term exposure to sounds exceeding 110 decibels. A subway train typically puts out about 90 decibels, while a rock concert typically exceeds 100 decibels. NASA's limit of 58 decibels is comparable to the ambient sound in a typical modern office building.)
In the most recent mission to the station this past spring, astronauts took earplugs to fend off the racket. That solution, however, has its own problems, again making it difficult for astronauts to talk and to hear warnings.
"They were in too much of a hurry to do it right the first time, so now they're accepting the work-arounds and patches that we're going to have to live with for years," said James Oberg, a 22-year NASA space engineer who now works as an independent space consultant.
"It's not merely a comfort issue or a quality of life issue," Oberg told space.com. "It's a health and safety issue."
Meanwhile, NASA has been working to reduce noise levels to within specifications on the two currently orbiting modules, as well as on those still to be launched, says Jerry Goodman, who leads the ISS acoustics team at the Johnson Space Center.
"It's a tough problem when you have a lot of hardware, a lot of different modules, and a lot of different partners," Goodman said in a telephone interview. "With the shuttle we learned the hard way. We frequently did not design in the acoustics. Now we're paying more attention to it."
The concerns are as numerous as the noise sources: A constant drone causes fatigue. Earplugs, worn for long periods, can also be tiring. Sharper noises, including controlled explosions in on-board experiments, might surprise astronauts and force an accident. The experiments, built into drawer-like containers that slide into wall racks, surround the station's inhabitants.
"The thing about space is there's no place for the noise to go," Mann said. "On Earth, you can open the doors and windows and the noise can go outside. You can't exactly do that in space."
Cut the clatter
In working with NASA, Mann found that his Dirt Devil experience wasn't entirely transferable. A vacuum cleaner might make many different sounds, he explained, but certain varieties are more annoying. "When you get rid of an annoying whine, the vacuum cleaner is not necessarily quieter, but it sounds better," he said. "You want to leave the sound of suction -- the sound of the thing working."
NASA, on the other hand, is more concerned with reducing the overall noise level. Mann found that rubber grommets were a big help in reducing vibrational noise. And the simple act of enclosing an experiment with a door proved helpful. Not exactly rocket science, but as Mann noted, NASA engineers are "not used to having to make things quiet, so they don't necessarily have the expertise."
Even after years of experience with Mir, Russian engineers are farther behind, says NASA's Goodman, who quickly adds that the Zarya module designers are catching up and "doing well."
Despite sharing technologies between countries, approaches vary wildly. Goodman said that the Zarya module is noisy even though its walls being covered in a Russian version of Velcro, to which cosmonauts can quickly attach sundry items. The interior of the American-built connector module, Unity, is mostly a painted metal surface, which tends to cause sound to reverberate, but it is quieter nonetheless. In designing mufflers and other sound-absorbing devices, the U.S. team uses a foam-like material, while the Russian version is more fibrous.
Goodman's Russian counterparts are "starting to pick up and learn" from the shared experiences.
And NASA is doing its part by fixing some problems in amazingly simple ways. Goodman describes a clattering Russian pump in the U.S. air-lock that was fixed with off-the-shelf rubber isolators costing $13.39 each. Another technique involves rubbery, sticky-back material that is affixed to surfaces, dampening vibration.
Next: Launching more problems?
The true test of all this effort to shush sounds in space is scheduled to come between December 26 and January 16, when Russia's service module is hooked up to the fledgling space station. The service module, designed similarly to Mir, will serve as the initial living quarters and laboratory facilities.
One thing space station dwellers will need, experts agree, is a good night's rest now and then. But earlier this year, Russian scientists warned that the module's noise level would be as high as 74 dBA. Instead of contemplating the supposed silence of space, dozing astronauts will feel as though they are lying next to a busy highway.
Are the Russians ready to launch the module?
"They're ready to launch something," said Oberg, the former NASA employee who is considered an expert on the Russian space program. But he warns that ISS officials will "compound the first mistake by launching the following modules before they're ready."
Oberg contends that if the service module is launched as is -- a state he says is "clearly not" ready -- valuable space time will be eaten up fixing problems that are already known. This squandered time would be layered atop the time needed to fix surprise problems that flight planners had budgeted for.
"Mir taught us that Russian equipment was too noisy," Oberg said. "Despite NASA's boasts of learning from Mir, they somehow missed it."
Goodman says he agrees that the service module "should not be what it is." But he is confident that the noise level is getting close to required specifications, and he said there are plans in place to get it under the limit, along with further plans to improve acoustics down the road.
"The only recourse is to shut things down and re-build the spacecraft, and I don't think we're going to do that," Goodman said, pointing out that the time lost would be significant and the cost alone would be prohibitive.
"The service module noise is higher than what I'd like and what the crew would like," Goodman said. "But we've agreed to try and live with it."
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