You're winging through space in a mosquito-shaped capsule the size of six school buses. You are 213 miles from Earth.
It's your job to crawl inside a 300-pound bubble suit made of Orlon, squeeze into a dark room with no oxygen, and use your gloved hands to reattach 11 cables the size of garden hoses. There's no gravity, of course, and you're likely to encounter floating shards of glass.
If you succeed, you'll restore some power to the 11-year-old Mir Space Station and quiet concerns about a string of recent technical mishaps. Fail, and you might jeopardize the future of the cash-poor Russian space program.
For Mir commander Anatoly Solovyov and his crew, this four-hour repair job is a matter of following a checklist and relying on hours of training in an earthbound submersion tank. For billions of onlookers across the world, it's one of the greatest hurdles yet in mankind's quest to establish a permanent presence in space.
"They're rolling on spare tires, and they've been very lucky so far," says former US astronaut William Thornton. "A lot of us are sitting here with bated breath."
Today's repair job represents one of those rare moments of high drama in the heavens. While some earlier space missions involved more danger and derring-do, this is one of those rare moments when the success or failure of a project pivots on the manual dexterity of two astronauts in moon mitts. But the Russians are noted for their make-things-work prowess.
Indeed, although Mir has suffered setbacks in the past, its recent troubles, combined with the planned construction of an international space station, have placed tremendous pressure on the spacewalk. Already this year, there has been a fire on board, a general failure of the station's computer navigation system, and a collision with a supply freighter.
The June 25 collision punctured one or more small holes in Mir's Spektr module, which houses the bulk of the American science projects. As the module lost pressure, the crew was forced to disconnect its four solar panels - nearly halving the station's total power.
The brownout has not affected crucial life-support systems, but it has reduced crew members' ability to conduct experiments and forced them to turn down the air conditioner.
Early this morning, Mr. Solovyov and his Russian engineer Pavel Vinogradov will don spacesuits and open the hatch to the damaged Spektr. American astronaut Michael Foale will monitor the procedure from the adjacent Soyuz escape capsule.
Once inside, Solovyov will reconnect the cables, which carry power and allow the crew to tilt the module's four solar panels toward the sun. Vinogradov will make sure his partner's umbilicals - cords that supply oxygen and communication lines to the spacesuit - do not get tangled.
Once the power cables are secure, Solovyov may try to locate damage to the module, and will retrieve several items, including a laptop computer and data disks belonging to Mr. Foale, and a vacuum cleaner the crew will use to remove any chemicals or debris that might collect on their suits.
IF the procedure works, Mir may return to at least 60 percent of its full-power capacity. This would allow the crew to resume some experiments and begin planning to repair the gashes in Mir's hull next month.
After some initial apprehension about the procedure's risk, American and Russian scientists are now downplaying the danger. Not only has the Russian crew spent dozens of hours in spacesuits before, they say, but they've trained specifically for this mission. NASA spacewalk manager Greg Harbaugh describes the repairs as "pretty straightforward."
Should one of the cosmonaut's spacesuits be torn open, Mr. Harbaugh notes, the air pockets inside the suit will provide at least 30 minutes of oxygen. If the Mir's life-support systems or airlocks fail, he adds, it would take several hours for all the oxygen inside Mir to dissipate. In extreme circumstances, cosmonauts will be able to join Foale in the Soyuz capsule and return to Earth.
"The environment itself is a harsh one, but there's not much on a space station that can kill you in a hurry," says Norm Thagard, a former Mir astronaut. "Once you ride that rocket up there, it's no more hazardous than riding in an automobile."
The real challenge, Mr. Thagard says, is performing highly dextrous repairs in limited space while wearing a pressurized suit with heavy gloves. Without gravity, he says, spacewalkers have to work doubly hard to exert force. This, he says, can turn a relatively simple task into an hours-long process that leaves the spacewalker tired and bruised.
Although most experts say technical glitches are not unusual in any 11-year-old machine, concerns about the quality of Russian technology aboard Mir and the availability of spare parts have prompted questions about NASA's involvement - particularly in light of the 1986 Challenger disaster.
"NASA will stop a launch or bring people down if there's even a chance of a mechanical problem," Dr. Thornton says. "It's beyond my imagination that NASA would even think of putting people in this vehicle under these circumstances."
Whatever the risks, today's repairs have broad implications for the future of the world's first manned space station.
"If the Mir crew can't restore an adequate level of power, then the capsule will have to be abandoned," says John Logsdon, a space expert at George Washington University. "As far as Mir is concerned, this is a question of life or death."