How to wield a wrench in zero gravity
HOUSTON — When Jerry Ross and James Newman begin connecting cables on the International Space Station next week, they won't be doing the work of typical telephone linemen.
Instead, they will be working in the perilous vacuum of space, where the object they are working is traveling at 17,500 miles per hour, temperatures plummet to 150 degrees below zero, and one false step can turn them into a human satellite.
But their spacewalk will not be just another testament to mankind's ability to overcome dangers of space: It is also a first step in a new era of unprecedented construction in the heavens. Over five years, American and Russian spacewalkers will piece together the largest orbiting outpost the world has ever seen, in an place as unforgiving as any humanity has encountered.
The shuttle flight taking Messrs. Ross and Newman into space, scheduled for Thursday morning, was delayed at least one day. But once construction on the $40 billion station begins, it will require more than 160 spacewalks, with astronauts and cosmonauts punching the clock for 960 man-hours of spacewalk time. They'll be assembling 100 major components with a combined weight of 500 tons.
"There is a tremendous body of work that lies before us. We call it the EVA wall," says Greg Harbaugh, who heads the the office that plans extravehicular activities at NASA's Johnson Space Center. "It's a daunting task, but I think we're prepared."
Daunting indeed. In space, an astronaut's "overalls" are a 300-pound pressurized space suit that - along with the vacuum of space - cuts these orbiting hard hats off from two cues vital to earthbound workers: touch and sound. Temperatures range from minus 100 degrees F on the night side to 150 degrees F. or more in sunlight. (Tools are certified for minus 200 F. to 250 F.) On orbit, everything is in a state of free fall. Lose your grip on a wrench, and it becomes a piece of orbiting space junk. Lose your grip on the station, and you join the wrench.
In the near absence of gravity and air resistance, inertia is very efficient at keeping a moving object in motion. And for a given amount of applied force, inertia will make moving a very massive object, such as a module, more difficult than a less-massive object, such as an astronaut. So without some type of physical restraint, an astronaut putting the final twists on a tightened bolt will do the turning, not the bolt. Much of an astronaut's energy is spent keeping motion under control.
"Spacewalks are incredibly hard work; they're tough as nails," says former astronaut Story Musgrave, who conducted spacewalks during the first Hubble Space Telescope repair mission in December 1993 and helped design and develop all the space shuttle's EVA equipment - from space suits to the rocket-like backpacks known as manned maneuvering units. Because EVAs are so physically demanding, "you're always working to simplify the job" astronauts must do on orbit, he says.
One way to simplify a job is to automate it. The US laboratory segment "Destiny," for example, uses a berthing mechanism common to the station's various modules. Using the shuttle's robotic arm and thrusters, astronauts will bring the lab within inches of its docking port on the station. Capture latches on the berthing mechanism will finish joining the module to the station. Once the capture latches have finished their job, 16 powered bolts will automatically thread into their receiving nuts and tighten, according to Steve Goo, Boeing Aerospace's chief engineer on the lab module.
"We're trying to keep the use of hand tools to a bare minimum," Mr. Goo says. Even so, it will be up to spacewalking astronauts using hand tools to connect cables and fluid lines, install handrails and antennas, assemble trusses, attach solar panels, set up batteries, and tighten any automatic bolts that fail to fully engage.
Ordinary tools, with a twist
Many of the tools are recognizable to anyone who has spent time walking down the aisles of their local hardware store. But ISS tools have unique differences that separate them from their terrestrial counterparts, according to Phil West, an engineer who spent the past six years managing the EVA tool project for the International Space Station before becoming the Bob Vila of Johnson Space Center's public-affairs office.
For example, one of the mainstays, battery-powered bolt drivers, look much like oversized Makita cordless drills, he says. But the sockets used are much deeper than usual to accommodate 7/16-inch bolt heads that are as much as four times the height of their terrestrial equivalents. "We make the socket deep and the bolt head tall so you're less likely to slip off of it," he says.
In addition to a wide variety of tools, NASA has developed three types of tethers and restraints to ensure that when hardware is jointed, the bolt doesn't turn the astronaut. And for hauling batteries weighing several hundred pounds along the trusses? NASA has crafted a small cart that rolls up and down a truss under astronaut power. The speed limit on that stretch of track is two miles an hour.
Ultimately, however, the most important "tools" are the astronauts, who by the time they launch know exactly how many turns of the wrench it will take to drive a given bolt home. Until the station gets its first live-in crew, shuttle EVA astronauts will be under intense pressure, NASA officials acknowledge. Each flight gets only one chance to perform its tasks.
"It's like going to the Olympics," Dr. Musgrave agrees. "You've got one shot at it."
A lifetime of experience
While some astronauts speak of EVA training in terms of months or years, Musgrave sees it in terms of lifetimes. "You reach for all you have, even into your childhood experiences," says the former astronaut, who grew up on a farm in Massachusetts' Berkshire Mountains and was fixing tractors at age 7 or 8.
Training, he says, is more than learning to perform a task, but learning to choreograph the entire EVA to make the most efficient use of energy, motion, and time - which is limited by life-support systems in space suits and on the shuttle.
NASA maintains a number of EVA training facilities, including the recently expanded Neutral Buoyancy Lab - 6 million gallons of water in a tank 200 feet long, 100 feet wide, and 40 feet deep. Astronauts don spacesuits with umbilical hoses and practice their assignments on full-scale mockups under water.
"You spend about 10 hours in the tank for every hour of an EVA," says Col. Mark Lee, who conducted EVAs during last year's Hubble upgrade mission. Weighted just enough to keep from rising to the surface, and not enough to sink, astronauts repeatedly rehearse and refine their approach to their spacewalk assignments.
Other facilities, including a new virtual-reality facility, try to mimic other aspects of on-orbit EVAs.
Yet as thorough as the training is, it provides astronauts with only a disparate set of tiles that they must assemble into a mental mosaic of an EVA, according to Musgrave. Until an astronaut floats out the shuttle's hatch and into the cargo bay, he says, "only in the imagination does a spacewalk exist."
Once out the hatch, the focus is on the task at hand. Yet that doesn't prevent astronauts from appreciating the view - having, in Musgrave's words, "a space experience."
Smith, who took part in last year's Hubble upgrade mission and is payload commander for the next Hubble mission in 2000, recalls emerging from the hatch for the first time. "The training can't do it justice," he says. "You can't simulate the awe of the thing."
Nor does training simulate how mission control will react to an astronaut's awe. "When I came out of the hatch for the first time, I said: Oh, my God! It's beautiful!" Mr. Smith recalls. "But after the word God, I paused for about two seconds. I was not visible to people on the ground at the time. In that two seconds, apparently, a lot of people started scurrying."