Window on the World
It's only a small pane in the International Space Station.
- By Leonard David
- Air & Space magazine, May 2000
NASA has certainly taken travel photography to new heights over the years. Beginning with the Mercury missions of the early 1960s, camera-toting astronauts have snapped more than 400,000 pictures of the globe, documenting everything from natural events to the impact humans have had on the environment to, well, the simple beauty of Earth from space.
But while the images made by orbiting astronauts are visually stunning and often scientifically rich, they are usually far from perfect. The problem is that even though the astronauts have excellent photographic equipment, they’re shooting through glass designed to stay intact under the pressures of space travel, rather than to allow photographers to capture fine detail several hundred miles away. It’s a little like buying a top-of-the-line Nikon or Hasselblad and then mounting a piece of thick household window glass to the front of the lens.
But now there’s a new photo opportunity on the horizon. When the U.S. Laboratory Module of the International Space Station (ISS) becomes operational—its launch date depends on that of the Russian-built service module—astronauts will study the planet through the highest quality optical window ever installed in a crewed spacecraft. This 20-inch-diameter circular window, which has been designed and manufactured to eliminate the distortions that plague conventional glass, will be the centerpiece of an active program of Earth observation and photography—and the culmination of a decades-long battle waged over a little bit of glass.
The view from the station will be striking. For starters, its path will give its crew plenty to look at. The ISS follows an orbital track inclined 51.6 degrees from Earth’s equator. That means it is flying over more than 75 percent of the planet’s surface, an area containing 95 percent of the world’s population. Thus, the U.S. Laboratory, along with its nadir window facing Earth, offers a vantage point from which to monitor, with specialized equipment, the global environment. “On the space station, we have people who are highly trained, very curious, and interested in doing something useful out the window,” says longtime window proponent Dean Eppler, a senior scientist in the Houston office of Science Applications International Corporation, a NASA program contractor. “By taking advantage of a good window, along with the interactive capability of the brain—the human computer—we will have an interactive remote sensing laboratory in space, and that’s a unique thing.”
NASA selected Corning, Inc., a high-performance glass veteran—and producer of windows for every manned NASA space program—for the job. “This is the best space window we have manufactured, and it was no small feat,” says Larry Sutton, space products account manager for Corning in Canton, New York. Design and fabrication of the window took Corning a year, with two other firms helping to deliver the final product, a four-piece assembly consisting of a tough, micrometeorite-resistant outside pane, primary and secondary panes that serve as the optical heart of the window, and a protective interior “scratch” pane. The assembly features external and internal shutters to further protect the glass. As scratches and contaminants accumulate, the external pane can be removed by spacewalking astronauts, returned to the ground for repolishing and recoating, and then reinstalled. The interior scratch pane, which protects against bumps from cameras and other instruments, can also be replaced.
The window’s glass is a special stock of high-purity, colorless, synthetic fused silicon dioxide—a material chosen for its resistance to the effects of thermal variations and its exceptional light transmission. Corning took extra care in producing the glass, making sure that tiny imperfections such as bubbles and other blemishes were minimized. The homogeneity of the window is very high—light waves pass through the glass with barely any distortion. A polishing job by Zygo Corporation, a high-performance testing, manufacturing, and measurement firm in Middlefield, Connecticut, made the glass almost perfectly smooth, and coatings by Optical Coating Laboratory, Inc., of Santa Rosa, California, will block out harmful ultraviolet radiation and enhance light transmission to give the space window its unequalled optical rating. “For the astronauts to be able to see without the distortion is going to be amazing,” Sutton says.
To take full advantage of the station’s high-quality port, engineers have designed a work closet to enclose the window. The closet—the Window Observational Research Facility—is a maneuverable open rack that will help position and operate all of the cameras, sensors, telescopes, and other equipment. Fit flush against the lab’s wall, the WORF will be installed after the U.S. Laboratory is itself in orbit and will frame the window. “Everything is going to be aimed at the center of that window, the sweet spot,” explains Scott Britnell, a lead technician working on the enclosure at Boeing Missiles and Space Division in Huntsville, Alabama. The WORF has a black interior to stop stray light from fouling sensitive devices aimed out of the viewing port, and to reduce stray glare from the lab itself, a flexible shroud, similar to a splash skirt on a kayak, fits tightly around the waist of the astronaut working at the window. Depending on the bulkiness of equipment installed within the rack, Britnell says, there may be enough room to squeeze three people inside. But, he adds, they’d better be pretty good friends.
Once in orbit, the lab window will be face to face with Earth’s surface most of the time. Those peering through the nadir window are promised an eyeful—a more color-true and vivid Earth, rich in detail and there for the taking, photographically speaking. Though the images won’t be any better than those from cameras mounted outside spacecraft, they will be far superior to previous hand-held efforts. This is key, as experience has shown that using the astronaut’s eye often produces better results than relying on remotely controlled equipment.
To date, though, camera work by astronauts has largely been a recreational activity practiced at the crew’s discretion, rather than a dedicated scientific duty. Former astronaut Story Musgrave, for example, sheepishly admits to doing whatever it took to get time at the shuttle windows: “I’ve got a lot of window time. You don’t eat. You stuff your pockets and eat at the window,” he says. Mary Cleave, who twice rode on Atlantis, says that such discretionary window time often produces important scientific observations. Now a deputy associate administrator at NASA’s Office of Earth Sciences in Washington, D.C., Cleave points out that the photographic record from successive shuttle flights clearly shows changes on Earth throughout the years, such as deforestation patterns and sediment accumulation around river deltas.
In one observation, an astronaut documented a then-theoretical phenomenon in oceanography called standing wave packets. “Nobody had ever seen them because they were too big to see from an airplane,” Cleave says. Standing waves occur when there is a tidal surge through a constriction, like the Straits of Gibraltar in the Mediterranean. “During the Second World War, the Germans used to get their U-boat submarines into the Mediterranean and back out again by surfing these waves, which they had figured out,” Cleave says. Thanks to sharp-eyed Apollo-Soyuz astronaut Vance Brand, orbiting in 1975, the standing waves were captured on film. “He looked down and saw something strange and took a picture of it,” Cleave says. “Sure enough, it was these standing packets of waves, which are now called V-brand waves.”
In the space station era, Earth science studies will be routinely carried out by astronauts as part of their research workload. Protracted spaceflight—as demonstrated by astronauts and cosmonauts who lived aboard the Russian space station Mir—will allow astronauts to become far more sensitized to Earth’s workings. “There is no question that the longer a person stays in space, the more they pick up some of the subtle rhythms of the planet,” says Cynthia Evans, manager of Lockheed Martin’s Houston-based Office of Earth Sciences. As a NASA contractor, she teaches astronauts to become “Earth smart” by instructing them to be on the lookout for phenomena of scientific interest. Her office will also keep station astronauts informed, via daily updates and Internet messages, about current environmental events to maximize the astronauts’ time and to take advantage of the crystal clarity that the new window provides. Ice packs, volcanoes, developing typhoons, snow lines on the continents, biomass burning in northern forests, and the stirrings of future El Niño events will be among the observers’ targets.
In addition to such training by Evans and her team, station crews will be taught how to use the WORF—specifically, the quick installation and removal of cameras and other equipment. Years of shuttle flights have yielded insight into how the handling of cameras, lenses, film, and other accessories can be made easy for astronauts afloat in microgravity, and less of an all-thumbs hassle. Nobody wants to miss that one-of-a-kind shot.
Despite the apparent advantage astronauts have while ogling Earth from on high, securing a little room with a view aboard the station has been a hard-fought battle. It turns out that window panes in astronaut-carrying craft are a real pain to engineers. In the first place, a spacecraft hull’s structural integrity is compromised by a window. “The structural engineers like to have a nice solid cylinder. They don’t like poking holes into metal to put in windows,” explains Karen Scott, senior project engineer at the Aerospace Corporation’s office at Johnson Space Center in Houston. And windows are brittle, not as predictable, in terms of yield-strength, as, say, aluminum. In other words, glass does not fail gracefully. Battle lines were drawn long ago between window-loving astronauts and spacecraft builders. It started with the Mercury astronauts and continued through Skylab and right into the space shuttle era. Though NASA once considered placing photo-quality windows aboard the shuttle, it nixed the idea in order to cut costs. Engineers instead installed the type of glass used in military aircraft—good enough to enable astronauts to safely pilot the shuttle to a touchdown. “They transferred those same window requirements from shuttle to the space station,” Scott says. “I pointed out very early on, what we had then were windows perfect for landing the space station.”
In 1995, Dean Eppler took up the cause of allocating station astronauts quality window time. He became a force in pushing for the space station’s super-quality window. He and his colleagues had to haggle with administrators and persuade the engineers to cut yet another hole in their closed container, then persuade everyone to spend additional money to support the project. In 1996, when station managers green-lighted a U.S. Laboratory window upgrade, Eppler launched a funding campaign that snagged some $700,000, mostly from the earth sciences office of the Department of Defense, as well as from NASA itself.
Like Eppler, astronaut Mario Runco has been a dogged supporter of the laboratory’s high-quality Earth-oriented port and has been a key force behind the design and fabrication of the WORF and the window. During Runco’s three shuttle missions, seeing was believing. He found comfort in the realization that the human eye was far more sensitive than camera and film in picking up details on Earth. As a professional meteorologist and oceanographer, the astronaut was struck, for example, by formation details he noticed in a Pacific typhoon and the fact that at certain angles, sunlight reflects off the sea surface and reveals amazing detail in the subsurface structure of the ocean—and he thinks that many of his fellow astronauts don’t yet realize what’s in store for them. “It will be better than anything they’ve experienced before,” says Runco, who himself isn’t yet scheduled for a space station mission.
Among the scientists and astronauts focused on the window, there is also a sense that the space station’s ultra-clear portal on the planet comes at the right time. Its on-duty role seems attuned to the increasing realization that environmental concern still outweighs environmental action, and that the planet has a long way to go before it can be called healthy.
Besides, a little bit of glass will ensure that homesick astronauts won’t feel as though they’re trapped in an orbiting submarine. “Windows are clearly one of the keys to crew sanity for long stays in space,” Eppler quips.