The piece of orbital junk closed in on the International Space Station at 29,000 mph. Six crew members evacuated to two Soyuz space capsules that would be their lifeboats if the debris made contact. The astronauts had no tools designed to find and repair significant damage and had only one option: Undock, and abandon the $100 billion Earth-orbiting laboratory. At 8:08 a.m. on June 28, 2011, the object and the station flew past each other—a harrowing 1,100 feet apart at closest approach.
That near-collision was the second time in two years a station crew had to seek shelter in the capsules. Nineteen other times between 1999 and August 2014, NASA has performed “debris avoidance maneuvers”—moving the entire station out of the way of incoming objects, which can be undertaken only when ground controllers detect the debris early enough. And then engineers must weigh the probability that the station will be hit against the potential impact of the maneuver on external station research and predict any possible danger the maneuver poses to the crew.
The risk associated with micrometeoroids and orbital debris is not trivial. Impacts happen regularly, although the station has so far been spared a major hit. Engineers and safety officers at NASA have given a lot of thought to the tools that a station crew could use to respond to a significant collision. The first solution is simply being able to inspect the exterior of the station for damage. Astronauts’ inability to adequately survey their spacecraft has been a problem ever since one of Apollo 13’s oxygen tanks exploded on the way to the moon and, more recently, when the space shuttle Columbia burned up on reentry because of an undetected breach in the leading edge of a wing.
“We should never allow an Apollo 13 or a Columbia to happen again, where we choose not to have an ability to see the exterior of the spacecraft,” says George Studor, a former senior project engineer at Johnson Space Center in Houston. Studor specializes in spacecraft inspection technologies, and now provides consulting for NASA contractors.
The goal now is to get real-time observation in as many places in and around the space station as possible. The range of technology that NASA and its partners are working on is broad—from high-definition external cameras to autonomous robots that can fly around or crawl on the outside of the station to investigate and repair damage.
Studor has been involved in the in-space inspection effort for decades. He joined NASA’s space shuttle program in 1983, as a U.S. Air Force pilot detailed to the agency to improve the shuttle turnaround in between flights. After the Columbia accident, he worked on impact detectors inside the shuttle’s wings. “Either you design [the spacecraft] for inspection and access, or you provide sensors that help you do the inspection,” he says.
The space station falls into the second category. It’s a huge, complex craft, designed and constructed over decades by numerous manufacturers from different countries. With everything that had to be done just to get its modules built, launched, and assembled, easy access for inspection was not high on the priority list, so many parts of the station are not visible through the windows or even by the exterior cameras, says Studor.
In the station’s orbit is a vast field of debris. Objects range from abandoned upper launch stages, to fragments of satellites that have exploded or collided—the main source of space trash—to tiny pieces, such as flecks of chipped-off paint. (Impacts from paint chips caused enough damage to require replacing several space shuttle windows.) All are dangerous because all are traveling at enormous speed—17,500 mph on average.
The U.S. Space Surveillance Network, part of the Department of Defense, routinely tracks more than 21,000 pieces of orbital debris larger than a softball. NASA says there are 500,000 pieces in orbit larger than a marble, and millions more that are so small they are impossible to detect and track.
The orbital trash problem began to balloon in 2007, when China intentionally blew up one of its old weather satellites in an anti-satellite weapons test, creating about 3,000 pieces of space junk. Two years later, a defunct Russian satellite collided with a U.S. commercial satellite, adding 2,000 more pieces. Of all the larger debris known and catalogued, NASA estimates that more than 800 objects routinely fly in the station’s orbit, according to an assessment last October; that’s a 60 percent increase over the last 15 years.
It’s impossible to know how often the space station is hit by small debris, but in 1984, NASA launched the Long Duration Exposure Facility to measure impact rates on spacecraft in low Earth orbit. Over nearly six years, the city-bus-size spacecraft was pelted by orbital debris and micrometeorites nearly 20,000 times—more than 3,000 times a year. This was decades before the debris field reached the density it has today. But “it is not how many hits we get, it’s what they hit, what they are made of, and what we do to take that risk into account,” says Studor. “It is the risk to the reentering spacecraft with crew in them that worries us the most.” The Soyuz capsule—the one astronauts would use as an escape should they have to flee the station—stays docked for six-month intervals in a position where it is unshielded by any part of the station. “We have counted a couple dozen of what appear to be impacts to the Soyuz thermal blankets that happened in less than six months,” he says.
Because NASA can’t always protect the station and the docked spacecraft from debris, the agency is seeking ways to find the damage from significant incidents and to patch the holes as fast as possible. The first order of business is to swap older cameras mounted around the outside of the station with Nikon D4s that can zoom, pan, and tilt, and can be controlled from the ground, significantly reducing the number of blind spots on the exterior. The Nikons, which have top-of-the-line sensors that capture significant detail even in extremely low light, will be installed during three spacewalks in 2015.
In addition to mounted or hand-held cameras, what if astronauts could send one floating out wherever they needed it to go? Currently on the station are prototypes of small free-flying vehicles called SPHERES—Synchronized Position Hold, Engage, Reorient, Experimental Satellites, a joint project of NASA, the Defense Advanced Research Projects Agency, and the Massachusetts Institute of Technology. (The project originated as a challenge by an MIT professor to his students to design something similar to the light saber training droid in a Star Wars prequel.) Astronauts have been testing the bowling-ball-size satellites inside the station since 2006. With self-contained power, propulsion, computers, and navigation equipment, a vehicle like SPHERES could autonomously monitor systems on board and conduct inspections, maintenance, and repairs. In October, NASA announced a plan to send a Free Flying Robot—an advanced version of SPHERES—to the station in 2017.
David Hinkley is an engineer with The Aerospace Corporation, which is developing small satellites, similar to SPHERES, called AeroCubes. “If the inspector was constantly flying around and imaging, and if it was autonomous, then the station crew could ignore it,” he says. “The Houston ground crew, which is much, much larger, could process the images and task the inspector directly.” A free-flying inspector for the station needs the ability to constantly communicate with controllers and image-recognition technology so it knows exactly where it is, Hinkley says, and that technology is not quite ready yet. Furthermore, he believes that station managers are not quite ready to let loose free-fliers yet, afraid of “unintended damage or other mischief” they might get in to.