In August 1993, the European Space Agency’s Olympus 1 experimental satellite was in trouble. The annual Perseid meteor shower, especially fierce that year, was just getting started. Usually, given sufficient warning of intense meteor activity, satellites can engage their defenses: They might,for example, protect themselves against incoming projectiles by orienting their solar panels against attacks, like shields. But Olympus 1 was at a disadvantage. A previous mishap had disabled the satellite’s ability to shift its solar arrays, leaving it defenseless. In short order, an incoming Perseid particle knocked out Olympus’s gyroscope stability, which sent the satellite spinning wildly. Attempts to regain control used up most of the craft’s fuel, leaving the US $850 million satellite with barely enough to propel itself into a graveyard orbit, where it could neither hit other satellites nor do much of anything useful. Olympus 1 will likely remain there forever, cold and dead before its time.
Meteoroids have taken out more than a few spacecraft. In addition to Olympus and Landsat 5, other possible victims were the Small Expendable Deployer System (March 1994) and the Miniature Sensor Technology Integration (also March 1994). [cont'd]
In 2009, Landsat 5, a satellite jointly operated by NASA and the U.S. Geological Service, also began to spin out of control, again during an August peak of the Perseid meteor shower. Far below, satellite trackers scrambled to find out what had happened. Had the satellite been hit by a stray rock from space? Was the culprit a solar storm or an impact with one of the thousands of pieces of orbiting debris shed from other spacecraft or booster rockets? Or was the cause more alarming: an attack from a hostile nation?
Satellite failures such as these have cost the governments of the world billions of dollars. So it might appear strange that there are still huge gaps in our understanding of what can go wrong in space. Space agencies all over the world often struggle to figure out what has happened when some piece of hardware in orbit goes haywire. How can they differentiate between a malfunction caused by a tiny rock hurtling in from interplanetary space and an errant screw left in orbit decades ago? And more important: How can engineers properly protect spacecraft from such projectiles—whatever their provenance?
We live in a time when sending people to Mars is beginning to look like a real possibility, China has announced its plans to set up a moon base by 2030, and soldiers in the field depend on GPS satellites. And that’s not to mention regular citizens, who are finding it hard to live without the things satellites provide: long-distance communications, much of their entertainment, and help navigating around town. Therefore, many of us in the space sciences community are renewing our efforts to understand the myriad natural and artificial dangers that spacecraft constantly face.
After 53 years of sending equipment into space, planet Earth has accumulated a thick mantle of space debris. We are able to track about 20 000 objects—although the estimates that account for objects under 10 centimeters in diameter put the total number closer to 600 000. When a satellite hits an object in this belt, the collision may cause the satellite to splinter into many fragments, which then add to the accumulating debris. And because the satellite has been destroyed or crippled, it becomes necessary to send a replacement, increasing the potential for more debris later on.
Satellite designers can fashion shields that guard reasonably well against impacts with small pieces of space debris. And satellite operators can usually track and avoid the larger chunks, although sometimes that process doesn’t go so smoothly. Within the past year, both the space shuttle Discovery and the International Space Station had to take rapid evasive action to dodge one especially treacherous object. And in February 2009, Russia’s defunct Cosmos 2251 satellite collided with an Iridium Communications satellite, unlikely to be the last accident of its kind. Such incidents have prompted spaceflight operators to coin the term ”space situational awareness.” It’s an acknowledgment that you need to see and understand what’s going on in space. The growing focus on space situational awareness comes partly from the sheer number of satellites now in orbit and partly from the vulnerabilities inherent in the crowded, busy lanes of near-Earth space.
Adding to these concerns, a 2007 Chinese antisatellite test showed that even this newcomer to the space race is capable of destroying a target in low orbit using a ground-based missile. Another worry is the growing popularity of small satellites, often dubbed microsats or nanosats—names that don’t reflect their real size—which typically measure a few centimeters. Because these objects are hard to track and maintain in their proper orbits, they pose headaches for the people whose job it is to catalog everything circling Earth.
In the United States, the Air Force and NASA bankroll most of the fundamental research on reducing the threat of collision in space. Both organizations have obvious interests in being able to travel in space or to place useful objects into orbit.