It’s hard to know whether to be more concerned about the debris spewed into orbit by the collision of two satellites or by the fact that no one was able to predict the collision before it happened. Neither bodes well for the long-term safety of space operations.

An American communications satellite owned by the Iridium network and a no-longer-functioning Russian communications satellite slammed into each other 790 kilometers above northern Siberia in what appears to be the first collision between two intact satellites.

Hundreds of fragments were strewn into space, where they will pose at least a small additional hazard to other satellites or spacecraft that move through the area. The international space station, orbiting 350 kilometers up with three astronauts aboard, will face an elevated but still very small risk of being struck by space debris.

Those who thought that our nation’s space tracking systems could see such things coming will be surprised to learn that there are gaps in coverage and capabilities. The military does indeed track some 19,000 objects in space, including active and nonfunctioning satellites, hordes of debris fragments, and thousands of unknown objects that might threaten the safety of American satellites. It publishes their coordinates and velocity in a catalog on a Web site that anyone can view free of charge.

But the military doesn’t calculate all possible collisions. It lacks the computing power, trained personnel and sensor capabilities to pull off that feat. Instead, it focuses primarily on potential collisions that might endanger the space station and shuttles, its own satellites and those of other federal agencies.

A private company fills part of the gap by assessing potential collision threats to other active satellites on a daily basis. It publishes a top 10 list of likely close encounters.

As it turned out, the satellite that was demolished did not make the top 10 list that day, partly because other satellites looked even more likely to pass close to debris and partly because these calculations are inherently imprecise. Iridium, which is ultimately responsible for its own satellites, apparently had no clue that one of them was about to be smashed.

The new debris adds to the growing amount of junk accumulating in orbit. Thus far the annoying objects have not had a major impact on human or robotic missions into space, but there are grave concerns for the future. At some cluttered altitudes, collisions are producing debris faster than gravity can eliminate it. If the trend is not reversed, one can imagine a time when it could be too risky or too expensive to fly spacecraft through the debris fields.

The United Nations has adopted voluntary guidelines to minimize the creation of new space debris. It recommends such steps as designing spacecraft so that no debris is released during normal operations, removing leftover propellants at the end of a mission and moving nonoperational satellites out of congested orbits.

The looming problem yet to be addressed is how to get rid of the debris and objects already up there and proliferating with every collision.