The in-orbit collision that destroyed a working Iridium communications satellite high above
Feb. 10 officially served notice that the threat posed by orbital debris is real, getting worse and must be addressed with a sense of urgency by governments and commercial satellite operators.
The danger cannot be eliminated, of course, but it can be mitigated through measures including disposal techniques for spent rocket stages and satellites nearing the end of their service lives; operating guidelines for satellite owners; close monitoring of the orbital environment; and collision avoidance procedures. These are all being implemented, to varying degrees, but clearly more needs to be done.
Experts have been warning for years about the growing danger of collisions as Earth orbit becomes increasingly crowded with man-made objects, the vast majority of them unattended space junk. The
U.S.
military’s Space Surveillance Network now tracks some 19,000 objects the size of a baseball or larger, substantially more than a decade ago. On-orbit smashups, such as the one between Iridium 33 and Cosmos
2251, a
spent Russian communications satellite that had drifted down from a higher orbit, further increase the risk by adding hundreds if not thousands of pieces of junk to the tally.
The probability of losing an operational satellite in an on-orbit collision remains low. But given the high cost of building and launching satellites, and the critical services they provide, even a low risk can be unacceptably high. In Iridium’s case, the risk inherent in operating a constellation of 66 satellites in the relative chaos of low Earth orbit is offset somewhat by the fact the loss of one can be absorbed with minimal disruptions of service. With geostationary-orbiting satellites, the collision risk is lower since they all move in the same direction at the same speed. But losing a geostationary orbiting satellite is costly – these platforms are often large and complex – and can result in major service outages across entire regions.
It is unclear whether the Iridium 33-Cosmos 2251 collision could have been avoided. Since both spacecraft had known orbits, whose parameters were updated regularly by the Space Surveillance Network, one could argue that Iridium’s flight controllers at Boeing should have seen this coming and perhaps taken evasive action. But moving satellites is risky and costs precious station-keeping fuel; meanwhile, close approaches, or conjunctions, involving Iridium satellites occur fairly frequently. Moreover, the data made publicly available via the Space Surveillance Network is fairly coarse; moving a satellite based on that alone could actually increase the danger of a collision. Under the U.S. Commercial and Foreign Entities (CFE) program, non-U.S. government satellite operators can request more detailed information and analysis from the U.S. Air Force-led Joint Space Operations Center when a conjunction appears likely. It is not clear whether Boeing did so in this case.
The Air Force, for its part, is responsible for the safety of
U.S.
government assets, with astronaut-carrying vehicles ranking first on the priority list, national security satellites second. The service has not been assigned the mission of warning non-government satellite operators of all brewing collision scenarios, and whether it has the resources to do so is a matter of debate.
This particular episode aside, however, there are things that can be done broadly to limit the probability of orbital collisions. The United Nations, for example, in 2007 endorsed debris mitigation guidelines similar to those adopted in 2002 by the Inter-Agency Space Debris Coordination Committee, which includes the major spacefaring nations. These guidelines are voluntary; nobody is 100 percent compliant. But some operators have gone the extra mile: The Iridium satellites, for example, were originally intended to be steered back into the atmosphere before the end of their service lives. Had the Cosmos 2251 satellite, which launched in 1993 – well before the guidelines were adopted – and operated for only two years, been designed with a similar specification, the Feb. 10 collision never would have happened.
Meanwhile, some of the world’s leading geostationary satellite operators are working to create a clearinghouse for posting and sharing high-precision satellite location and maneuvering data. A prototype of this center already is up and operating.
The center’s effectiveness – and orbital safety in general – would be enhanced if CFE procedures for providing more precise data and conjunction analyses to non-U.S. government operators were streamlined; some complain the current arrangement is cumbersome and time consuming. Also worth examining is whether some higher-precision data can be made regularly available to certain parties, such as operators of low Earth orbiting satellites.
Under any circumstances, the CFE, currently a pilot program due to expire at the end of this year, must be reauthorized by the U.S. Congress as a full-fledged program.
Finally, governments with space surveillance capabilities should begin a dialogue aimed at creating a system for sharing orbital data among themselves and perhaps with commercial satellite operators as well. This dialogue could be conducted as part of, or in parallel to, negotiations on operating rules for spacefaring nations, known informally as rules or the road, which U.S. President BarackObama has said he would pursue.
Orbital debris is everybody’s problem; limiting the hazard is a collective responsibility that requires action on several fronts. The destruction of Iridium 33 was a wake up call, a reminder to all stakeholders that current debris mitigation efforts and initiatives must be strengthened in the months and years ahead.
