Space Debris: What Are We Waiting For?
Space debris threatens not only spacefaring nations but all people who rely on the myriad services empowered from space: telecommunications, weather, space exploration, Earth observation, space science and national security. In short, debris is an international problem for all humankind. Moreover, much debris is at high-enough altitudes that it could threaten space assets for hundreds of years before final destruction upon Earth re-entry. Orbital debris is a long-lived problem threatening future generations.
The recently released U.S. National Research Council study on NASA’s meteoroid and orbital debris programs highlighted that the debris hazard has increased in severity and scope in the last decade, just as it has every decade previously since the dawn of the space age. Recent analysis shows that regions in low Earth orbit (LEO) have officially exceeded the critical population density whereby on-orbit collisions will create more debris than can be cleansed by atmospheric drag. Once this point is reached, the debris population will grow exponentially even without any new launches. It is not a question of “if” the debris environment will cascade out of control without new space launches; without active intervention, it is only a matter of “when.” If future launches leave more mass on orbit, then, together with other deliberate collisions and accidental explosions, the deleterious growth of debris will accelerate.
In 2009, the accidental collision of the33 and Cosmos 2251 satellites was a precursor of likely events if action is not taken to actively curtail debris. Additionally, the deliberate collision orchestrated by China in 2007 to demonstrate an anti-satellite capability contributed significantly to the on-orbit debris collision risk. The combination of these two accidental and purposeful debris-generating events has increased the debris collision hazard by more than 50 percent in large portions of LEO over the last four years. So why has the space community not been roused into action?
We believe that there are two major reasons, both tied to uncertainty.
First, the analysis depicting the chain reaction of collisions on orbit usually shows events unfolding over timelines of around 100 years. It is highly uncertain how the events will unfold in the next decade or two — the much shorter timeframe that motivates any U.S. administration, corporate leaders or other decision-makers to act. It is also uncertain if instability of the space environment is the best metric to catalyze action. The collision hazard from smaller but still lethal-upon-impact debris is likely to rise to levels that will reduce operational lifetimes of satellites in LEO and increase insurance rates well before the “cascade” of breakups occurs. Of course, government-owned satellites are “self-insured,” so the taxpayers bear the financial costs of actual and potential debris impacts. However, the focus on the mathematical singularity of environmental stability may not be as relevant as identifying and monitoring mission-terminating impacts. In other words, reaching the point of instability of the environment may not manifest itself for years in observable breakup events whereas degradation of mission operations from small yet lethal debris may serve as the first indicator by which the effects of the breakup events will be felt by operational space systems. Unfortunately, while models suggest that tens of these events likely have occurred, only two have been documented since it is so difficult to determine the linkage between satellite mission degradation and impacts by debris too small to be sensed from the ground.
Second, it is difficult to quantify the financial cost of orbital debris. The costs of shielding or maneuvering to mitigate against debris impact vary widely, but some experts suggest that it may range up to about 10 percent of mission cost. However, there are very few detailed data about these costs, and it appears that most missions have managed the risk from debris with no apparent cost to actual operations. This means that thus far shielding and collision avoidance maneuvers needed to mitigate the debris hazard have been implemented within existing designs and operations. In the case of commercially owned and operated spacecraft, companies typically insure their operations against loss of service, including that which would be potentially caused by debris. Insurers report that the portion of space insurance premiums attributed to the possibility of a debris impact is less than 2 percent. But this is only part of the story.
Insurers do not account for the harm posed to other spacecraft should the insured craft create debris (e.g. nuts, bolts, paint fragments, lens caps). As stated previously, the costs to government-owned and -operated craft suffering debris impact are borne by taxpayers. We know very little about these additional costs. Taken together, then, our data are so limited about the actual operational cost of debris that we are poorly equipped to argue for investing in debris remediation or active debris removal. The problem is similar to other long-lived environmental problems such as management of nuclear waste, pharmaceutical residue in our water supplies, and greenhouse gases. As a society we are poorly prepared to tackle problems today to avoid harm tomorrow.
We applaud the greater resources going to the study of the orbital debris problem and the means to remediate risks. But the time is now for real action. While there is great uncertainty as to when the debris hazard will become unacceptable — and even more uncertainty as to how to measure the economic costs of this forcing function — it is clear that the sooner the community acts, the more manageable and less expensive the solution will be.
Darren McKnight and Molly Macauley served on the National Research Council’s (NRC) Committee for the Assessment of NASA’s Orbital Debris Programs. McKnight is technical director at Integrity Applications Inc. Macauley is vice president for research at Resources for the Future. This article represents the personal view of the authors and does not reflect the voice of their institutions or the NRC committee as a whole, nor is the article affiliated with the committee or the NRC.