Published Aerospace Power Journal - Winter 2000

Using Lasers to Remove Orbital Debris

Col Jonathan W. Campbell, USAFR*

 *Colonel Campbell is the individual mobilization augmentee to the commander of the College of Aerospace Doctrine, Research and Education at Maxwell AFB, Alabama.

For several years now, the Air Force and the National Aeronautics and Space Administration have been working to understand orbital space debris with respect to the amount of risk it presents to spaceflight. Although the debate concerning the quantitative risk continues, everyone agrees that such risk exists and is expected to grow as our use of space expands. Associated with the first debate is a second question dealing with the threshold at which the risk becomes too high. This brief article does not attempt to answer these nontrivial questions concerning the definition of acceptable risk; however, it does bring to the reader’s attention the following thoughts.

Mankind’s expansion into space is vital to our future for many reasons. One of the most immediate and compelling is the need to respond to the threat of a potentially catastrophic impact from a meteorite, asteroid, or comet. We have no choice. We must expand into space, regardless of the risks. We must increase our capabilities there.

In addition to orbital debris, there are many other risks associated with spaceflight, and take-action thresholds must be balanced across the entire set of risks associated with a mission. In the space business, we decide at what threshold risks become too high and what action is warranted. The take-action threshold we assign to a particular risk is balanced against the possible impact on the mission, resources available to accomplish that mission, and our perception of the technical and cost feasibility of approaches for reducing that risk. The bottom line is that if we can conveniently reduce risk, then we should. With regard to the risk posed by orbital debris, we can—because of a promising, convenient solution.

Presently, we have significant quantities of orbital debris of all sizes at all altitudes and inclinations. The distributions are not uniform, with debris ranging in size from the microscopic to several meters, such as worn-out satellites and upper stages of rockets. Fortunately, small objects far outnumber the large ones. However, speed as much as size creates risk. Typical closing velocities for a collision with orbital debris are on the order of 20,000 miles per hour. It is therefore hardly surprising that a collision with a satellite could result in mission failure.

The state of the art in protection from orbital debris allows us reasonably affordable, effective shielding against hypervelocity objects less than one centimeter (cm) in size. Yet, as size increases, so does cost—to prohibitive levels. We have calculated the cost for increasing the protection for critical modules on the space station from 1 cm to 2 cm to be on the order of $100 million for launch costs alone, not to mention research and development as well as manufacturing costs.

For objects greater than 10–30 cm in size, the space station relies on Space Command’s tracking network to provide early warning. If an object is expected to come too close, the station maneuvers to avoid it. The total costs of this maneuvering system, however, are also substantial. In addition, this protection is not foolproof since Space Command may have difficulty maintaining continuous tracking of objects below 30 cm in size. In the event of a solar flare, for example, some objects may be lost for days at a time.

Presently, we have no protection against the approximately 150,000 objects within the size range of 1–10 cm. A hypervelocity collision between a tennis ball (approximately 5 cm) and a satellite would probably convert that satellite into orbital debris. Indeed, the cascade effect resulting from a large object being broken up into many smaller objects is a great concern for many scientists who study orbital debris.

Although the probability of a collision with a single asset is very low, one must also ask the global question, What is the probability of a collision occurring within the fleet—the entire population of space assets? When we look at the entire cross section, the probabilities become significantly larger. Indeed, current analysis indicates that, given current levels of orbital debris and asset cross sections, the probability is one collision per year. Something, somewhere is probably going to get hit next year, and hardware loss may be significant.

This is a global problem, as most environmental problems tend to be. We cannot make a single project responsible for cleaning it up. Indeed, costs to the fleet will be astronomical if each and every asset has to provide its own shielding and maneuver capabilities. Therefore, we must attack this problem at a higher level, and the most appropriate level may be an international collaboration led by the United States.

So what can be done, if anything? The answer lies in the convenient approach mentioned earlier. We have identified an elegant, cost-effective, feasible laser-technology approach as a global solution to solve a global problem. Further, this solution is international in scope because it solves the problem for everyone.

If a high-energy laser pulse of sufficient intensity strikes a piece of orbital debris, a micro-thin layer of material is ablated from the object’s surface. This superhot vapor rapidly expands outward, imparting a tiny amount of force to the object. Since current laser technology easily produces 10 to one hundred pulses per second, the ablation interaction can be rapidly repeated, over and over. The cumulative thrust acting on the object, if applied at the appropriate point in the object’s orbit, is sufficient to lower its perigee below two hundred kilometers (km). At that altitude, atmospheric drag increases sufficiently to terminate the object within a few hours.

Using this approach, studies have shown that a single laser facility, costing less than $200 million and operating near the equator, could remove all orbital debris up to 800 km elevation in two years. Since satellites typically cost several hundred million dollars each and given the half-billion-dollar price tags on shuttle and Titan launches, this investment is relatively small, considering the potential return. In addition, as discussed above, we are already well above these levels of funding to provide risk reduction to some individual assets. In addition, technology development in this area will serve as a springboard to many other approaches on a larger scale, such as using laser-power beaming to deflect meteorites, asteroids, and comets, as well as propulsion for interstellar missions.

Again, we have identified a promising, convenient, and elegant laser approach to reduce the risk to spaceflight posed by orbital debris. Only this nation has the capability to accomplish this project. If it is going to happen, we have to make it so.  n

Maxwell AFB, Alabama

Disclaimer

The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.

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