Document created: 21 February 01
Published Aerospace
Power Journal - Spring 2001
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APJ continues to stimulate aerospace integration with great material like Col Jonathan W. Campbell’s “Using Lasers to Remove Orbital Debris” (Winter 2000). Such ideas are exactly what we need as we evaluate the Air Force’s core missions in space beyond force enhancement and space support.
An operational capability to remove orbital debris from our space lanes of commerce and communication is a logical step to make space a safer place to operate. However, we must be careful not to oversimplify the problem, lest the common observer develop a mental picture of Air Force men and women shooting down debris like Han Solo and Luke Skywalker popping off TIE fighters in the movie Star Wars.
Such a capability would provide a tremendous opportunity to train a new cadre of space operators and maintainers. It would also give us an ability to develop operational concepts of air-space clearance, deconfliction, and collateral-damage estimation, as well as improve our modeling and simulation of laser effects in space.
However, at least three considerations will probably make clearing the skies in two years for “less than $200 million” highly unlikely. First, Colonel Campbell states that a laser pulse, “applied at the appropriate point in the object’s orbit,” could lower the object’s perigee and hasten its disintegration in the upper atmosphere. Since he advocates only a single laser on the equator, Kepler will dictate very few such opportunities. A single ground site will have few (on the order of two to six, depending on altitude and inclination) opportunities per day to see an object, let alone at the required “appropriate point.”
Second, for every laser pulse, there will always be some finite chance that it will create more debris rather than eliminate it. Laser effects on specific materials can be modeled and tested on the ground, but often we have no way of absolutely predicting the ultimate effect in space. We may very well find that after a number of laser pulses, we no longer have a single 8 cm piece of debris but two untrackable and equally deadly 4 cm pieces of debris.
This leads to my last point. US Space Command currently tracks nearly nine thousand objects orbiting Earth. The real worry is not the objects we see but those we don’t. There are potentially as many debris items lurkingout there that are too small to track (down to 1 cm). Investment in a debris-removal system must be accompanied by an improved search/ surveillance capability.
These issues are not insurmountable but point to the complex issues facing the Air Force in space and serve to show that there are few easy answers in this growing mission area. The threat to space assets and the Space Station Alpha crew is real, if remote, and an 80 percent solution is probably better than no solution. A modest test using existing lasers, like the US Army’s mid infrared advanced chemical laser (MIRACL), would provide an opportunity to demonstrate the feasibility of this approach for a fraction of the cost.
Maj Brad Broemmel, USAF
Colorado Springs, Colorado
First of all, thanks to Major Broemmel for his thoughtful comments and for providing the opportunity to continue the dialogue on "Using Lasers to Remove Orbital Debris." This relates to an issue facing the Air Force in space that is becoming increasingly important. While we feel that our development and research of this idea at the conceptual level has been comprehensive, and while we respectfully disagree with Major Broemmel’s opinion that this approach is unlikely to be successful, we always welcome additional looks at our advanced research.
Major Broemmel is correct in saying that our proposed single ground-based laser facility would only "see" any one 1–10 cm debris object two to six times per day, depending on altitude. Estimates continue to be debated and vary widely as to the total amount of 1–10 cm orbital debris. However, middle-of-the-road estimates place it at 150,000 objects, with roughly 80,000 objects below 800 km altitude. Since we are interested in all 80,000 objects passing over our facility two to six times per day, we will have in the beginning 160,000– 480,000 potential targets per day. This works out to be over 50 potential targets of opportunity per minute. Extending our facility’s capabilities with additional funding to 1,500 km coverage would simply increase the number of potential targets.
Laboratory experimentation in vacuum at Oak Ridge National Laboratories and Wright-Patterson Air Force Base have shown that for typical orbital-debris materials, microablation tends to fuse the object’s surface. This fusing actually strengthens the structural integrity of the object and reduces the probability of particle breakup. Furthermore, should particle-debris breakup occur after a 200 km perigee has been achieved, the cloud of particles will simply deorbit faster due to drag than as a single object. There is no current protection against 1–10 cm objects. If an 8 cm object is broken into two 4 cm objects, then at least one of those objects will be deorbited in the engagement. Hence, an 8 cm object will have been replaced with a 4 cm object (that will be brought down on a later orbit), achieving our mission of reducing the risk to spaceflight. Should an unlikely breakup occur, resulting in reducing the object to less than 1 cm in size, then we are now within the envelope for protection by onboard shielding. Major Broemmel is astute in recognizing that the laser is only half the solution. The other half is a sufficiently capable sensor system. Our conclusions are based not only on extensive laser research, but also on thorough radar, optical sensor, and pointing and tracking findings as well. One example is the Haystack radar, which has demonstrated the capability to track objects in low earth orbit (LEO) down to 1 cm in size.
Again, we reaffirm the derivation obtained from years of research analysis and experimentation. All 1–10 cm orbital debris up to 800 km in altitude can be removed in two years with one laser facility located near the equator for approximately $200 million. We heartily agree with Major Broemmel that a demonstration is the next step. Part of that is planned to be a joint Air Force/NASA collaboration to conduct a laser-calibration demonstration in space from Maui that will demonstrate the capability of existing technology to successfully engage a debris object in LEO.
Col Jon Campbell, USAFR
Huntsville, 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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