Commentary | Space Debris Mitigation: A New Hope for a Realistic Solution?
On Jan. 11, 2007, a Chinese antisatellite missile test completely fragmented a Chinese target satellite into millions of pieces of debris — nearly 800 debris fragments 10 centimeters or larger, nearly 40,000 debris fragments between 1 and 10 centimeters, and some 2 million fragments of 1 millimeter or larger.
On Feb. 10, 2009, the operational33 and decommissioned Kosmos-2251 satellites collided at a speed of 42,120 kilometers per hour, destroying both satellites. In July 2011, more than 2,000 large debris fragments resulting from this collision were detected.
The international space station is routinely dodging debris that are tracked by ground-based radars.
Space debris constitutes a continuously growing threat to satellites and manned spacecraft. Very small debris creates potentially nonthreatening damage. Large debris can be detected by ground-based radars and avoided by spacecraft maneuvers. However, small- to medium-sized debris in low or medium Earth orbits constitutes the biggest threat. These orbits have the largest density of debris and the highest relative speeds, while the atmospheric drag is small enough that it may take centuries to have the debris re-enter the atmosphere.
In 1978, NASA scientist Donald J. Kessler showed that if the density of space debris in low Earth orbit is high enough, each collision generating space debris would increase the likelihood of further collisions. One serious implication is that the multiplication of debris in orbit will render space exploration, and even the use of satellites, increasingly dangerous and costly for many generations.
Multiple solutions to remove space debris have been explored and published.
One of these solutions involves physical contact between debris and the spacecraft:
- Shielding of in-orbit spacecraft has been considered. However, the satellite community has recognized that the sheer weight of any reasonably efficient shielding would make launch not economically viable. Furthermore, the speeds involved in physical contacts would generate a cloud of additional debris.
- “Catcher” spacecraft have also been proposed. Conceptually, highly mobile and agile spacecraft equipped with a “catching device” like a net or a robotic arm could be launched from Earth to intercept and catch debris. However, unless the catcher spacecraft are able to precisely match the speed and direction of the debris, any high-speed physical contact between a component of the catcher spacecraft and space debris will result in a collision, multiplying the debris. The cost of designing, developing, testing and launching such a spacecraft, with sufficient fuel onboard to repeatedly intercept multiple debris fragments at different speeds, orbits and altitudes, does not seem to be economically viable.
Other solutions would use high-power lasers that could vaporize the surface of the debris in space, deflecting it and possibly changing its orbit to intersect the atmosphere. These solutions have the advantage of not requiring physical contact with the debris.
- Space-based laser systems require designing, building, launching and operating a spacecraft equipped with a very high-power laser system. Such a design is utterly complex and expensive and very likely will not be economically viable.
- Airborne laser systems are facing the same obstacles: The Boeing YAL-1 Airborne Laser Test Bed program, which was designed as a missile defense system to destroy tactical ballistic missiles, was terminated because of cost.
- Ground-based laser systems are handicapped by the very long propagation distance, atmospheric absorption and distortion of the laser beam. Such parameters make this solution also not economically viable. Furthermore, being located in a single country, a ground-based laser system would raise serious political issues within the international community because of its implied antisatellite capability.
In summary, the cost/benefit ratio of the above solutions appears to be the main reason none has been implemented to date to proactively mitigate the most dangerous debris.
A more affordable approach for cleaning low and medium Earth orbits of small- to medium-sized orbital debris may be achievable. This approach would use the principle of deflecting an electrically charged, moving object in a magnetic field. The old television tube is probably the most common example of this principle, where electrical charges (electrons) are deflected by the magnetic fields generated by the tube deflection coils.
The application of this principle would use a space-based electron gun to generate an electron beam directed at the orbital debris. The beam would remotely impart an electric charge to the debris. Earth’s magnetic field would exert a force on the electric charge of such debris crossing the magnetic field at high speed, modifying its orbit. Over time, the orbit would become highly elliptical and would intersect the upper atmosphere, where the debris would vaporize or fall to Earth. Preliminary calculations have shown that this concept is sound. The benefits include:
- Cost: Lower cost is the major advantage of electromagnetic deflection.
- Feasibility: There is no new or speculative technology to develop. Used in particle accelerators and in millions of old-style television tubes, the electron gun technology is very mature. The energy used to generate the electron beam is orders of magnitude lower than high-power lasers.
- Risk: It would reduce the probability of creating additional debris by avoiding any physical contact.
The electron gun device could be integrated in an add-on module to the international space station.
The ISS is already in space, and there would be no new spacecraft to develop and launch.
The ISS has a large power-generation capability, while the electron gun would require only intermittent and modest amounts of energy to operate.
This solution would be more easily adopted by the international space community, since it does not have the capability to damage or destroy a spacecraft. This feature would be expected to encourage support and funding of the project by all the nations involved in space operations. The electromagnetic deflection concept would best be implemented as an international program, managed and coordinated by the space agencies of several countries.
As with any new technology development, there are still open questions associated with the deployment of this concept. A formal study would have to be conducted by space specialists to validate and test the concept and determine the optimum design parameters.
Areas that should be explored include:
- The ability to precisely direct the electron beam at the debris. Although electrons can be sent at near-light speed, they are also deflected by the very magnetic field that will act on the debris, requiring precise aiming of the electron gun.
- The ability of the target to store the electrons.
- The retention of the charge by the target. Due to the constant bombardment of the target by the solar wind that comprises ionized particles, it is expected that the charge of the target will dissipate over time.
- The dynamic response of the target trajectory under the influence of the deflecting force.
In conclusion, civil and government satellites as well as manned missions are currently exposed to the growing risk of collisions with debris, which may result in costly incidents, or accidents that could take human lives. It is essential to have a solution implemented as soon as possible. As of today, the electromagnetic deflection approach seems to be one of the most cost effective, most realistically achievable and least risky. It deserves to be further evaluated and pursued.
Michael Bonard is former director of Aeronautical Services for Comsat Mobile Communications. He has held other positions in engineering, marketing and program management with Comsat and Rockwell International Collins Radio, specializing in telecommunications systems, avionics engineering and satellite communications.