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article imageNEOShield to address global threat of near-Earth objects

By JohnThomas Didymus     Jan 27, 2012 in Science
Recent cases of close approaches to the Earth by space bodies called near-Earth objects (NEOs) have lead to the emergence of a new international effort to address the threat posed by these celestial flotsam.
According to, the project christened NEOShield is being supported by the European Commission and involves research institutes, universities and other organizations in Germany, France, United Kingdom, Spain, U.S. and Russia.
BBC reports Professor Alan Harris, senior scientist and NEOShield project leader at the German Aerospace Center's Institute of Planetary Research (DLR) in Berlin-Adlershof, Germany, explained: "We're going to collate all the scientific information with a view to mitigation. What do you need to know about an asteroid in order to be able to change its course, to deflect it from a catastrophic course with the Earth?"
NeoShield, according to BBC, will be conducting a three-and-half-year study at the end of which it will recommend feasible measures for addressing the NEO threat, and organize for implementation of the measures it recommends. While the WISE project has identified close to 1,000 very large NEOs (greater than 1,000m in size) representing an estimated 90 percent of the total, there is evidence that there may be as many as 19,500 NEOs in the 100-1,000m size range that have not been identified and tracked. Astronomers are looking to deploy new improved telescopes to help track objects in this size range.
The goal of NEOShield, according to, is to "organize, prepare and implement mitigation measures" for averting a major asteroid or meteor impact event. NEOShied will be investigating the most technically feasible and promising methods yet identified for countering asteroid impact threat, namely, kinetic impactors, gravity tractors and explosive blast-deflection method.
Kinetic impactor
The kinetic impactor method, according to, involves launching bodies which impact with and nudge the targeted space body out of its Earth threatening trajectory. According to Professor Alan Harris, "The scientific side of this will include the analysis of observational data on NEOs and laboratory experiments in which projectiles are fired at asteroid surface....with different compositions, densities, porosities and structures. We need to understand how the momentum transfer from a kinetic impactor to an asteroid depends on the physical characteristics of the asteroid."
BBC reports Harris explains that the effect of such impact will depend on "what sort of asteroid it is, that is, its physical characteristics. What's its surface like; how porous or dense it is? This is really something you would want to test with a demonstration mission."
Gravity tractor
The concept of gravity tractor involves using the gravitation pull of a space craft, as it flies close to the NEO, to deflect the trajectory of the NEO. According to Harris: "We'll be looking in detail at the tricky technical issues associated with autonomous control of a spacecraft in the immediate vicinity of a large, rotating, potato-shaped asteroid, and ion thrusters that may have to function continuously and reliably over a period of 10 years or more."
According to BBC, the gravity tractor method involves positioning a spacecraft close to the NEO and using long-lived ion thrusters to maintain separation between the two. The craft can then exploit the gravitational attraction between both bodies to pull the asteroid or comet off its trajectory. According to Harris: "It's like using gravity as a tow-rope. It's not straightforward of course. Can you be sure those thrusters will keep working for the time they're needed - a decade or more? Do you have confidence that the spacecraft can look after itself autonomously all that time? These are the sorts of technical problems we will look at."
Explosive blast-deflection method
In the explosive blast-deflection method, a nuclear bomb is used to blow up the asteroid. The option, according to, is considered politically controversial and delicate, but some scientists considered it is worth investigating because it could be the only available option in the event of a major impact threat looming at very short notice. Harris explains: "For an asteroid with a diameter of more than half a mile or a warning time of less than five years, the 'blast-deflection' method may be the only feasible approach. Our Russian colleagues will be looking in detail at the physics of how an asteroid would respond to a nuclear explosion near, or on, its surface."
While there is some skepticism about the blast-deflection method, BBC reports Dr. Ralph Cordy, one of the scientists involved in the project, says: "What we want to do is take a comprehensive view, to try to draw everything we know together, with the right expertise so that this thing has momentum. We will look at the spectrum of techniques, trying to see which ones might be applicable in different cases. And then taking it to a level where we do some detailed design work on a possible mission to demonstrate one or more of these techniques."
Daily Mail reports that the European Commission is investing about 4 million Euros, and an additional 1.8 million Euros is coming from institutional partners. It is hoped that at the end of the study NEOShield would have developed an implementable plan to present to the European Commission for consideration.
More about NEOShield, nearearth objects, Asteroids
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