Using a long tether to deflect threatening asteroids

possibility, but have considerable political and technical obstacles. Would the rest of the world trust us to nuke an asteroid? Would we trust anyone else? And would the asteroid break into multiple asteroids, giving us more problems to solve?” (we note two other methods being proposed — gravity tractor and reflective sheeting; see below).

The research was first presented last month at the NC State Graduate Student Research Symposium in Raleigh, North Carolina. The research, “Trajectory Diversion of an Earth-Threatening Asteroid via Elastic, Massive Tether-Ballast System,” has also been reviewed and accepted for presentation this September at the American Institute of Aeronautics and Astronautics SPACE 2009 Conference and Exposition in Pasadena, California.

Two other methods for deflecting incoming asteroids are being proposed (see more details, and references, in “New Ideas for Deflecting Earth-threatening Asteroids,” 26 March 2009 HS Daily Wire):

Gravity tractor
A “gravity tractor” could deflect an Earth-threatening asteroid if it were deployed when the asteroid was more than one orbit away from the potential impact, according to a new study. If the space rock was found heading straight for Earth, a combination of techniques — including a gravity tractor — may save the day (see 29 July 2008 HS Daily Wire). The study, carried out by NASA’s Jet Propulsion Laboratory in Pasadena, California, shows that the weak gravitational pull of a nearby spacecraft could deflect a hypothetical asteroid 140 meters across, big enough to cause regional devastation if it hit Earth. “Prior to this study, the gravity tractor deflection technique had been proven in only a conceptual way,” says Clark Chapman of the Southwest Research Institute in Boulder, Colorado, who was not involved in the study. “Although there were few, if any, substantive criticisms of these concepts, some of us had the feeling that the ideas were viewed as quaint but not-ready-for-prime-time,” he says. “The JPL study gives it the solid engineering underpinnings that we never really doubted, but now are there for anyone to see.” Exactly how much of a push is needed to deflect an asteroid depends on how long before a potential impact the intervention begins, and what kind of orbit the object is going to follow in the interval, says Rusty Schweickart, a former Apollo astronaut and chairman of the B612 Foundation, which funded the study.
Reflective sheeting
A Ph.D. student with the University of Queensland’s School of Engineering has won top prize in an international competition for her plan to wrap a giant asteroid with reflective sheeting to prevent a collision with the Earth. Her proposal was made specifically for Apophis — an asteroid estimated to be about 270 meters across which will pass close to Earth in 2029, well inside the orbit of the Moon — but it applies to other asteroids as well.
Mary D’Souza put forward her proposal and took out the top prize in an international competition to find new ways of stopping asteroids from hitting our humble, little planet. With her paper, entitled “A Body Solar Sail Concept for the Deflection of 99942 Apophis,” D’Souza beat entries from around the world in the Space Generation Advisory Council’s Move An Asteroid 2008 competition. She later presented her ideas at the International Astronautical Congress, the world’s largest space conference, held in Glasgow at the end of September 2008.