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- Gravity tractor solves
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Gravity Tractor – SolvesGravity tractor solvesStone ‘8 (Richard, editor for Science Magazine, National Geographic, “Target Earth,” 8-1, lexis) Then he and Stanley Love, a fellow astronaut, realized pulling would be much easier. A spacecraft could hover nearby and fire its thrusters, gently tugging the asteroid along. No harpooning or lassoing would be required. "Rather than having a physical line between you and the thing you're towing, you're just using the force of gravity between them," Lu says. The "gravity tractor" would tug the asteroid off course at a mere fraction of a mile an hour. But this subtle shift, magnified over the vastness of space, could mean missing Earth by tens of thousands of miles. Gravity tractor solvesEasterbrook ‘8 (Gregg, Editor of The Atlantic and The New Republic and Sr. Fellow at Brookings, “The Sky is Falling,” June, http://www.theatlantic.com/doc/200806/asteroids) Then what? In the movies, nuclear bombs are used to destroy space rocks. In NASA’s 2007 report to Congress, the agency suggested a similar approach. But nukes are a brute-force solution, and because an international treaty bans nuclear warheads in space, any proposal to use them against an asteroid would require complex diplomatic agreements. Fortunately, it’s likely that just causing a slight change in course would avert a strike. The reason is the mechanics of orbits. Many people think of a planet as a vacuum cleaner whose gravity sucks in everything in its vicinity. It’s true that a free-falling body will plummet toward the nearest source of gravity—but in space, free-falling bodies are rare. Earth does not plummet into the sun, because the angular momentum of Earth’s orbit is in equilibrium with the sun’s gravity. And asteroids and comets swirl around the sun with tremendous angular momentum, which prevents them from falling toward most of the bodies they pass, including Earth. For any space object approaching a planet, there exists a “keyhole”—a patch in space where the planet’s gravity and the object’s momentum align, causing the asteroid or comet to hurtle toward the planet. Researchers have calculated the keyholes for a few space objects and found that they are tiny, only a few hundred meters across—pinpoints in the immensity of the solar system. You might think of a keyhole as the win-a-free-game opening on the 18th tee of a cheesy, incredibly elaborate miniature-golf course. All around the opening are rotating windmills, giants stomping their feet, dragons walking past, and other obstacles. If your golf ball hits the opening precisely, it will roll down a pipe for a hole in one. Miss by even a bit, and the ball caroms away. Tiny alterations might be enough to deflect a space rock headed toward a keyhole. “The reason I am optimistic about stopping near-Earth-object impacts is that it looks like we won’t need to use fantastic levels of force,” Schweickart says. He envisions a “gravitational tractor,” a spacecraft weighing only a few tons—enough to have a slight gravitational field. If an asteroid’s movements were precisely understood, placing a gravitational tractor in exactly the right place should, ever so slowly, alter the rock’s course, because low levels of gravity from the tractor would tug at the asteroid. The rock’s course would change only by a minuscule amount, but it would miss the hole-in-one pipe to Earth. Gravity tractor solves best—simplest and most feasible optionMerali ‘5 (Zeeya, phd in physics, New Scientist, lexis) WHEN it comes to deflecting an asteroid that is on a collision course with Earth, "most people think of the Hollywood treatment – throw a nuclear weapon at it", says NASA astronaut Edward Lu. "That's the blast-and-hope strategy." It is hard to predict where the shattered pieces would go, and many smaller chunks might still head towards Earth. Now Lu and fellow astronaut Stanley Love at NASA's Johnson Space Center in Houston, Texas, have come up with the simplest – and least glamorous – solution yet: park a heavy spacecraft near the asteroid and use gravity as an invisible towline to tug the rock off its deadly course. Other ideas for dealing with such threats have included detonating nuclear bombs near the asteroid – rather than nuking it directly – to nudge it off track. But this carries the same risks as shattering the asteroid. Some have advocated painting the asteroid white to change the amount of solar energy it reflects, thus altering the forces acting upon it and hopefully changing its course. However, the sheer amount of paint this would require makes it impractical, says Lu. In another attempt to come up with a practical solution, the researchers envisioned landing a spacecraft on an asteroid and then steering it off course using the craft's propulsion. But an asteroid's weak gravity may not hold the spacecraft down, so it would have to be anchored to the surface – a complicated task on a surface that could be loose rubble, says Lu. To make matters worse, asteroids often rotate, and pushing on one might just set it spinning faster rather than alter its trajectory. It was then that Lu and Love realised that the spacecraft does not need to land. Just getting close and staying there is enough. For instance, their calculations showed that for a 200-metre asteroid, a 20-tonne spacecraft hovering 50 metres above the rock for about a year would change the asteroid's speed by roughly 2 millimetres per second – enough to knock it off course given time (Nature , vol 438, p 177). "This is hands down the best idea I have seen," says Erik Asphaug, an asteroid and comet specialist at the University of California, Santa Cruz. "This will work. But you need to put a large enough spacecraft out there at the right time." The spacecraft would need to begin deflecting the asteroid 20 years before a potential impact with Earth, but that is feasible, given that astronomers can predict asteroid paths decades in advance. And such large spacecraft launches are within our grasp, Lu says. NASA's multi-billion-dollar Prometheus programme, which was set to explore the outer solar system but has now been delayed, included just such a heavy vehicle, propelled by nuclear fission. Gravity tractor better than any alternativeChapman ‘7 (Clark, senior scientist at the Southwest Research Institute and president of B612 Foundation, response to Andrew Hicks & Harris Park, “Asteroid Deflection,” New Scientist, Aug. 4, lexis) Clark Chapman writes: * though there wasn't space in my comment to describe the various deflection technologies, but these things have in fact been thought about. The thrusters on the gravity tractor would be canted at about a 45-degree angle, so that their thrust misses the asteroid, yet provides the balance required. (It would be a "fatal flaw" and remarkably stupid to do otherwise, for the reason Andrew Hicks mentions.) The gravity tractor that has been discussed need not be massive. The mass of an ordinary deep-space spacecraft is sufficient to move a very small near-Earth object away from the Earth, or an NEO of almost any size away from a keyhole. As for his preferred option of using a series of explosive charges, they don't need to be explosive at all. Simply colliding with the asteroid at high velocity provides plenty of wallop. This, indeed, would be the way to deal with cases requiring more momentum than a gravity tractor can provide. Any method that requires interaction with the surface - whether those "kinetic impactors", nuclear blasts, or almost any other approach besides the gravity tractor - has a lot of uncertainties about how the asteroid will respond. It is not simple like billiard balls. As the Deep Impact mission showed when it fired a projectile into a comet, there can be an enormous blow-back of ejecta, providing additional momentum. You can't calculate in a computer how much blow-back there will be (or even spallation of a piece off the opposite side of the body) without knowing a lot about what the body is made of, its internal structure, and so on. That's the beauty of the gravity tractor. The amount of acceleration is precisely known and continuously measured during the drawn-out deflection phase. Unfortunately, there are cases for which the gravity tractor won't be powerful enough. The good news, however, is that small NEOs with long warning times are the cases we are most likely to face, not the big ones with short warning times that would have to be dealt with by kinetic impactors or even nukes. 1000s of killer asteroids, -center of gravity trickSpace Daily 09, (4/20/09, Space Daily, How to deflect asteroids and save the earth”, http://www.sciencedaily.com/releases/2009/04/090416125212.htm, SH) French, a doctoral candidate in aerospace engineering at North Carolina State University, has determined a way to effectively divert asteroids and other threatening objects from impacting Earth by attaching a long tether and ballast to the incoming object. By attaching the ballast, French explains, "you change the object's center of mass, effectively changing the object's orbit and allowing it to pass by the Earth, rather than impacting it." Sound far-fetched? NASA's Near Earth Object Program has identified more than 1,000 "potentially hazardous asteroids" and they are finding more all the time. "While none of these objects is currently projected to hit Earth in the near future, slight changes in the orbits of these bodies, which could be caused by the gravitational pull of other objects, push from the solar wind, or some other effect could cause an intersection," French explains. So French, and NC State Associate Professor of Mechanical and Aerospace Engineering Andre Mazzoleni, studied whether an asteroid-tether-ballast system could effectively alter the motion of an asteroid to ensure it missed hitting Earth. The answer? Yes. "It's hard to imagine the scale of both the problem and the potential solutions," French says. "The Earth has been hit by objects from space many times before, so we know how bad the effects could be. For example, about 65 million years ago, a very large asteroid is thought to have hit the Earth in the southern Gulf of Mexico, wiping out the dinosaurs, and, in 1907, a very small airburst of a comet over Siberia flattened a forest over an area equal in size to New York City. The scale of our solution is similarly hard to imagine. "Using a tether somewhere between 1,000 kilometers (roughly the distance from Raleigh to Miami) to 100,000 kilometers (you could wrap this around the Earth two and a half times) to divert an asteroid sounds extreme. But compare it to other schemes," French says, "They are all pretty far out. Other schemes include: a call for painting the asteroids in order to alter how light may influence their orbit; a plan that would guide a second asteroid into the threatening one; and of course, there are nukes. Nuclear weapons are an intriguing 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?" The research was first presented last month at the NC State Graduate Student Research Symposium in Raleigh, N.C. 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, CA. Directory: files files -> Answer True False 2 points Question 2 files -> Integer programming and game theory files -> 4 Integer Programming files -> Bpa vehicle Window Repair Scenario #1 task: Procure vehicle window relacement. 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