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NASA Outlines Asteroid Deflection Program
An anonymous reader submitted a link to an International Herald Tribune story about NASA's answer to the movie 'Armageddon'. Specifically, they've outlined a plan to deflect a planet-killer asteroid. "In 1998, Congress gave NASA's Spaceguard Survey program a mandate of 'discovering, tracking, cataloging and characterizing' 90 percent of the near-Earth objects larger than one kilometer (3,200 feet) wide by 2008. An object that size would probably destroy civilization. The consensus at the conference was that the initial survey is doing fairly well although it will probably not quite meet the 2008 goal." With this tracking system in place, scientists are hopeful an intervention could be staged before any grim choices have to be made. Assuming they have the money and manpower needed for the effort, NASA has actually outlined a pair of procedures that dove-tail with each other: "First we would deflect the asteroid with kinetic impact from a missile (that is, running into it); then we would use the slight pull of a 'gravity tractor' -- a satellite that would hover near the asteroid -- to fine-tune its new trajectory to our liking. (In the case of an extremely large object, probably one in 100, the missile might have to contain a nuclear warhead.) To be effective, however, such missions would have to be launched 15 or even 30 years before a calculated impact."
There was an interview with a guy on NPR concerning this...from what he was saying, the answer is basically, yes...things in space don't change direction unless something else hits them, so in theory, it is possible to predict an impact 30 years in advance. The main problem is that our ability to model trajectories isn't fine-grained enough to do so, yet.
ZuluPad, the wiki notepad on crack
1 km could be a civilisation killer? don't think so: http://www.lpl.arizona.edu/impacteffects/
Your Inputs:
Distance from Impact: 250.00 km = 155.25 miles
Projectile Diameter: 1000.00 m = 3280.00 ft = 0.62 miles
Projectile Density: 3000 kg/m3
Impact Velocity: 40.00 km/s = 24.84 miles/s
Impact Angle: 80 degrees
Target Density: 2500 kg/m3
Target Type: Sedimentary Rock
Energy:
Energy before atmospheric entry: 1.26 x 1021 Joules = 3.00 x 105 MegaTons TNT
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.8 x 106years
Atmospheric Entry:
The projectile begins to breakup at an altitude of 67700 meters = 222000 ft
The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 39.8 km/s = 24.7 miles/s
The impact energy is 1.25 x 1021 Joules = 2.98 x 105MegaTons.
The broken projectile fragments strike the ground in an ellipse of dimension 1.1 km by 1.08 km
Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the Earth's rotation period or the tilt of its axis.
The impact does not shift the Earth's orbit noticeably.
Crater Dimensions:
What does this mean?
Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.
Transient Crater Diameter: 17.2 km = 10.7 miles
Transient Crater Depth: 6.08 km = 3.77 miles
Final Crater Diameter: 25 km = 15.5 miles
Final Crater Depth: 0.78 km = 0.484 miles
The crater formed is a complex crater.
The volume of the target melted or vaporized is 10.9 km3 = 2.62 miles3
Roughly half the melt remains in the crater , where its average thickness is 47.1 meters = 154 feet
Thermal Radiation:
What does this mean?
Time for maximum radiation: 0.54 seconds after impact
Visible fireball radius: 16.6 km = 10.3 miles
The fireball appears 15.1 times larger than the sun
Thermal Exposure: 6.78 x 106 Joules/m2
Duration of Irradiation: 280 seconds
Radiant flux (relative to the sun): 24.2 (Flux from a burner on full at a distance of 10 cm)
Effects of Thermal Radiation:
Much of the body suffers third degree burns
Newspaper ignites
Plywood flames
Deciduous trees ignite
Well, the inverse square law plus the low albedo (http://en.wikipedia.org/wiki/Albedo/) of http://www.aanda.org/articles/aa/full/2002/39/aah3 638/aah3638.right.html/ most asteroids would necessitate an incredibly bright "light". Anyone feel like whipping out a napkin to do some calculations? I doubt if the visible spectrum would be better than radio wavelengths (after all, we're mainly after large objects, right?). I wonder what the design restrictions would be for a radar which has to wait several hours for an echo would be: I'd guess a fluorescent screen wouldn't be optimal! :-)
To improve results, you'd like to have at least two or preferably more observation points. Looking at NEO asteroid orbits http://neo.jpl.nasa.gov/orbits// projected onto the ecliptic is a scary sight. Looking at them in three dimensions is rather more reassuring.
Right now, I'd guess that Earth-based telescopes are the more economical alternative: easier to service, no pesky problem with energy supply or orbital station keeping. One drawback is that we need longer series of observations in order to resolve asteroidal orbits: hence the recurring "alarm bells" when a newly discovered asteroid rates high on the Palermo or Torino scales, only to be downgraded once more observations are matched to it.
Ya know, Armageddon (the movie) cost about $140 million to make. For that same budget, we probably could have finished a very good survey of any Near-Earth Asteroids, create a detailed mitigation plan, and start building prototype hardware to send up. You probably could even get Jerry Bruckheimer to film an overly dramatic documentary filled with lots of sound effects in space and slow-mo hero scenes.