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"      This afternoon, NASA scientists announced the findings of their NEOWISE Space Infrared Survey of near-Earth asteroids. The good news: They found 40 percent fewer medium-sized ones than were previously believed to exist, meaning that perhaps there aren&amp;#039;t as many potentially dangerous rocks passing near the planet as scientists once believed. The bad news: Even so, tens of thousands are left to be discovered.  While NASA can now keep tabs on (most of) these asteroids, its next big objective is to visit one. &amp;quot;[Sending a manned mission to an asteroid] is a natural stepping stone of our exploration into the solar system,&amp;quot; says Lindley Johnson, executive of NASA&amp;#039;s Near-Earth Object Program.  NASA plans to send astronauts to an unspecified asteroid by 2025\u2014but how the spacecraft carrying them will land is still an open question; an asteroid&amp;#039;s gravity is too weak to hold a lander. Instead, astronauts will have to grapple the asteroid to secure their ship to its surface. Inspired by fishermen, hikers and mountaineers, researchers at MIT are investigating techniques for shooting projectiles into the rock to stabilize spacecraft with cables. A capsule could travel down the tether on mechanized rollers or fly around the entire asteroid to wrap it with cable, providing astronauts with downward pressure that would serve as artificial gravity.   Projectiles would need to be tailor-made for each target (see below). &amp;quot;Some asteroids might have a metallic core, and trying to anchor to them would be like banging a nail into an anvil,&amp;quot; says Jeffrey Hoffman, a professor of aeronautics and astronautics at MIT and a former astronaut. &amp;quot;Others may just be a rubble pile, which would be like trying to pitch a tent on a snowfield.&amp;quot; Astronauts could also use these docking techniques on the moons of Mars\u2014which the Obama administration has cited as possible destinations\u2014because of their similarly weak surface gravity.  LAUNCHERS    Spring-Loaded Gun Simple and lightweight, this launcher could repeatedly shoot a projectile without using an energy source.     Electromagnetic Launcher Two metal rails flank the projectile, zapping it with a large electric current to cause high acceleration.     Steam Catapult Steam pressure drives a shuttle carrying the projectile. The shuttle shoots to the end of the rail and propels the projectile into space.  PROJECTILES    Piton Made of steel alloy and aimed at surface cracks, pitons are well-suited for asteroids with metal cores.    Harpoon Barbs on the harpoon open once it sinks into rock, preventing the anchor from coming loose.    Corkscrew After sinking the tip into its target, a motor twists the corkscrew to secure it in granular rubble. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/space/a6856/how-nasa-will-harpoon-an-asteroid/>