As if landing on an asteroid wouldn't be dangerous enough. A microgravity experiment on the forces generated by an asteroid and its make-up suggests landing on one may cause a big avalanche.
The rubble and dust covering asteroids and comets can feel changes in what is known as 'force-chains" between particles over much larger distances than on Earth, making these surfaces less stable than previously imagined said Dr. Ben Rozitis of the Open University who presented his experiment's findings on July 4 at the National Astronomy Meeting.
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"We see examples of force-chains everywhere. When you pick an orange from a pile in a supermarket, some come away easily but others bring the whole lot crashing down. Those weight-bearing oranges are part of a force-chain in the pile," said Dr. Naomi Murdoch, a researcher at the Institut Supérieur de l'Aéronautique et de l'Espace in Toulouse in a statement. "One important aspect of such chains is that they give a granular material a 'memory' of forces that they have been exposed to. Reversing the direction of a force can effectively break the chain, making the pile less stable."
Murdoch said many smaller asteroids are thought to be entirely granular in nature -- piles of rock and gravel held together by gravity. Understanding the physics of granular materials is important for interpreting spacecraft images of these small bodies, to understand their evolution, and also to help design space missions that will interact with their granular surfaces.
The researchers said they conducted experiments inside an Airbus A300, which flew in a series of parabolic maneuvers that gave the students around 30 minutes of microgravity conditions. The Asteroid Experiment (AstEx) consisted of a cylinder filled with glass beads with a rotating drum at the center.
During several free-fall phases of the parabolic flights, AstEx's inner drum was spun and then the direction of rotation reversed. High-speed cameras imaged the top and bottom layers of beads through glass plates. After the flight, a particle-tracking program was then applied to the images, and the behavior of the beads analyzed. The team found that although particles close to the rotating surface of the drum were affected less in microgravity by the change in direction, those at the edge of the cylinder moved more than in the experiment on Earth. This implies that any changes to force-chains in low-gravity environments could be felt over much larger distances.
"A lander touching down on the surface on one side of a small, rubble-pile asteroid could perhaps cause an avalanche on the other side, by long-range transmission of forces through chains. It would, however, depend on the angle and location of the impact, as well as the history of the surface -- what kind of memories the regolith holds, " said Murdoch.
Danger certainly would be a major component of landing anything on a flying hunk of rocks but such problems would hopefully be accounted for. The movement toward landing and perhaps mining asteroids has been gaining momentum for quite a while now with NASA, Planetary Resources and Deep Space Industries all moving toward developing asteroid landing and/or mining systems.
NASA recently wrote that because asteroids are loaded with minerals that are rare on Earth, near-Earth asteroids and the asteroid belt could become the mining centers for remotely operated excavators and processing machinery. In 20 years, an industry barely imagined now could be sending refined materials, rare metals and even free, clean energy to the Earth from asteroids and other bodies," according to NASA scientists in a recently published paper entitled: "Affordable, Rapid Bootstrapping of the Space Industry and Solar System Civilization."
The scientists say two fundamental developments make this prospect possible: robotics and the discovery of fundamental elements to make plastic and rubber and metals existing throughout space. Another critical technology also is coming in at just the right time: manufacturing in the form of 3D printers that can turn out individual pieces that can be assembled into ever-more-complex machinery and increasingly capable robots.
"Now that we know we can get carbon in space, the basic elements that we need for industry are all within reach," said one of the paper's authors, NASA physicist Phil Metzger said. "That was game-changing for us. The asteroid belt has a billion times more platinum than is found on Earth. There is literally a billion times the metal that is on the Earth, and all the water you could ever need. The idea is you start with resources out of Earth's gravity well in the vicinity of the Earth. But what we argued is that you can establish industry in space for a surprisingly low cost, much less than anybody previously thought."
A near-Earth asteroid or other nearby body presumably will contain enough material to allow a robotic system to mine the materials and refine them into usable metal or other substances. Those materials would be formed into pieces and assembled into another robot system that would itself build similar models and advance the design.
"The first generation only makes the simplest materials, it can include metal and therefore you can make structure out of metal and then you can send robots that will attach electronics and wiring onto the metal," Metzger said. "So by making the easiest thing, you've reduced the largest amount of mass that you have to launch."
Metzger said the first generation of machinery would be akin to the simple mechanical devices of the 1700s, with each new generation advancing quickly to the modern vanguard of abilities. They would start with gas production and the creation of solar cells, vital for providing a power source. Each new robot could add improvements to each successive model and quickly advance the mining and manufacturing capabilities. It would not take long for the miners to produce more material than they need for themselves and they could start shipping precious metals back to Earth, riding on heat shields made of the leftover soil that doesn't contain any precious material.
Perhaps the most unusual aspect of the whole endeavor is that it would not take many launches from Earth to achieve, Metzger said. Launch costs, which now run at best $1,000 per pound, would be saved because robots building themselves in space from material gathered there wouldn't need anything produced by people. Very quickly, only the computer chips, electronics boards and wiring would need to come from Earth.
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