It seems that right now, only Arecibo and Goldstone can do radar astronomy,
and Arecibo is 20 times more powerful than Goldstone.
Only some of the new arrays will be able to do this,
and they will be busy with other tasks.
Campbell was among five scientists to address the Subcommittee on Space and Aeronautics of the House Committee on Science and Technology. He discussed the role of Arecibo's radar system, which is one of only two high-powered radars in the world used for studying solar system bodies, on characterizing NEOs and their potential threat to Earth.
Arecibo's radar is over 20 times more sensitive than its counterpart, NASA's Deep Space Network 70-meter antenna at Goldstone, Calif., Campbell noted. But because it is less maneuverable, both systems are vital and complementary.
"The more we know about NEOs in general and about specific ones that pose a threat to Earth, the easier it will be to design effective mitigation strategies," said Campbell. "NEOs form a very diverse population encompassing a large range of sizes, shapes, rotation states, densities, internal structure and binary nature."
Radar provides the best way to survey and categorize such objects, he said. "For an object that we know poses a direct threat to Earth, radar can provide vital input to mitigation planning, including planning for any precursor space mission."
http://www.news.cornell.edu/stories/Nov07/arecibo.congress.html“An impact hazard is a risk comparable to other natural hazards, like earthquakes or hurricanes,” said Prof. Jean-Luc Margot, astronomy. “Lots of money goes to mitigating the effects of earthquakes and hurricanes, but we can really do nothing about them. We can actually do something about impact hazards. If we identify a potential impactor, we have the technology to deflect it.” Margot and other scientists use Arecibo to characterize the orbits of NEAs to incredible accuracies, so that they can identify which objects are worth worrying about.
“No other instruments can do that,” said Margot.
http://www.naic.edu/aorss/cornell_daily_sun.htmlThe purpose of the Congressional hearing was to discuss the issue of potentially hazardous Near Earth Objects, asteroids or comets whose trajectories bring them close enough to Earth to make experts worry about a collision. Congress issued an act in 2005 that directed NASA to “detect, track, catalogue and characterize the physical characteristics” of all the nearby objects that have a diameter of 140 meters or larger — about the size of a luxury liner. Congress asked NASA to find 90 percent of these objects by 2020 at the latest. This past March, NASA replied with a report saying that, unless they could build a new telescope by 2015, the goal was unrealistic.
“It was essentially a feasibility request,” said Campbell. “Finding and characterizing 90 percent of NEOs by the 2020 deadline cannot be done using current plans for ground-based telescopes.”
NASA expects several telescopes that would have the necessary survey capabilities to be completed in the next five years, but most of them are intended for purposes other than just searching for asteroids. One of these is the Large Synoptic Survey Telescope, expected in 2012, which will survey the entire sky every seven days. In these frequent wholesale sweeps of the sky, the LSST will inevitably discover thousands of asteroids, said Campbell. However, its primary purpose is to study dark energy — not to catalogue asteroids.
“If the LSST spent full time searching for asteroids, it could probably meet the objective, if it in fact is in operation by 2012,” said Campbell. “But since they don’t plan to spend all of their time looking for asteroids, it would take them a number of years longer than that to achieve the 90 percent goal.”
NASA’s report proposed that the only way they could meet Congress’s objectives using ground-based telescopes was if they had a telescope similar to the LSST that was dedicated exclusively to finding asteroids. Such a telescope combined with the LSST and other telescopes could finish the project by 2020, but a dedicated asteroid-hunting telescope alone would take until 2024.
In addition to finding the majority of potentially hazardous NEOs, Congress has also asked NASA to determine how likely it is that any of these objects will collide with the Earth, and to figure out how we would stop it. To do this, NASA needs to determine things like the object’s size, mass, orbit around the sun and composition to a very high accuracy. This sort of measurement is the forte of planetary radar, a method of observation where scientists bounce radio waves off of the objects they wish to study, and make detailed images of them by listening to the echoes.
Arecibo’s planetary radar system is the most sensitive in the world, making it an enormous asset to scientists trying to prevent an asteroid impact. The Puerto Rico-based observatory’s financial future, though, has been in flux since early November 2006, when a Senior Review committee appointed by the National Science Foundation recommended that the observatory’s operating funds be cut by more than 50 percent by 2011. If Cornell and the observatory could not raise funds from another source, the NSF recommended that it close.
According to Campbell, “the Senior Review did not make any reference to the planetary program, even though many planetary astronomers wrote letters to them — to which little or no attention was paid.”
http://cornellsun.com/node/26103