ناسا تتخلف عن الموعد النهائى للكونغرس لكى تتبع الكويكبات

NASA won't meet Congressional orders to track most city-smashing-sized asteroids in Earth's neighborhood by 2020, an expert panel concluded Friday, because the government didn't provide the money to detect such Near-Earth Objects.

In the National Research Council Report, "Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies", the panel finds the 2005 order to find 90% of Earth-threatening asteroids 460 feet or larger infeasible, "because for the past 5 years the administration requested no funds, and the Congress appropriated none, for this purpose."

If Congress wants the survey completed by 2022, NASA should launch twin space probes to the orbit of Venus to look back at Earth neighborhood, the study finds. The cheaper option would fund telescopes and complete the 90% goal around 2030. Right now, the federal government spends about $4 million a year to detect asteroids. More research should be done on asteroids, the report argues, particularly since some recent studies suggest impacts from objects as small as 100 feet wide would wipe out a city-sized area.

"Somebody needs to decide who is in charge," says astronomer Michael A'Hearn of the University of Maryland in College Park, who led the report panel's committee on diverting asteroids. "No method for diverting asteroids has been experimentally demonstrated," he says.

Options include a "gravity tractor" orbiting slow-moving objects and tugging them off course with tidal tugs, a "kinetic" impact of a heavy spacecraft into an asteroid, or a nuclear explosion, "only for the really big and really late discoveries," A'Hearn says. International accords for handling an incoming asteroid don't exist either, he notes. "If you try and divert an asteroid and miss, you might end up landing it on someone else," he says.

"The larger question is whether the remaining hazard from impacts is worth a 'crash program' to shorten that time, which implies space missions costing hundreds of millions, typically," says asteroid expert Alan Harris of the Space Science Institute in La Canada, Calif. "First, and most simply, my answer is no, it's not worth it, solely for impact risk reduction."

Getting a space mission approved by Congress would likely take until about 2030, he suggests, making it pointless to argue for one." However continuing the existing surveys in concert with other astronomical work seems worthwhile, Harris says, "in a sense, the asteroid survey is like a whole-life insurance policy. Even if you don't find a killer asteroid out there, you reap a tremendous scientific reward at the end of the 'policy period'."

"It doesn't surprise me that we can't yet address these questions -- there is yet to be a Congressionally directed research dollar toward the asteroid hazard. Everything to date has been on a shoe string, piggy-backed on other programs," says astronomer Richard Binzel of the Massachusetts Institute of Technology.

The NRC report endorses continuing work at facilities such as the 1,000-foot-wide Arecibo radar astronomy facility in Puerto Rico, which is threatened with closure. However, A'Hearn notes the asteroid detection and characterization work at Arecibo can't be completed on the funds devoted to such work, and relies on other astronomical research covering some of the costs of the mammoth facility. "If other research shuts down at Arecibo, the (asteroid detection) share goes up substantially," he says.

"Simply by there being a National Research Council report issued on the asteroid hazard problem, this is a huge milestone. The asteroid problem is now a grownup, joining the table of other natural disasters for which mitigation strategies are developed," Binzel adds. "Unlike the dinosaurs, we are smart enough to do the math and figure out the answer that modest resources should be dedicated to the problem."