永利皇宫手机版:Touch down

 作者:任蛐     |      日期:2019-03-07 09:08:02
By Adrian Cho The final preparations to try to crash-land a dying spacecraft onto an asteroid are underway. NASA plans to use the last remaining fuel on the Near Earth Asteroid Rendezvous probe to “gently drop” it onto Eros. NEAR has been orbiting Eros since Valentine’s Day 2000. The descent will begin at 1631 GMT on Monday 12 February. While NEAR falls, researchers hope to take pictures revealing rocks just five to 10 centimetres across, about one-tenth the size of those in pictures taken from NEAR’s latest orbit 35 kilometres from the centre of Eros. They will try to ease the spacecraft down at no more than 11 kilometres per hour. But even at that speed the delicate machine probably won’t survive its “controlled descent” onto the boulder-strewn surface, says Edward Weiler, associate administrator for space science at NASA: “Note that I didn’t say landing: it is not a landing.” The descent will serve as a test run for future attempts to land probes on asteroids. “In the future, we’d like to land a space package on an asteroid and maybe bring back a sample,” says Andrew Cheng, a planetary scientist at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. NEAR was launched in 1996 and has been orbiting Eros since February 2000. The potato-shaped rock measures roughly 33 by 13 by 13 kilometres and is currently more than 300 million kilometres from Earth, between the orbits of Mars and Jupiter. NEAR has returned hundreds of thousands of pictures, and reams of other data that have transformed researchers’ understanding of asteroids. But now NEAR has spent almost all the fuel for its thrusters and will soon become uncontrollable. “We decided to do some bonus science, and to try some new things with a spacecraft,” says Robert Farquhar,