【问题】 One of the most daring deep-space missions NASA has ever launched is turning out to be one of the least publicized. The target is a large asteroid (小行星) named 1992KD, which orbits the sun millions of miles from Earth. But that destination is almost incide

One of the most daring deep-space missions NASA has ever launched is turning out to be one of the least publicized. The target is a large asteroid (小行星) named 1992KD, which orbits the sun millions of miles from Earth. But that destination is almost incidental to the performance of the spacecraft that will make the trip. Though it looks little different from countless other unmanned probes NASA has launched, the ship will be navigated by an electronic brain that has been likened to HAL, the independent-minded computer in the film 2001, and will move through space under power of a system that has long been the stuff of technological fantasies: an ion propulsion (离子推进) engine.If all goes as planned, Deep Space 1, scheduled for launch later this month, will be the forerunner of a new’ generation of spacecraft. While flight planners hope the ship will make some interesting observations about the target asteroid, including its composition and the structure of its surface, DS1 ‘s primary assignment is to validate a host of new technologies NASA has always considered too risky to try on a mission that may attract a great deal of public attention. Says Mar Rayman of Jet Propulsion Laboratory, DS1’ s chief engineer, “We have an unproven propulsion system, powered by an unproven solar panel, commanded by an unproven navigation system.What is most remarkable about the spacecraft is how it gets from place to place. After being launched by an ordinary rocket, DS1 will be pushed through space by an engine that works by firing electrons into atoms of xenon gas, stripping each of an electron and giving the atoms an electric charge-ionizing them. The ions are then accelerated through an electric field and emitted from the thrusters at 65,000 m. p. h. Despite that speed, the particles produce little thrust, comparable to the weight of a piece of paper.41. What is special about NASA’s planned deep-space mission regarding its publicity? A) It is targeted at a large asteroid. B) It is much less reported by the media. C) It is the same as other unmanned probes. D) It isn’t certain whether it will be successful.42. What is the primary, purpose of the DS1 mission? A) Testing new technologies for future spacecraft. B) Calculating risks for the benefit of other missions. C) Studying the surface of a large asteroid. D) Proving a new generation of spacecraft.43. Once launched, whether the spacecraft will reach its destination is incidental to the performance of all the following EXCEPT ___________. A) the self-navigation system B) the ion-powered engine C) the solar cells D) the flight planners44. How does the DS1 leave the earth’s orbit? A) By its special propulsion engine. B) By a conventional rocket engine. C) By firing electrons into the atoms of xenon gas. D) By accelerating through an electric field.45. Which of the following is NOT true according to this article? A) The author likens the DS1’s navigation system to an electronic brain. B) The DS1 is the first of a new breed of spacecraft. C) The DS1 chief engineer has nothing to lose in such a mission. D) The DS1’s power system used to be the dream of scientists.

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