单选题
Aristotle believed that the heavens were perfect. If they ever were, they are no longer. The skies above Earth are now littered with the debris of dead satellites, bits of old rockets and the odd tools dropped by a spacewalking astronaut. Such is the extent of the detritus that the first accidental collision between two satellites has already taken place. It happened in February 2009, when a defunct Russian Cosmos smashed into a functioning American Iridium, destroying both and creating even more space junk. To stop this sort of thing happening again, Vaios Lappas of the University of Surrey, in England, has designed a system that will remove satellites from orbit at the end of their useful lives—and as a bonus will scour part of the sky clean as it does so. Dr. Lappas's satellite-removal system employs a solar sail. As light from the sun hits the sail, it imparts a minuscule but continuous acceleration. When a satellite is first launched, the sail is angled in a way that causes this acceleration to keep the satellite in orbit. (Orbits gradually decay as a result of collisions with the small number of air molecules found even at altitudes normally classified as "outer space". ) Solar sails have yet to be used widely to propel spacecraft in this way—several earlier versions came unstuck when the sails failed to unfurl properly—but doing so is not a novel idea in principle. The novelty Dr. Lappas envisages is to change the angle of the sail when the satellite has become defunct. Instead of keeping the derelict craft in orbit, it will, over the course of a couple of years, drag it into the atmosphere and thus to a fiery end. Not only that, but the sail will also act like a handkerchief, mopping up microscopic orbital detritus such as flecks of paint from previous launches: A fleck of paint may not sound dangerous, but if travelling at 27,000kph (17,0OOmph), as it would be in orbit, it could easily penetrate an astronaut's spacesuit. A prototype of Dr. Lappas's design, called CubeSail, will be launched late next year. It weighs just 3kg (71b) and, when folded up, measures 30cm (12 inches) by 10cm by 10cm. Once unfurled, however, the sail will have an area of 25 square metres. If this prototype, which is paid for by EADS, a European aerospace company, proves successful, solar sails might be added to many future satellites. That would enable them to be removed rapidly from orbit when they became useless and would restore to the skies some measure of Aristotelian perfection.
单选题
In the first paragraph, the author mentioned the collision between satellites ______. A. to introduce a satellite-removal system B. to make a contrast with past and present skies C. to make a comparison between past and present skies D. to let people focus on the conditions of the outer space
单选题
When a satellite is first launched, the sail ______. A. can make a minuscule but continuous speed B. is angled and makes the acceleration to keep the satellite in orbit C. makes the satellite off the orbit because the satellite collides with the small number of air molecules D. keeps the satellite in orbit because the satellite collides with the small number of air molecules
单选题
According to Paragraph 3, which one is NOT the function of the solar sail? A. Protecting the space environment. B. Dragging the dead satellite into the atmosphere. C. Cleaning up microscopic orbital debris. D. Disabling satellites in orbit.
单选题
According to the text, which of the following is true? A. A fleck of paint may be dangerous sometimes. B. Satellites can be mopped up by solar sails. C. There is nothing new in Dr. Lappas' idea. D. The concept of solar sails is novel.
单选题
We can learn from the text that the solar sail can ______. A. clean the orbit after added to many future satellites B. dispose of defunct satellites quickly C. help to sweep the debris and return the skies' clean D. make the skies perfect now