(1)Space may seem remote, but it's really not that far away. The popular orbits for satellites begin twice as far up—about 400 miles above our heads. There telecommunications and weather satellites orbit at the same rate that Earth rotates, allowing them to hover above a single spot on the Equator.
(2)It was the explosions of derelict rockets that first drew NASA's attention to debris. In the 1970s Delta rockets left in orbit began blowing up after delivering their payloads. An investigation showed that the bulkheads separating the leftover fuels were probably cracking as a result of the rocket's passing in and out of sunlight. NASA began recommending that leftover fuels be burned at the end of a flight, or that they be vented into space. Still, every few months on average an old rocket or satellite explodes, flinging a cloud of debris into space.
(3)For many years NASA and the Department of Defense were skeptical about the dangers of space debris. The problem seemed abstract, residing more in computer models than in hard experience. And it challenged the can-do mentality of space enthusiasts. Earth's orbit seemed too large and empty to pollute. To its credit, NASA has long maintained a debris-research program, staffed by top-notch scientists who have persisted in pointing out the long-term hazards of space junk even when the higher-ups at NASA didn't want to hear about it. Then the Challenger accident came in 1986. NASA officials realized that their emphasis on human space flight could backfire. If people died in space, public support for the shuttle program could unravel.
(4)Engineers took a new look at the shuttle and the international Space Station. Designed in the 1970s, when debris was not considered a factor, the shuttle was determined to be clearly vulnerable. After almost every mission windows on the shuttle are so badly pitted by microscopic debris that they need to be replaced. Soon NASA was flying the shuttle upside down and backward, so that its rockets, rather than the more sensitive crew compartments, would absorb the worst impacts. And engineers were adding shielding to the space station's most vulnerable areas. At this point the modules should be able to survive impacts with objects measuring up to half an inch across, and NASA is developing repair kits for plugging larger holes in the walls.
(5)But adding shielding and repair kits won't solve the real problem. The real problem is that whenever something is put into an orbit, the risk of collision for all objects in that orbit goes up. Therefore, the only truly effective measure is a process known as deorbiting—removing objects from orbit when they reach the end of their useful lives. With current technology deorbiting requires that a satellite or a rocket reserve enough fuel for one last trip after its operations are finished. With enough fuel a spacecraft can promptly immolate itself in the atmosphere or fly far away from the most crowded orbits. If less fuel is available, it can aim for an orbit where atmospheric drag will eventually pull it to Earth. The logic behind deorbiting has been inescapable since the beginning of the Space Age, yet it has just begun to penetrate the consciousness of spacecraft designers and launchers.
(6)Furthermore, the character of the Space Age is changing. The private sector now puts more payloads into orbit than do NASA and the U.S. and Russian militaries combined. A score of communications companies in the United States and other countries have announced plans that will put hundreds of satellites into orbit over the next decade. Many will fly in relatively low orbits within a few hundred miles above where the space station will orbit, so that they can relay signals coming from hand-held phones.
(7)None of these companies is under any obligation to limit orbital debris. Companies that are launching large constellations of satellites are worried about collisions between the satellites, and they are well aware that a public-relations disaster would ensue if a piece of a shattered satellite smacked the station. As a result, some plan to deorbit satellites at the end of their useful lives. But other companies are leaving their satellites up or are counting on atmospheric drag to bring them down.
(8)Government regulations covering orbital debris are still rudimentary. For now, the federal agencies that have authority over commercial launches are waiting to see if the private sector can deal with the problem on its own. But deorbiting rockets and satellites is expensive. A satellite could keep operating for several additional months if it didn't need to reserve fuel for deorbiting. Some industry representatives say they want regulations, but only if the regulations apply to everyone and cannot be evaded.
(9)One reason for our nonchalance is that new technologies have gotten us out of many past scrapes— and maybe they will with orbital debris, too. Perhaps a future spaceship will race around Earth grabbing old spacecraft and flinging them back into the atmosphere, though it is hard to imagine a similar clean-up method for the small pieces of debris generated by collisional cascading. Maybe Star Wars technologies will produce a laser that can shoot orbital junk from the sky. In 1987 the World Commission on Environment and Development defined sustainable development as meeting the needs of the present generation without compromising the ability of future generations to meet their needs. In space we are failing the sustainability test miserably. A hundred years from now, when our descendants want to put satellites into orbits teeming with debris, they will wonder what we could have been thinking. The simple answer is we weren't thinking at all.

单选题 NASA began to pay attention to the debris problem because _____.

单选题 What can be inferred from the third paragraph?

单选题 NASA has used all the following methods EXCEPT _____.

单选题 All private companies will deal with space debris when_____.

单选题 A suitable title for the passage would be _____.