早稲田政経2015 II

What began as a minor trash, problem in space has recently developed into something very serious. Many experts now regard the problem of space junk as a real threat to the future use of space. Hundreds of thousands of pieces of space debris―including broken satellites, discarded rocket parts, and tools lost by astronauts―now crowd the space surrounding Earth.

A report released recently by the Space Security Index, an international research consortium, identified space debris as a primary issue. Such objects, it declared, could do serious damage to working spacecraft if they were to hit them, and might even pose a risk to people and property on the ground if they fall back to Earth and are large enough to survive reentering the atmosphere. Similar recognition of the trash threat in space emerged in the national space policy of the United States revealed by President Obama in June 2010. Such growing awareness of the space-debris problem builds on harsh warnings issued in past years by scientists and military commanders. It could also pave the way for U.S. agencies and others to better ( A ) the space surrounding Earth.

Consideration of space debris as a major threat may cause countries―including the United States―to take a more global view on the threat of space weapons, said Brian Weeden, a former U.S. Air Force analyst who now belongs to an organization dedicated to the sustainable use of space. "This is an important realization because, before that, most of the security focus was on threats from other countries with the ability to send weapons into space," Weeden explained. "This is the first national policy recognition that threats can simply come from the space environment and nonhostile events."

All those bits of garbage in space could eventually create a floating artificial barrier that endangers space flight for any nation, experts said. Even fictional space navigator Han Solo from Star Wars might prefer to risk turbolaser blasts from Imperial starships than to confront the danger of Earth's growing cloud of space debris, where objects whizz by at up to 7.8 km per second.

The possibility of a damaging collision between spacecraft and orbital junk only continues to grow with more functional and nonfunctional hardware flying above Earth. Both the International Space Station and space-shuttle missions have been forced to take action to avoid space debris in the past. There are more than 21,000 objects larger than 10 cm in diameter being tracked by the U.S. Department of Defense (DOD). DOD estimates suggest there are more than 300,000 larger than 1 cm, not to mention several million smaller pieces.

"The shuttle was more likely to be wiped out by something you didn't see than by something you were trying to avoid," said Donald Kessler, a former NASA researcher. Since Kessler began studying the issue decades ago with a fellow researcher at NASA, the problem has become much worse. Their 1978 research described how the debris cloud might continue expanding on its own because of an ever-higher probability of collisions that build upon each past collision. That prediction, known as the Kessler Syndrome, may have already been realized. In one well-documented case, a U.S. communications satellite and an abandoned Soviet spacecraft were destroyed in an unintended head-on collision in 2009. That incident added more than 1,000 pieces of trackable debris to the mess, adding to the number of possible targets and therefore increasing the chances of future collisions.

The overall trackable amount of space debris grew by about 15.6 percent, according to the 2010 Space Security report. NASA and other U.S. agencies could use national space policy as a chance to aggressively pursue solutions, such as using spacecraft or other objects to take down a few select pieces of debris, experts said. "If we only bring down four objects per year, we can stabilize [the debris field] as long as we carefully select those most likely to contribute to debris," Kessler told SPACE.com.

( B ) More likely is a strictly voluntary consensus that would put pressure on countries with a space program to address these issues. The criticism of past space-weapons tests that have created space debris has already changed how countries plan their actions, said Joan Johnson-Freese, a space- policy analyst at the U.S. Naval War College.

"When the United States tested an antisatellite (ASAT) weapon in 1985 by destroying its Solwind satellite, and China tested its ASAT in 2007, neither broke any 'rules,'" she states. "But each created a substantial amount of space debris potentially dangerous to other spacecraft." Both countries have since changed their policies and said future tests will be aimed only at destroying targets that won't leave lingering debris. "In terms of space debris, it is simply not in U.S. interests to pursue paths that encourage actions that result in debris creation."

1 Choose the most suitable answer from those below to complete the following sentence.
A recent report suggests that
(a) even the smallest amount of space debris would damage property if it fell back to Earth.
(b) people need not take the issue of space debris too seriously at the present time.
(c) space debris can result from large pieces of junk reentering the atmosphere.
(d) space junk is a considerable danger to vehicles working in space.
(e) the president of the United States should start to consider the issue of space debris.

2 Use the six words below to fill in blank space (A) in the best way. Indicate your choices for the
second, fourth, and sixth positions.
(a) clean (b) figure (c) how (d) out  (e) to  (f) up

3 Choose the most suitable answer from those below to complete the following sentence.
Weeden suggests that the new attitude toward space debris is important because
(a) it changes the idea that danger in space comes mostly from the actions of hostile countries.
(b) it will discourage countries from sending weapons into space.
(c) it will help the U.S. Air Force to become more dedicated to the sustainable use of space.
(d) space debris has been regarded until now mostly as a subject of science-fiction movies.
(e)  the barrier created by space debris interferes with the formation of clouds.

4 Choose the most suitable answer from those below to complete the following sentence.
The increasingly serious nature of the threat from space debris is shown by the fact that
(a) a shuttle was badly damaged on a recent space mission.
(b) collisions between spacecraft and debris in space have become frequent.
(c) DOD estimates no longer include objects that are larger than 1 cm.
(d) millions of pieces of debris are now thought to be flying round Earth.
(e) turbolaser blasts have been ineffective in destroying space junk.

5 Choose the most suitable answer from those below to complete the following sentence.
The Kessler Syndrome refers to the idea that
(a) collisions in space create debris whose existence increases the chance of future collisions.
(b) it is easier to be wiped out by unseen pieces of debris than by visible pieces of debris.
(c) researchers at NASA need to study more carefully how space debris is formed.
(d) using communications satellites is a suitable method of tracking space debris.
(e) vehicles sent into space by countries such as the U.S. are the main problem.

6 Choose the most suitable answer from those below to complete the following sentence.
One suggested solution to the space debris problem is to
(a) allow the amount of debris to grow by no more than about 15 percent per year.
(b) make NASA and other American agencies cooperate more closely.
(c) stop sending so many vehicles into space until some of the debris disappears.
(d) target just a few pieces of debris every year and then get rid of them.
(e) track the amount of space debris more carefully with better instruments.

7 Choose the most suitable order of sentences from those below to fill in blank space (B).
(a) An international initiative along these lines would set the playing field for what is to come, which would be helpful, though not the solution itself.
(b) Based on the work of Kessler and other researchers, policymakers in the United States have finally begun to take action.
(c) Even so, the United States and other countries could then begin discussing informal codes of conduct about how to minimize space debris from new missions and deal with old space debris.

(d) However, legally binding agreements remain politically unlikely, at least for the time being.

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