人工衛星衝突 宇宙ごみ対策を強化せねば

The Yomiuri Shimbun　(Feb. 13, 2009)
Space debris measures must be strengthened
人工衛星衝突　宇宙ごみ対策を強化せねば（2月13日付・読売社説）

Our planet is surrounded by space debris, a matter that is becoming of increasing concern.
　地球の周りが「宇宙ごみ」だらけになってしまう。それが心配だ。

The collision of a U.S. satellite weighing about half a ton with a Russian satellite about twice that size, about 800 kilometers above the Earth's surface, reportedly produced a huge amount of debris. We wonder if the collision could have been avoided if their orbits had been adjusted.
　米露の人工衛星が高度約８００キロ・メートルで衝突した。露の衛星は１トン、米の衛星はその半分程度で、どちらも標準的な大きさだ。大量の破片が散らばったという。軌道変更で回避できなかったのか。

Since the world's first satellite was launched in 1957, thousands of satellite launches have taken place, meaning there are a large number of objects drifting around the Earth.
　世界で衛星打ち上げが始まったのは１９５７年だ。それ以来、数千回の打ち上げが実施された。これにより、地球の周りには、今も多数の物体が漂う。

Among the space debris in orbit around our planet are satellites that are no longer functioning, either because they have outlived their usefulness or have malfunctioned. Space debris also includes rocket booster parts, the remains of collisions among space vehicles and equipment dropped by astronauts. It is estimated that there are between 30 million and 40 million items of space debris currently adrift, weighing a total of about several thousand tons.
　耐用年数を過ぎたり、壊れたりして休止した衛星、打ち上げロケットの破片、これらの衝突で生じたごみ、宇宙飛行士が落とした工具など、その数は３０００万～４０００万個、重量で数千トンに達すると推計される。

In 2007, China's destruction of one of its weather satellites produced a huge amount of debris.
　中国が一昨年、衛星破壊実験でごみを大量に出した例もある。

If nothing is done to address the problem, mankind faces serious problems in its use of space as space debris has massive destructive potential.
　このままでは人類の宇宙利用に支障が出かねない。宇宙ごみは猛烈な破壊力を持つ。

Such debris can travel at speeds of about 5 kilometers per second, while the energy generated from a collision of debris even just 1 centimeter across can be equivalent to that of a car crash on a highway. The smashing of satellites into one another is clearly disastrous.
　漂うと言っても、秒速５キロ・メートル前後の速度で飛ぶ。衝突時のエネルギーは、約１センチの破片でも、自動車が高速で突っ込んだのと変わらない。まともにぶつかれば、衛星はひとたまりもない。

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An international problem

Previously, a French satellite was seriously damaged after colliding with space debris. In the United States, a rocket launch was postponed to prevent a collision with space debris.
　過去に、宇宙ごみとの衝突により、仏の衛星が機能損傷した例がある。米では、宇宙ごみとの衝突を避けるため、ロケット打ち上げが延期されたことがある。

What is of particular concern this time is the threat to the International Space Station, which has been under construction with the participation of Japan and other nations. The ISS orbits about 400 kilometers beneath where the latest collision took place, and it is unlikely that debris will hit the ISS. But it is still possible that debris could pass over the ISS.
　今回心配なのは、日本も参加して建設が進む「国際宇宙ステーション」だ。米露の衛星が衝突した軌道より４００キロ・メートルほど下にあり、直撃はないとみられる。だが破片が飛来する恐れはある。

An extended stay at the ISS by Koichi Wakata, the first of its kind for a Japanese astronaut, is expected to begin soon, and it is of some concern that the space shuttle flying to the ISS could be affected by the debris.
　日本人宇宙飛行士としては初めて、若田光一さんのステーション長期滞在が近く始まる予定だ。ステーションに向かうスペースシャトルの飛行に問題はないか。

The ISS is equipped with protective walls designed to absorb shocks from small debris and the station would alter its orbit to avoid large pieces of debris, which are tracked by radar from the ground by the U.S. military when a shuttle is to be launched.
　ステーションには、小さな破片なら衝撃を吸収する防護壁がついている。大きなごみは、軌道を変えて避ける。シャトル打ち上げも、米軍が地上からレーダーで大きなごみを監視している。

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Breaking the cycle

But if the amount of debris continues to increase, it will become more difficult to take all possible preventive measures. Greater precautions must therefore be taken to try and prevent troubles that could affect the ISS.
　だが、ごみが増えれば万全の対策は難しい。警戒は怠れない。

A further concern is the apparent vicious circle of increased space debris from collisions, which in turn creates more potential for destruction, as can be seen in the latest collision. The growing amount of debris means the probability of more collisions is set to explode in about a decade or so.
　今回のような衝突・破壊で、ごみがさらに増える悪循環も懸念されている。そうなれば、あと１０年で宇宙ごみとの衝突確率が爆発的に増える、とも言われる。

International guidelines state that large satellites should be brought back to Earth. But is this enough? Is there no way that space debris can be collected? Japan needs to call on other nations that have space development programs to address the issue and play a more active role in strengthening measures to tackle the problem.
　大型衛星は地球に落とす、などの国際ガイドラインはあるが、それで十分か。ごみの回収はできないのか。日本は、他の宇宙開発国にも呼びかけ、対策強化に積極的な役割を果たす必要がある。

(From The Yomiuri Shimbun, Feb. 13, 2009)
（2009年2月13日01時45分 読売新聞）