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发射窗口到底是个啥？嫦娥七号为何不能过几天再发？_我的网站

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A | 　　昨晚官方消息：嫦娥七号任务不满足发射条件，不能在今年预定窗口实施。很多朋友问：啥叫窗口?为啥不能过几天再发? 发射窗口到底是个啥？嫦娥七号为何不能过几天再发？　　简单说，发射窗口就是允许火箭发射的一段时间范围。 BRUSSELS -- A European Union decision on whether to authorize the use of the controversial chemical herbicide glyphosate in the 27-nation bloc for at least 10 more years was delayed for a month after member countries failed to agree on Friday.The chemical, which is widely used in the 27-nation bloc, is approved on the EU market until mid-December. Representatives of the EU’s executive arm and member countries voted Friday in favor of renewing its authorization until 2033, despite protests from environmental groups. But to be adopted, the 10-year extension proposed by the European Commission required a “qualified majority,” defined as 55% of the 27 members representing at least 65% of the total EU population of some 450 million people. Several member states abstained, and that was not achieved. The European Commission is now expected to amend its proposal before another vote takes place next month. Ultimately, if no consensus is found, the Commission will have the final say.Green members of the European Parliament welcomed the delay and urged member states to vote for a complete ban of glyphosate.“It is irresponsible to again renew the authorization of the use of glyphosate,” said Bas Eickhout, the vice-chair of the Parliament's environment committee. "This would give the big agri a blank check to earn billions by selling a pesticide for which there are still big gaps in knowledge about the effects on our health, and at the same time poses large risks for European biodiversity.”Over the past decade, glyphosate, used in products like the weedkiller Roundup, has been at the heart of heated scientific debate about whether it causes cancer and its possible disruptive effect on the environment. The chemical was introduced by Monsanto in 1974 as an effective way of killing weeds while leaving crops and plants intact.The France-based International Agency for Research on Cancer, which is part of the World Health Organization, classified it as a “probable human carcinogen” in 2015. The EU’s food safety agency had paved the way for the 10-year extension when it said in July it “did not identify critical areas of concern” in the use of glyphosate. The U.S. Environmental Protection Agency found in 2020 that the herbicide did not pose a health risk to people, but a federal appeals court in California ordered the agency last year to reexamine that ruling, saying it wasn’t supported by enough evidence.EU member states are responsible for authorizing the use of products including the chemical on their national markets, following a safety evaluation.In France, President Emmanuel Macron had committed to ban glyphosate before 2021 but has since backpedaled. Germany, the EU's biggest economy, plans to stop using it from next year, but the decision could be challenged. Luxembourg’s national ban, for instance, was overturned in court earlier this year.Greenpeace had called on the EU to reject the market reapproval, citing studies indicating that glyphosate may cause cancer and other health problems and could also be toxic to bees. The agroindustry sector, however, claims there are no viable alternatives.“Whatever the final decision that emerges from this re-authorization process, there is one reality that member states will have to face up to,” said Copa-Cogeca, a group representing farmers and agricultural cooperatives. “There is as of yet no equivalent alternative to this herbicide, and without it, many agricultural practices, notably soil conservation, would be rendered complex, leaving farmers with no solutions.”。航天器能不能发、啥时候发，要看轨道、天体位置、测控、天气等一堆条件。

B | 普通近地卫星任务窗口相对宽松，错过几天等下一轮就行。但对于飞行距离远的航天器来说，发射窗口就没有那么宽裕。　　因此对于嫦娥七号任务来说，发射窗口的条件很苛刻。发射窗口到底是个啥？嫦娥七号为何不能过几天再发？　　先来了解嫦娥七号这次任务，它要去的是月球南极，寻找水冰存在的证据。那为什么选择南极，是因为月球自转轴倾角极小，太阳在南极几乎贴着月平线扫过地表面，部分高地遮挡极少，年光照率可达80%以上，形成“永昼”区;而周边撞击坑底部是永久阴影区，温度低至-230℃左右，水冰可能就藏在那里。发射窗口到底是个啥？嫦娥七号为何不能过几天再发？　　嫦娥七号主要靠太阳能供电，必须精准卡点，在南极优质极昼窗口开启前顺利抵达着陆。初步估算，全年真正适宜探测器稳定作业的优质光照窗口，大约只有100天。这个窗口不是每个月都有，更不是晚几天就能补上。一旦错过今年最佳时机，探测器抵达时南极光照已经衰减，设备供电、导航都会出问题，月面探测的作业窗口期也会压缩甚至丧失。　　所以官方说的是“不能在今年预定窗口实施”，而不是“延迟若干天”。发射窗口到底是个啥？嫦娥七号为何不能过几天再发？　　航天工程有一句老话：稳妥可靠，万无一失。这不是一句口号，而是一种选择——看似“错过”了一个窗口，其实是守住了航天的底线，也守住了对科学目标的敬畏。