2020 marks the 20th anniversary of the International Space Station (ISS) since the first group of astronauts arrived at the ISS on Nov 2, 2000.
2020年是国际空间站运行20周年。2000年11月2日，第一批宇航员抵达国际空间站。

As a milestone of space exploration, the ISS didn’t come cheap. It cost about 989 billion yuan, took decades to build and is by far the world’s largest space project.
作为太空探索的一块里程碑，国际空间站造价不菲。其耗资约9890亿元，历时数十年建成，是目前全球最大的太空项目。

When it comes to achievements, ISS has accommodated at least 3,000 research projects, from research on Alzheimer’s to toothpaste.
在成就方面，国际空间站已为至少3000个研究项目提供平台，研究类别从阿兹海默症到牙膏。

But still, with a 26-billion-yuan bill annually, ISS can’t make ends meet. NASA has been promoting to commercialize ISS. In 2019, NASA announced that the ISS would open for business to private citizens. According to Reuters, NASA will allow up to two private trips to the station per year, each lasting up to 30 days. NASA estimated the cost of a flight would be around $50 million (about 330 million yuan) per seat.
但每年260亿元的花销仍令国际空间站入不敷出。美国航空航天局一直在推动国际空间站商业化。2019年，美国航空航天局宣布国际空间站将向个人开放。据路透社消息，美国航空航天局每年将允许最多两次私人的国际空间站旅行，每次旅行长达30天。美国航空航天局预计每次太空之旅的人均花费为5000万美元左右（约合3.3亿元人民币）。

However, ISS isn’t in the same state as it was in its youth. After 20 years of circling the Earth, ISS has suffered multiple problems. For example, there have been several air leak issues, the most recent of which was announced by NASA on Sept 29. Meanwhile, without enough propellant, ISS will not stay in orbit and could fall, leading to disaster.
然而，国际空间站却不复当年的状态。绕地球运行20年后，国际空间站存在诸多问题。比如，国际空间站已发生几次气体泄漏问题，最近的一次由美国航空航天局于去年9月29日发布。此外，如果没有充足的推进剂，国际空间站便停留在轨道上，或许会发生坠落，引发灾难。

“Worst, worst case, I guess it’s a 9/11, right?” Jonathan McDowell, an astronomer at Harvard told Space.com. “Because it’s at worst case a plane crashing, part of which is in a populated area.”
“最坏、最坏的情况，我猜是像911那样的，对吧？”哈佛大学天文学家乔纳森·麦克道尔向太空网表示。“因为没有比飞机坠毁、其中一部分还落在人口密集区更糟糕的了。”

So how can the space station make a safe re-entry? Despite certain risks, NASA is considering a scheduled de-orbit – maneuvering the station to a special angle in its orbit, making the re-entry more predictable and allowing managers to target the debris to the vast, sparsely populated southern Pacific Ocean.
所以，国际空间站能够如何安全重新进入大气层呢？尽管存在一定风险，美国航空航天局正在考虑脱离轨道的计划 —— 将空间站移至轨道中的特定角度，使其返回过程更可预测，以便管理人员将残骸投放至广阔无人的南太平洋。

An alternative is to launch new station modules to replace the old ones. “Each module is going to be designed with its own guidance, navigation and control, its own thruster capabilities,” said Christian Maender, director of in-space manufacturing and research for Houston-based company Axiom. “So when they need to, they can separate and return through Earth’s atmosphere on their own.”
另一种方法是发射新的模块舱来取代旧的。“每个模块舱都将配有自身制导、导航和控制系统，并具备自主推进性能，”总部位于休斯顿的Axiom公司的太空制造和研究主管克里斯蒂安·马恩德说道。“所以在有需要的时候，它们可以自行分离，自主穿过大气层返回地球。”

For now, ISS will continue through at least 2024.
目前，国际空间站运行延至2024年。

(Translator & Editor: Wang Yue (Intern) AND Wang Xingwei)
https://www.i21st.cn/story/3647.html