Space Exploration

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1Summary 重點摘要

Rockets overcome gravity to reach space: from satellites and crewed flight to space stations, with probes and space telescopes exploring the Solar System and deep space; China's Tiangong station, Chang'e lunar missions and Tianwen Mars mission are landmark achievements. Space exploration offers technology, resources and cooperation, and demands that space be used peacefully and cleanly.

2Vocabulary cards Vocabulary

3Step by step Steps

1. Step 1: See how a rocket risesA rocket rises by action and reaction: it blasts gas backwards at high speed and the stream pushes the rocket forward — the recoil principle. Example: release an inflated balloon and it darts opposite its escaping air. Three-stage rockets drop each empty tank in turn, growing ever lighter, until they reach the speed needed to enter space. A frequent exam point: unlike an aeroplane, a rocket must carry both fuel and oxidiser, so it works even in airless space, while a jet engine needs to breathe air and can only fly inside the atmosphere.
2. Step 2: Do the speed sumsEscaping Earth's pull needs tremendous speed, which is exactly why space exploration is so hard. Example: a high-speed train moves about 0.1 kilometres per second, while a spacecraft needs 7.9 to circle the Earth — as if flying from Hong Kong to London and back within an hour. Only powerful multi-stage rockets can accelerate a craft that fast. The 7.9 kilometres per second is called the orbital velocity; to reach farther destinations such as the Moon a craft needs the higher escape velocity of about 11.2 kilometres per second, demanding far more fuel.
3. Step 3: Know satellites' daily giftsSatellites quietly support weather forecasting, navigation and communication — space technology at its closest to daily life. Example: three or four days before a typhoon, the observatory forecasts its path from weather-satellite cloud images; your map app finds you by navigation satellites. Without satellites, modern life would hardly run. Satellites can be sorted by purpose: weather satellites watch the clouds, communication satellites relay television and international signals, and navigation satellites fix positions; their heights and orbits differ too.
4. Step 4: Value the space stationA space station is a laboratory circling the Earth, where microgravity makes possible experiments no ground lab can do. Example: protein crystals grow more perfectly in microgravity, letting scientists see their shapes and design new drugs; an astronaut sees sixteen sunrises a day, one every ninety minutes — truly amazing. For scale, the International Space Station weighs about four hundred tonnes and was built by many countries together; China's Tiangong station has three modules and is one of the few laboratories in space with long-term crews.
5. Step 5: Reach deep space and its telescopesDeep-space probes and space telescopes extend human sight beyond the solar system. Example: the Webb telescope caught light from galaxies over thirteen billion years old — because light took that long to arrive, telescopes photograph history. Looking farther means looking further back, helping us trace the origin of the universe. Here the light-year comes in: one light-year is the distance light covers in a year, about 9,500 billion kilometres, so light from galaxies over thirteen billion light-years away set out when the universe was very young.
6. Step 6: Order China's milestonesChina's space programme has advanced steadily for half a century, with several missions among the world's firsts. Example: 2003 Shenzhou 5 crewed flight; 2019 Chang'e 4's first far-side landing; 2020 Chang'e 5's returned lunar soil; 2021 Tianwen 1 landing on Mars and deploying Zhurong. The timeline shows how technology builds step by step. The latest milestone came in 2024, when Chang'e 6 returned about 1,935 grams of samples from the far side of the Moon — the first such material ever collected, another world first.
7. Step 7: Think about responsible useSpace belongs to all humanity, and its use must be safe, peaceful and sustainable. Example: a dead satellite striking at kilometres per second can destroy a working one, and the fragments then threaten other spacecraft; nations therefore push debris reduction and space treaties, keeping outer space peaceful. Responsibility is part of the explorer's spirit. Data show how serious this is: tens of thousands of fragments larger than ten centimetres are estimated to orbit the Earth, so nations require dead satellites to leave orbit within a set time or burn up in the atmosphere.

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5Worked example Example

6Common mistakes Mistakes

7Quick check Quick check

8Recap Recap

• Rockets rise by action and reaction; about 7.9 kilometres per second keeps a craft in orbit.
• Satellites serve daily life: weather warnings, navigation, communication and remote sensing.
• Space stations host microgravity experiments; probes and space telescopes reach the Solar System and deep space.
• China's feats include crewed Shenzhou flights, the Tiangong station, Chang'e lunar missions and Tianwen to Mars.
• Space debris threatens orbiting craft; outer space belongs to all humanity and must be used peacefully and responsibly.