Space words you need
- Rocket / launch vehicle: the machine that carries things to space.
- Payload: what the rocket carries (a satellite, a probe, people).
- Satellite: anything that goes round a planet. The Moon is natural; weather satellites are artificial.
- Orbit: the curved path around a planet or star.
- Probe: a robot craft sent to study other worlds (for example Voyager, Mangalyaan).
- Rover / lander: a craft that lands, and a rover that drives on the surface.
- Space station: a large craft where people live and work in orbit.
- Astronaut: a person trained to travel in space (also cosmonaut, taikonaut, vyomanaut).
How rockets fly
A rocket burns fuel with an oxidiser (it must carry its own oxygen, because space has no air). Hot gas shoots out of the nozzle downward. By Newton's third law the gas pushes the rocket upward. This push is called thrust.
Rockets drop empty fuel tanks as they go. These parts are called stages. Dropping weight lets the rest go faster. Some modern rockets land their first stage to reuse it, which makes launches cheaper.
Orbits and what satellites do
Throw a ball: it curves down. Throw it faster: it lands further away. At about 7.9 km/s (near the ground, ignoring air) it would fall around the curve of the Earth forever. That is an orbit. At 11.2 km/s (escape speed) a craft leaves Earth for good.
| Orbit | Height | Uses |
|---|---|---|
| Low Earth orbit | 160–2,000 km | space stations (≈ 400 km, one turn in ≈ 90 min), Earth photos, internet satellites |
| Medium orbit | ≈ 20,000 km | navigation: GPS, Galileo, GLONASS, BeiDou |
| Geostationary | 35,786 km | TV, weather, communication; turns once in 24 h so it stays over one spot |
The full physics is in Escape speed and orbital velocity.
Milestones: from the first satellite to today
- 1957 Sputnik 1 (USSR), the first artificial satellite.
- 1961 Yuri Gagarin (USSR), first person in space. 1963 Valentina Tereshkova, first woman.
- 1969 Apollo 11 (USA): Neil Armstrong and Buzz Aldrin walk on the Moon.
- 1969 India founds ISRO. 1975 Aryabhata, India's first satellite. 1984 Rakesh Sharma flies to space.
- 1990 Hubble Space Telescope. 1998 first part of the International Space Station (ISS).
- 2003 Yang Liwei, China's first astronaut. 2008 Chandrayaan-1 finds signs of water on the Moon.
- 2014 Mangalyaan (India) reaches Mars on its first try. 2019 Chang'e 4 (China) lands on the Moon's far side.
- 2021 James Webb Space Telescope launched. 2022 China's Tiangong station completed.
- 2023 Chandrayaan-3 lands near the Moon's south pole; Aditya-L1 sets off to study the Sun.
Rivalry and cooperation in space
During the Cold War the USA and USSR raced to show their power in space. The same rockets could also carry weapons, so space was about security as well as science.
Later, rivals started to work together: the ISS is run by the USA, Russia, Europe, Japan and Canada. Today many countries and private companies launch rockets. China has its own station and Moon and Mars missions. India offers low-cost launches to other countries.
Like the deep oceans, space is a “last frontier”: it belongs to no country. The Outer Space Treaty (1967) says no nation can own the Moon or other bodies, and nuclear weapons must not be placed in orbit. New questions remain: who may mine the Moon, and who cleans up debris?
Benefits, risks and the future
Benefits: weather and cyclone warnings, navigation, phone and TV links, maps of crops, forests and floods, climate data, and inventions first made for space (better water filters, memory foam, small cameras).
Risks and costs: launches are expensive; rockets release gases; space debris (old satellites and broken bits) moves at about 7–8 km/s, so even a tiny piece can damage a satellite. Astronauts face radiation and muscle and bone loss.
Future: people returning to the Moon to build bases, crewed trips to Mars, space telescopes finding planets around other stars, India's Gaganyaan crewed flights, and reusable rockets. The big rule: explore in a way that keeps space usable for everyone.
Try it: balloon rocket
Thread a straw on a long string tied across a room. Tape a blown-up balloon to the straw and let go. Air rushes one way, the balloon rushes the other: that is thrust. Predict first: will a bigger balloon go further? Then test. After that, use the launch-speed slider in the 3D and find the lowest speed that gives an orbit.
Key formulas and definitions
- Rocket thrust: gas pushed back ⇒ rocket pushed forward (Newton's 3rd law)
- Orbital speed near Earth ≈ 7.9 km/s
- Escape speed from Earth ≈ 11.2 km/s
- Low Earth orbit: 160–2,000 km; ISS ≈ 400 km, ≈ 90 min per orbit
- Geostationary orbit: 35,786 km above the equator, period 24 h
- Payload = what a rocket carries; stages = parts dropped on the way
Worked examples
1. Why must a rocket carry an oxidiser, but an aeroplane does not?
Fuel needs oxygen to burn. An aeroplane takes oxygen from the air. Space has no air, so a rocket must carry its own oxygen supply.
2. The ISS goes round Earth once in about 90 minutes. How many orbits does it make in one day?
1 day = 24 × 60 = 1,440 minutes. 1,440 ÷ 90 = 16 orbits a day.
3. A TV satellite must seem to stay still in the sky. Which orbit should it use and why?
Geostationary orbit, 35,786 km above the equator. It goes round once in 24 hours, the same as Earth spins, so it stays above the same place and dishes need not move.
4. A craft is launched sideways at 6 km/s, 9 km/s and 12 km/s. What happens in each case?
6 km/s is below 7.9 km/s, so it falls back. 9 km/s is between 7.9 and 11.2, so it orbits (in an oval). 12 km/s is above 11.2, so it escapes from Earth.
5. Give two ways the space race and today's space activity differ.
The space race (1957–1970s) was mainly two rival governments; today many countries and private companies take part. Then it was mostly competition; today there is also cooperation, like the ISS.
Common mistakes
- Thinking there is no gravity on the ISS. Gravity there is about 90% of that on the ground; astronauts float because they are falling around Earth together with the station.
- Saying rockets push against the air. They push against their own exhaust gas, which is why they work in empty space.
- Thinking all satellites are at the same height. Different jobs need different orbits.
- Believing that countries can claim the Moon. International law says no nation owns it.