Every now and then you may see news ofsatellites(卫星)sent into space. On Feb 21, for example, US company SpaceX took 46 satellites intoorbit (轨道). China sent 22 satellites into space. Why do we need so many satellites? What do they do out there?

At present, there are more than 3,000 active satellites moving around the Earth, according to Statista, a German company working on market data. Satellites do all kinds of work, fromtransmitting(传送) TV signals to giving you directions on the road to helping scientists do research.

For example, the 22 satellites China just sent up are part of theBeidou Navigation Satellite System (北斗卫星导航系统). Shared bikes that use BeiDouchips (芯片) can have more accurate(精准的) positioning, making them easier to find. Drones(无人机) use BeiDouto fly.

Before satellites, TV signals didn't go very far. Mountains or tall buildings wouldblock(阻碍) them. Phone calls to faraway places were also a problem. Setting up telephonewires(线) over longdistances(距离) is difficult. With satellites, TV signals and phone calls can be sent directly to a satellite and back down to different locations on Earth. SpaceX's Starlink project is trying to go further. It plans to use satellites to provide Internet in the future.

Satellites can also provide information about clouds, oceans, land and ice. They help scientists predict changes in weather and climate. Bymonitoring(监测) wildfires and volcanoes, satellites helpemergencyworkers(应急人员) deal with natural disasters.

Farmers can use satellite images to decide the best time to water their fields.

Some satellites fly near other planets. They may look for water on Mars or take close-up pictures ofSaturn's rings(土星环). In 2020, video website Bilibili sent a satellite into space. Its job is to look at other planets and share the pictures and videos with Bilibili's users.