Every now and then you may see news of satellites sent into space. On Feb 21, for example, US company Space X took 46 satellites into orbit(轨道). On Feb 27, 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, from sending 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 the Beidou Navigation Satellite System(北斗卫星导航系统). Shared bikes that use BeiDou chips(芯片) can have more accurate(精准的) positioning, so people will find them easily. Drones(无人机) can also use BeiDou to fly.

Before satellites, TV signals didn’t go very far. Mountains or tall buildings would stop them. Phone calls to faraway places were also a problem. Setting up telephone wires (线) over long distances is difficult. With satellites, TV signals and phone calls can be sent directly to a satellite and back down to different places 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. By watching and checking wildfires and volcanoes, satellites help emergency workers deal with natural disasters. Farmers can use satellite pictures 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 of Saturn’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.

A．

B．

C．

D．

How our travel choices impact the climate

Travelling in cars, trucks, planes, and other vehicles has an effect on climate change. But how bad is each type of transportation? Let’s take a look. For more information, see the 2022 book The Carbon Footprint of Everything by Mike.

Buses and trains carry a lot of people. So the carbon impact (影响) of the ride gets divided among all the passengers. The fuel powering a bus or train also needs to push all the weight of the people and the bus or train itself. Trains are extremely large and heavy. All that extra weight makes the climate impact of a typical train ride more than the impact of a typical bus ride.

—Bus wins!

When people must drive, what type of car is best? Electric cars are fantastic, but they’re not perfect. According to Mike, the fuel powering a car only accounts for about 50 percent of its impact. The other half comes mostly from building and maintaining a car. Factories make or assemble (组装) parts for new cars. All of this requires energy.

In general, Mike says, the most climate-friendly choice is to keep an old car as long as possible, or buy a small used car instead of a new one.

—Old car wins!

Only about two percent of global emissions (排放) come from air travel. But that is mainly because it’s much less common than other forms of travel. Even though planes carry more people than cars, a plane trip is usually far worse for the climate. Getting a heavy plane up into the sky and keeping it there burns lots of fuel. And today we can’t switch to electric passenger planes because batteries aren’t yet powerful enough. Also, burning fuel high in the sky has a greater impact on climate change than burning the same amount of fuel close to the ground. “It’s hard to avoid the conclusion that we need to fly less,” writes Mike.

—Car wins!

Many people dream of traveling into the space. ________ That’s why astronauts shouldn’t spend more than six months on the International Space Station (ISS) at a time.

Muscle (肌肉) and bone loss. In a weightless environment, astronauts don’t need to use their muscles to support themselves, so their muscles start shrinking (萎缩). To keep their muscles strong, astronauts need to exercise about two hours each day on the ISS.

Sleep disorder (混乱). In space, the sun rises every ninety minutes. It is hard for astronauts to get used to this light-dark cycle when they sleep. Also, they need to sleep in a sleeping bag that is fixed to a wall, and it is uncomfortable. Astronauts now have individual sleeping pods (分离舱)   that help shut out some of the light. Still, studies have found that most astronauts only sleep about six hours each night, even though they should have eight and a half hours.

Brain changes. Scientists have found that the position (位置) of the brain changes during spaceflight. It can affect (影响) how the brain deal with how we see, stay balanced and move around. That’s why some astronauts can’t control their movement and balance after returning to the earth. Scientists have also found that astronauts may get used to this change after going on more spaceflights. But they still need to do more research.

A．

B．

C．