We are all space travelers. But we’

We are all space travelers. But we’ve stayed close to home until now. One day, we may leave our “mother ship” Earth to make our home among the stars. A giant, spherical “spaceship”, about 8,000 miles in diameter, is speeding through the solar system right now. It is cruising at an incredible 66,600 miles per hour. It’s not a giant, Star Wars mother ship. It’s spaceship Earth, the home of over four billion people. This water coated spaceship has been traveling through the universe for about five billion years. Only within the past 25 years, however, have some of its passengers broken free of Earth’s gravity. But 25 years from now, many people, including you, might live in an orbiting space station 200 miles above the Earth.Space CitiesScientists have already designed special space factories. These factories will take advantage of the absence of gravity (zero gravity) to produce everything from life-saving drugs to perfect ball bearings. Other scientists have designed space colonies, complete with farms, schools, and artificial day and night. Hundreds, or even thousands, of people will live, work, play—even go to school, far above the Earth. Our conquest of space, of course, has already begun. We have explored part of the Moon, sent robot spaceships onto the surface of Venus and Mars, and aimed space probes past the planets of Jupiter and Saturn.Last June, one robot ship, Pioneer 10, left our solar system forever. And astronauts from both the Soviet Union and the United States have lived in space stations. The conquest of space, without question, is one of the greatest adventures human beings have ever set out on. But it may be more than a great adventure. Some scientists think the conquest of space may be a necessity for survival of the human species. We are tearing up more and more of the Earth to get raw materials for industry. And we are polluting the air and water as we manufacture products that we need or want. Almost everything that seems to make our lives more comfortable, and from electricity to pesticides, uses up or alters a piece of our planet’s natural environment.Why Go into Space?Yet our solar system is full of resources. The moon is chockfull of valuable metals. So are the asteroids, the small, rocky, planet-like bodies orbiting the sun most of them between Mars and Jupiter. These metals, if we can get them, could be used to build factories and space stations. Also, in space, there is no atmosphere to filter out the sun’s energy. There is plenty of solar energy to be turned into electricity for manufacturing, for creating comfortable living conditions.Getting away from Earth has other advantages, too. Modern industry uses many kinds of metal alloys (mixtures of metal that are better for certain purposes than pure metals). Yet some metal alloys either can’t be made or are very expensive to make on Earth because of gravity. For instance, certain metals don’t mix well on Earth. But in zero gravity, molten (hot, liquid) metals mix more evenly. This is because there is no gravity to pull the heavier metals down, while the lighter ones float on top.