Practice 4　　The furthest we have been is the Moon. If we want to travel into deep space, beyond our own backyard, the Solar System, we’ll need a new breed of spacecraft.　　It may be the oldest clich6 in town, but in the not too distant future science fiction will turn into science fact. The fantastic spaceships of sci-fi comic books and novels will no longer be a figment of our creative imagination; they may be the real vision of our future.　　Engineers and designers are already designing craft capable of propelling us beyond Earth’s orbit, the Moon and the planets. They’re designing interstellar spaceships capable of travel across the vast emptiness of deep space to distant stars and new planets in our unending quest to conquer and discover. Our Universe contains over a billion galaxies; star cities each with a hundred billion inhabitants. Around these stars must exist planets and perhaps life. The temptation to explore these new realms is too great.　　First things first-we’ll have to build either a giant orbiting launch platform, far bigger than the International Space Station (ISS), or a permanently manned lunar base to provide a springboard for the stars. Some planners feel we should limit ourselves to robotic probes, but others are firmly committed to sending humans. “There’s a debate right now about how to explore space,” says astronaut Bill Shepherd, destined to be the first five-aboard Commander of the ISS. “Humans or machines-I think they’re complementary.”　　The Human Problem　　Space is the most hostile environment we will ever explore. Even a single five-hour spacewalk requires months of training, and a vast technical backup to keep it safe. The astronauts and cosmonauts who live aboard the ISS will be there for only a few weeks or months; if we want to travel into deep space it could take years. First we’ll have to find out just how long the human body can survive in a weightless environment. In zero gravity, four pints of body fluid rush from the legs to the head where it stays for the duration of the mission. Astronauts often feel as if they have a permanent cold, and disorientation can become a major problem. In space there’s no physical sensation to let you know when you’re upside down and astronauts have to rely on visual clues from their surroundings. A few hours after reaching orbit, one in three of all astronauts will experience space sickness-a feeling rather like carsickness.  And weightless conditions lead to calcium being leached from the bones, and problems with the astronauts’ immune systems.　　Trillions of rocky fragments-meteoroids-roam our Solar System at speeds of up to150, 000 miles an hour. A meteoroid no bigger than a grain of salt could pierce a spaceship window. Protection from the extreme hazards of space is going to need some clever technology. Space is also full of lethal radiation-X-rays, gamma rays and the high-speed particles called cosmic rays.