SPACE TRAVEL II
Since the Apollo Moon missions were completed in 1972, no astronauts have been further than Earth orbit, but many unmanned spacecraft, called space probes, have visited the other planets in our Solar System. Probes carry cameras and sensing equipment that send back photographs and other data. Some probes actually land on the planets’ surfaces. Hundreds of satellites for communications, weather forecasting, scientific research and astronomy, have also been launched into Earth orbit.
The first permanent space station, Salyut 1, was launched in 1971. Inside space stations, astronauts carry out experiments to see how people react to staying in space for long periods, and how plants and animals cope with very low gravity. Probes, satellites, space stations and their crews are lifted into space by launch vehicles such as the European Ariane space rocket, or by the American space shuttle.
At lift-off, the shuttle is made up of the winged orbiter, where the astronauts travel, a huge fuel tank, which supplies fuel to the orbiter’s three main rocket engines, and two booster rockets, attached to the fuel tank. The fuel tank contains liquid oxygen and hydrogen. The booster rockets use solid fuel. They work like huge fireworks, and cannot be switched off after ignition. The orbiter also has two smaller engines called the orbital manoeuvring system (OMS), and clusters of small gas-powered thrusters at the nose and tail, used for small manoeuvres in orbit.
Soon after lift-off, the shuttle turns on to its back. The booster rockets last for two minutes, then separate from the fuel tank and parachute back to Earth for re-use. The fuel in the external tank runs out after nine minutes, after which the orbiter jettisons it and it falls back into the atmosphere, where it burns up because of the intense heat created. The orbiter is now on its own. The OMS engines are fired for a short time to accelerate the orbiter into its correct orbit.
The space shuttle was designed as a re-usable spacecraft because of the huge cost of rockets and craft such as the Saturn V and Apollo, all the parts of which were completely destroyed during a mission. The shuttle flies into space like a rocket and glides back to Earth like an aeroplane.
During “extra-vehicular activity” outside their spacecraft, astronauts are protected from the cold, high-speed meteorites and radiation from the Sun by a complex spacesuit. Astronauts sometimes use a manned-manoeuvring unit (MMU), powered by tiny gas jets, which allows them to manoeuvre freely in space.
Less than fifteen minutes after launch, the shuttle is in orbit at an altitude of about 200 km. Now the astronauts can carry out their mission – in this case, launching a satellite from the “payload bay” (in the upper part of the orbiter’s fuselage) using the orbiter’s remotely-controlled robot arm. With the mission complete, the OMS engines slow down the orbiter so that it begins to fall back to Earth.
During re-entry into the atmosphere, heat-resistant ceramic tiles protect the orbiter from the intense heat. It gradually slows as it descends, and finally glides back on to a runway like an aeroplane.
The whole shuttle, except for the large fuel tank, which is destroyed during launch, can be re-used. The first shuttle mission was flown by the shuttle Columbia in 1981. Since then, there have been dozens of missions to launch or repair satellites, service space stations, and carry out scientific and military research.
FUTURE SPACE TRAVEL
At the beginning of the twenty-first century, travelling even to Earth’s closest neighbour planet Mars, let alone planets in other solar systems, is still impractical. A trip to Mars and back would take more than a year. The equipment, supplies and fuel for such a trip would require a vast rocket to launch a spacecraft from Earth. A return trip to the outer planets would take a lifetime without some new form of propulsion with much greater power than a rocket engine. For the time being, space probes remain the best way of exploring distant worlds.
Work is under way on a new international space station, which will be a base for scientific research. It is a modular structure, being built in space module-by-module, with sections being delivered into orbit by the shuttle and unmanned launch vehicles. In the future, space stations such as this, or permanent bases on the Moon, could be a starting point for space journeys. Spacecraft would be built and launched from there rather than from Earth.
New types of reusable vehicles, called spaceplanes, which will carry supplies to space stations, are under development. They will take off and gain altitude like aeroplanes, with their engines working like jet engines, and then make the jump to orbit with their engines working like rocket engines. Spaceplanes could also make passenger flights, cutting the journey time between Europe and Australia to under two hours. The international space station will have a spaceplane “lifeboat” for the crew.
Picture Credit : Google
