Meeting basic needs in space

  Piloted space vehicles have life-support systems designed to meet all the physical needs of the crew members. In addition, astronauts can carry portable life-support systems in backpacks when they work outside the main spacecraft.

Breathing

   A piloted spacecraft must have a source of oxygen for the crew to breathe and a means of removing carbon dioxide, which the crew exhales. Piloted space vehicles use a mixture of oxygen and nitrogen similar to Earth's atmosphere at sea level. Fans circulate air through the cabin and over containers filled with pellets of a chemical called lithium hydroxide. These pellets absorb carbon dioxide from the air. Carbon dioxide can also be combined with other chemicals for disposal. Charcoal filters help control odors.

Eating and drinking

   The food on a spacecraft must be nutritious, easy to prepare, and convenient to store. On early missions, astronauts ate freeze-dried foods -- that is, frozen foods with the water removed. To eat, the astronauts simply mixed water into the food. Packaging consisted of plastic tubes. The astronauts used straws to add the water.

   Over the years, the food available to space travelers became more appetizing. Today, astronauts enjoy ready-to-eat meals much like convenience foods on Earth. Many space vehicles have facilities for heating frozen and chilled food.

    Water for drinking is an important requirement for a space mission. On space shuttles, devices called fuel cells produce pure water as they generate electricity for the spacecraft. On long missions, water must be recycled and reused as much as possible. Dehumidifiers remove moisture from exhaled air. On space stations, this water is usually reused for washing.

Eliminating body wastes

   The collection and disposal of body wastes in microgravity poses a major challenge. Astronauts use a device that resembles a toilet seat. Air flow produces suction that moves the wastes into collection equipment under the seat. On small spacecraft, crew members use funnels for urine and plastic bags for solid wastes. While working outside the spacecraft, astronauts wear special equipment to contain body wastes.

Bathing
 

   The simplest bathing method aboard a spacecraft is a sponge bath with wet towels. Astronauts on early space stations used a fully enclosed, collapsible plastic shower stall. This allowed the astronauts to spray their bodies with water, then vacuum the stall and towel themselves dry. Newer space stations have permanent shower stalls. 

Sleeping

  Space travelers can sleep in special sleeping bags with straps that press them to the soft surface and to a pillow. However, most astronauts prefer to sleep floating in the air, with only a few straps to keep them from bouncing around the cabin. Astronauts may wear blindfolds to block the sunlight that streams in the windows periodically during orbit. Typically, sleep duration in space is about the same as that on Earth. 

 

  Recreation

  Recreation on long space flights is important to the mental health of the astronauts. Sightseeing out the spacecraft window is a favorite pastime. Space stations have small collections of books, tapes, and computer games. Exercise also provides relaxation.

Controlling inventory and trash

  Keeping track of the thousands of items used during a mission poses a major challenge in space. Drawers and lockers hold some materials. Other equipment is strapped to the walls, ceilings, and floors. Computer-generated lists keep track of what is stored where, and computerized systems check the storage and replacement of materials. The crew aboard the spacecraft may stow trash in unused sections of the vehicle, throw it overboard to burn up harmlessly in the atmosphere, or bring it back to Earth for disposal.

Communicating with Earth  

  Communication between astronauts in space and mission control, the facility on Earth that supervises their space flight, occurs in many ways. The astronauts and mission controllers can talk to each other by radio. Television pictures can travel between space vehicles and Earth. Computers, sensors, and other equipment continuously send signals to Earth for monitoring. Facsimile machines on spacecraft also can receive information from Earth.

Working in space
 
  Once a space vehicle reaches its orbit, the crew members begin to carry out the goals of their mission. They perform a variety of tasks both inside and outside the spacecraft.

Navigation, guidance, and control
 
  Astronauts use computerized navigation systems and make sightings on stars to determine their position and direction. On Earth, sophisticated tracking systems measure the spacecraft's location in relation to Earth. Astronauts typically use small firings of the spacecraft's rockets to tilt the vehicle or to push it in the desired direction. Computers monitor these changes to ensure they are done accurately.

Activating equipment
 
  Much of the equipment on a space vehicle is turned off or tied down during launch. Once in space, the astronauts must set up and turn on the equipment. At the end of the mission, they must secure it for landing.

Conducting scientific observations and research
 
  Astronauts use special instruments to observe Earth, the stars, and the sun. They also experiment with the effects of microgravity on various materials, plants, animals, and themselves.

Docking

  As a spacecraft approaches a target, such as a space station or an artificial satellite, radar helps the crew members control the craft's course and speed. Once the spacecraft reaches the correct position beside the target, it docks (joins) with the target by connecting special equipment. Such a meeting in space is called a rendezvous. A space shuttle can also use its robot arm to make contact with targets.

Maintaining and repairing equipment

  The thousands of pieces of equipment on a modern space vehicle are extremely reliable, but some of them still break down. Accidents damage some equipment. Other units must be replaced when they get old. Astronauts must find out what has gone wrong, locate the failed unit, and repair or replace it.

Assembling space stations
 
  Astronauts may serve as construction workers in space, assembling a space station from components carried up in the shuttle. On existing space stations, crews often must add new sections or set up new antennas and solar panels. Power and air connectors must be hooked up inside and outside the station.

 To sleep aboard a spacecraft, astronauts can zip themselves into sleeping bags strapped to the wall. Blindfolds block the sunlight that streams in the windows periodically during orbit. Image credit: NASA

Microgravity

  Once in orbit, the space vehicle and everything inside it experience a condition called microgravity. The vehicle and its contents fall freely, resulting in an apparently weightless floating aboard the spacecraft. For this reason, microgravity is also referred to as zero gravity. However, both terms are technically incorrect. The gravitation in orbit is only slightly less than the gravitation on Earth. The spacecraft and its contents.

  continuously fall toward Earth. But because of the vehicle's tremendous forward speed, Earth's surface curves away as the vehicle falls toward it. The continuous falling seems to eliminate the weight of everything inside the spacecraft. For this reason, the condition is sometimes referred to as weightlessness.

  Microgravity has major effects on both equipment and people. For example, fuel does not drain from tanks in microgravity, so it must be squeezed out by high-pressure gas. Hot air does not rise in microgravity, so air circulation must be driven by fans. Particles of dust and droplets of water float throughout the cabin and only settle in filters on the fans.

  The human body reacts to microgravity in a number of ways. In the first several days of a mission, about half of all space travelers suffer from persistent nausea, sometimes accompanied by vomiting. Most experts believe that this "space sickness," called space adaptation syndrome, is the body's natural reaction to microgravity. Drugs to prevent motion sickness can provide some relief for the symptoms of space adaptation syndrome, and the condition generally passes in a few days.

  Microgravity also confuses an astronaut's vestibular system -- that is, the organs of balance in the inner ear -- by preventing it from sensing differences in direction. After a few days in space, the vestibular system disregards all directional signals. Soon after an astronaut returns to Earth, the organs of balance resume normal operation.

An apparently weightless floating makes some tasks challenging inside an orbiting spacecraft. In this photograph, a shuttle astronaut struggles with a floating computer printout. Image credit: NASA

Recording medical information on a spacecraft enables physicians to identify any abnormal changes in the body that could indicate physical disorders or stress. Image credit: NASA

Space Exploration

  Space Exploration

  

  Space exploration is our human response to curiosity about Earth, the moon, the planets, the sun and other stars, and the galaxies. Piloted and unpiloted space vehicles venture far beyond the boundaries of Earth to collect valuable information about the universe. Human beings have visited the moon and have lived in space stations for long periods. Space exploration helps us see Earth in its true relation with the rest of the universe. Such exploration could reveal how the sun, the planets, and the stars were formed and whether life exists beyond our own world.

    The space age began on Oct. 4, 1957. On that day, the Soviet Union launched Sputnik (later referred to as Sputnik 1), the first artificial satellite to orbit Earth. The first piloted space flight was made on April 12, 1961, when Yuri A. Gagarin, a Soviet cosmonaut, orbited Earth in the spaceship Vostok (later called Vostok 1).

    Unpiloted vehicles called space probes have vastly expanded our knowledge of outer space, the planets, and the stars. In 1959, one Soviet probe passed close to the moon and another hit the moon. A United States probe flew past Venus in 1962. In 1974 and 1976, the United States launched two German probes that passed inside the orbit of Mercury, close to the sun. Two other U.S. probes landed on Mars in 1976. In addition to studying every planet except Pluto, space probes have investigated comets and asteroids. 

   The first piloted voyage to the moon began on Dec. 21, 1968, when the United States launched the Apollo 8 spacecraft. It orbited the moon 10 times and returned safely to Earth. On July 20, 1969, U.S. astronauts Neil A. Armstrong and Buzz Aldrin landed their Apollo 11 lunar module on the moon. Armstrong became the first person to set foot on the moon. United States astronauts made five more landings on the moon before the Apollo lunar program ended in 1972. 

   During the 1970's, astronauts and cosmonauts developed skills for living in space aboard the Skylab and Salyut space stations. In 1987 and 1988, two Soviet cosmonauts spent 366 consecutive days in orbit.

   On April 12, 1981, the United States space shuttle Columbia blasted off. The shuttle was the first reusable spaceship and the first spacecraft able to land at an ordinary airfield. On Jan. 28, 1986, a tragic accident occurred. The U.S. space shuttle Challenger tore apart in midair, killing all seven astronauts aboard. The shuttle was redesigned, and flights resumed in 1988. A second tragedy struck the shuttle fleet on Feb. 1, 2003. The Columbia broke apart as it reentered Earth's atmosphere, killing all seven of its crew members.

    In the early years of the space age, success in space became a measure of a country's leadership in science, engineering, and national defense. The United States and the Soviet Union were engaged in an intense rivalry called the Cold War. As a result, the two nations competed with each other in developing space programs. In the 1960's and 1970's, this "space race" drove both nations to tremendous exploratory efforts. The space race had faded by the end of the 1970's, when the two countries began to pursue independent goals in space. 

   A major dispute in the development of space programs has been the proper balance of piloted and unpiloted exploration. Some experts favor unpiloted probes because they may be cheaper, safer, and faster than piloted vehicles. They note that probes can make trips that would be too risky for human beings to attempt. On the other hand, probes generally cannot react to unexpected occurrences. Today, most space planners favor a combined, balanced strategy of unpiloted probes and piloted expeditions. Probes can visit uncharted regions of space or patrol familiar regions where the data to be gathered fall within expected limits. But in some cases, people must follow the probes and use human ingenuity, flexibility, and courage to explore the mysteries of the universe.

 

The solar-powered Helios Prototype aircraft, piloted by remote control, soars above the Hawaiian Islands. In August 2001, the aircraft reached a record-breaking altitude of 96,863 feet (29,524 meters). Helios, designed by engineers at the National Aeronautics and Space Administration (NASA), tested concepts that could be applied to an aircraft designed to fly in the thin atmosphere of Mars or Earth's upper atmosphere. Helios crashed during a test flight in June 2003. Image credit: NASA

What is space?
    Space is the near-emptiness in which all objects in the universe move. The planets and the stars are tiny dots compared with the vast expanse of space.

The beginning of space

  Earth is surrounded by air, which makes up its atmosphere. As the distance from Earth increases, the air becomes thinner. There is no clear boundary between the atmosphere and outer space. But most experts say that space begins somewhere beyond 60 miles (95 kilometers) above Earth. 

  Outer space just above the atmosphere is not entirely empty. It contains some particles of air, as well as space dust and occasional chunks of metallic or stony matter called meteoroids. Various kinds of radiation flow freely. Thousands of spacecraft known as artificial satellites have been launched into this region of space.

Earth's magnetic field, the space around the planet in which its magnetism can be observed, extends far out beyond the atmosphere. The magnetic field traps electrically charged particles from outer space, forming zones of radiation called the Van Allen belts.

   The region of space in which Earth's magnetic field controls the motion of charged particles is called the magnetosphere. It is shaped like a teardrop, with the point extending away from the sun. Beyond this region, Earth's magnetic field is overpowered by that of the sun. But even such vast distances are not beyond the reach of Earth's gravity. As far as 1 million miles (1.6 million kilometers) from Earth, this gravity can keep a satellite orbiting the planet instead of flying off into space.

  Space between the planets is called interplanetary space. The sun's gravity controls the motion of the planets in this region. That is why the planets orbit the sun.

    Huge distances usually separate objects moving through interplanetary space. For example, Earth revolves around the sun at a distance of about 93 million miles (150 million kilometers). Venus moves in an orbit 68 million miles (110 million kilometers) from the sun. Venus is the planet that comes closest to Earth -- 25 million miles (40 million kilometers) away -- whenever it passes directly between Earth and the sun. But this is still 100 times as far away as the moon.

   Space between the stars is called interstellar space. Distances in this region are so great that astronomers do not describe them in miles or kilometers. Instead, scientists measure the distance between stars in units called light-years. For example, the nearest star to the sun is Proxima Centauri, 4.2 light-years away. A light-year equals 5.88 trillion miles (9.46 trillion kilometers). This is the distance light travels in one year at its speed of 186,282 miles (299,792 kilometers) per second.

   Various gases, thin clouds of extremely cold dust, and a few escaped comets float between the stars. Interstellar space also contains many objects not yet discovered.

Getting into space and back  

    Overcoming gravity is the biggest problem for a space mission. A spacecraft must be launched at a particular velocity (speed and direction).

   Gravity gives everything on Earth its weight and accelerates free-falling objects downward. At the surface of Earth, acceleration due to gravity, called g, is about 32 feet (10 meters) per second each second.

   A powerful rocket called a launch vehicle or booster helps a spacecraft overcome gravity. All launch vehicles have two or more rocket sections known as stages. The first stage must provide enough thrust (pushing force) to leave Earth's surface. To do so, this stage's thrust must exceed the weight of the entire launch vehicle and the spacecraft. The booster generates thrust by burning fuel and then expelling gases. Rocket engines run on a special mixture called propellant. Propellant consists of solid or liquid fuel and an oxidizer, a substance that supplies the oxygen needed to make the fuel burn in the airlessness of outer space. Lox, or liquid oxygen, is a frequently used oxidizer. 

   The minimum velocity required to overcome gravity and stay in orbit is called orbital velocity. At a rate of acceleration of 3 g's, or three times the acceleration due to gravity, a vehicle reaches orbital velocity in about nine minutes. At an altitude of 120 miles (190 kilometers), the speed needed for a spacecraft to maintain orbital velocity and thus stay in orbit is about 5 miles (8 kilometers) per second. 

   In many rocket launches, a truck or tractor moves the rocket and its payload (cargo) to the launch pad. At the launch pad, the rocket is moved into position over a flame pit,  and workers load propellants into the rocket through special pipes. 

   At launch time, the rocket's first-stage engines ignite until their combined thrust exceeds the rocket's weight. The thrust causes the vehicle to lift off the launch pad. If the rocket is a multistage model, the first stage falls away a few minutes later, after its propellant has been used up. The second stage then begins to fire. A few minutes later, it, too, runs out of propellant and falls away. If needed, a small upper stage rocket then fires until orbital velocity is achieved.

  The launch of a space shuttle is slightly different. The shuttle has solid-propellant boosters in addition to its main rocket engines, which burn liquid propellant. The boosters combined with the main engines provide the thrust to lift the vehicle off the launch pad. After slightly more than two minutes of flight, the boosters separate from the shuttle and return to Earth by parachute. The main engines continue to fire until the shuttle has almost reached orbital velocity. Small engines on the shuttle push it the remainder of the way to orbital velocity.

 To reach a higher altitude, a spacecraft must make another rocket firing to increase its speed. When the spacecraft reaches a speed about 40 percent faster than orbital velocity, it achieves escape velocity, the speed necessary to break free of Earth's gravity.

  Returning to Earth involves the problem of decreasing the spacecraft's great speed. To do this, an orbiting spacecraft uses small rockets to redirect its flight path into the upper atmosphere. This action is called de-orbit. A spacecraft returning to Earth from the moon or from another planet also aims its path to skim the upper atmosphere. Air resistance then provides the rest of the necessary deceleration (speed reduction). 

  At the high speeds associated with reentering the atmosphere from space, air cannot flow out of the way of the onrushing spacecraft fast enough. Instead, molecules of air pile up in front of it and become tightly compressed. This squeezing heats the air to a temperature of more than 10,000 degrees F (5,500 degrees C), hotter than the surface of the sun. The resulting heat that bathes the spacecraft would burn up an unprotected vehicle in seconds. Insulating plates of quartz fiber glued to the skin of some spacecraft create a heat shield that protects against the fierce heat. Refrigeration may also be used. Early spacecraft had ablative shields that absorbed heat by burning off, layer by layer, and vaporizing. 

   Many people mistakenly believe that the spacecraft skin is heated through friction with the air. Technically, this belief is not accurate. The air is too thin and its speed across the spacecraft's surface is too low to cause much friction.

    For unpiloted space probes, deceleration forces can be as great as 60 to 90 g's, or 60 to 90 times the acceleration due to gravity, lasting about 10 to 20 seconds. Space shuttles use their wings to skim the atmosphere and stretch the slowdown period to more than 15 minutes, thereby reducing the deceleration force to about 11/2 g's.

    When the spacecraft has lost much of its speed, it falls freely through the air. Parachutes slow it further, and a small rocket may be fired in the final seconds of descent to soften the impact of landing. The space shuttle uses its wings to glide to a runway and land like an airplane. The early U.S. space capsules used the cushioning of water and "splashed down" into the ocean.

Launch vehicles used in the United States include the Titan 4 rocket, the Atlas 5 rocket, and the space shuttle. These vehicles carry space probes and artificial satellites into outer space. The space shuttle has also carried people and International Space Station modules. Image credit: World Book illustrations by Oxford Illustrators Limited

Launch vehicles used by Asian nations include India's PSLV rocket, China's Long March 3B rocket, and Japan's H-IIA rocket. These vehicles carry space probes and artificial satellites into outer space. The Long March rocket also launches the Shenzhou spacecraft, which can carry people into orbit. Image credit: World Book illustrations by Oxford Illustrators Limited

Launch vehicles used by European nations include the European Space Agency's Ariane 5 rocket and Russia's A class and Proton rockets. These vehicles carry space probes and artificial satellites into outer space. The A Class rocket has also carried people into space, and the Proton rocket has carried International Space Station modules. Image credit: World Book illustrations by Oxford Illustrators Limited

Living in space

  When people orbit Earth or travel to the moon, they must live temporarily in space. Conditions there differ greatly from those on Earth. Space has no air, and temperatures reach extremes of heat and cold. The sun gives off dangerous radiation. Various types of matter also create hazards in space. For example, particles of dust called micrometeoroids threaten vehicles with destructive high-speed impacts. Debris (trash) from previous space missions can also damage spacecraft.

  On Earth, the atmosphere serves as a natural shield against many of these threats. But in space, astronauts and equipment need other forms of protection. They must also endure the physical effects of space travel and protect themselves from high acceleration forces during launch and landing.

  The basic needs of astronauts in space must also be met. These needs include breathing, eating and drinking, elimination of body wastes, and sleeping.

Protection against the dangers of space  

   Engineers working with specialists in space medicine have eliminated or greatly reduced most of the known hazards of living in space. Space vehicles usually have double hulls for protection against impacts. A particle striking the outer hull disintegrates and thus does not damage the inner hull.

  Astronauts are protected from radiation in a number of ways. Missions in earth orbit remain in naturally protected regions, such as Earth's magnetic field. Filters installed on spacecraft windows protect the astronauts from blinding ultraviolet rays.

  The crew must also be protected from the intense heat and other physical effects of launch and landing. Space vehicles require a heat shield to resist high temperatures and sturdy construction to endure crushing acceleration forces. In addition, the astronauts must be seated in such a way that the blood supply will not be pulled from their head to their lower body, causing dizziness or unconsciousness.

   Aboard a spacecraft, temperatures climb because of the heat given off by electrical devices and by the crew's bodies. A set of equipment called a thermal control system regulates the temperature. The system pumps fluids warmed by the cabin environment into radiator panels, which discharge the excess heat into space. The cooled fluids are pumped back into coils in the cabin.

Dwarf Planets

What is a planet? We've been asking that question at least since Greek astronomers came up with the word to describe the bright points of light that seemed to wander among fixed stars. Our solar system's planet count has soared as high as 15 before it was decided that some discoveries were different and should be called asteroids.

Many disagreed in 1930 when Pluto was added as our solar system's ninth planet. The debate flared again in 2005 when Eris - bigger than Pluto - was found deep in a zone beyond Neptune called the Kuiper Belt. Was it the 10th planet? Or are Eris and Pluto examples of an intriguing, new kind of world?

The International Astronomical Union decided in 2006 that a new system of classification was needed to describe these new worlds, which are more developed than asteroids, but different than the known planets. Pluto, Eris and the asteroid Ceres became the first dwarf planets. Unlike planets, dwarf planets lack the gravitational muscle to sweep up or scatter objects near their orbits. They end up orbiting the Sun in zones of similar objects such as the asteroid and Kuiper belts.

Our solar system's planet count now stands at eight. But the lively debate continues as we enter another exciting decade of exploration and discoveries.

Beyond Our Solar System

Before 1991, the worlds of our own solar system were the only known planets. Astronomers did not believe that our sun's environment was the only planet producer in the universe. But they had no evidence of planets outside our solar system.
How quickly things change.
In 1991 radio astronomers detected the first extrasolar planets orbiting a dying pulsar star. Although the deadly radiation from the pulsar would not sustain life, it was the first example of a star other than our Sun producing planets.
Since then more than 450 planets have been found orbiting other stars. Some of them are orbiting extremely close to their parent star like the 51 Peg planetary system, while others are found to be at distances comparable to where Mars and Jupiter orbit in our solar system.

Our Solar System

From our small world we have gazed upon the cosmic ocean for thousands of years. Ancient astronomers observed points of light that appeared to move among the stars. They called these objects planets, meaning wanderers, and named them after Roman deities - Jupiter, king of the gods; Mars, the god of war; Mercury, messenger of the gods; Venus, the goddess of love and beauty, and Saturn, father of Jupiter and god of agriculture. The stargazers also observed comets with sparkling tails, and meteors - or shooting stars apparently falling from the sky.

Since the invention of the telescope, three more planets have been discovered in our solar system: Uranus (1781), Neptune (1846), and Pluto (1930). Pluto was reclassified as a dwarf planet in 2006. In addition, our solar system is populated by thousands of small bodies such as asteroids and comets. Most of the asteroids orbit in a region between the orbits of Mars and Jupiter, while the home of comets lies far beyond the orbit of Pluto, in the Oort Cloud.
The four planets closest to the Sun - Mercury, Venus, Earth, and Mars - are called the terrestrial planets because they have solid rocky surfaces. The four large planets beyond the orbit of Mars - Jupiter, Saturn, Uranus, and Neptune - are called the gas giants. Beyond Neptune, on the edge of the Kuiper Belt, tiny, distant, dwarf planet Pluto has a solid but icier surface than the terrestrial planets.