Geostationary Orbit

A satellite in a geostationary orbit appears to be in a fixed position to an earth-based observer. A geostationary satellite revolves around the earth at a constant speed once per day over the equator.
The geostationary orbit is useful for communications applications because ground based antennas, which must be directed toward the satellite, can operate effectively without the need for expensive equipment to track the satellite’s motion. Especially for applications that require a large number of ground antennas (such as direct TV distribution), the savings in ground equipment can more than justify the extra cost and onboard complexity of lifting a satellite into the relatively high geostationary orbit.

The concept of the geostationary communications satellite was first proposed by Arthur C. Clarke, building on work by Konstantin Tsiolkovsky and on the 1929 work by Herman Potočnik (writing as Herman Noordung) Das Problem der Befahrung des Weltraums - der Raketen-motor. In October 1945 Clarke published an article titled “Extra-terrestrial Relays” in the British magazine Wireless World. The article described the fundamentals behind the deployment of artificial satellites in geostationary orbits for the purpose of relaying radio signals. Thus Arthur C. Clarke is often quoted as being the inventor of the communications satellite.
The first truly geostationary satellite launched in orbit was the Syncom 3, launched on August 19, 1964. It was placed in orbit at 180° east longitude, over the International Date Line. It was used that same year to relay television coverage on the 1964 Summer Olympics in Tokyo to the United States, the first television transmission sent over the Pacific Ocean.
Shortly after Syncom 3, Intelsat I, aka Early Bird, was launched on April 6, 1965 and placed in orbit at 28° west longitude. It was the first geostationary satellite for telecommunications over the Atlantic Ocean.

On November 9, 1972, North America's first geostationary satellite serving the continent, Anik A1, was launched by Telesat Canada, with the United States following suit with the launch of Westar 1 by Western Union on April 13, 1974.
On December 19, 1974, the first geostationary communications satellite in the world to be three-axis stabilized was launched : the franco-German Symphonie.
After the launchings of Telstar, Syncom 3, Early Bird, Anik A1, and Westar 1, RCA Americom (later GE Americom, now SES Americom) launched Satcom 1 in 1975. It was Satcom 1 that was instrumental in helping early cable TV channels such as WTBS (now TBS Superstation), HBO, CBN (now ABC Family), and The Weather Channel become successful, because these channels distributed their programming to all of the local cable TV headends using the satellite. Additionally, it was the first satellite used by broadcast TV networks in the United States, like ABC, NBC, and CBS, to distribute their programming to all of their local affiliate stations. Satcom 1 was so widely used because it had twice the communications capacity of the competing Westar 1 in America (24 transponders as opposed to Westar 1’s 12), resulting in lower transponder usage costs. Satellites in later decades tended to even higher transponder counts.
By 2000 Hughes Space and Communications (now Boeing Satellite Development Center) had built nearly 40 percent of the satellites in service worldwide. Other major satellite manufacturers include Space Systems/Loral, Lockheed Martin (owns former RCA Astro Electronics/GE Astro Space business), Northrop Grumman, Alcatel Space, now Thales Alenia Space, with the Spacebus series, and EADS Astrium

source: wikipedia

Manned Spaceflight

A human spaceflight

is a spaceflight with a human crew, and possibly passengers. This makes it unlike robotic space probes or remotely-controlled satellites. Human spaceflight is sometimes called manned spaceflight, a term now deprecated by major space agencies in favor of its gender-neutral alternative.
As of 2008, only the American Space Shuttle program, the Russian Soyuz programme and the Chinese Shenzhou program are actively launching human spaceflights.

Early attempts at human spaceflight
In the early Christian era, a Greek satirist named Lucian wrote a book on space flight called True Histories. The book was full of tall, unbelieveable tales and travelogues on visits to the sun and the moon. Today, the book could easily be discarded as the fantasy of a people of a bygone era. But it was significant in the sense that it kindled the curiosities of the people of the day and stimulated interest in outer space and space travel.
In 1638, a Christian writer from England named Wilkins wrote a book on moon travel and suggested four methods to accomplish it. Firstly, he said, the divine soul could take man to the moon; secondly, some large and powerful birds could transport man to the moon; thirdly, man himself could make the journey by tying wings to his arms and fourthly, he said, a flying machine could transport man to the moon.
American author Herbert S. Zim claimed in 1945 that there is a Chinese legend where a scientist named Wan Hu in the early Ming dynasty attempted to travel through space with the help of rockets. In the story, Wan tied 47 rockets filled with explosives to the chair in which he was sitting and ignited them. There was a large explosion, but when the smoke cleared Wan Hu was gone and never seen again.

History
The first human spaceflight was undertaken on April 12, 1961, when cosmonaut Yuri Gagarin made one orbit around the Earth aboard the Vostok 1 spacecraft launched by the Soviet Union. Valentina Tereshkova became the first woman in space on board Vostok 6 on June 16, 1963. Both spacecraft were launched by Vostok 3KA launch vehicles. Alexei Leonov made the first spacewalk when he left the Voskhod 2 on March 8, 1965. Svetlana Savitskaya became the first woman to do so on July 25, 1984.

The United States became the second nation to achieve manned spaceflight with the suborbital flight of astronaut Alan Shepard aboard Freedom 7, carried out as part of Project Mercury. The spacecraft was launched on May 5, 1961 on a Redstone rocket. The first U.S. orbital flight was that of John Glenn aboard Friendship 7, which was launched February 20, 1962 on an Atlas rocket. Since April 12, 1981 the U.S. has conducted all its huan spaceflight missions with reusable Space Shuttles. Sally Ride became the first American woman in space in 1983. Eileen Collins was the first female Shuttle pilot, and with Shuttle mission STS-93 in July of 1999 she became the first woman to command a U.S. spacecraft.

The People's Republic of China became the third nation with human spaceflight when astronaut Yang Liwei launched into space on a Chinese-made vehicle, the Shenzhou 5, on October 15, 2003. This flight made China the third nation capable of launching its own manned spacecraft using its own launcher. Previous European (Hermes) and Japanese (HOPE-X) domestic manned programs were abandoned after years of development, as was the first Chinese attempt, the Shuguang spacecraft.

The furthest destination for a human spaceflight mission has been the Moon, and as of 2007 the only missions to the Moon have been those conducted by NASA as part of the Apollo program. The first such mission, Apollo 8, orbited the Moon but did not land.

The first Moon landing mission was Apollo 11, during which -- on July 20, 1969 -- Neil Armstrong became the first person to set foot on the Moon. Six missions landed in total, numbered Apollo 11–17, excluding Apollo 13. Altogether twelve men reached the Moon's surface, the only humans to have been on an extraterrestrial body.

The Soviet Union discontinued its program for lunar orbiting and landing of human spaceflight missions on June 24, 1974 when Valentin Glushko became General Designer of NPO Energiya.

The longest single human spaceflight is that of Valeriy Polyakov, who left earth on January 8, 1994, and didn't return until March 22, 1995 (a total of 437 days 17 hr. 58 min. 16 sec. aboard). Sergei Krikalyov has spent the most time of anyone in space, 803 days, 9 hours, and 39 seconds altogether.

Mankind has had a presence in space for as long as 3,644 days in a row, eight days short of 10 years, spanning the launch of Soyuz TM-8 on September 5, 1989 to the landing of Soyuz TM-29 on August 28, 1999.

For many years beginning in 1961, only two countries, the USSR (later Russia) and United States, had their own astronauts. Later, cosmonauts and astronauts from other nations flew in space, beginning with the flight of Vladimir Remek, a Czech, on a Soviet spacecraft on March 2, 1978. As of 2007, citizens from 33 nations (including space tourists have flown in space aboard Soviet, American, Russian, and Chinese spacecraft.

Space programs
As of 2007, human spaceflight missions have been conducted by the Soviet Union, the United States, Russia, the People's Republic of China and by the private spaceflight company Scaled Composites.

Several other countries and space agencies have announced and begun human spaceflight programs by their own technology, including Japan (JAXA), India (ISRO), Iran (ISA), Malaysia (MNSA) and Turkey.

Currently the following spacecraft and spaceports are used for launching human spaceflights:

Soyuz with Soyuz launch vehicle—Baikonur Cosmodrome

Space Shuttle—Kennedy Space Center
International Space Station (ISS)—Assembled in orbit; crews transported by

the previous two spacecraft

Shenzhou spacecraft with Long March rocket—Jiuquan Satellite Launch Center

Historically, the following spacecraft and spaceports have also been used for

human spaceflight launches:

Vostok— Baikonur Cosmodrome
Mercury— Kennedy Space Center
Voskhod— Baikonur Cosmodrome
X-15— Edwards Air Force Base, (two internationally recognized suborbital flights in program)
Gemini— Kennedy Space Center
Apollo— Kennedy Space Center
Salyut space station— Baikonur Cosmodrome
Almaz space station— Baikonur Cosmodrome
Skylab space station— Kennedy Space Center
Mir space station— Baikonur Cosmodrome
SpaceShipOne with White Knight— Mojave Spaceport

Numerous private companies attempted human spaceflight programs in an effort to win the $10 million Ansari X Prize.

The first private human spaceflight took place on June 21, 2004, when SpaceShipOne conducted a suborbital flight. With its second flight within one week, SpaceShipOne captured the prize on October 4, 2004.

Most of the time, the only humans in space are those aboard the ISS, whose crew of three spends up to six months at a time in low Earth orbit.

NASA and ESA now use the term "human spaceflight" to refer to their programs of launching people into space. Traditionally, these endeavors have been referred to as "manned space missions".

Adverse effects of radiation
The effect of radiation on space travelers depends on two main factors: the intensity of the radiation, and the time over which the exposure occurs. Astronauts in low earth orbit are exposed to radiation of relatively low intensity for long periods of time. The Apollo astronauts were exposed to much more intense radiation, but only for a matter of days. Astronauts on hypothetical future interplanetary missions would be exposed to high intensities for long periods, causing the accumulation of very large doses; this is currently one of the most important unsolved problems facing planners of such efforts.

Adverse effects of the microgravity environment
Medical data from astronauts in low earth orbits for long periods, dating back to the 1970's, show several adverse effects of a microgravity environment: loss of bone density, decreased muscle strength and endurance, postural instability, and reductions in aerobic capacity. Over time these deconditioning effects can impair astronauts’ performance or increase their risk of injury

In human spaceflight

the life support system is a group of devices that allow a human being to survive in outer space. NASA often uses the phrase Environmental Control and Life Support System or the acronym ECLSS when describing these systems for its human spaceflight missions. The life support system may supply: air, water and food. It must also maintain the correct body temperature, an acceptable pressure on the body and deal with the body's waste products. Shielding against harmful external influences such as radiation and micro-meteorites may also be necessary. Components of the life support system are life-critical, and are designed and constructed using safety engineering techniques

Life support functions

Human physiological & metabolic needs
A crewmember of typical size requires approximately 5 kg (total) of food, water, and oxygen per day to perform the standard activities on a space mission, and outputs a similar amount in the form of waste solids, waste liquids, and carbon dioxide.

The mass breakdown of these metabolic parameters is as follows: 0.84 kg of oxygen, 0.62 kg of food, and 3.52 kg of water consumed, converted through the body's physiological processes to 0.11 kg of solid wastes, 3.87 kg of liquid wastes, and 1.00 kg of carbon dioxide produced.

These levels can vary due to activity level, specific to mission assignment, but will correlate to the principles of mass balance. Actual water use during space missions is typically double the specified values mainly due to non-biological use (i.e. personal cleanliness).

Additionally, the volume and variety of waste products varies with mission duration to include hair, finger nails, skin flaking, and other biological wastes in missions exceeding one week in length. Other environmental considerations such as radiation, gravity, noise, vibration, and lighting also factor into human physiological response in space, though not with the more immediate effect that the metabolic parameters have.

Atmosphere
Space life support systems provide atmospheres composed primarily of oxygen, nitrogen, water, carbon dioxide, and other trace gases. The partial pressures of each component gas additively combine to the overall barometric pressure, typically 101.3 kPa (Earth standard atmospheric pressure at sea-level). However, atmospheric pressure can be significantly lower (25-26 kPa for EVAs) given a corresponding increase in the partial pressure of oxygen. Lower atmospheric pressures are advantageous for designing spacecraft with less structural mass and reduced atmospheric loss. The two primary ways of achieving this are by reducing atmospheric pressure while keeping the percent of oxygen the same (~21%) or through allowing the oxygen concentration to remain at sea-level pressure while reducing the overall barometric pressure.

source: wikipedia