How Space Stations Work

There are a variety of reasons for building and operating space stations, including research, industry, exploration and even tourism. The first space stations were built to study the long-term effects of weightlessness on the human body. After all, if astronauts will ever venture to Mars or other planets, then we must know how prolonged microgravity on the order of months to years will affect their health.

Space stations are a place to do cutting edge scientific research in an environment that cannot be matched on Earth. For example, gravity alters the way that atoms come together to form crystals. In microgravity, near-perfect crystals can be formed. Such crystals can yield better semi-conductors for faster computers or for more efficient drugs to combat diseases. Another effect of gravity is that it causes convection currents to form in flames, which leads to unsteady flames. This makes the study of combustion very difficult. However, in microgravity, simple, steady, slow-moving flames result; these types of flames make it easier to study the combustion process. The resulting information could yield a better understanding of the combustion process, and lead to better designs of furnaces or the reduction of air pollution by making combustion more efficient.

From high above the Earth, space stations offer unique views to study the Earth's weather, landforms, vegetation, oceans and atmosphere. In addition, because space stations are above the Earth's atmosphere, they can be used as manned observatories where space telescopes can look out upon the heavens. The Earth's atmosphere doesn't interfere in the views of space station telescopes. In fact, we've already seen the advantages of unmanned space telescopes like the Hubble space telescope.

Space stations might be used for space hotels. Here, private companies like Virgin Galactic could ferry tourists from Earth to space hotels for brief visits or extended stays. To this end, Galactic Suite, a private company based in Barcelona Spain and lead by space engineer Xavier Calramunt, claims to be on track for having a space hotel in orbit by 2012. Even grander extensions of tourism are that space stations could become space ports for expeditions to the planets and stars or even new cities and colonies that could relieve an overpopulated planet.

Now that you know why we might need them, let's "visit" some space stations. We will start with the Russian Salyut program -- the first space station.

Russia (then known as the Soviet Union) was the first to place a space station. The Salyut 1 station, which went into orbit in 1971, was actually a combination of the Almaz and Soyuz spacecraft systems. The Almaz system was originally designed for space military purposes, but repurposed for the civilian Salyut space station. The Soyuz spacecraft ferried cosmonauts from Earth to the space station and back.

Salyut 1 was about 45 feet (15 meters) long and held three main compartments that housed dining and recreation areas, food and water storage, a toilet, control stations, exercise equipment and scientific equipment. Initially, the Soyuz 10 crew was supposed to live aboard Salyut 1, but their mission was plagued with docking problems that prevented them from entering the space station. The Soyuz 11 crew was the first crew to successfully live on Salyut 1, which they did for 24 days. However, the crew of Soyuz 11 tragically died upon returning to Earth when the Soyuz 11 capsule depressurized during reentry. Further missions to Salyut 1 were canceled, and the Soyuz spacecraft was redesigned.

After Soyuz 11, the Soviets launched another space station, Salyut 2, but it failed to reach orbit. The Soviets followed with Salyuts 3-5. These flights tested the new Soyuz spacecraft and crews manned these stations for increasingly longer missions. One drawback with these space stations was that they had only one docking port for the Soyuz spacecraft and could not be re-supplied from Earth by other ships.

On Sept. 29, 1977, the Soviets launched Salyut 6. This station had a second docking port where the station could be resupplied by an unmanned docking supply ship called Progress. Salyut 6 operated between 1977 and 1982. In 1982, Salyut 7, the last of the Salyut program was launched. It hosted 11 crews and was inhabited for 800 days. The Salyut program eventually led to the development of Russia's Mir space station, which we will talk about a little later. But first, let's look at America's first space station: Skylab.

The United States placed its first, and only, space station, called Skylab 1, in orbit in 1973. During the launch, the station was damaged. A critical meteoroid shield and one of the station's two main solar panels were ripped off and the other solar panel was not fully stretched out. That meant that Skylab had little electrical power and the internal temperature rose to 126 degrees Fahrenheit (52 degrees Celsius).

The first crew, Skylab2, was launched 10 days later to fix the ailing station. The crew consisted of Commander Charles "Pete" Conrad, Paul Weitz and Joseph Kerwin. The Skylab 2 astronauts stretched out the remaining solar panel and set up an umbrella-like sunshade to cool the station. With the station repaired, the astronauts spent 28 days in space conducting scientific and biomedical research.

Modified from the third stage of a Saturn V moon rocket, Skylab had the following parts:

Skylab was manned by two additional crews. Skylab 3 consisted of Commander Alan Bean and astronauts Jack Lousma and Owen Garriot. They spent 59 days in space. The final crew, Skylab 4, consisted of Commander Gerald Carr and astronauts William Pogue and Edward Gibson. This crew spent 84 days in orbit, conducted experiments and photographed comet Kohoutek.

Skylab was never meant to be a permanent home in space, but rather a workshop where the United States could test the effects of long-duration space flights (that is, greater than the two weeks required to go to the moon) on the human body. When the flight of the third crew was finished, Skylab was abandoned. Skylab remained aloft until intense solar flare activity caused its orbit to decay sooner than expected. Skylab re-entered the Earth's atmosphere and burned over Australia in 1979.

Next up, Mir -- the first permanent space station.

In 1986, the Russians launched the Mir space station, which was intended to be a permanent home in space. The first crew, cosmonauts Leonid Kizim and Vladymir Solovyov, shuttled between the retiring Salyut 7 and Mir. They spent 75 days aboard Mir. Mir was continually manned and constructed over the next 10 years and contained the following parts:

In 1994, as preparation for the International Space Station (ISS), NASA astronauts (including Norm Thagard, Shannon Lucid, Jerry Linenger and Michael Foale) spent time aboard Mir. During Linenger's stay, Mir was damaged by an onboard fire. During Foale's stay, a Progress supply ship crashed into Mir.

The Russian space agency could no longer afford to maintain Mir, so NASA and the Russian space agency had planned to junk the station in order to concentrate on the ISS. A private movement (Keep Mir Alive!) and a company (MirCorp) publicly campaigned to repair and privatize the aging space station. However, the Russian Space Agency decided on November 16, 2000, to bring Mir down to Earth. In February 2001, Mir's rocket engines were fired to slow it down. Mir re-entered the Earth's atmosphere on March 23, 2001, burned and broke up. Debris crashed in the South Pacific Ocean about 1,000 miles (1,667 km) east of Australia. This marked the end of the first permanent space station.

Now, we'll take a glance at the International Space Station.

In 1984, President Ronald Reagan proposed that the United States, in cooperation with other countries, build a permanently inhabited space station. Reagan envisioned a station that would have government and industry support. To help with the enormous costs of the station, the U.S. forged a cooperative effort with 14 other countries (Canada, Japan, Brazil, and the European Space Agency, which is comprised of: United Kingdom, France, Germany, Belgium, Italy, the Netherlands, Denmark, Norway, Spain, Switzerland and Sweden). During the planning of the ISS and after the fall of the Soviet Union, the United States invited Russia to cooperate in the ISS in 1993; this brought the number of participating countries to 16. NASA took the lead in coordinating the ISS's construction.

The assembly of the ISS in orbit began in 1998. On October 31, 2000, the first crew of the ISS was launched from Russia. The three-member crew spent almost five months aboard the ISS, activating systems and conducting experiments. The ISS has been manned ever since and is scheduled to be finished in 2011.

Also set for 2011 is the launch of an orbiting laboratory by China called Tiangong-1. In October, 2003, China became the third nation ever to launch manned spacecraft. Since then, China has been developing a full-fledged space program including a space station. The Tiangong-1 will be capable of docking multiple Shenzhou spacecraft and will serve as the first module of a proposed Chinese space station planned to be completed by 2020. The space station may have both civilian and military purposes.

Speaking of the future, let's take a look at what could be in the stars, so to speak, for space stations.

We are just beginning the development of space stations. The ISS will be a vast improvement over Salyut, Skylab and Mir; but we are still a long way from the realization of large space stations or colonies as envisioned by science fiction writers. None of our space stations thus far have had any gravity. One reason for this is that we want a place without gravity so that we can study its effects. Another is that we lack the technology to practically rotate a large structure, like a space station, to produce artificial gravity. In the future, artificial gravity will be a requirement for space colonies with large populations.

Another popular idea deals with where a space station should be placed. The ISS will need periodic reboosting because of its position in low Earth orbit. However, there are two places between the Earth and moon called Lagrange Points L-4 and L-5. At these points, the Earth's gravity and the moon's gravity are counter-balanced so that an object placed there would not be pulled toward the Earth or moon. The orbit would be stable and require no boosting. A society called the L5 Society was formed more than 20 years ago to push the idea of placing space stations in orbit at these points. As we learn more from our experiences on the ISS, we may build larger and better space stations that would enable us to live and work in space, and the dreams of von Braun and the early space scientists may someday become reality.

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