The Russians were the first to orbit a space station, the Salyut 1,  in June 1971. The first crew decked with the space station but because they couldn't open the hatch, didn't enter it. The second crew entered and stayed for 22 days. This second crew perished during the final phase of the Soyuz capsule recovery due to cabin depressurization.

On Salyut 1 hydroponic program studied the effects of microgravity on growing plants, and biomedical observations were made of the cosmonauts themselves in order to determine the effects of prolonged weightlessness on human physiology. The second space station, Salyut 2, was launched in April 1973; but the vehicle suffered a catastrophic explosion, which tore the solar panels, the docking apparatus, and the radio transponder from the craft and left it tumbling in a low-Earth orbit from which it decayed in late May 1973.

Skylab

On May 14, 1973, NASA launched the Skylab space station which was inhabited by three successive crews for 28 days, 59 days, and 84 days. The first crew repaired the space station, which had been damaged during launch.

Studies in the effects of long-duration spaceflight on astronauts included physical and psychological medical experiments on the human adaptability to zero gravity. The effectiveness of Skylab crews exceeded expectations, especially in their ability to perform complex repair tasks. They demonstrated excellent mobility, both internal and external to the space station, showing man to be a positive asset in conducting research in space.

The capability to conduct longer manned missions was conclusively demonstrated in Skylab, first by the crew returning from the 28-day mission and, more forcefully, by the good health and physical condition of the second and third Skylab crews who stayed in weightless space for 59 and 84 days, respectively.

Skyab astronaut Charles (Pete) Conrad

Skylab astronauts exercised regularly and were tested extensively. The Skylab payload was equipped to study the cardiovascular, musculoskeletal, hematological, vestibular, metabolic, and endocrine systems of the body. Analysis of the heart's electrical forces, conducted on Skylab, was used to study microgravity-induced changes in astronauts during and after flight.

Astronaut Paul Weitz gets physical examination from Astronaut Joseph Kerwin

Parameters were measured before, during, and after exercise on the bicycle ergometer to study cardiovascular deconditioning (weakening of the heart and lungs). In addition, the metabolic analyzer, a device that measures oxygen consumption, was used on Skylab to study respiratory responses to bicycle exercise to determine how the capacity to do physical work in space differed from doing work on the ground.

In-flight cardiovascular measurements indicated that fluid shift occurred in the human body during weightlessness. However, it was found that the cardiovascular deconditioning was stabilizing after 4 to 6 weeks of microgravity. Mineral loss was another topic of concern during Skylab. Some bone loss was noted in the lower extremities, and a significant increase in the urinary excretion of calcium during flight was measured in the third Skylab crew.

Salyut 4-7

The mission was primarily military, but crewmembers did use a treadmill for 2 hours a day and were able to climb from their descent module without assistance. The Salyut 4 was launched in 1975 and housed two crews for 29 and 62 days. In 1976-1977, the Salyut 5 space station housed two crews for 47 and 17 days. The first crew departed the station suddenly due to a fire in the environmental control system and resulting health problems.

Cosmonauts inside the Salyut 6 spacecraft

From 1977–1982, the Russian Salyut 6 space station housed 16 crews including 6 principal expeditions lasting 96, 140, 175, 185, 13, and 75 days, respectively. Several other countries sent visiting expeditions to the space station during this time including Poland, East Germany, Cuba, Mongolia, Vietnam, Romania, and Hungary.

From 1982-1986 the Salyut 7 housed 10 crews including 5 principal expeditions lasting 211, 149, 237, 112, 65, and 51 days. The Salyut 7 had some improvements over Salyut 6 including hot plates for heating food and continuously available hot water, improved exercise equipment, and better medical facilities. The portholes were shielded by covers when not in use to protect against micrometeorite damage. A shower still took an entire day to complete. Visiting expeditions included Svetlana Savitskaya, the first woman to visit space in 20 years (since Valentina Tereshkova). Savitskaya was given a separate module for privacy. After 3½ months on board, cosmonaut Valentin Lebedev wrote in his diary "Now I think of it as home…Many little details such as photographs, children’s drawings, flowers, and green plants in the garden turn this high tech complex into our warm and comfortable, if a bit unusual, home." The crew fixed emergency situations including a propulsion system failure and plumbing problems. A window impact significantly cratered but did not crack one of the windows.

Mir

In 1986, the Russian Mir space station was launched. It was continuously manned with Russian and International crews since 1990 until August last year.

It is composed of seven separate modules, three instrumentation and life support modules (Mir, Kvant, and Kvant 2), three science modules (Kristall, Spektr, and Priroda), and a docking module added to allow the U.S. Space Shuttle to dock with Mir. The Space Shuttle has docked with Mir 10 times, and has had 7 astronauts live with Russian crews for stays up to 6 months. Cosmonaut Dr. Valeri Polyakov set the world record for long-duration spaceflight of 438 days in 1994-1995. Click here to see some movies of the Mir space station.

The primary goal of the Shuttle-Mir program from 1995-1998 was to give the United States valuable experience in operating a space station for long periods of time. The Space Shuttle docked with the Russian Mir space station a total of 10 times, and 6 U.S. astronauts lived on board the space station.

Through Shuttle-Mir, NASA gained experience in rendezvous and docking, spacewalks, and long-duration stays aboard a space station. The emergency situations experienced on Mir, including a serious fire and the crash of a supply ship and subsequent depressurization of the Spektr module, have helped understand how we can better train and prepare our crews for future missions and crises. The program allowed U.S. and Russian engineers and planners to learn to overcome cultural differences and work together in the operation of a long-term spacecraft. Significant data regarding human response to long-duration exposure to the microgravity environment ("weightlessness") was collected; for example it was discovered that bone loss does not lessen over time.

The International Space Station, currently under construction, will allow us to study in depth how humans react physically and psychologically to longer and longer stays in space and to other emergency situations that may arise. This knowledge will enable us to leave the confines of Earth orbit, establish preliminary bases on the Moon, and make the long trip to Mars.

The international cooperation effort of 16 nations in this project will be the forerunners for more complex international projects like a mission to Mars.

Questions to think about:

• What differences are there between living in low-Earth orbit on a space station and living aboard a spaceship going to Mars?

• What are the most important lessons we can learn from living on a space station in preparation for the longer trip to Mars?

• What kinds of experiments would you design to test human adaptability to long-duration spaceflights on the International Space Station?

The Hazards