Salyut first flew April 19, 1971. Two crews visited Salyut 1, but one visiting crew could not actually dock. The first crew experienced problems with the docking system, and so they ended up coming home early without actually staying on the station. The second crew successfully docked and stayed for approximately 23 days. However, due to a failure of the Soyuz capsule when they re-entered the atmosphere, all the crewmembers died. These experiences show that leaving Earth and going to space has tremendous risks. The Russians developed several more Salyut and Almaz space stations. The next three after Salyut-1 were failures. Either the Proton rocket they used blew up on the pad, or the station simply did not achieve orbit. So it was not until Salyut-4 that they were finally able to reestablish an orbiting station and carry out a succession of successful missions. Salyuts 4, 5, 6, and 7 were very successful, having a number of crewmembers visit and demonstrating a lot of space capabilities.
In the United States we had a military Manned Orbiting Laboratory (MOL) program that was planned but eventually did not get funded and did not fly. Although the United States decided not to carry out the MOL program, we did decide to do the civilian NASA Skylab program. Skylab was our first U.S. space station. It was a 75-ton laboratory built from a Saturn IVB stage, the upper stage of the Saturn V rocket. Skylab was launched into space on May 14, 1973, and was occupied by three crews, Skylab 2, 3, and 4. The crews stayed for periods of 28, 59, and then 84 days, respectively, during 1973 and 1974. From Figure 4.3 you can see that Skylab is asymmetric. During launch, aerodynamic forces caused one of the solar arrays to be ripped off. Fortunately this problem did not damage the pressurized module. The aerodynamic forces also ripped off some of the thermal protection system. So one of the first orders of business with Skylab was to actually do an in-flight repair and deploy a new sunshade during a spacewalk. That spacewalk was performed by the first crew and allowed the Skylab to function very well for the three missions.
The Skylab crews performed a number of microgravity physical science experiments and a number of physiological experiments, looking at how microgravity affected the human body, and also operated a solar observator (Figure 4.4).
Skylab stayed in space until 1979. After the Apollo
program ended in 1975, there was a plan that called for the space shuttle to fly to Skylab and re-boost it, giving it extra time on orbit. Unfortunately the first flight of the shuttle was delayed until 1981. Skylab’s orbit decayed, and it re-entered Earth’s atmosphere and mostly burned up. However, some charred hardware landed in Australia.