Launched by a Saturn V on 14 May 1973, SL-1 was the unmanned portion of the Skylab project. Then things get interesting. The SL-2 mission was in the Skylab 2 vehicle, and was called SLM-1/Skylab I. SL-3/Skylab 3 was called SLM-2/Skylab II, and SL-4/Skylab 4 was called SLM-3/Skylab 3. Hey, NASA is part of the government. You really don't expect these things to make sense, do you? The naming convention was also confusing to the astronauts involved.
There was a proposed 4th manned mission to Skylab. It would have been a short 20 day mission and would have boosted Skylab into a higher orbit. It was decided the mission was not needed and Skylab could stay in orbit until the space shuttle was ready. The shuttle was delayed and Skylab reentered in 1979.
Skylab was the first¹ (and only) orbiting American space station. It orbited Earth at an altitude of approximately 300 miles. A shield tore loose during launch and damaged one of the solar panels. The first manned mission was delayed until it could be determined how to best make repairs. An "umbrella" was used to shield the station, but the damage to the solar wing could not be repaired and Skylab had power problems throughout its life. On 11 July 1979, parts of Skylab crashed into Australia and the Indian Ocean. Most of it burned up in the atmosphere.
The missing solar array would be on
the left. A gold colored Umbrella covers
the missing micro-meterorite shield.
(Credit: NASA, Click to enlarge)
The cost to develop and fly Skylab was USD 2.2 billion (1973 dollars).
There was consideration of launching a second Skylab in 1975 or 1976 using surplus hardware from the Apollo missions, the ASTP, and the first Skylab, but the hardware was mothballed in 1973. The orbital workshop portion of the second Skylab is on display at the National Air and Space Museum's Space Hall in Washington, D.C.
1. While Skylab was the first orbiting American space station, it was not the first proposed. Long before there was Skylab, there was Outpost.