"Before leaving the station on Feb. 8, 1974, the Skylab-4 crew boosted it into a higher 269-by-283-mile orbit, in the hope that Skylab would remain in space until 1983. By then, the Space Shuttle would be flying and NASA hoped that astronauts could attach a rocket to the station to either boost it to a higher orbit or safely deorbit it over the Pacific Ocean. But delays in the Shuttle program and higher than expected solar activity resulting in increased atmospheric drag on the station ultimately thwarted those plans. It became apparent that Skylab would reenter in mid-1979, forcing NASA to devise plans to control its entry point as much as possible by adjusting the station’s attitude to adjust atmospheric drag.
On July 11, 1979, during its 34,981st orbit around the Earth, engineers in Mission Control at the Johnson Space Center in Houston sent the final command to Skylab to turn off its control moment gyros, sending it into a slow tumble. This was the best that flight controllers could do to ensure that Skylab would not reenter over a populated area such as North America. They expected that it would begin its breakup over the southern tip of Africa and fall into the Indian Ocean. As it happened, the breakup occurred slightly later and while the majority of the debris that survived reentry did fall into the Indian Ocean, some pieces fell over sparsely populated areas of southern Western Australia." -- https://www.nasa.gov/feature/40-years-ago-skylab-reenters-ea...
"Before leaving the station on Feb. 8, 1974, the Skylab-4 crew boosted it into a higher 269-by-283-mile orbit, in the hope that Skylab would remain in space until 1983. By then, the Space Shuttle would be flying and NASA hoped that astronauts could attach a rocket to the station to either boost it to a higher orbit or safely deorbit it over the Pacific Ocean. But delays in the Shuttle program and higher than expected solar activity resulting in increased atmospheric drag on the station ultimately thwarted those plans. It became apparent that Skylab would reenter in mid-1979, forcing NASA to devise plans to control its entry point as much as possible by adjusting the station’s attitude to adjust atmospheric drag.
On July 11, 1979, during its 34,981st orbit around the Earth, engineers in Mission Control at the Johnson Space Center in Houston sent the final command to Skylab to turn off its control moment gyros, sending it into a slow tumble. This was the best that flight controllers could do to ensure that Skylab would not reenter over a populated area such as North America. They expected that it would begin its breakup over the southern tip of Africa and fall into the Indian Ocean. As it happened, the breakup occurred slightly later and while the majority of the debris that survived reentry did fall into the Indian Ocean, some pieces fell over sparsely populated areas of southern Western Australia." -- https://www.nasa.gov/feature/40-years-ago-skylab-reenters-ea...