Skylab

Did You Know?

• The mission computer used aboard Skylab was the IBM System/4Pi TC-1, a relative of the AP-101 Space Shuttle computers.
• Prior to departure about 80 experiments were named, although they are also described as 'almost 300 separate investigations'.
• Because the solar scientific airlock was occupied by the 'parasol' that replaced the missing meteorite shield, some experiments were installed outside during spacewalks or shifted to the Earth-facing scientific airlock.

Background

Rocket engineer Wernher von Braun, science fiction writer Arthur C. Clarke, and other early advocates of crewed space travel expected until the 1960s that a space station would be an important early step in space exploration. Von Braun participated in publishing a series of influential articles in Collier's magazine from 1952 to 1954, titled "Man Will Conquer Space Soon!", envisioning a large, circular station 250 ft in diameter that would rotate to generate artificial gravity and require a fleet of 7000 ST space shuttles for construction in orbit. The 80 men aboard would include astronomers, meteorologists, and soldiers. He expected future expeditions to the Moon and Mars would leave from the station. The development of the transistor, the solar cell, and telemetry led in the 1950s and early 1960s to uncrewed satellites that could photograph weather patterns or enemy nuclear weapons, making a large station no longer necessary for such purposes. The Apollo program chose a mission mode not needing in-orbit assembly, but a smaller station launched by a single rocket retained value for scientific purposes. In 1959, von Braun submitted his final Project Horizon plans to the U.S. Army, detailing an orbiting laboratory built out of a Horizon upper stage, an idea used for Skylab. Various NASA centers studied space station designs in the early 1960s, generally looking at platforms launched by the Saturn V with crews launched on Saturn IB using an Apollo command and service module, or a Gemini capsule on a Titan II-C. Proposals ranged from an Apollo-based station for two to three men to a large rotating station with 24 men and a five-year lifetime. A proposal to study the use of a Saturn S-IVB as a crewed space laboratory was documented in 1962 by the Douglas Aircraft Company.

Development

After the Moon landing in 1969, NASA worried about losing the 400,000 Apollo workers. Wernher von Braun, who led the Marshall Space Flight Center in the 1960s, pushed for a smaller space station because his larger design was never built; he wanted to keep his team employed after the Saturn rocket work ended. NASA created the Apollo Logistic Support System Office to study how to repurpose Apollo hardware for science. Its early ideas included a longer lunar mission needing two Saturn V rockets, a lunar truck based on the Lunar Module, a big solar telescope using an LM for crew quarters, and small stations built from LM or Command/Service Module parts. Over two years, this office focused more on space stations, and in August 1965 it became the Apollo Applications Program. In August 1964, the Manned Spacecraft Center proposed Apollo X, an expendable lab that swapped the LM on top of the S-IVB stage for a small station slightly bigger than the CSM’s service module, supporting 15- to 45-day missions. That study served as a baseline for further mission plans over the next six months. In November 1964, von Braun suggested a bigger station using the Saturn V’s S-II second stage. His design replaced the S-IVB third stage with an aeroshell and a 10-foot cylindrical equipment section. Once in orbit, the S-II stage would be vented of leftover hydrogen, and the equipment section would slide inside through a large hatch—a “wet workshop” conversion. This created a huge living area 33 feet wide and 45 feet long, with solar cells on the S-II’s exterior for power.

Operational history

In August 1969, McDonnell Douglas was hired to turn two existing S-IVB stages into an Orbital Workshop. A NASA contest in February 1970 gave the workshop the name "Skylab." The actual stage used in flight was the S-IVB 212, the upper stage of the AS-212 rocket. The Saturn V bearing serial number SA-513, originally built for Apollo missions that were later canceled, was modified to launch Skylab by removing its third stage and placing Skylab in its spot, though the instrument unit stayed in its usual position. The launch happened on May 14, 1973, using this modified Saturn V, sometimes called Skylab 1. During launch and deployment, the station suffered heavy damage: it lost its micrometeoroid shield and one main solar panel, and debris from the shield jammed the other panel, causing a major power shortage. Right after the launch, Pad 39A was shut down and rebuilt for the Space Shuttle program, while crewed trips to Skylab used a Saturn IB from Pad 39B. Skylab 1 remained the last uncrewed launch from LC-39A until SpaceX CRS-10 lifted off from there on February 19, 2017.

Plans for re-use after the last mission

After nearly 172 days, Skylab exceeded its planned 140 day habitation. The station held up well but onboard supplies were low and systems were degrading. One of three control-moment gyroscopes failed 8 days into Skylab 4, and another showed signs of impending failure; with a single CMG Skylab could not control its attitude, and repair or replacement on-orbit was not possible. Virtually all prepackaged food had been consumed, though enough water and oxygen/nitrogen remained. A fourth crewed mission using an Apollo CSM was considered, which would have used the launch vehicle kept on standby for the Skylab Rescue mission, a 20-day mission to boost Skylab to a higher altitude and conduct more experiments. Another plan involved a Teleoperator Retrieval System launched aboard the Space Shuttle to robotically re-boost the orbit. When Skylab 5 was cancelled, it was expected Skylab would stay in orbit until the 1980s, overlapping with Shuttle launches, but no option received the level of effort and funding needed before Skylab's sooner-than-expected re-entry.