Editing Skylab (section)

== Development ==
[[File:NASA Skylab Pre-Flight Orbital Workshop Overview-1972.ogv|thumb|NASA's Skylab pre-flight orbital workshop overview, circa 1972]]
[[File:Assembling the Skylab Orbital Workshop 7014162.jpg|thumb|The floor grating of Skylab under construction]]

=== Apollo Applications Program ===
{{main|Apollo Applications Program}}

NASA management was concerned about losing the 400,000 workers involved in Apollo after landing on the Moon in 1969.<ref>{{harvp|Benson|Compton|1983|pp=20, 22}}.</ref> A reason von Braun, head of NASA's [[Marshall Space Flight Center]] during the 1960s, advocated a smaller station after his large one was not built was that he wished to provide his employees with work beyond developing the Saturn rockets, which would be completed relatively early during Project Apollo.<ref>{{harvp|Heppenheimer|1999|p=61}}.</ref> NASA set up the Apollo Logistic Support System Office, originally intended to study various ways to modify the Apollo hardware for scientific missions. The office initially proposed a number of projects for direct scientific study, including an extended-stay lunar mission which required two Saturn V launchers, a "lunar truck" based on the [[Lunar Module]] (LM), a large, crewed solar telescope using an LM as its crew quarters, and small space stations using a variety of LM or CSM-based hardware. Although it did not look at the space station specifically, over the next two years the office became increasingly dedicated to this role. In August 1965, the office was renamed, becoming the [[Apollo Applications Program]] (AAP).<ref>{{harvp|Benson|Compton|1983|p=20}}.</ref>

As part of their general work, in August 1964 the [[Lyndon B. Johnson Space Center|Manned Spacecraft Center]] (MSC) presented studies on an expendable lab known as ''Apollo X'', short for ''Apollo Extension System''. ''Apollo X'' would have replaced the LM carried on the top of the S-IVB stage with a small space station slightly larger than the CSM's service area, containing supplies and experiments for missions between 15 and 45 days' duration. Using this study as a baseline, several mission profiles were looked at over the next six months.

=== Wet workshop ===
{{main|Wet workshop}}
[[File:Wet Workshop.svg|left|thumb|An early "[[wet workshop]]" version of Skylab]]

In November 1964, von Braun proposed a more ambitious plan to build a much larger station built from the [[S-II]] second stage of a Saturn V. His design replaced the S-IVB third stage with an aeroshell, primarily as an adapter for the CSM on top. Inside the shell was a {{convert|10|ft}} cylindrical equipment section. On reaching orbit, the [[S-II]] second stage would be vented to remove any remaining [[hydrogen]] fuel, then the equipment section would be slid into it via a large inspection hatch. This became known as a "[[wet workshop]]" concept, because of the conversion of an active fuel tank. The station filled the entire interior of the S-II stage's hydrogen tank, with the equipment section forming a "spine" and living quarters located between it and the walls of the booster. This would have resulted in a very large {{convert|33|by|45|ft}} living area. Power was to be provided by [[solar cell]]s lining the outside of the S-II stage.<ref>{{harvp|Benson|Compton|1983|p=22}}.</ref>

One problem with this proposal was that it required a dedicated Saturn V launch to fly the station. At the time the design was being proposed, it was not known how many of the then-contracted Saturn Vs would be required to achieve a successful Moon landing. However, several planned Earth-orbit test missions for the LM and CSM had been canceled, leaving some Saturn IBs free for use. Further work led to the idea of building a smaller "wet workshop" based on the S-IVB, launched as the second stage of a Saturn IB.

A number of S-IVB-based stations were studied at MSC from mid-1965, which had much in common with the Skylab design that eventually flew. An [[airlock]] would be attached to the hydrogen tank, in the area designed to hold the [[Apollo Lunar Module|LM]], and a minimum amount of equipment would be installed in the tank in order to avoid taking up too much fuel volume. Floors of the station would be made from an open metal framework that allowed the fuel to flow through it. After launch, a follow-up mission launched by a Saturn IB would launch additional equipment, including solar panels, an equipment section and docking adapter, and various experiments. [[Douglas Aircraft Company]], builder of the S-IVB stage, was asked to prepare proposals along these lines. The company had for several years been proposing stations based on the S-IV stage, before it was replaced by the S-IVB.<ref>{{harvp|Benson|Compton|1983|p=25}}.</ref>

On April 1, 1966, MSC sent out contracts to Douglas, [[Grumman]], and [[McDonnell Aircraft Corporation|McDonnell]] for the conversion of an S-IVB spent stage, under the name Saturn S-IVB spent-stage experiment support module (SSESM).<ref>{{harvp|Benson|Compton|1983|p=30}}.</ref> In May 1966, astronauts voiced concerns over the purging of the stage's hydrogen tank in space. Nevertheless, in late July 1966, it was announced that the Orbital Workshop would be launched as a part of Apollo mission AS-209, originally one of the Earth-orbit CSM test launches, followed by two Saturn I/CSM crew launches, AAP-1 and AAP-2.

The Manned Orbiting Laboratory (MOL) remained AAP's chief competitor for funds, although the two programs cooperated on technology. NASA considered flying experiments on MOL or using its [[Titan IIIC]] booster instead of the much more expensive Saturn IB. The agency decided that the Air Force station was not large enough and that converting Apollo hardware for use with Titan would be too slow and too expensive.<ref>{{harvp|Benson|Compton|1983|pp=45–48}}.</ref> The DoD canceled MOL in June 1969.<ref>{{harvp|Benson|Compton|1983|p=109}}.</ref>

=== Dry workshop ===
Design work continued over the next two years, in an era of shrinking budgets.<ref name="mc670127">{{cite news|agency=[[United Press International|UPI]]|work=The Mid-Cities Daily News|title=Space Hut Workshop Planned|page=8 |date=January 27, 1967 |url=https://news.google.com/newspapers?id=OEhgAAAAIBAJ&pg=3540,1271581&dq=space+hut+is+an&hl=en|via=[[Google News]]}}</ref> (NASA sought US$450 million for Apollo Applications in fiscal year 1967, for example, but received US$42 million.)<ref>{{harvp|Heppenheimer|1999|pp=64–65}}.</ref> In August 1967, the agency announced that the lunar mapping and base construction missions examined by the AAP were being canceled. Only the Earth-orbiting missions remained, namely the [[Orbital Workshop]] and [[Apollo Telescope Mount]] [[solar observatory]]. The success of [[Apollo 8]] in December 1968, launched on the third flight of a Saturn V, made it likely that one would be available to launch a dry workshop.<ref>{{harvp|Heppenheimer|1999|p=66}}.</ref> Later, several Moon missions were canceled as well, originally to be [[Canceled Apollo missions|Apollo missions 18 through 20]]. The cancellation of these missions freed up three Saturn V boosters for the AAP program. Although this would have allowed them to develop von Braun's original S-II-based mission, by this time so much work had been done on the S-IV-based design that work continued on this baseline. With the extra power available, the wet workshop was no longer needed;<ref>{{harvp|Benson|Compton|1983|pp=109–110}}.</ref> the S-IC and S-II lower stages could launch a "dry workshop", with its interior already prepared, directly into orbit.

=== Habitability ===
[[File:Skylab astronauts have fun.ogv|thumb|Jumping and flying in weightlessness]]

A dry workshop simplified plans for the interior of the station.<ref>{{harvp|Benson|Compton|1983|p=130}}.</ref> Industrial design firm [[Raymond Loewy]]/William Snaith recommended emphasizing habitability and comfort for the astronauts by providing a wardroom for meals and relaxation<ref>{{harvp|Benson|Compton|1983|pp=133–134}}.</ref> and a window to view Earth and space, although astronauts were dubious about the designers' focus on details such as color schemes.<ref name="ReferenceB">{{harvp|Benson|Compton|1983|p=137}}.</ref> Habitability had not previously been an area of concern when building spacecraft due to their small size and brief mission durations, but the Skylab missions would last for months.<ref>{{harvp|Benson|Compton|1983|p=133}}.</ref> NASA sent a scientist on [[Jacques Piccard]]'s ''[[Ben Franklin (PX-15)|Ben Franklin]]'' submarine in the [[Gulf Stream]] in July and August 1969 to learn how six people would live in an enclosed space for four weeks.<ref>{{harvp|Benson|Compton|1983|pp=139–140}}.</ref>

Astronauts were uninterested in watching movies on a proposed entertainment center or in playing games, but they did want books and individual music choices.<ref name="ReferenceB"/> Food was also important; early Apollo crews complained about its quality, and a NASA volunteer found it intolerable to live on the Apollo food for four days on Earth. Its taste and composition were unpleasant, in the form of cubes and squeeze tubes. [[space food#Skylab (1973–1974)|Skylab food]] significantly improved on its predecessors by prioritizing palatability over scientific needs.<ref>{{harvp|Benson|Compton|1983|pp=141–142}}.</ref>

For [[sleeping in space]], each astronaut had a private area the size of a small [[walk-in closet]], with a curtain, sleeping bag, and locker.<ref>{{harvp|Belew|1977|p=82}}.</ref> Designers also added a shower<ref>{{harvp|Benson|Compton|1983|p=139}}.</ref><ref name="harvp|Belew|1977|p=80|ps">{{harvp|Belew|1977|p=80}}.</ref> and a [[space toilet|toilet]]<ref>{{harvp|Benson|Compton|1983|pp=152–158}}.</ref><ref>{{harvp|Belew|1977|p=30}}.</ref> for comfort and to obtain precise urine and feces samples for examination on Earth.<ref>{{harvp|Benson|Compton|1983|p=165}}.</ref> The waste samples were so important that they would have been priorities in any [[#Launchers, rescue, and cancelled missions|rescue mission]].<ref name="evans20120812">{{cite web|last=Evans |first=Ben|title=Launch Minus Nine Days: The Space Rescue That Never Was |url=https://www.americaspace.com/2012/08/12/launch-minus-nine-days-the-space-rescue-that-never-was/|access-date=2020-07-09 |publisher=AmericaSpace|date=2012-08-12}}</ref>

Skylab did not have recycling systems such as the conversion of urine to drinking water; it also did not dispose of waste by dumping it into space. The S-IVB's {{convert|73280|L|sp=us}} [[liquid oxygen]] tank below the Orbital Work Shop was used to store trash and wastewater, passed through an [[airlock]].