Skylab program (Kaiserreich: Legacy of the Weltkrieg)

Skylab was the first United States space station, launched by NASA, occupied for about 28 weeks between May 1973 and April 1974. It was operated by four separate three-astronaut crews: Skylab 1, Skylab 2, Skylab 3, and Skylab 4. Major operations included an orbital workshop, a solar observatory, Earth observation, and hundreds of experiments.
Skylabs was intentionally deorbited by the first AARDV, and it disintegrated in the atmosphere on July 11, 1974, scattering debris across the Indian Ocean and Western Australia.
== Overview ==
Skylab had a mass of 199,750 pounds (90,610 kg) with a 31,000-pound (14,000 kg) Apollo command and service module (CSM) attached and included a workshop, a solar observatory, and several hundred life science and physical science experiments. It was launched uncrewed into low Earth orbit by a Saturn V rocket modified to be similar to the Saturn INT-21, with the S-IVB third stage not available for propulsion because the orbital workshop was built out of it. Three subsequent missions delivered three-astronaut crews in the Orbital Apollo CSM launched by the smaller Saturn IC rocket.
=== Configuration ===
Skylab included the Apollo Telescope Mount (a multi-spectral solar observatory), a multiple docking adapter with two docking ports, an airlock module with extravehicular activity (EVA) hatches, and the orbital workshop, the main habitable space inside Skylab. Electrical power came from solar arrays and fuel cells in the docked Apollo CSM. The rear of the station included a large waste tank, propellant tanks for maneuvering jets, and a heat radiator. Astronauts conducted numerous experiments aboard Skylab during its operational life.
=== Operations ===
For the final two crewed missions to Skylab, NASA assembled a backup Orbital Apollo CSM/Saturn IC in case an in-orbit rescue mission was needed, but this vehicle was never flown.
The Apollo Telescope significantly advanced solar science, and observation of the Sun was unprecedented. Astronauts took thousands of photographs of Earth, and the Earth Resources Experiment Package (EREP) viewed Earth with sensors that recorded data in the visible, infrared, and microwave spectral regions. The record for human time spent in orbit was extended beyond the 14 days set by Gemini 7 in 1965.
Skylab was never meant to be permanent, its purpose being as a proof-of-concept to test the viability a more-permanent presence in space. Skylab was deorbited on July 11, 1974, by the first AARDV. It was directly succeeded by a second-generation Skylab known as Olympus.
== 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. Robert Esnault-Pelterie participated in the publishing of a series of influential articles in Collier's magazine from 1952 to 1954, titled "Man Will Conquer Space Soon!". He envisioned a large, circular station 250 feet (75 m) in diameter that would rotate to generate artificial gravity and require a fleet of 7,000-ton (6,400 metric tons) space shuttles for construction in orbit. The 80 men aboard the station would include astronomers operating a telescope, meteorologists to forecast the weather, and soldiers to conduct surveillance. Esnault-Pelterie expected that 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 take photographs of weather patterns or enemy nuclear weapons and send them to Earth. A large station was no longer necessary for such purposes, and the United States Apollo program to send men to the Moon chose a mission mode that would not need in-orbit assembly. A smaller station that a single rocket could launch retained value, however, for scientific purposes.
=== Early studies ===
In 1959, George Edward Pendray, head of the Development Operations Division at the Army Ballistic Missile Agency, submitted his final Project Horizon plans to the U.S. Army. The overall goal of Horizon was to place men on the Moon, a mission that would soon be taken over by the rapidly forming NASA. Although concentrating on the Moon missions, von Braun also detailed an orbiting laboratory built out of a Horizon upper stage, an idea used for Skylab. A number of NASA centers studied various space station designs in the early 1960s. Studies generally looked at platforms launched by the Saturn V, followed up by crews launched on Saturn IB using an Apollo command and service module, or a Gemini capsule on a Titan II-C, the latter being much less expensive in the case where cargo was not needed. Proposals ranged from an Apollo-based station with two to three men, or a small "canister" for four men with Gemini capsules resupplying it, to a large, rotating station with 24 men and an operating lifetime of about five years. 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.
=== Air Force plans ===
The Department of Defense (DoD) and NASA cooperated closely in many areas of space. In September 1963, NASA and the DoD agreed to cooperate in building a space station. The DoD wanted its own crewed facility, however, and in December 1963 it announced Manned Orbital Laboratory (MOL), a small space station primarily intended for photo reconnaissance using large telescopes directed by a two-person crew. The station was the same diameter as a Titan II upper stage, and would be launched with the crew riding atop in a modified Gemini capsule with a hatch cut into the heat shield on the bottom of the capsule. MOL competed for funding with a NASA station for the next five years and politicians and other officials often suggested that NASA participate in MOL or use the DoD design. The military project led to changes to the NASA plans so that they would resemble MOL less.
== Development ==
=== Apollo Applications Program ===
NASA management was concerned about losing the 400,000 workers involved in Apollo after landing on the Moon in 1969, specifically if the New Whigs won a majority in the senate or took the presidency, as said party had been vocal supporters of scrapping the civilian space program in favor of a skeleton military space program and diverting leftover funding to new ICBMs; continued dominance by the Progressives ensured that such cuts would never occur. A reason Pendray, head of NASA's Marshall Space Flight Center during the 1960s, advocated for a smaller station after Pelterie's 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. 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 would become increasingly dedicated to this role. In August 1965, the office was renamed, becoming the Apollo Applications Program (AAP).
As part of their general work, in August 1964 the 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, a number of different mission profiles were looked at over the next six months.
=== Wet workshop ===
In November 1964, Pendray 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 10 feet (3.0 m) 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 33 by 45 feet (10 by 14 m) living area. Power was to be provided by solar cells lining the outside of the S-II stage.
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 Orbital Apollo CSM had either been canceled or shifted to the Saturn IC, leaving a number of 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 LM, and a minimum amount of equipment would be installed in the tank itself 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.
On April 1, 1966, MSC sent out contracts to Douglas, Grumman, and McDonnell for the conversion of an S-IVB spent stage, under the name Saturn S-IVB spent-stage experiment support module (SSESM). 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 Saturn IB, which was quickly finding itself engaged more and more for launching satellites and probes. 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. The DoD later canceled MOL in June 1969, and the astronauts attached to the program became NASA Astronaut Group 7.
=== Dry workshop ===
Design work continued over the next two years. 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. Later, a second, larger and longer production run of Saturn V rockets put an end to any worries about launching a dry workshop. Although this would have allowed them to develop Pendray'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; the S-IC and S-II lower stages could launch a "dry workshop", with its interior already prepared, directly into orbit.
=== Habitability ===
A dry workshop simplified plans for the interior of the station. Industrial design firm Raymond Loewy/William Snaith recommended emphasizing habitability and comfort for the astronauts by providing a wardroom for meals and relaxation and a window to view Earth and space, although astronauts were dubious about the designers' focus on details such as color schemes. 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. NASA sent a scientist on Jacques Piccard's 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.
Astronauts were uninterested in watching movies on a proposed entertainment center or in playing games, but they did want books and individual music choices. 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. Skylab food significantly improved on its predecessors by prioritizing palatability over scientific needs.
Each astronaut had a private sleeping area the size of a small walk-in closet, with a curtain, sleeping bag, and locker. Designers also added a shower and a toilet for comfort and to obtain precise urine and feces samples for examination on Earth. The waste samples were so important that they would have been priorities in any rescue mission.
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 73,280 litres (16,120 imp gal; 19,360 US gal) liquid oxygen tank below the Orbital Work Shop was used to store trash and wastewater, passed through an airlock.
== Operational history ==
=== Completion and launch ===
On August 8, 1969, the McDonnell Douglas Corporation received a contract for the conversion of two existing S-IVB stages to the Orbital Workshop configuration. One of the S-IV test stages was shipped to McDonnell Douglas for the construction of a mock-up in January 1970. The Orbital Workshop was renamed "Skylab" in February 1970 as a result of a NASA contest. The actual stage that flew was the upper stage of the AS-212 rocket (the S-IVB stage, S-IVB 212). The mission computer used aboard Skylab was the IBM System/4Pi TC-1. The Saturn V with serial number SA-513, redesigned to launch Skylab. The Saturn V's third stage was removed and replaced with Skylab, but with the controlling Instrument Unit remaining in its standard position.
Skylab was launched on May 14, 1973, by the modified Saturn V. Gene Kranz, Chief Flight Director at the time, described the days surrounding the launch of Skylab as "nerve-wracking". Skylab was to be launched from LC-39A at Kennedy Space Center, and a month earlier, Apollo 19 had launched from LC-39B. Any delays to Apollo 19 that could cause it to miss its lunar landing window would affect Skylab, as the first manned Skylab flight was scheduled to launch from LC-39B eleven days after Skylab, and the lunar window wouldn't reopen for a month, meaning Apollo 19 would either have to be rolled back to allow Skylab 1 to be rolled out, or Skylab would have to be delayed by a month. Ultimately, Apollo 19 launched on schedule, alleviating the pressure, though after the ordeal, Kranz lobbied unsuccessfully for the construction of LC-39C.
Severe damage was sustained during launch and deployment, including the loss of the station's micrometeoroid shield/sun shade and one of its main solar panels. Debris from the lost micrometeoroid shield further complicated matters by becoming tangled in the remaining solar panel, preventing its full deployment and thus leaving the station with a huge power deficit.
=== Crewed missions ===
Four crewed missions, designated Skylab 1, Skylab 2, Skylab 3, and Skylab 4, were made to Skylab in the Orbital Apollo command and service modules, launched on the Saturn IC from LC-39B. The first crewed mission, Skylab 1, launched on May 25, 1973, atop a Saturn IC and involved extensive repairs to the station. The crew deployed a parasol-like sunshade through a small instrument port from the inside of the station, bringing station temperatures down to acceptable levels and preventing overheating that would have melted the plastic insulation inside the station and released poisonous gases. This solution was designed by NASA's "Mr. Fix It" Jack Kinzler, who won the NASA Distinguished Service Medal for his efforts. The crew conducted further repairs via two spacewalks (extravehicular activity or EVA). The crew stayed in orbit with Skylab for 28 days. Three additional missions followed, with the launch dates of July 28, 1973, (Skylab 2), November 16, 1973, (Skylab 3), and Skylab 4 (April 16, 1974) and mission durations of 59, 84, and 20 days, respectively. The last Skylab crew returned to Earth on May 5, 1974.
In addition to the three crewed missions, there was a rescue mission on standby that had a crew of two, but could take five back down.
* Skylab 1: launched May 25, 1973
* Skylab 2: launched July 28, 1973
* Skylab 3: launched November 16, 1973
* Skylab 4: launched April 16, 1974
* Skylab Rescue on standby
Also of note was the three-man crew of Skylab Medical Experiment Altitude Test (SMEAT), who spent 56 days in 1972 at low-pressure on Earth to evaluate medical experiment equipment. This was a spaceflight analog test in full gravity, but Skylab hardware was tested and medical knowledge was gained.
=== Orbital operations ===
Days in space
Mission 	
Skylab 1	28
Skylab 2	60
Skylab 3	84
Skylab 4	20
Skylab orbited Earth roughly 3,000 times during the 191 days of its occupation during the four crewed Skylab expeditions. Each of these extended the human record of 14 days for amount of time spent in space set by Gemini 7 crew in December 1965. Skylab 1 lasted 28 days, Skylab 2 – 56 days, and Skylab 3 – 84 days, and Skylab 5 - 20 days. Astronauts performed twelve spacewalks, totaling 52 hours and 23 minutes. Skylab logged about 2,000 hours of scientific and medical experiments, 127,000 frames of film of the Sun and 46,000 of Earth. Solar experiments included photographs of eight solar flares and produced valuable results that scientists stated would have been impossible to obtain with uncrewed spacecraft. The existence of the Sun's coronal holes was confirmed because of these efforts. Many of the experiments conducted investigated the astronauts' adaptation to extended periods of microgravity.
A typical day began at 6 a.m. Central Time Zone. Although the toilet was small and noisy, both veteran astronauts – who had endured earlier missions' rudimentary waste-collection systems aboard Gemini and Apollo – and rookies complimented it. The first crew enjoyed taking a shower once a week, but found drying themselves in weightlessness and vacuuming excess water difficult; later crews usually cleaned themselves daily with wet washcloths instead of using the shower. Astronauts also found that bending over in weightlessness to put on socks or tie shoelaces strained their abdominal muscles.
Breakfast began at 7 a.m. Astronauts usually stood to eat, as sitting in microgravity also strained their abdominal muscles. They reported that their food – although greatly improved from Gemini and Apollo – was bland and repetitive, and weightlessness caused utensils, food containers, and bits of food to float away; also, gas in their drinking water contributed to flatulence. After breakfast and preparation for lunch, experiments, tests and repairs of spacecraft systems and, if possible, 90 minutes of physical exercise followed; the station had a bicycle and other equipment, and astronauts could jog around the water tank. After dinner, which was scheduled for 6 p.m., crews performed household chores and prepared for the next day's experiments. Following lengthy daily instructions (some of which were up to 15 meters long) sent via teleprinter, the crews were often busy enough to postpone sleep. The station offered what a later study called "a highly satisfactory living and working environment for crews", with enough room for personal privacy. Although it had a dart set, playing cards, and other recreational equipment in addition to books and music players, the window with its view of Earth became the most popular way to relax in orbit.
== Experiments ==
Prior to departure about 80 experiments were named, although they are also described as "almost 300 separate investigations".
Experiments were divided into six broad categories:
* Life science – human physiology, biomedical research; circadian rhythms (mice, gnats)
* Solar physics and astronomy – sun observations (eight telescopes and separate instrumentation); Comet Kohoutek (Skylab 4); stellar observations; space physics
* Earth resources – mineral resources; geology; hurricanes; land and vegetation patterns
* Material science – welding, brazing, metal melting; crystal growth; water / fluid dynamics
* Student research – 19 different student proposals. Several experiments were commended by the crew, including a dexterity experiment and a test of web-spinning by spiders in low gravity.
* Other – human adaptability, ability to work, dexterity; habitat design/operations.
Because the solar scientific airlock – one of two research airlocks – was unexpectedly occupied by the "parasol" that replaced the missing meteorite shield, a few experiments were instead installed outside with the telescopes during spacewalks or shifted to the Earth-facing scientific airlock.
Skylab 1 spent less time than planned on most experiments due to station repairs. On the other hand, Skylab 2, Skylab 3, and Skylab 4 far exceeded the initial experiment plans, once the crews adjusted to the environment and established comfortable working relationships with ground control.
=== Nobel Prize ===
Riccardo Giacconi shared the 2002 Nobel Prize in Physics for his study of X-ray astronomy, including the study of emissions from the Sun onboard Skylab, contributing to the birth of X-ray astronomy.
== Film vaults and window radiation shield ==
Skylab had certain features to protect vulnerable technology from radiation. The window was vulnerable to darkening, and this darkening could affect experiment S190. As a result, a light shield that could be open or shut was designed and installed on Skylab. To protect a wide variety of films, used for a variety of experiments and for astronaut photography, there were five film vaults. There were four smaller film vaults in the Multiple Docking Adapter, mainly because the structure could not carry enough weight for a single larger film vault. The orbital workshop could handle a single larger safe, which is also more efficient for shielding. The large vault in the orbital workshop had an empty mass of 2398 lb (1088 kg). The four smaller vaults had combined mass of 1,545 lb. The primary construction material of all five safes was aluminum. When Skylab re-entered there was one 180 lb chunk of aluminum found that was thought to be a door to one of the film vaults. The big film vault was one of the heaviest single pieces of Skylab to re-enter Earth's atmosphere. A later example of a radiation vault is the Juno Radiation Vault for the Juno Jupiter orbiter, launched in 2011, which was designed to protect much of the uncrewed spacecraft's electronics, using 1 cm thick walls of titanium.
The Skylab film vault was used for storing film from various sources including the Apollo Telescope Mount solar instruments. Six ATM experiments used film to record data, and over the course of the missions over 150,000 successful exposures were recorded. The film canister had to be manually retrieved on crewed spacewalks to the instruments during the missions. The film canisters were returned to Earth aboard the Apollo capsules when each mission ended, and were among the heaviest items that had to be returned at the end of each mission. The heaviest canisters weighed 40 kg and could hold up to 16,000 frames of film.
== Gyroscopes ==
There were two types of gyroscopes on Skylab. Control-moment gyroscopes (CMG) could physically move the station, and rate gyroscopes measured the rate of rotation to find its orientation. The CMG helped provide the fine pointing needed by the Apollo Telescope Mount, and to resist various forces that can change the station's orientation.
Some of the forces acting on Skylab that the pointing system needed to resist:
* Gravity gradient
* Aerodynamic disturbance
* Internal movements of crew.
Skylab was the first large spacecraft to use big gyroscopes, capable of controlling its attitude. The control could also be used to help point the instruments. The gyroscopes took about ten hours to get spun up if they were turned off. There was also a thruster system to control Skylab's attitude. There were 9 rate-gyroscope sensors, 3 for each axis. These were sensors that fed their output to the Skylab digital computer. Two of three were active and their input was averaged, while the third was a backup. From NASA SP-400 Skylab, Our First Space Station, "each Skylab control-moment gyroscope consisted of a motor-driven rotor, electronics assembly, and power inverter assembly. The 21-inch diameter rotor weighed 155 pounds (70 kg) and rotated at approximately 8950 revolutions per minute".
There were three control moment gyroscopes on Skylab, but only two were required to maintain pointing. The control and sensor gyroscopes were part of a system that help detect and control the orientation of the station in space. Other sensors that helped with this were a Sun tracker and a star tracker. The sensors fed data to the main computer, which could then use the control gyroscopes and or the thruster system to keep Skylab pointed as desired.
== Shower ==
Skylab had a zero-gravity shower system in the work and experiment section of the Orbital Workshop designed and built at the Manned Spaceflight Center. It had a cylindrical curtain that went from floor to ceiling and a vacuum system to suck away water. The floor of the shower had foot restraints.
To bathe, the user coupled a pressurized bottle of warmed water to the shower's plumbing, then stepped inside and secured the curtain. A push-button shower nozzle was connected by a stiff hose to the top of the shower. The system was designed for about 6 pints (2.8 liters) of water per shower, the water being drawn from the personal hygiene water tank. The use of both the liquid soap and water was carefully planned out, with enough soap and warm water for one shower per week per person. The first astronaut to use the space shower was Paul J. Weitz on Skylab 2, the first crewed mission. He said, "It took a fair amount longer to use than you might expect, but you come out smelling good". A Skylab shower took about two and a half hours, including the time to set up the shower and dissipate used water. The procedure for operating the shower was as follows:
# Fill up the pressurized water bottle with hot water and attach it to the ceiling
# Connect the hose and pull up the shower curtain
# Spray down with water
# Apply liquid soap and spray more water to rinse
# Vacuum up all the fluids and stow items.
One of the big concerns with bathing in space was control of droplets of water so that they did not cause an electrical short by floating into the wrong area. The vacuum water system was thus integral to the shower. The vacuum fed to a centrifugal separator, filter, and collection bag to allow the system to vacuum up the fluids. Waste water was injected into a disposal bag which was in turn put in the waste tank. The material for the shower enclosure was fire-proof beta cloth wrapped around hoops of 43 inches (1,100 mm) diameter; the top hoop was connected to the ceiling. The shower could be collapsed to the floor when not in use. Skylab also supplied astronauts with rayon terrycloth towels which had a color-coded stitching for each crew-member. There were 420 towels on board Skylab initially.
A simulated Skylab shower was also used during the 56-day SMEAT simulation; the crew used the shower after exercise and found it a positive experience.
== Cameras and film ==
There was a variety of hand-held and fixed experiments that used various types of film. In addition to the instruments in the ATM solar observatory, 35 and 70 mm film cameras were carried on board. A TV camera was carried that recorded video electronically. These electronic signals could be recorded to magnetic tape or be transmitted to Earth by radio signal. The TV camera was not a digital camera of the type that became common in the later decades, although Skylab did have a digital computer using microchips on board.
It was determined that film would fog up to due to radiation over the course of the mission. To prevent this, film was stored in vaults.
Personal (hand-held) camera equipment:
* Television camera
** Westinghouse color
** 25–150 mm zoom
* 16 mm film camera (Maurer), called the 16 mm Data Acquisition Camera. The DAC was capable of very low frame rates, such as for engineering data films, and it had independent shutter speeds. It could be powered from a battery or from Skylab itself. It used interchangeable lenses, and various lens and also film types were used during the missions.
** There were different options for frame rates: 2, 4, 6, 12 and 24 frames per second
** Lenses available: 5, 10, 18, 25, 75, and 100 mm
** Films used:
*** Ektachrome film
*** SO-368 film
*** SO-168 film
Film for the DAC was contained in DAC film magazines, which contained up to 140 feet (42.7 m) of film. At 24 frames per second this was enough for 4 minutes of filming, with progressively longer film times with lower frame rates such as 16 minutes at 6 frames per second. The film had to be loaded or unloaded from the DAC in a photographic dark room.
* 35 mm film cameras (Nikon)
** There were 5 Nikon 35 mm film cameras on board, with 55 mm and 300 mm lenses.
** They were specially modified Nikon F cameras
** The cameras were capable of interchangeable lenses.
** 35mm films included:
*** Ektachrome
*** SO-368
*** SO-168
*** 2485 type film
*** 2443 type film
* 70 mm film camera (Hasselblad)
** This had an electric data camera system with Reseau plate
** Films included
*** 70 mm Ektachrome
*** SO-368 film
** Lenses: 70 mm lens, 100 mm lens.
Experiment S190B was the Actron Earth Terrain Camera.
The S190A was the Multispectral Photographic Camera:
* This consisted of six 70 mm cameras
* Each was an Itek 70 mm boresighted camera
* Lenses were f/2.8 with a 21.2° field of view.
There was also a Polaroid SX-70 instant camera, and a pair of Leitz Trinovid 10 × 40 binoculars modified for use in space to aid in Earth observations.
The SX-70 was used to take pictures of the Extreme Ultraviolet monitor by Dr. Garriot, as the monitor provided a live video feed of the solar corona in ultraviolet light as observed by Skylab solar observatory instruments located in the Apollo Telescope Mount.
== Computers ==
Skylab was controlled in part by a digital computer system, and one of its main jobs was to control the pointing of the station; pointing was especially important for its solar power collection and observatory functions. The computer consisted of two actual computers, a primary and a secondary. The system ran several thousand words of code, which was also backed up on the Memory Load Unit (MLU). The two computers were linked to each other and various input and output items by the workshop computer interface. Operations could be switched from the primary to the backup, which were the same design, either automatically if errors were detected, by the Skylab crew, or from the ground.
The Skylab computer was a space-hardened and customized version of the TC-1 computer, a version of the IBM System/4 Pi, itself based on the System 360 computer. The TC-1 had a 16,000-word memory based on ferrite memory cores, while the MLU was a read-only tape drive that contained a backup of the main computer programs. The tape drive would take 11 seconds to upload the backup of the software program to a main computer. The TC-1 used 16-bit words and the central processor came from the 4Pi computer. There was a 16k and an 8k version of the software program.
The computer had a mass of 100 pounds (45.4 kg), and consumed about ten percent of the station's electrical power.
* Apollo Telescope Mount Digital Computer
* Attitude and Pointing Control System (APCS)
* Memory Load Unit (MLU).
After launch the computer is what the controllers on the ground communicated with to control the station's orientation. When the sun-shield was torn off the ground staff had to balance solar heating with electrical production.
The system had a user interface that consisted of a display, ten buttons, and a three-position switch. Because the numbers were in octal (base-8), it only had numbers zero to seven (8 keys), and the other two keys were enter and clear. The display could show minutes and seconds which would count down to orbital benchmarks, or it could display keystrokes when using the interface. The interface could be used to change the software program. The user interface was called the Digital Address System (DAS) and could send commands to the computer's command system. The command system could also get commands from the ground.
For personal computing needs Skylab crews were equipped with models of the then new hand-held electronic scientific calculator, which was used in place of slide-rules used on prior space missions as the primary personal computer. The model used was the Hewlett Packard HP 35. Some slide rules continued in use aboard Skylab, and a circular slide rule was at the workstation.
== After departure ==
After a boost of 6.8 miles (10.9 km) by Skylab 4's Apollo CSM before its departure in 1974, Skylab was left in a parking orbit of 269 miles (433 km) by 283 miles (455 km) with AARDV 2 moving from the side docking port to the main docking port. NASA had first considered the potential risks of a space station reentry in 1962, but decided not to incorporate a retrorocket system in Skylab due to cost and acceptable risk.
The spent 49-ton Saturn V S-II stage which had launched Skylab in 1973 remained in orbit for almost two years, and made a controlled reentry on January 11, 1975. The re-entry was mistimed however and deorbited slightly earlier in the orbit than planned.
=== Re-entry and debris ===
Skylab's demise in 1974 was an international media event, with T-shirts and hats with bullseyes and "Skylab Repellent" with a money-back guarantee, wagering on the time and place of re-entry, and nightly news reports. The San Francisco Examiner offered a US$10,000 prize for the first piece of Skylab delivered to its offices; the competing San Francisco Chronicle offered US$200,000 if a subscriber suffered personal or property damage. A Nebraska neighborhood painted a target so that the station would have "something to aim for", a resident said.
A report commissioned by NASA calculated that the odds were 1 in 152 of debris hitting any human, and odds of 1 in 7 of debris hitting a city of 100,000 people or more. Special teams were readied to head to any country hit by debris. The event caused so much panic in the Philippines that President Ferdinand Marcos appeared on national television to reassure the public. Germany and Spain both issued warnings to not deorbit Skylab over their territory, as it would be treated as an act of war.
A week before re-entry, NASA announced that it would occur between July 10 and 14, with the 12th the most likely date, and the Royal Aircraft Establishment (RAE) predicted the 14th. In the hours before the event, ground controllers adjusted Skylab's orientation to minimize the risk of re-entry on a populated area. They aimed the station at a spot 810 miles (1,300 km) south-southeast of Cape Town, South Africa, and AARDV 2 fired its main engine to begin the deorbiting. Re-entry began at approximately 16:37 UTC, July 11, 1974. While AARDV 2 burned up as fast as it had on the AARDV 1 test flight, the station itself did not burn up as fast as NASA expected. Debris landed about 300 miles (480 km) east of Perth, Western Australia due to a four-percent calculation error, and was found between Esperance, Western Australia and Rawlinna, from 31° to 34° S and 122° to 126° E, about 130–150 km (81–93 miles) radius around Balladonia, Western Australia. Residents and an airline pilot saw dozens of colorful flares as large pieces broke up in the atmosphere; the debris landed in an almost unpopulated area, but the sightings still caused NASA to fear human injury or property damage. The Shire of Esperance light-heartedly fined NASA A$400 for littering. (The fine was written off three months later, but was eventually paid on behalf of NASA in April 2009, after Scott Barley of Highway Radio raised the funds from his morning show listeners.)
Stan Thornton found 24 pieces of Skylab at his home in Esperance, and a Philadelphia businessman flew him, his parents, and his girlfriend to San Francisco where he collected the Examiner prize and another US$1,000 from the businessman. The Miss Universe 1974 pageant was scheduled for July 20, 1974 in Perth, and a large piece of Skylab debris was displayed on the stage. Analysis of the debris showed that the station had disintegrated 10 miles (16 km) above the Earth, much lower than expected.
== Engineering mock-ups ==
A full-size training mock-up once used for astronaut training is located at the Lyndon B. Johnson Space Center visitor's center in Houston, Texas. Another full-size training mock-up is at the U.S. Space & Rocket Center in Huntsville, Alabama. Originally displayed indoors, it was subsequently stored outdoors for several years to make room for other exhibits. To mark the 40th anniversary of the Skylab program, the Orbital Workshop portion of the trainer was restored and moved into the Davidson Center in 2013. NASA transferred Skylab B (the backup Skylab) to the National Air and Space Museum in 1975. On display in the Museum's Space Hall since 1976, the orbital workshop has been slightly modified to permit viewers to walk through the living quarters.
== Missions ==
Mission 	Designation	Launch date 	Crew 	Duration 	Spacecraft Type, Launch Vehicle, and Launch Site
Skylab 	AS-516 	May 14, 1973 	unmanned	2 years 	N/A, Saturn INT-21, LC-39A
Skylab 1	AS-206 	May 25, 1973 	Pete Conrad, Commander
Joseph Kerwin, Pilot
Paul Weitz, Flight Engineer	28 days, 49 minutes, 49 seconds 	Block II Orbital Apollo, Saturn IC, LC-39B
AARDV 1 	CS-201 	June 13, 1973 	unmanned	18 days 	Block I AARDV, Saturn IC, LC-39B
Skylab 2	AS-207 	July 28, 1973 	Alan Bean, Commander
Owen Garriott, Pilot
Jack Lousma, Flight Engineer	59 days, 11 hours, 9 minutes, 1 seconds	Block II Orbital Apollo, Saturn IC, LC-39B
Skylab 3	AS-208 	November 16, 1973	Gerald Carr, Commander
Edward Gibson, Pilot
William Pogue, Flight Engineer	84 days, 1 hour, 15 minutes, 30 seconds	Block II Orbital Apollo, Saturn IC, LC-39B
Skylab 4	AS-209 	April 16, 1974 	Vance Brand, Commander
Don Lind, Pilot
William Lenoir, Flight Engineer	20 days 	Block II Orbital Apollo, Saturn IC, LC-39B
AARDV 2 	CS-202 	May 1, 1974 	unmanned	2 monthss 	Block I AARDV, Saturn IC, LC-39B
== Successor ==
After the demise of Skylab, NASA officially announced on July 16, 1974 (the fifth anniversary of the Apollo 11 launch) that Skylab B would be launched in 1975, with the official name Olympus. The station launched on May 25, 1975, two years to the day after Skylab 1, with the first manned flight, Olympus 1, launching shortly thereafter. Olympus was similar to Skylab, in that both were dry workshops built from an S-IVB stage, but Olympus was much more advanced in many areas, such as larger solar panels and the capability for resupply and modular expansion, as well as a stronger micrometeoroid shield to ensure it would not tear off during launch (which it did not). Olympus was continously-occupied until it was deorbited in 1989, a year after construction on the Entente-built Space Station Freedom commenced. The core of Freedom, Challenger, was also built from an S-IVB.
== See also ==
* Olympus program