Skylab

For other uses, see Skylab (disambiguation).

Skylab

A view of Skylab from the departing Skylab 4 mission
Station statistics
COSPAR ID	1973-027A
SATCAT no.	06633
Call sign	Skylab
Crew	3
Launch	1973-05-14 17:30:00 UTC
Launch pad	LC-39A, Kennedy Space Center
Reentry	1979-07-11 16:37:00 UTC near Perth, Australia
Mass	77,088 kg
Periapsis altitude	269.7 miles (434 km)
Apoapsis altitude	274.6 miles (442 km)
Orbital inclination	50 degrees
Orbital period	93.4 minutes
Orbits per day	15.4
Days in orbit	2,249 days
Days occupied	171 days
No. of orbits	34,981
Distance travelled	~890,000,000 miles (~1,400,000,000 km)
Statistics as of deorbit on 1979-07-11
Configuration
Skylab configuration with docked Apollo Command/Service Module

Skylab was the first space station the United States launched into orbit, and the second space station ever visited by a human crew. The 75 metric ton station was in Earth orbit from 1973 to 1979, and it was visited by crews three times in 1973 and 1974. It included a laboratory for studying the effects of microgravity and a solar observatory.

Background

The origin of the project is difficult to pinpoint because a number of different but related proposals were floated by various NASA centers before Skylab itself was launched.

Early studies

A key event took place in 1959, when Wernher von Braun submitted his final Project Horizon plans to the US Army. The overall goal of Horizon was to place man 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. This basic concept of re-using existing boosters would lead directly to a number of follow-on designs, and eventually the Skylab that actually flew.

In 1963, the US Air Force started development of the Manned Orbiting Laboratory (MOL), a small space station primarily intended for photo reconnaissance using large telescopes directed by a two-man crew. It also had the designation KH-10 - Dorian. The station was the same diameter as a Titan II upper stage. The stations were to 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.

A number of NASA centers saw the MOL as something of a threat, and started back-room studies on various space station designs of their own. Most of these were simply "back of a napkin" type designs with no official backing. 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 (CSM), or alternately Gemini capsule on a Titan II-C, the latter being much less expensive in the case where cargo was not needed.

But at the same time NASA was also looking for proposals for a major post-Apollo follow-on mission, including studies of a very large 24-man station with an operating lifetime of about five years. Lockheed Martin was involved in this project, and proposed a station that they felt would be a natural follow-on to the moon missions. One requirement for a permanent station would be periodic resupply, and for this role Lockheed suggested both Apollo-derived cargo vehicles and a new lifting body craft. After a lengthy and circuitous history, the new supply vehicle would emerge as the Space Shuttle, and their space station proposal as Space Station Freedom.

The Apollo Applications Program

In June 1964, NASA headquarters in Washington 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 manned solar telescope using an LM as its crew quarters, and small space stations using a variety of LM or CSM-based hardware. Although it didn't look at the space station specifically, over the next two years the office would become increasingly dedicated to this role. In 1965 the office was renamed, becoming the Apollo Applications Program (AAP).

As part of their general work, in August 1964 MSC presented studies on an expendable lab known as Apollo "X", short for Apollo Extension System. Apollo X replaced the LM carried on the top of the S-IVB stage with a small space station just 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.

Wernher von Braun proposed a more ambitious plan to build a much larger station. His design replaced the S-IVB stage of a complete Saturn V with an aeroshell, primarily as an adaptor for the CSM on top. Inside the shell was a cylindrical equipment section slightly smaller in diameter than the CSM. On reaching orbit, the S-II booster would be vented to remove any remaining hydrogen fuel, then the equipment section would be slid into it via a large inspection hatch. The station filled the entire interior of the S-II stage's hydrogen tank, with the equipment section forming a "spine" and living quarters between it and the walls of the booster. This would have resulted in a very large 33 x 45 foot 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. You could not "piggyback" the station's launch on a lunar mission; those required a working S-IVB stage. At the time the design was being proposed, all of the then-contracted Saturn V's were already earmarked for moon launches. Further work led to the idea of launching a smaller station based on the S-IVB instead, launching it on a surplus Saturn IB. Several planned Earth-orbit test missions for the LM and CSM had been cancelled, leaving a number of Saturn IB's free for use.

An early "wet workshop" version of Skylab.

Since the Saturn I had a much lower throw weight capability, the S-IV stage could not be left empty; its thrust would be needed for the mission. This limitation led to the development of the wet workshop concept, which led naturally out of von Braun's idea of using an existing stage after its fuel had burned off. However, in this case the station was to be built out of the S-IVB stage itself, as opposed to the S-II below it. A number of S-IVB-based stations were studied at MSC, but even the earliest, from mid-1965, had much in common with the Skylab design that actually flew. An airlock was placed in the equipment area immediately below where the LM sat on a moon mission, and a minimum amount of equipment was installed in the tank itself in order to avoid taking up too much fuel volume. After launch, a follow-up mission launched by a Saturn IB would carry up additional equipment in place of its LM, including solar panels, an equipment section and docking adaptor, and various experiments. Douglas Aircraft, builder of the S-IVB stage, was asked to prepare proposals along these lines.

On 1 April 1966, MSC sent out contracts to Douglas, Grumman, and McDonnell for conversion of a S-IVB spent stage under the name Saturn S-IVB spent-stage experiment support module (SSESM). In May the Apollo astronauts voiced concern over purging the stage's hydrogen tank in space. Nevertheless, in late July 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.

Design work continued over the next two years, in an era of shrinking budgets. In August 1967 NASA announced that the lunar mapping and base construction missions examined by the AAP were being cancelled. Only the Earth-orbiting missions remained, namely the Orbital Workshop and Apollo Telescope Mount solar observatory. Later several Moon missions were cancelled as well, originally to be 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; the S-IC and S-II lower stages could launch a "dry workshop" directly into orbit.

Vehicle

On 8 August 1969, McDonnell Douglas 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 for the construction of a mockup in January 1970. They named the manned workshop Skylab after a contest was held by NASA for someone to create a name.

Skylab was actually the refitted S-IVB second stage of a Saturn IB booster (from the AS-212 vehicle), a leftover from the Apollo program originally intended for one of the canceled Apollo Earth orbital missions. A product of the Apollo Applications Program (a program tasked with finding long-term uses for Apollo program hardware), Skylab was originally planned as a minimally-altered S-IVB to be launched on a Saturn IB. The small size of the IB would have required Skylab to double as a rocket stage during launch, only being retrofitted as a space station once in orbit. With the cancellation of Apollo missions 18-20, a Saturn V was made available and thus the "wet workshop" concept, as it was called, was put aside and Skylab was launched dry and fully outfitted. Skylab's grid flooring system was a highly visible legacy of the wet workshop concept.

The mission computer used aboard Skylab was the IBM System/4Pi TC-1, a relative of the AP-101 Space Shuttle computers.

Mission

Launch of the last Saturn V rocket (Actually a Saturn INT-21) carrying the Skylab space station

Skylab was launched 14 May 1973 by a Saturn INT-21 (a two-stage version of the Saturn V launch vehicle) into a 235 nautical mile (435 km) orbit. The launch is sometimes referred to as Skylab 1, or SL-1. Severe damage was sustained during launch, 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 pinning the remaining solar panel to the side of the station, preventing its deployment and thus leaving the station with a huge power deficit. The station underwent extensive repair during a spacewalk by the first crew, which launched on 25 May 1973 (the SL-2 mission) atop a Saturn IB. Two additional missions followed on 28 July 1973 (SL-3) and 16 November 1973 (SL-4) with stay times of 28, 59, and 84 days, respectively. The last Skylab crew returned to Earth on 8 February 1974.

File:Skylab and Earth Limb.jpg

View of Skylab space station cluster in Earth orbit from the departing Skylab 4 command module.

Operations in orbit

Skylab orbited Earth 2,476 times during the 171 days and 13 hours of its occupation during the three manned Skylab missions. Astronauts performed ten spacewalks totalling 42 hours 16 minutes. Skylab logged about 2,000 hours of scientific and medical experiments, including eight solar experiments. The Sun's coronal holes were discovered thanks to these efforts. Many of the experiments conducted investigated the astronauts' adaptation to extended periods of microgravity. Each Skylab mission set a record for the amount of time astronauts spent in space.

End of Skylab

Following the last mission, Skylab was left in a parking orbit expected to last at least eight years. The Space Shuttle was planned to dock with and elevate Skylab to a higher safe altitude in 1979; however, the shuttles were not able to launch until 1981. A planned unmanned satellite called the Teleoperator was to be launched to save Skylab, but funding never materialized. Skylab was in need of a major overhaul, including new gyroscopes, and was low on fuel. Some systems were not designed for maintenance in space; however this type of problem had been overcome before such as when the primary coolant loop was repaired.

Vanguard (T-AGM-19) seen here as a NASA Skylab tracking ship. Note the SatCom tracking radar and telemetry antennas.

Increased solar activity, heating the outer layers of the Earth's atmosphere and thereby increasing drag on Skylab, led to an early reentry at approximately 16:37 UTC 11 July 1979. In the weeks leading up to the reentry, ground controllers had re-established contact with the six year old vehicle, and were able to adjust its attitude for optimal reentry dynamics. Earth reentry footprint was a narrow band (approx. 4° wide) beginning at about 48°S 87°E and ending at about 12°S 144°E, an area covering portions of the Indian Ocean and Western Australia. Debris was found between Esperance, Western Australia, and Rawlinna, Western Australia, 31–34°S, 122–126°E. An Australian municipality, the Shire of Esperance, fined the United States $400 for littering. In 2004, the History Channel documentary "History Rocks" stated, in an episode covering major events of 1979, that this fine has never been paid.

The largest fragment of Skylab recovered after its reentry through Earth's atmosphere. It is on display at the United States Space & Rocket Center.

Skylab's demise was an international media event, with merchandising, wagering on time and place of re-entry and nightly news reports. The San Francisco Examiner offered a $10,000 prize for the first piece of Skylab to be delivered to their offices. 17-year-old Stan Thornton scooped a few pieces of Skylab off the roof of his home in Esperance, Western Australia and caught the first flight to San Francisco, where he collected his prize. In a coincidence for the organizers, the annual Miss Universe pageant was scheduled to be held a few days later, on 20 July 1979 in nearby Perth, Western Australia. A large piece of Skylab debris was displayed on the stage.

Two flight-quality Skylabs were built. The first was de-orbited and crashed in Western Australia in 1979; the second, a backup, is on display at the National Air and Space Museum in Washington, DC. A full scale training mockup once used for astronaut training is located at the Lyndon B. Johnson Space Center visitor's center in Houston, Texas. Another full scale training mockup is now kept at Huntsville, Alabama, made from spare parts. It is currently being restored.

Skylab missions

The number identification of the manned Skylab missions is the cause of much confusion. Originally, the unmanned launch of Skylab and 3 manned missions were numbered SL-1 through SL-4. During the preparations for the manned missions, some documentation was created with a different scheme--SLM-1 through SLM-3--for those missions only. William Pogue credits Pete Conrad with asking the Skylab program director which scheme should be used for the mission patches and the astronauts were told to use 1-2-3, not 2-3-4. By the time NASA administrators tried to reverse this decision, it was too late, as all the in-flight clothing had already been manufactured and shipped with the 1-2-3 mission patches.

Mission	Patch	Commander	Pilot	Science Pilot	Launch date	Landing date	Duration (days)
Skylab 1 SL-1		unmanned launch			1973-05-14 17:30:00 UTC	1979-07-11 16:37:00 UTC	2248.96
Skylab 2 SL-2 (SLM-1)		Pete Conrad	Paul Weitz	Joseph Kerwin	1973-05-25 13:00:00 UTC	1973-06-22 13:49:48 UTC	28.03
Skylab 3 SL-3 (SLM-2)		Alan Bean	Jack Lousma	Owen Garriott	1973-07-28 11:10:50 UTC	1973-09-25 22:19:51 UTC	59.46
Skylab 4 SL-4 (SLM-3)		Gerald Carr	William Pogue	Edward Gibson	1973-11-16 14:01:23 UTC	1974-02-08 15:16:53 UTC	84.04

Cultural References

• The Skylab missions were contemporaneously satirized in the comic strip Doonesbury in a multi-strip arc that lampooned the repair efforts (in one strip, a spacewalking astronaut asks a colleague for some scotch tape) and the public's diminished interest in the post-moonflight space program. (For example, the astronauts are congratulated not by the President, nor the Vice-President, but rather the Lieutenant-Governor of Iowa, leading one of the astronauts to mutter, "I'll bet we don't get a parade, either....")
• The rap-rock band 2 Skinnee J's wrote a song titled "Skylab" inspired by the station's reentry. The song appears on their first album, Sing, Earthboy, Sing!
• The indie rock band PAIN(t)bynumbers wrote a song titled "Skylab Bluz" discussing the vivid scope of the Skylab project.
• The Monks recorded a song called "Skylab (Theme from the Monks)" on their 1979 album Bad Habits.
• Minneapolis indie rock band Manplanet released an EP entitled "Skylab". Known for their costumes and theatrics, when performing the title song they would drop a tin foil and cardboard model of the spacestation on the crowd while igniting pyrotechnics.
• Brazilian singer Rogério Skylab took his stage name from the space station.
• The 1983 computer game Manic Miner features a level called "Skylab Landing Bay", in which the main obstacle is multiple Skylabs vertically falling and crashing into the ground.
• The 1987 Australian film Dogs in Space is set in a chaotic house in Melbourne at the time of Skylab's re-entry, with the crash paralleling the death of one housemate from a drug overdose.
• In Bart vs. Australia, a 1995 episode of The Simpsons, a passing reference is made to Skylab's plummet when a fragment of it is seen underneath Australia's international airport.
• In the 2001 movie Wet Hot American Summer, the plot revolves around a college professor who has to come up with a plan to save a summer camp from a rogue piece of Skylab, which is re-entering the atmosphere. The film takes place in 1981.

Gallery

• 
  The waste management facilities of Skylab, as seen in the mockup at the National Air and Space Museum.
• 
  An astronaut dines aboard Skylab, as depicted by the mockup at the Smithsonian NASM.

See also

• Salyut
• Mir
• International Space Station
• Space station for statistics of occupied space stations
• Project Apollo
• Apollo Spacecraft

External links

• SKYLAB: A CHRONOLOGY by Roland W. Newkirk and Ivan D. Ertel with Courtney G. Brooks (NASA SP-4011 1977)
• SP-402 A New Sun: The Solar Results from Skylab
• Skylab Mission Evaluation - NASA report (PDF format)
• Skylab Reactivation Mission Report 1980 - NASA report (PDF format)
• Skylab Our First Space Station - NASA report (PDF format)
• Skylab Restoration Project
• Skylab Orbit Video of Skylab orbitting Earth as Skylab Mission 2 approaches it
• NASA History Series Publications (many of which are on-line)