Skylab

Skylab

A view of Skylab from the departing Skylab 4 mission
Station statistics
NSSDC ID	1973-027A
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 (169,950 lb)
Pressurised volume	10,000 cu ft (283.17 m3)
Perigee	269.7 mi (434.0 km)
Apogee	274.6 mi (441.9 km)
Orbital inclination	50°
Orbital period	93.4 min
Orbits per day	15.4
Days in orbit	2,249 days
Days occupied	171 days
Number of orbits	34,981
Distance travelled	~890,000,000 mi (1.43×109 km)
Statistics as of deorbit on 1979-07-11
Configuration
Skylab configuration with docked Apollo Command/Service Module

Skylab was the United States' first space station, and the second space station visited by a human crew. It was also the only space station NASA launched alone. The 100-ton space station was in Earth's orbit from 1973 to 1979 and it was visited by crews three times in 1973 and 1974.

Background

The exact 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 U.S. Army. The overall goal of Horizon was to place a human 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,^[1]:23 an idea used for Skylab.^[1]:9

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 (CSM),^[1]:10 or a Gemini capsule^[1]:14 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.^[1]:13-14

Air Force competition

In September 1963, NASA and the Department of Defense (DoD) agreed to cooperate in building a space station.^[1]:17 In December, the Air Force nonetheless announced Manned Orbital Laboratory (MOL), a small space station primarily intended for photo reconnaissance using large telescopes directed by a two-man 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.^{[1]:17-19[2][3]} MOL competed for funding with a NASA station for the next five years,^[1]:15 and caused changes to the NASA plans so they would resemble MOL less.^[1]:17

Development

Apollo Applications Program

NASA management was concerned about, after landing on the moon, losing the 400,000 workers involved in Apollo.^[1]:20,22 It 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 (LEM), a large manned solar telescope using an LEM as its crew quarters and small space stations using a variety of LEM 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 August 1965 the office was renamed, becoming the Apollo Applications Program (AAP).^[1]:20

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" would have replaced the LEM 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

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 adapter 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-by-45-foot (10.1 by 13.7 m) living area. Power was to be provided by solar cells lining the outside of the S-II stage.^[1]:22

One problem with this proposal was that it required a dedicated Saturn V launch to fly the station. Engineers could not "piggyback" the station's launch on a lunar mission, which 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 LEM and CSM had been canceled, 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 LEM 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 LEM, 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. The company had for several years been proposing stations based on the S-IV that the S-IVB replaced.^[1]:25

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).^[1]:30 In May 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.

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, but decided that the Air Force station was not large enough and converting Apollo hardware for use with Titan would be too slow and too expensive.^[1]:45-48 DoD canceled MOL in June 1969, however.^[1]:109

Dry workshop

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 canceled. Only the Earth-orbiting missions remained, namely the Orbital Workshop and Apollo Telescope Mount solar observatory. Later several Moon missions were canceled 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;^[1]:109-110 the S-IC and S-II lower stages could launch a "dry workshop", with its interior already prepared, directly into orbit.

Habitability

Jack Lousma takes shower during Skylab 3 mission.

A dry workshop simplified plans for the interior of the station.^[1]:130 Industrial design firm Raymond Loewy/William Snaith recommended emphasizing habitability and comfort for the astronauts by, for example, providing a wardroom for meals and relaxation,^[1]:133-134 and a window to view the Earth and space, although astronauts who participated in Skylab planning were dubious about designers' focus on areas such as color schemes.^[1]:137 Habitability had not previously been an area of concern when building spacecraft due to their small volume and brief mission durations, but Skylab missions would last for months.^[1]:133 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.^[1]:139-140

Astronauts were uninterested in watching movies on a proposed entertainment center or playing games, but did want books and individual music choices.^[1]:137 Food was also important; early Apollo crews complained about its quality, and a NASA volunteer found living on the Apollo food for four days on Earth to be intolerable; its taste and composition, in the form of cubes and squeeze tubes, were unpleasant. Skylab food significantly improved on its predecessors by prioritizing habitability over scientific needs.^[1]:141-142

Each astronaut had a private sleeping area the size of a small walk-in closet with a curtain, sleeping bag, and locker.^[4]:82 Designers also added a shower^{[1]:139[4]:80} and a toilet;^{[1]:152-158[4]:30} the latter was for both comfort and to obtain precise urine and feces samples for examination on Earth.^[1]:165

Operational history

On 8 August 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.^[1]:115 The actual stage that flew was the upper stage of the AS-212 rocket (the S-IVB stage). The mission computer used aboard Skylab was the IBM System/4Pi TC-1, a relative of the AP-101 Space Shuttle computers.

Launch of the modified Saturn V rocket carrying the Skylab space station

Skylab was launched 14 May 1973 by a Saturn V with the upper stage removed, but with the avionics remaining in the same position. (different from the Saturn INT-21 rocket which could launch payloads not based on the S-IV) 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 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 pinning the remaining solar panel to the side of the station, preventing its deployment and thus leaving the station with a huge power deficit.^[1]:253-255 The station underwent extensive repair during a spacewalk by the crew of the SL-2 mission, which launched on 25 May 1973 atop a Saturn IB. If the crew had failed to repair Skylab in time, the plastic insulation inside the station would have melted, releasing poisonous gas and making Skylab completely uninhabitable. They stayed in orbit with Skylab for 28 days. Two additional missions followed with the launch dates of 28 July 1973 (SL-3) and 16 November 1973 (SL-4) with mission durations of 59 and 84 days, respectively. The last Skylab crew returned to the Earth on 8 February 1974.

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 totaling 42 hours 16 minutes. Skylab logged about 2,000 hours of scientific and medical experiments, 127,000 frames of film of the sun and 46,000 of the Earth.^[1]:340 Solar experiments included photographs of eight solar flares, and produced valuable results^[4]:155 that scientists stated would have been impossible to obtain with unmanned spacecraft.^[1]:342-344 The existence of the Sun's coronal holes were confirmed because of these efforts.^[1]:357 Many of the experiments conducted investigated the astronauts' adaptation to extended periods of microgravity.

Life in orbit

Each Skylab mission set a record for the amount of time astronauts spent in space. The station offered "a highly satisfactory living and working environment for crews."^[5]:2-4 Although it had a dart set,^[6] playing cards, and other recreational equipment in addition to books and music players, the window became the most popular way to relax in orbit.^{[4]:79-80,134-135} Crews enjoyed taking a shower once a week but found drying themselves in weightlessness difficult.^[7] Although the toilet was noisy, both veteran astronauts—who had endured earlier missions' rudimentary waste-collection systems—and rookies complimented it.^{[1]:165[4]:80[7]}

Plans for reuse

Skylab was abandoned after the end of the SL-4 mission in February 1974. In 1977 and 1978, when NASA still believed the shuttle would be ready by 1979, it completed two studies on reusing the station.^[8][5]:3-1 As of September 1978^[update] the agency believed Skylab was safe for crews, with all major systems intact and operational.^[5]:3-2 It still had 180 man-days of water and 420 man-days of oxygen, and astronauts could refill both;^[8] the station could hold up to about 600 to 700 man-days of drinkable water and 420 man-days of food.^[5]:2-7

Valuable resource

The studies cited several benefits from reusing Skylab, which one called a resource worth "hundreds of millions of dollars"^[5]:1-13 already in orbit. Since no more Saturn Vs existed, four to five shuttle flights and extensive space architecture would be needed to build another station as large as Skylab's 12,400 cubic feet (350 m³) volume.^{[5]:1-12 to 1-13} Its ample size—much greater than that of the shuttle alone or shuttle plus Spacelab^[5]:2-8—was enough with some modifications for up to seven astronauts^[5]:2-31 of both sexes,^[5]:3-14 and experiments needing long duration in space;^[5]:1-13 even a movie projector for recreation was possible.^[5]:3-11

Repairing and upgrading Skylab would provide information on the results of long-duration exposure to space for future stations.^[8] The most serious issue for reactivation was stationkeeping, as one of the gyroscopes had failed^[1]:361 and the attitude control system needed refueling; they would need extra-vehicular activity (EVA) to fix or replace. The station had not been designed for extensive resupply. However, while plans had originally called for Skylab crews to perform only limited maintenance^[4]:34 they successfully made major repairs during EVA, such as the SL-2 crew's deploying of the solar panel^[4]:73-75 and the SL-4 crew's repair of the primary coolant loop.^{[5]:3-21[1]:317[4]:130} The SL-2 crew fixed one item during EVA by "hit[ting] it with the hammer."^[4]:89

Beyond the opportunity for space construction and maintenance experience, reactivating the station would free up shuttle flights for other uses,^[5]:1-13 and reduce the need to modify the shuttle for long-duration missions.^{[5]:2-9 to 2-10} Even if the station were not manned again, it would serve as a useful experimental platform.^[5]:2-61

Planned shuttle missions

The reactivation would occur in four phases:^[8]

1. An early Shuttle flight would boost Skylab to a higher orbit that would add five years of life. The shuttle might have pushed or towed the station, but attaching a booster—the Tele-operated Reboost System (TRS)—to the station was more likely based on astronauts' training for the task. Martin Marietta won the contract for the $26 million^[9] TRS, which contained about three tons of propellant,^[10] and began work in April 1978.^[9]
2. In two shuttle flights, Skylab would be refurbished. In January 1982, the first mission would attach a docking adapter and conduct repairs. In August 1983, a second crew would replace several system components.
3. In March 1984, shuttle crews would attach a solar-powered Power Expansion Package, refurbish scientific equipment, and conduct 30- to 90-day missions using the Apollo Telescope Mount and the earth resources experiments.
4. Over five years Skylab would be expanded to accommodate six to eight astronauts, with a new large docking/interface module, additional logistics modules, Spacelab modules and pallets, and an orbital vehicle space dock using the shuttle's external tank.

The first three phases would require about $60 million in 1980s dollars, not including launch costs.

Abandonment and re-entry

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

After an 6.8 miles (10.9 km) boost by SL-4's Apollo CSM before its departure, Skylab was left in a parking orbit of 269 miles (433 km) by 283 miles (455 km)^[1]:361 that was expected to last until at least the early 1980s based on estimates of the 11-year sunspot cycle that began in 1976.^[1]:361[11] At the end of SL-4, only one Saturn IB rocket remained in the inventory—later used for Apollo-Soyuz Test Project—while all other Saturn IB and Saturn V rocket parts had been donated to museums. NASA began considering the risks from space station reentry as early as 1962, but decided to not incorporate a retrorocket system in Skylab due to cost and acceptable risk.^[1]:127-129

Solar activity

Greater-than-expected solar activity^[1]:362 heated the outer layers of the Earth's atmosphere and thereby increased drag on Skylab. By late 1977 NORAD accurately forecast a reentry in mid-1979;^[11] a NOAA scientist criticized NASA for using an inaccurate model for the second most-intense sunspot cycle in a century, and for ignoring NOAA predictions published in 1976.^[1]:362-363

The reentry of the USSR's Cosmos 954 in January 1978 and the resulting radioactive debris in northern Canada drew more attention to Skylab's orbit. Although Skylab did not contain radioactive materials, the State Department warned NASA about diplomatic repercussions from station debris.^[1]:363 Ground controllers re-established contact with Skylab in March 1978^[11] and recharged its batteries.^[12] Although NASA worked on plans to reboost Skylab with the shuttle through 1978 and the TRS was almost complete, the agency gave up in December when it became clear that the shuttle would not be ready in time;^{[1]:363-367[9]} its first flight, STS-1, did not occur until April 1981. Also rejected was a proposal to launch the TRS using one or two unmanned rockets.^[8]

Reentry

The largest fragment of Skylab recovered after its re-entry 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.^[12] The San Francisco Examiner offered a $10,000 prize for the first piece of Skylab delivered to its offices; the competing Chronicle offered $200,000 if a subscriber suffered personal or property damage.^[12] NASA calculated that the odds of station re-entry debris hitting a human were 152 to 1^[1]:369—although the odds of debris hitting a city of 100,000 or more were 7 to 1—and teams were ready to head to any country hit by debris and requesting help.^[12]

Ground controllers adjusted Skylab's orientation for ideal re-entry dynamics in the hours before reentry^[12] at approximately 16:37 UTC 11 July 1979. They aimed the station at a spot 810 miles (1,300 km) south southeast of Cape Town, South Africa. The station did not burn up as fast as NASA expected, however. Due to a 4% calculation error, debris landed southeast of Perth, Western Australia,^[1]:371 and was found between Esperance and Rawlinna, from 31° to 34°S and 122° to 126°E. The Shire of Esperance fined the United States $400 for littering, a fine which remained unpaid for 30 years.^[13] The fine was paid in April 2009, when radio show host Scott Barley of Highway Radio raised the funds from his morning show listeners and paid the fine on behalf of NASA.^[14]

17 years-old Stan Thornton found a few pieces of Skylab at his home in Esperance and caught the first flight to San Francisco, where he collected the Examiner prize.^[1]:371 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 Perth. A large piece of Skylab debris was displayed on the stage.^[15]

Unflown planned missions

Skylab 5

Skylab 5 would have been a short 20-day mission to conduct scientific experiments and boost Skylab into a higher orbit. Vance Brand (commander), Don Lind (command module pilot), and William B. Lenoir (science pilot) would have been the crew for this mission, with Brand and Lind being the prime crew for the never-flown Skylab Rescue flights. Brand and Lind also trained for a mission that would have aimed Skylab for a controlled deorbit.^[16]

Skylab B

A flight-quality backup Skylab was built. NASA considered using it for a second Skylab B station in May 1973 or later, but decided against it. Launching another Skylab with another Saturn V rocket would have been very costly, and it was decided to spend this money on the development of the Space Shuttle, instead. The backup is on display at the National Air and Space Museum in Washington, D.C.

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, made from spare parts, has been rotting for years in a museum parking lot exposed to the elements at Huntsville, Alabama after it was moved outdoors to make way for an exhibit on the Russian space station MIR. This Skylab engineering mockup is currently being considered for restoration to the pristine condition it originally enjoyed inside the U.S. Space and Rocket Center.^[17]

Skylab mission designations

Robbins Medallions issued for Skylab Missions

The numeric identification of the manned Skylab missions is the cause of much confusion. Originally, the unmanned launch of Skylab and three 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.^[18]

Mission	Emblem	Commander	Pilot	Science Pilot	Launch date	Landing date	Duration (days)
Skylab 1 SL-1		unmanned launch of space station			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

Gallery

The waste management facilities in the backup Skylab at the National Air and Space Museum.

An astronaut dines aboard the backup Skylab at the Smithsonian NASM.

SkyLab commemorative issue, Issue of 1974. The commemorative stamp reflects initial repairs to the station, including the parasol sunshade.

References

Further reading

• 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)

External links

• NASA History Series Publications (many of which are on-line)
• a cutaway drawing of skylab
• Sklyab reboost module
• Skylab De-orbit
• Skylab cutaway drawing from Encyclopedia Britannica

Project Skylab missions Flown Skylab 1 · Skylab 2 · Skylab 3 · Skylab 4 Canceled Skylab 5 Unflown Skylab Rescue · Skylab B

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