On May 14, 1973, the ultimate Saturn V rocket lifted off to deploy Skylab, America’s first space station. Despite a troubled begin to its life, Skylab pioneered long-duration spaceflight, and fifty years later lessons learned on this program are still contributing to the success of the International Space Station.
With Apollo 11’s successful landing on the Moon in July 1969, NASA had met President Kennedy’s challenge of landing a person on the moon and returning him safely to the Earth by the top of the Sixties. While six more crewed lunar missions would follow over the following three and a half years, the target had been achieved and funding was cut. With missions past Apollo 17 canceled, NASA’s attention returned to low Earth orbit, and the event of an area station using Apollo hardware. This is able to allow the agency to proceed scientific research and study the consequences of spaceflight on crews over the course of long-duration missions.
The launch of Skylab got here two years after the Soviet Union had deployed the world’s first space station, Salyut 1. This station only hosted a single crew, which arrived aboard the ill-fated Soyuz 11 mission in June 1971, the sooner Soyuz 10 mission having did not dock. After three weeks aboard Salyut 1 the Soyuz 11 crew returned to Earth, but were killed when their capsule depressurized during re-entry.
Although the Soviet Union would launch three extra space stations in 1972 and early 1973, the primary of those failed to achieve orbit and the following two malfunctioned shortly after deployment, with no Soyuz missions being launched to any of them. Skylab was, subsequently, the second space station to be crewed in orbit, but as of 2023 it stays the one crewed station to have been operated exclusively by america.
Design and Launch
With a mass of 76,500 kilograms (168,800 lb) and a length of 25 meters (82 feet), Skylab was considerably larger than Salyut and still stays the biggest monolithic space station (i.e. deployed as a single unit) ever launched and certainly one of the biggest spacecraft ever to operate in Earth orbit. Only modular space stations assembled in orbit (specifically Mir and the International Space Station), the Space Shuttle orbiters, and Buran have surpassed it in mass. The Soviet Polyus experimental military platform also had a greater mass than Skylab, nonetheless it failed to achieve orbit.
Skylab’s large size was a results of its use of surplus hardware from the Apollo program. Its Orbital Workshop (OWS), the principal section of Skylab, was converted from an S-IVB stage that had been intended for a Saturn IB rocket. A Saturn V rocket left over from the cancellation of the last three planned lunar Apollo missions can be used to put it into orbit.
Alongside the lunar program, NASA had planned the Apollo Applications Programme (AAP) to benefit from hardware and technologies developed during Apollo for a variety of other missions. The Orbital Workshop had originated from this project, with two concepts being considered: the “Dry Workshop” – which might see the stage converted before launch – and the “Wet Workshop” which might convert a live S-IVB stage from a Saturn IB launch on-orbit.
As a dedicated station, the Dry Workshop – which might later evolve into Skylab – would supply extra space for astronauts, have the opportunity to hold more equipment, and never require as much of their time to convert – allowing for more time on-orbit to conduct experiments. Since its principal propulsion system and propellant tanks were removed, the station wouldn’t have the opportunity to contribute to its own ascent to orbit, so a modified Saturn V can be needed to deploy it.
McDonnell Douglas, the manufacturer of the S-IVB, can be chargeable for converting the stage into Skylab’s Orbital Workshop, under a contract signed in August 1969.
In addition to the Orbital Workshop, Skylab incorporated a Multiple Docking Adapter (MDA) with two ports for Apollo spacecraft to dock, an airlock, and the Apollo Telescope Mount (ATM) observatory which carried instruments to review the Sun. Although the station had two docking ports, the second was intended as a backup, relatively than a way of getting two spacecraft docked concurrently – although this might have been supported if obligatory. Power was to be generated by two principal solar panels attached to the OWS, with 4 additional panels mounted at right angles on the ATM.
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The Saturn V with Skylab (right) and Saturn IB with Skylab 2, prior to launch from KSC. (Credit: NASA)
Skylab’s launch would mark the thirteenth and final flight of the legendary Saturn V rocket, which had powered previous Apollo missions on their journeys to the Moon. For the Skylab mission, the rocket flew in a two-stage configuration, with the Orbital Workshop taking the place of the S-IVB third stage. The rocket’s instrument unit (IU) was incorporated on the forward end of the OWS, with a four-sector payload fairing encapsulating the airlock, MDA and ATM.
For launch, the ATM stowed forward of the principal docking port. Once in orbit, it was relocated to its operational position perpendicular to the remainder of the station. The Skylab launch was the one time a Saturn V would fly with a payload fairing. Like earlier Saturn V missions, the rocket was assembled within the Vehicle Assembly Constructing on the Kennedy Space Center, with build-up commencing on Aug. 2, 1972. The rocket was stacked atop Mobile Launcher 2, which was then moved to Launch Complex 39A (LC-39A) by Crawler Transporter.
Saturn V SA-513, the rocket tasked with deploying Skylab, would have an eventful climb toward orbit. Liftoff occurred at 1:30:00 p.m. EDT (17:30:00 UTC) on May 14, 1973, with the five F-1 engines of the S-IC first stage powering Saturn aloft. After clearing the tower the rocket began a pitch-and-roll maneuver to ascertain itself on its planned trajectory, increase speed because it climbed and reaching Mach 1, the speed of sound, just over a minute after liftoff.
About 63 seconds into the flight, the Orbital Workshop’s micrometeoroid shield – which was also designed to act as a critical a part of the station’s thermal control system – suffered a structural failure and detached. Debris from this damaged tie-down fittings holding the No.2 solar array in its launch position, jammed the No.1 solar array and in addition damaged the separation systems on the interstage between the primary and second stages of the rocket. These events occurred about ten seconds before the rocket passed through Max-Q, or the realm of maximum dynamic pressure.
The launch continued, with the S-IC burning all five engines until T+140 seconds, when its center F-1 was shut down as planned to scale back acceleration. The remaining engines shut down in pairs, about 18 seconds later, before the primary and second stages separated. Retro-rockets pushed the S-IC away from the S-II second stage, whose five J-2 engines ignited to take over the job of boosting Skylab towards orbit.
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Skylab launches aboard the ultimate Saturn V rocket. (Credit: NASA)
Somewhat under 20 seconds after S-II ignition, the interstage must have been jettisoned from the aft end of the stage. This didn’t occur as scheduled, with a post-flight evaluation determining that certainly one of the shaped charges chargeable for separating the interstage had probably been damaged by debris from the micrometeoroid shield. As an alternative, the interstage remained attached all of the method to orbit, with higher temperatures being recorded across the base of the stage consequently. The rocket had sufficient reserve propellant to make up for any underperformance consequently of its additional mass.
Five minutes and 14 seconds into the flight, the S-II’s center engine was commanded to shut down with the 4 outboard engines continuing to fireside until the nine-minute, 48-second mark. About two seconds after shutdown, Skylab was released from the second stage, which then fired retro motors to maneuver itself away and reduce the danger of recontact between itself and the space station. The No.2 solar array, whose tie-downs had been severed by the initial debris incident earlier within the launch, was caught within the exhaust of the retro rockets and ripped away from the station.
Despite this incident, Skylab’s deployment sequence continued as scheduled, with the payload fairing separating at quarter-hour, 20 seconds mission elapsed time. The station then re-oriented itself to the planned sun-angle for solar array deployment, and shortly afterward began to deploy the ATM to its post-launch position.
With this in place, the ATM’s solar panels were deployed successfully, nonetheless the one remaining solar panel on the OWS did not open. This left the station with insufficient power to support long-duration missions beyond the lifespan of the fuel cells on visiting Apollo spacecraft, while the lack of thermal protection from the lost micrometeoroid shield meant that temperatures aboard the station were uninhabitable.
The launch of the primary crew to Skylab was delayed while NASA evaluated data from the launch to plan a rescue plan. On May 16, the National Reconnaissance Office (NRO) launched a KH-8 Gambit spy satellite, OPS-2093, from Vandenberg Air Force Base, tasked with capturing images of the crippled Skylab to assist assess the damage. One in every of the satellite’s two film-return capsules was used to send these back to Earth on May 21, by which point plans for a repair mission were in a sophisticated stage of planning, with launch 4 days away.
Crewed Missions
Three long-duration crews, each consisting of three astronauts, visited Skylab aboard Apollo Command and Service Modules (CSMs). All three missions were launched in 1973, with each setting a brand new record for the longest-duration human spaceflight as much as that point. The crewed missions launched atop Saturn IB rockets, flying from the modified Mobile Launcher 1 (later MLP-3) at LC-39B using a “milkstool” adaptor which enabled the smaller Saturn IB to utilize the Launch Umbilical Tower (LUT) that had been built for the Saturn V.
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The Skylab 2 crew with their rocket. Left to right: Conrad, Kerwin, Weitz. (Credit: NASA)
Skylab’s first crew was commanded by Gemini and Apollo 12 veteran Pete Conrad, who was joined by rookies Joseph P. Kerwin and Paul J. Weitz. Designated Skylab 2, their mission lifted off on May 25, 1973, having been delayed from May 15 attributable to the damage Skylab had sustained during launch. While the astronauts had trained for a mission of scientific research, they found themselves responsible first for putting NASA’s rescue plan into effect to avoid wasting the space station that was to turn into their home for the following few weeks.
After rendezvous with Skylab, the crew performed a flyaround of the outpost to examine the damage. After the CSM was maneuvered near the stuck solar array, Weitz performed a stand-up spacewalk from the Command Module hatch in an try to free the panel using tools mounted on a three-meter (10-foot) long pole, but was unsuccessful as a strip of metal blocking its deployment was wrapped around a beam and couldn’t be freed with the available tools.
The crew proceeded to dock with the station, nonetheless their spacecraft’s docking system failed to interact. After some troubleshooting, including depressurizing the Command Module again and removing the back plate of the docking probe, a successful docking was achieved.
When the crew boarded Skylab the next day, certainly one of their first tasks was to deploy a substitute sun shield which had been rapidly improvised on the bottom. This consisted of a “parasol” device in a canister which could possibly be deployed from a small science airlock on the Orbital Workshop. Once this was accomplished, temperatures aboard the station began to stabilize and the crew were in a position to begin their planned science mission.
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The Skylab Orbital Workshop and its jammed solar array, seen during Skylab 2’s flyaround. (Credit: NASA)
Owing partly to concerns across the reliability of Skylab’s batteries, which could have jeopardized future missions to the station, one other try to free the jammed solar panel was made on June 7. Conrad and Kerwin performed a three-hour, 25-minute EVA to chop away the debris and fasten a tether that was then used to tug the solar array free. With this achieved successfully, concerns about Skylab’s ability to generate electrical power became less acute.
An extra EVA was conducted on June 19 by Conrad and Weitz, the primary of several to vary out film cassettes within the Apollo Telescope Mount. The crew returned to Earth on June 22, completing their 28-day mission.
The second crewed mission – Skylab 3 – was commanded by one other former member of the Apollo 12 crew in Alan Bean. Bean was joined by rookies Owen Garriott and Jack Lousma for the mission, which lifted off on July 28, 1973, and splashed down 59 and a half days in a while Sept. 25. The ultimate mission was launched on Nov. 16, with an all-rookie crew: Gerald P. Carr commanding with Edward G. Gibson and William R. Pogue.
Skylab 4’s stay aboard the station can be the longest, at over 83 days. The crew returned to Earth on Feb. 8, 1974, after which no more astronauts would set foot aboard the Skylab station.
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Owen Garriott using a Lower Body Negative Pressure Device as a part of life science research on Skylab 3. (Credit: NASA)
Although its three expeditions are short by modern standards – the astronauts of Dragon ‘s Crew-4 mission last yr spent roughly the identical time aboard the International Space Station as Skylab was crewed across all three missions – these were the longest human spaceflights in history for his or her time. As such, medical research was a big focus for studies to make sure crews could remain fit and healthy during prolonged stays in space.
A bicycle ergometer was provided for crew exercise, with the metabolic responses of the astronauts being monitored to trace their physiological condition. Other experiments included a rotating chair that was used to check the astronauts’ sensitivity to motion sickness and pre-and-post-flight x-rays to search for mineral loss – combined with the examination of urine samples that showed the astronauts were excreting greater amounts of calcium and hydroxyproline than expected.
The one research that took up more time than life science research was solar physics. The Apollo Telescope Mount contained instruments to review the Sun intimately, with the crew in a position to fine-tune the observations. A key objective achieved by the Skylab 2 mission was to record a solar flare in progress. Paul Weitz achieved this on June 15, 1973, tracking a flare for 2 minutes because it rose and fell.
Throughout the lifetime of the station, crews made numerous spacewalks to gather film cassettes from the telescope mount and to put in replacements. A complete of 127,000 frames of film were captured by the Skylab’s telescopes.
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Image of a Solar flare captured by Skylab in December 1973. (Credit: NASA)
Other research carried out aboard the station included Earth statement, using photography and multispectral imaging, and microwave measurement of soil moisture. During Skylab 4, the crew was tasked with observing designated areas and briefed on what to search for and photograph, in an try to assess the utility of using crew to focus on observations.
Crew time was also given over to technology development research – including tests of an astronaut maneuvering device aboard the station – materials science and manufacturing, astrophysics, and student experiments.
Legacy
While crewed Skylab operations ended with the departure of the Skylab 4 crew, NASA had hoped to reactivate the station once the Space Shuttle became operational. Ultimately this was prevented by a mix of increased atmospheric drag causing Skylab to decay from orbit more quickly than expected, and delays to the Shuttle program.
Under early plans, the third Space Shuttle mission would have been flown by astronauts Jack Lousma and Fred Haise, who would have deployed a module called the Teleoperator Retrieval System (TRS). TRS would have then been docked with Skylab via handheld remote control from the Shuttle. Once docked, its thrusters would have been used to boost the space station into the next orbit — or to deorbit it to a controlled re-entry if deemed obligatory. TRS was later moved to the second Shuttle mission as this system began to fall behind schedule, but can be abandoned when it became clear that Skylab was going to re-enter before the Shuttle can be able to fly.
Skylab re-entered the atmosphere over the Indian Ocean on July 11, 1979, with some debris reaching the coast of Australia.
When the Space Shuttle finally flew in 1981, NASA gained a spacecraft able to carrying out significant amounts of on-orbit research independently – particularly when equipped with a Spacelab or later Spacehab, module in its payload bay. As such, the agency pivoted away from space stations and as an alternative focussed on the Shuttle. A brand new station called Freedom was proposed within the mid-Nineteen Eighties, using the Space Shuttle to assemble multiple modules in orbit. While this was never built as designed, its design would later form the premise for the International Space Station which began on-orbit construction in 1998.
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The International Space Station, seen from the departing Crew Dragon Endeavour in November 2021, continues Skylab’s legacy. (Credit: NASA)
The tip of the Space Shuttle program has seen NASA’s primary focus shift back towards missions of exploration, with the Artemis program aiming to return humans to the Moon, while crewed missions in low Earth orbit are being outsourced to industrial operators. The appearance of economic human spaceflight has seen a renewed interest in space station development, with several corporations investigating the event of recent orbital outposts. These include Orbital Reef – a partnership between Blue Origin and Sierra Space – and Starlab, which is being built by a consortium including Lockheed Martin, NanoRacks, and Voyager Space.
Axiom Space has already flown one industrial mission to the International Space Station, with one other planned for later this month. These function precursors to the corporate deploying its own space station modules – initially as an annex of the ISS, but these may lead to a free-flying station in the long run.
One other startup, Vast, has announced plans within the last week to launch a small space station called Haven-1 in 2025 aboard SpaceX’s Falcon 9 rocket. That is planned to host a four-person crew for thirty days, launching aboard a Crew Dragon spacecraft.
Announcing the Haven-1 and Vast-1 missions to low-Earth orbit. Launched by @SpaceX, Haven-1 is scheduled to be the world’s first industrial space station and might be visited by a crew of 4 aboard a Dragon spacecraft during Vast-1 → https://t.co/ToxFSiyQJj pic.twitter.com/YSPrM9Krtr
— VΛST (@vast) May 10, 2023
The impact of SpaceX’s own Starship on the long run of space stations is yet to be seen. With the power to hold greater numbers of humans or larger amounts of cargo into orbit, it could vastly reduce the fee of transporting crew and equipment to outposts in low Earth orbit. Alternatively, it is likely to be adapted as a research platform in its own right, much because the Shuttle was with the addition of research modules, taking the place of space stations.
Regardless of what the long run holds, Skylab was certainly one of the primary steps on a journey towards understanding human reactions to long-duration spaceflight which has enabled space stations to flourish over the following a long time. Constructing on its legacy, and that of the Soviet Salyut and Mir stations, the ISS continues to deliver invaluable science. The experience with long-duration missions that has been honed aboard these outposts may also be key to future spaceflight beyond Earth’s orbit.