A Tour of Skylab

Perhaps the best way to begin a tour of Skylab is to begin where its crews did—on the outside, with a look at the station’s exterior.

If a crew in an Apollo Command Module were to approach Skylab with its docking port before them, the nearest module would be the Multiple Dock­ing Adapter (mda) . From the exterior, the mda was basically a nondescript cylinder, marked primarily by its two docking ports. One of the docking ports, the one used by the crews docking with Skylab, was located on the end of the cylinder. The second, the radial docking port, was at a ninety – degree angle from the first, on the circumference of the mda.

The other notable feature of the Multiple Docking Adapter was the truss structure that surrounded it and connected it to the Apollo Telescope Mount (atm), on the side of Skylab opposite the radial docking port. The atm is easily recognized by its four solar arrays, which had a very distinctive wind­mill appearance. Between the four rectangular arrays was a cylinder that housed the atm’s eight solar astronomy instruments. Covers over the instru­ment apertures rotated back and forth, revealing the instruments when they were in use and protecting them from possible contamination when they were not.

Continuing from mda, the crew would next come to the Airlock Mod­ule (am), a smaller cylinder partially tucked into the end of the exterior hull of the larger workshop cylinder. The Airlock Module was most nota­ble, as the name suggests, for its airlock featuring an exterior door allow­ing the crew to egress to conduct spacewalks outside the station. While the program that spawned Skylab had been dubbed “Apollo Applications” for its extensive use of Apollo hardware and technology, the Airlock Module was actually a “Gemini Application” — the door used for evas was a Gem­ini spacecraft hatch.

The airlock and all the spacewalk equipment on Skylab were designed for one purpose — to allow the crew to retrieve and replace film from the solar

telescope cameras on the Apollo Telescope Mount. “There was no thought of the crews doing repairs or maintenance on other things,” Kerwin said. “Little did we know!”

The airlock was partly covered by the Fixed Airlock Shroud, a stout alu­minum cylinder that was a forward extension of the skin of the workshop. The aft struts from which the Apollo Telescope Mount was suspended were mounted here. The truss structure included a path, complete with handholds that spacewalking astronauts could use to move from the airlock hatch to the atm so that they could change out the film.

Finally moving farther past the Airlock Module, the crew would reach the largest segment of Skylab, the cylindrical Orbital Workshop. This was the portion that consisted of the modified s-ivb stage. As it was originally con­structed, the most distinctive features of the station were the two solar array wings, which stretched out to either side and which were to be the primary source of electrical power for the workshop. Prior to launch the photovolta­ic cells that made up the arrays folded up flat against the beam that would hold them out from the sides of the workshop. These beams, in turn, fold­ed down against the outside of the s-ivb stage in its launch configuration, making the wings much more aerodynamic for the flight into orbit.

After completing their fly around, a crew would return to the top of the Multiple Docking Adapter and dock their spacecraft to the station. A com­plete tour of the interior of Skylab should begin right there on their cap­sule. After docking, the Command and Service Module became a part of the cluster. While there were occasions when things needed to be done in the Command Module, they were few. Perhaps its primary use while docked with Skylab was essentially as a telephone booth; crewmembers could float up to the Command Module to find a little privacy for conducting space – to-ground communications with their loved ones at home on a back-up fre­quency that was not available in the workshop.

Upon opening the hatch and entering Skylab, the crew would first find themselves inside the mda. Originally planned to have a total of four dock­ing ports around its circumference, the mda lost three as a result of the switch from the wet workshop to the dry. When the wet workshop cluster, which had to be assembled individually on orbit, was replaced with a facil­ity launched all at once as a dry workshop, the additional ports at which to dock separately launched modules were not needed. Eliminating the three

14- A cutaway view of the Skylab space station.

extra docking ports freed up a large amount of wall space around the mda’s circumference, space that was utilized to turn the module into essentially an additional science annex.

The design of the interior of the Multiple Docking Adapter was itself one of Skylab’s experiments. The argument had been made that in the micro­gravity environment in orbit there was no need to follow the same design paradigms that were unavoidable on the ground. There was no need to leave a floor empty to walk on. The ceilings were no more out of reach than walls, and equipment could be placed on them just as easily as on a wall. The mda was an experiment in designing for that environment, with no up or down. Equipment was located all the way around the wall of the cylin­der, allowing more complete use of the available space than would be prac­tical on Earth.

Foremost among the scientific equipment located in the module was the operator’s station for the Apollo Telescope Mount, a large flat panel featur­ing the controls and displays for the atm with a narrow table in front of it.

The atm console was arguably evidence of the extent to which the module’s designers were influenced by Earthbound thinking. Though care was tak­en to design the mda as an ideal microgravity work environment, the atm console was furnished with a chair for the astronauts to sit in while oper­ating the controls. “We called it the ‘Commander’s Chair,’ because it was Pete’s idea,” notes first crew science pilot Joe Kerwin. “It didn’t survive lon­ger than about the first two weeks of our mission; we then put it away some­where, and I don’t think anyone retrieved it.”

Also located in the mda was the Materials Processing Facility. Included in this experiment was a furnace used to study flammability and melting of solid materials in microgravity. The adapter also housed the Earth resourc­es experiment equipment.

Leaving the Multiple Docking Adapter and heading farther down into Skylab, one would next come into the Airlock Module, the function of which was very aptly described by its name. Joining the mda and the Air­lock Module together was the Structural Transition Section, which con­nected the larger diameter of the Docking Adapter on one end to that of the smaller Airlock Module on the other. The Structural Transition Sec­tion housed extensive systems operation equipment. The Airlock Module provided a way for astronauts to egress the station for spacewalks. Before they could go outside, the Airlock Module would have to be shut off from the rest of the station and then depressurized. Once the atmosphere had been removed, the airlock hatch could be opened, and the eva crewmem­bers could go outside.

To prepare for an eva, all three crewmembers would put on their space- suits in the larger open area of the Orbital Workshop, where the equipment was stored. The astronaut who would be staying inside stopped short of don­ning his helmet and gloves but suited up the rest of the way in case a prob­lem occurred. The eva umbilicals were stored in the Airlock Module, and the ends of these were pulled down into the workshop during this time and connected to the suits of the two eva crewmen. These provided oxygen, cooling, and communications for the two astronauts who would be going outside as well as tethering them to the station.

Once all three were suited up, the non-EVA crewman would precede the others, move through the airlock and into the MDA/Structural Transition Section. There he would attach himself to a shorter umbilical. With his

helmet off, he would be breathing the atmosphere in the mda, but in the bulky spacesuit, he needed the umbilical for cooling as well as for communi­cations. The eva crewmen would move to the airlock and close both hatches (helped on the mda side by the third crewmember). Once the hatches were closed, the Airlock Module would be depressurized by venting its atmo­sphere into space. The outside hatch would be opened, and the two space – walkers could venture outside.

Once the eva was completed, the two astronauts would return to the Airlock Module and close the outside hatch. The am would be repressur­ized, and they would open equalization valves in both end hatches to assure equal pressure with the rest of the station. Finally, they’d open both hatch­es, return to the workshop and doff their suits. The normal pressure regu­lation system would add gas to the workshop as needed.

The Airlock Module’s location in the middle of Skylab meant that a prob­lem with repressurization could mean the end of the mission. If for some reason the module were unable to hold an atmosphere, the third crewman would put on his helmet and gloves and depressurize the Multiple Docking Adapter. The other two would disconnect their umbilicals from the Air­lock Module and rely on a reserve oxygen supply in their suits while they opened the hatch between the two modules, and moved into the docking adapter. Once there, they would reconnect their umbilicals in the mda, and then seal it off from the Airlock Module and repressurize it. If they and the ground were then unable to figure out a way to fix the problem with the Air­lock Module, the mission would be aborted. They would leave the mda for the Command Module and return home.

Continuing deeper into the station, one would next reach the large Orbit­al Workshop volume. This section was divided into two “stories,” with a hole in the middle of the floor of the top story that allowed the crew to move between them.

Like the Multiple Docking Adapter, the workshop was part of the exper­iment in designing for microgravity. Whereas the mda was designed with­out consideration for the direction of gravitational force on the ground, the approach to the workshop design had been to keep in mind that it would be used by men whose brains had long been wired for the one-G environment in which they had lived their entire lives. The “bottom” story of the work­shop was arranged with a very definite up and down. Furnishings and large

equipment sat on the floor like they would on Earth (with a few exceptions), and the walls functioned more or less the way walls normally do. The upper compartment was more of a hybrid, with variations from the one-G—based design of the lower section.

The area at the top of the workshop was very unusual by spacecraft stan­dards. Traditionally spacecraft design is a field in which mass, and by exten­sion volume, are at a premium, reflecting the challenge of moving anything from the surface of the Earth into orbit. As a result spacecraft tend to be rel­atively cramped with every inch utilized as much as possible. While mod­ern spacecraft like the Space Shuttle and the International Space Station are roomy compared to early vehicles like the Mercury and Gemini cap­sules, their designs still reflect the basic limitations in putting any mass into orbit. Skylab had a couple of advantages that made it exceptional in that respect. The availability of the Saturn v as the launch vehicle and the deci­sion to use an s-ivb for the Orbital Workshop meant that it was much less constrained by the traditional mass and volume limitations. Nowhere was that more apparent than at the top of the workshop, which featured an open volume that by spacecraft standards was incredibly large. While the low­er floor was divided into separate “rooms,” the upper floor, the larger of the two, was not divided. An astronaut could float freely in the middle of this volume without bumping into the walls.

In fact Skylab’s designers were concerned that this could present a real problem. They feared that an astronaut could get stranded in the middle of this open volume; without anything nearby to push off, he would have to rely on air currents or his crewmates to push him back toward a solid sur­face. To eliminate this danger and to provide for easier movement through Skylab, they provided a “fireman’s pole” in the middle of the workshop, running from one end to the other. The idea was that the astronauts would hold on to the pole to move “up” and “down” the workshop. The pole, how­ever, proved unnecessary, and the crews found that it just got in the way. It turned out to be quite easy to push off from a surface and glide to one’s des­tination —no pole required. The first crew took it down for the duration of their stay, but at the end, politely restored Skylab to factory specs, reinstall­ing the pole for the second crew. They in turn did the same—promptly tak­ing it out of their way but putting it back before they left so that the third crew could remove it one last time.

The upper portion of the workshop dome volume was left almost vacant for experiments requiring a lot of volume for checkout, like a Manned Maneu­vering Unit prototype. Just below this was a ring of white storage lock­ers, which the first crew found provided an excellent “track” to enable easy shirt-sleeve jogging and tumbling around the inside circumference of the workshop. Also located in the upper deck were storage of food supplies for all three missions, a refrigerator and a very heavy (on Earth, at least) steel vault for film storage.

A few experiments were also located in this area, including Skylab’s equiv­alent of bathroom scales, the body mass measurement device, which the astronauts used to keep track of how much “weight” they had lost or gained. The upper dome volume was also where the two astronaut maneuvering units were kept. One was a backpack device that was the forerunner of the Manned Maneuvering Unit later used on some Space Shuttle missions and of safer, the Simplified Aid for eva Rescue, used on the Internation­al Space Station. (Ironically, a member of the one Skylab crew that did not get to test the maneuvering unit, Joe Kerwin, was a co-inventor of the saf­er unit, while working at Lockheed Martin years later.) The other device was a maneuvering aid that astronauts operated with their feet, rather than their hands.

The upper story of the workshop also featured a pair of airlocks. Too small for a person to go through—only about ten inches square—the two Scientific Airlocks (sals) were designed for solar physics, astronomy, Earth photography, and space exposure experiments, allowing astronauts to pass materials samples through to see how they weathered the harsh environs outside. The two airlocks were on opposite sides of the compartment from each other; a solar airlock pointed in the same direction as the Apollo Tele­scope Mount, while the antisolar sal faced in the opposite direction. (This solar-looking airlock would be an important part of addressing problems that occurred during launch.)

Also located at the top of the dome was Skylab’s unofficial “Lost and Found.” “Most of us have enough trouble keeping up with our pencils, notes, paper clips, and other small items here on Earth in a largely ‘two dimension­al’ world,” Garriott explained. “By two dimensions, we mean that an object may get pushed around horizontally, but it seldom floats away vertically in a third dimension, like a feather might do. But space is different—everything floats away unless it is tethered or tied down. But our eyes and our minds

have been trained for years to look only on the tops of surfaces to find lost articles. We may not ‘see’ a small floating object in space, or may not look in all the more obscure places a lost article may have become lodged.

“But serendipity came to the rescue here,” he said. “The very slow air cir­culation from the lower decks up to the single air intake duct in the top of the dome volume slowly urged all drifting objects to come to it. We found that each morning when we arose, we could find many of our small, lost articles on the screen on the intake duct!”

At the bottom of each of the workshop’s two “stories” were floors with an open-grid construction that was a fortunate relic of Skylab’s development. During the wet-workshop phase of Skylab’s history, engineers looked at whether any of the station’s infrastructure could be included in the s-ivb stage while it was being used as a fuel tank up to, and during, the launch. Anything that could be built into the tank would mean mass that would not have to be carried up later, and installation work that the crew would be spared. The catch of course was that it would also have to be something that could withstand the environment of an s-ivb filled with cryogenic pro­pellants, that it could not pose a risk of igniting the propellants, and that it must not interfere with the function of the rocket stage. One item that the engineers decided they could include was the floors of the workshop. How­ever, solid floors could not be used, since they would impede the flow of fuel through the tank. As a result, special floors were designed with a grid pattern that would allow fuel to flow through them.

When the switch was made from the wet workshop to the dry, the grid – pattern floors were no longer needed for their original purpose. However, the design was kept for the dry workshop because it was realized that the grid could serve another purpose as well, solving one of the challenges of life in microgravity. The Skylab astronauts were given special sneakers that had triangular fittings attached to their soles. These pieces would fit into the tri­angles that made up the floor’s grid pattern and lock in place with a small rotation of one’s foot. This allowed the crewmembers to stand in place on the floor without the help of gravity.

Finally, one would reach the farthest point from the Command Module, the bottom “story” of the Orbital Workshop. This was the primary living area of the space station and included its bedrooms, bathroom, kitchen, and gym. This area was divided into four major areas: the sleep compartments, the waste-management compartment, the wardroom, and the experiment volume.

Skylab had three sleep compartments, one for each of the astronauts aboard at any time. To make the most of the available space, the beds were arranged vertically in the quarters. Without gravity to keep a sleeper in place, the beds were essentially sleeping bags with extra slits and a vent to make them more comfortable. These were mounted on an aluminum frame with a firm sheet of plastic stretched within it to serve as a “mattress.” A privacy curtain took the place of a door at the entrance to each “bedroom.” Also in each sleep compartment were storage lockers, in which crewmembers could keep their personal items, and an intercom for communications.

The intercoms in the sleep quarters were among several located around the station, which served a dual purpose—they allowed communication both with the ground and throughout the station. Because of the low air pressure on Skylab, sound did not carry far, which could make it difficult to be heard in other parts of the station.

Voice communications with the ground were carried out in two major ways. The primary means of communication was the A Channel, which was used for real-time conversations with Mission Control. The other was в Channel, which was recorded on an onboard tape recorder and periodi­cally “dumped” to the ground and transcribed. This allowed the astronauts to pass along their thoughts about such things as habitability issues on Sky­lab, things that were not urgent but were needed for future reference. The crews were given questionnaires about aspects of life aboard the station and would dictate their answers into the intercom on в Channel.

For Project Mercury, NASA had to quickly develop a worldwide satellite­tracking network so that voice communications, data from spacecraft sys­tems, and commands from the ground could be sent and received. Stations were placed in exotic locations such as Zanzibar and Kano, Nigeria — often with help from the State Department — and were staffed by small teams of NASA employees and contractors. There was no real-time communication between Mission Control and most of these stations; data was relayed via leased commercial phone lines, undersea cables, and radios.

Capability of the system was continuously upgraded during the Gemini program. By the time Apollo 7 flew in late 1968, satellite relay of voice and data permitted Houston to communicate directly with the spacecraft; the remote-site teams were called home, and a unique travel experience disap­peared. But communication was still only via the transmitters and receiv­ers at the tracking stations.

The system inherited by Skylab was called the “Spacecraft Tracking and Data System.” It consisted of twelve stations: Bermuda, Grand Canary island, Ascension Island, St. Johns (Newfoundland), Madrid, Carnarvon and Hon­eysuckle Creek (Australia), Guam, Hawaii, Goldstone (California), Cor­pus Christi (Texas), Merritt Island (Florida), plus the ship Vanguard off the east coast of South America, and sometimes an aircraft (call sign aria) used to fill gaps during launch and reentry. As a result, communication between Skylab and Houston took place only in the brief passes over these stations, often interspersed by an hour or more of silence. The crew could tell where they were around the world by Houston’s calls — “Skylab, Houston, with you at Guam for eight minutes.”

To the left of the sleep compartments was the waste-management com­partment. This room featured a water dispenser that was the microgravity equivalent of a sink, a mirror for personal hygiene, and, of course, the space toilet. The Skylab mission required a level of innovation in this area not achieved in previous spaceflights. While the bag-based system used on pre­vious spaceflights for defecation had not been particularly pleasant, there was not really room on the smaller vehicles for a better means of dealing with the issue. For the comparatively short durations of those missions, it was something that astronauts simply had to bear.

Skylab, however, involved both a long-enough duration to merit finding a better solution as well as the space needed to provide one. For urination, the crewman stood in front of the collection facility with his feet beneath straps to hold himself in place. He urinated directly into a funnel with modest air­flow drawing urine into individual collection bags, one for each crewman. For defecation, he rotated about 180 degrees and seated himself on a small chair on the wall, rather like a child’s potty chair. But here a plastic bag had been placed beneath the seat for each use, which maintained a simple and hygienic “interface” with the astronaut. A lap belt and handholds were pro­vided to allow the user to stay in one place. As with the urine system, air­flow took on some of the role that gravity would play on Earth. An innova­tive feature of the fecal collection system allowed these bags to be placed in a heating unit after mass measurement, then exposed to the vacuum, which dried their contents completely. It was then much lighter and quite hygienic. The dried feces and samples of the urine were saved and returned to Earth for post-mission analysis.

To the left of the waste-management compartment was the wardroom, the station’s combination kitchen, dining, and meeting room. (Explained Kerwin: “Why was it called the wardroom? Because the first crew was all­Navy, and they got to name stuff. The wardroom is the officers’ dining and meeting room in a Navy ship.”) In the center of the room was Skylab’s high-tech kitchen table. Its round center was surrounded by three leaves, one for each crewmember. The flat surface of each of the leaves was actu­ally a lid, which could be released with the push of a button. Underneath the lids were six holes in which food containers could be placed, three of which could be heated to warm food. The trays had magnets for holding utensils in place. The table also featured water dispensers, which could pro­vide diners with both hot and cold water. Both thigh constraints and foot loops on the deck provided means for the astronauts to keep themselves in place while eating.

The walls of the wardroom were lined with stowage lockers and with a small refrigerator-freezer for food storage. The wardroom was one of the most popular places on Skylab for spending time—partially because it had the largest window on Skylab, which could be used for Earth – or star-gazing.

The largest portion of the bottom floor was the experiment area, which was home to several of the major medical experiments. The Lower Body Negative Pressure experiment was a cylindrical device, which an astronaut would enter, legs first, until the lower half of his body was inside. After a pressure seal was made around his waist, suction would then decrease the pressure against his lower body relative to the atmospheric pressure around his upper torso. The pressure difference would cause more blood to pool in his lower extremities, simulating the conditions he would experience when he returned to Earth and gravity caused a similar effect.

Also in the experiment volume was the ergometer, essentially a wheelless exercise bicycle modified for use in microgravity. Like its Earthbound equiv­alents, the ergometer featured pedals, a seat, and handlebars, but it was also equipped with electronics equipment for biomedical monitoring.

The Metabolic Analyzer was used with the ergometer to monitor the crew’s respiration. The device itself was a rectangular box with a hose connected to a mouthpiece. The user would put on a nose clip and then breathe in and out through the mouthpiece. The analyzer could not only measure respira­tion rate and breath volume but also, via a mass spectrometer, the composi­tion of the air he exhaled and thus oxygen consumption and carbon diox­ide production.

Another experiment in that area of the workshop was the Human Vestib­ular Function device, which was basically a rotating chair. With an astro­naut sitting in it, the chair could be rotated about the axis of the subject’s spine at speeds up to thirty revolutions per minute, either clockwise or coun­terclockwise. The purpose of the experiment was to test how their vestibu­lar systems (responsible for balance and detection of rotation and gravity) adapted to the microgravity environment. The experiment had been per­formed with the astronauts on the ground to provide a baseline and was per­formed again in orbit for comparative results.

Another major item located in the experiment room was only an experi­ment in the broadest sense—that life on Skylab was all part of research into long-duration spaceflight habitability factors. Because of the way the low­er deck was divided and because the shower was a later addition to the sta­tion’s equipment, the shower was instead located in the larger, open experi­ment area instead of being located in the waste-management facility, which in other respects was Skylab’s bathroom.

Water posed a potential hazard in Skylab. In weightlessness water would coalesce into spheres, which could float around the spacecraft. If they weren’t collected, they presented the risk that they could get into electronic devic­es or other equipment and cause damage. Small amounts of water could be easily managed, but large amounts were generally avoided in spaceflight. To wash their hands, for example, astronauts would squirt water into a cloth and then clean their hands with it rather than putting the water directly on their hands.

The shower provided means for a true spaceflight luxury. In it, astronauts could clean themselves in a manner that, while not quite the same as the way they would shower on Earth, was much closer. They would pull a cylindri­cal curtain up around themselves and then squirt warm water directly on their bodies using a handheld spray nozzle. Confined within the curtain, the water posed no risk to the spacecraft and after the shower could be cleaned up with towels or a suction device. The crews found the suction it provided inadequate for drying off completely and so used lots of towels. Nevertheless,

15- Lousma demonstrates Skylab’s shower.

at least one crewmember thought this “luxury” was both unnecessary and a gross waste of time.

At the center of this lowest floor of Skylab, the very opposite point from where the tour began, was the Trash Airlock. The s-ivb stage from which Skylab was modified had two tanks that originally would have been used to store the propellant: a larger tank for the fuel, liquid hydrogen, and a small­er tank for the oxidizer, liquid oxygen. The entire manned volume of the workshop was inside the stage’s liquid hydrogen tank. The liquid oxygen tank, which was exposed to vacuum, was used for trash storage. Between the two was an airlock that was used to transfer trash into the storage area. The oxygen tank was vented to space, creating a vacuum that helped pull the trash through, but it had a screen to prevent any trash from escaping. The arrangement meant that the waste generated on Skylab was stored safe­ly instead of becoming orbital debris.