SP-400 Skylab, Our First Space Station

 

2

Our First Space Station

 

[15] On the afternoon of May 14, 1973, Skylab was ready to begin its mission. Saturn V launch vehicles had roared off Launch Complex 39 at Kennedy Space Center many times before, sending astronauts on journeys to the Moon. On this warm spring day, a complex cluster of scientific hardware, which would become an orbiting home and laboratory in space, was to be the passenger.

Skylab's story began more than a full decade earlier. The Apollo command and service module was a versatile spacecraft, capable of carrying sophisticated scientific equipment into orbit, but its capability for manned scientific operations was extremely limited. To perform the scientific tasks envisioned for Skylab, skilled astronauts would have to live and work in a well-equipped scientific laboratory for long periods of time, and be essentially independent of the need for frequent resupply. This requirement demanded that electrical power be generated by systems aboard the space station and that highly reliable communications, data collection, instrumentation, and control systems be provided. A rocket stage, its tanks emptied of propellant, and modified inside for living and working quarters, seemed a logical means of providing such a roomy space station. Skylab evolved slowly from an initial concept in which the tank was to be converted into a habitable volume in orbit; in the final concept, the stage was launched dry ready for occupancy by the flight crews once it reached orbit. Power, communication, instrumentation, and control systems evolved....

 


An intermediate concept envisioned a cluster which included a lunar module, the solar observatory with its windmill-like solar arrays, and a command and service module.

An intermediate concept envisioned a cluster which included a lunar module, the solar observatory with its windmill-like solar arrays, and a command and service module.



[16]

In a

In a "wet workshop" concept, the Skylab cluster consisted of a lunar module with the solar observatory mounted above it, a command and service module, a docking adapter, and a Saturn upper stage, emptied of its propellants in achieving orbit. This spent stage would be outfitted in orbit for occupancy.


 

....as the workshop design matured. Provisions were made for crew health and comfort. Equipment for making precise scientific measurements and conducting experiments was developed. The result was a space laboratory of unequaled sophistication, ready to be propelled into orbit by the giant Saturn.

 

Skylab To Provide Answers to Many Questions

The Gemini 7 crew of Frank Borman and James Lovell had remained aloft for nearly 2 weeks and the Russian cosmonauts of Soyuz 9 had orbited Earth for 18 days. But bioscientists remained concerned about man's ability to adapt readily to the length of mission planned for Skylab, whose crews were to spend as long as 8 weeks in space. The long-range physiological and psychological effects of weightlessness on man were still not fully understood. Nor was it known whether even the highly trained and superbly conditioned astronauts could perform the varied tasks expected of them for such extended periods of time in space.

Other scientists wanted to use zero-gravity conditions for materials research, even with a view to eventual commercial applications, such as precision in manufacturing.

The ability to make more exact observations of both Earth and the solar system than ever before possible spurred additional interest in Skylab and imposed new requirements on the design. Solar scientists had long dreamed of observing the Sun without interference from the Earth's atmosphere. The shell of atmospheric gases which nourishes and protects the Earth also severely limits man's ability to view celestial objects, even with the finest and largest telescopes made. An observatory orbiting above the Earth's atmosphere and equipped with fine resolution instruments would be an extremely valuable tool for solar scientists.

Other scientists, desiring to know more about the planet Earth, saw in Skylab a platform from which photographs and visual observations could be made on a vastly larger scale than ever before. Others of the scientific community saw in this orbiting laboratory an ideal environment for conducting unique experiments in space physics and life sciences.

The development of an orbiting laboratory with so varied a capability was a technical challenge [17] without precedent. As envisioned, Skylab was to be self-sufficient, with direct communication with ground crews. This required a highly complex spaceflight tracking and data network for the transmission of instructions, for the recording of data, and for voice and TV communication.

Living in space in a controlled environment dictated the further development of a comprehensive and extremely reliable life-support system. And long-duration spaceflight required that provisions be made for crew recreation and relaxation, exercise, and for moving around easily within the space station.

Many factors influenced the final design configuration of Skylab. However, one of the most important was an economic necessity to use components and equipment, where possible, that had been developed for other programs.

When launched, Skylab contained all the elements needed to sustain the crews and their planned operations. Breathing gases, food, and water were stored on board, along with medicine and other expendable supplies. Systems within the space station provided for the collection and disposal of human waste and an atmosphere controlled as to temperature, pressure, and humidity so that the crewmen could live and work in comfort. Solar arrays mounted on the workshop and the solar observatory produced electrical power by the direct conversion of solar energy. Two precise control systems permitted the astronauts to orient the workshop to collect experimental data and to position Skylab so that its solar arrays faced the Sun.

 

Design Problems Were Many

Transforming an empty rocket tank into a home and laboratory imposed some tough problems in engineering. Their solution often required that designers break with earthly tradition.

How does one equip living and working quarters where up and down have no real meaning? What controls, displays, instruments, and sensors are needed? How will the occupants keep their home free of floating debris? Where will they stand or sit while working? How will they bathe, shave, brush their teeth, or use the toilet? How will they get from one place to another quickly and safely when they cannot walk? These were typical questions which had to be answered before the interior of Skylab could be designed.

 


Skylab resembled a home and workshop only in its functional capability. Floors and ceilings were open grids; up and down became relative; and voices carried only a few feet in the thin atmosphere. But the flight crews quickly adjusted and carried out their tasks skillfully.

Skylab resembled a home and workshop only in its functional capability. Floors and ceilings were open grids; up and down became relative; and voices carried only a few feet in the thin atmosphere. But the flight crews quickly adjusted and carried out their tasks skillfully.


 

[18] The manned spaceflight program conducted by NASA has been evolutionary. Mercury paved the way for Gemini. Gemini provided information essential to Apollo. And lessons learned in Apollo were applied to Skylab.

Answers came, too, from habitability studies. Exhaustive studies were conducted at the NASA spaceflight centers and at a number of the aerospace contractor facilities. Data came from Navy studies of long-duration submarine voyages. Information useful in designing compact systems came from designers of railway passenger cars, marine designers, and others. Out of such studies emerged a wealth of information about man under stress in confined and isolated environments.

Astronauts and support crews took part in numerous studies which simulated conditions that were nearly identical to those to be encountered in space.

An important habitability study was the medical experiments altitude test conducted at the Johnson Space Center. This test was a simulation of a 56-day mission, which included all significant features of the Skylab environment with the exception of weightlessness. The atmosphere was identical to that of Skylab, a 74-percent oxygen and 26-percent nitrogen breathing mixture at 5 pounds per square inch (versus 14.7 pounds per square inch on Earth). Crew quarters were simulated; crew activities (principally those associated with medical experiments) were identical to those to be carried out in Skylab; three astronauts performed tasks in accordance with a schedule of events prepared for the actual mission; and support personnel manned a mission control room. Many problems were identified and corrected. Medical data were collected before, during, and after the test to evaluate the health of the flight crew.

At the Marshall Space Flight Center, astronauts and engineers spent hundreds of hours in a neutral buoyancy zero-gravity simulator rehearsing procedures to be used during the Skylab mission, developing techniques, and detecting and correcting potential problems.

This simulator is a huge water tank, into which full-scale Skylab hardware was placed. Astronauts and other subjects were then weighted and their equipment was made neutrally buoyant by the addition of light foam pads. In this way the effective gravity conditions under which they worked were nearly identical to those they would later encounter during Skylab flights.

Later, this simulator was to play a vital role in supporting "real time" development of equipment, techniques, and procedures for emergency repairs in space.

Valuable data also came from other sources. For example, when the noted Swiss oceanologist, Jacques Piccard, assembled his six-man crew for the summer 1969 voyage of the submarine Ben Franklin, a NASA engineer was aboard as a member of the crew to obtain data on human reactions in a confined environment. Later, a number of the NASA engineers participated in the Tektite II underwater research program.

Even with this exhaustive preparation, many new problems arose. That they were solved satisfactorily is a tribute to the ingenuity and dedication of those men and women who labored so long to make the program a success.

The needs of the Skylab home and laboratory were considerably different from those for homes and laboratories on Earth, where designers must...

 


Extensive testing and many hours of practice in simulators such as the neutral buoyancy tank helped prepare the Skylab crewmen for spacesuited performance in the weightless environment. This huge water tank simulated the weightless environment which the astronauts would encounter in space.

Extensive testing and many hours of practice in simulators such as the neutral buoyancy tank helped prepare the Skylab crewmen for spacesuited performance in the weightless environment. This huge water tank simulated the weightless environment which the astronauts would encounter in space.


[19]

Much valuable data about behavior and the problems associated with living in close quarters came from underwater studies. NASA engineers took part both in the Ben Franklin (pictured above) voyage in 1969, and later in the Tektite 11 underwater research program

Much valuable data about behavior and the problems associated with living in close quarters came from underwater studies. NASA engineers took part both in the Ben Franklin (pictured above) voyage in 1969, and later in the Tektite 11 underwater research program

 

....consider a constant force of gravity. Earth structures are designed to withstand the stresses caused by the weight of the structure, permanent and transient equipment, and the loads which occur due to people who occupy or pass into and out of the structure. Dynamic stress occurs primarily from wind loads or other natural phenomena such as earthquakes.

Design of Skylab also considered gravity, but not as a constant force. The compressive forces exerted on Skylab during its mission ranged from zero to about four and one-half times the force of gravity on Earth. Thus, loads of nearly 500 tons occurred where the space station joined the Saturn V second stage during the period of maximum acceleration, when engine thrust was accelerating Skylab into orbit. Wind loads were compounded by aerodynamic forces as the speed of Skylab increased rapidly while in the Earth's atmosphere. Aerodynamic loads caused both compressive and bending forces. Additional bending forces, even more severe than compressive forces, resulted from steering movements of the rocket engines which kept Skylab on course as it ascended.

Docking the command and service module to the space station caused shock forces similar to the effects of earthquakes on Earth-based structures.

Structural designers assured that the total Skylab [20] assembly could withstand all reasonable loads encountered during handling, launch and ascent, solar observatory deployment, attitude changes, and docking operations with the command and service modules, and also could maintain a pressure-tight enclosure suitable for habitation.

It was impractical to make the habitable area completely leakproof, because of the mating surfaces and many penetrations for electrical cables, tubing, windows, and hatches. But leakage was held to a minimum to avoid carrying an excessive amount of gas to replenish the habitable atmosphere.

Each habitable structure was pressure tested prior to launch. The workshop was pressurized during launch to provide rigidity; controlled venting during ascent maintained the required strength without the differential pressure increase that would have resulted otherwise. The airlock and docking adapter were launched with sea-level pres....

 


this photo indicates the location of the different modules that make up the space station. [small picture- it's a link to a larger picture on a separate page]

A

B

C

D

E

.

Module

Command and service module

Docking adapter

Solar observatory

Airlock

Workshop

.

Manufacturer

Rockwell International

Martin Marietta

MSFC

MDAC-Eastern

MDAC-Western

.

Module name (development)

Command and service module

Multiple docking adapter

Apollo Telescope Mount

Airlock module/ fixed airlock shroud

Orbital workshop

.

Function

Crew ascent and descent

Docking interface

Solar observation

Power control and distribution

Primary living and working area

Controls and displays

Power source

Environmental control

Laboratory

Earth observation

Attitude control

Data center

Power source

Stowage

Extravehicular activity hatch

Stowage

Caution and warning

.

Length

10.45 m (34.3 ft)

5.27 m (17.3 ft)

4.05 m (13.3 ft)

5.36 m (17.6 ft)

14.66 m (48.1 ft)

Diameter

3.96 m (13.0 ft)

3.04 m (10.0 ft)

3.35 m (11.0 ft)

3.04/1.67/6.70 m (10.0/5.5/22.0 ft)

6.70 m (22.0 ft)

Habitable working volume

5.95 m3 (210 ft3)

32.28 m3 (1140 ft3)

-

17.66 m3 (624 ft3)

295.23 m3 (10 426 ft3)



[21]

General characteristics of the Skylab cluster. [small picture- it's a link to a larger picture on a separate page]

General characteristics of the Skylab cluster.

 

....sure internally and this pressure was allowed to decay through valves as Skylab ascended, since pressurization was not required to strengthen these modules.

Each of the five major assemblies making up the Skylab cluster played an important role in the mission. In orbit, the cluster resembled a series of essentially cylindrically shaped components joined together with solar wings extending outward from the sides of the largest cylinder. Extending outward perpendicularly from the center cylinder was another cylindrical device on top of which was mounted four windmill-like rectangular solar wings.

The command and service module, the crew ascent and descent vehicle, consisted of the manned command module and the unmanned service module. The command module was conical in shape, about 13 feet in diameter and 12 feet high; it contained a crew compartment approximately 7 feet wide, 6 feet high, and 4 feet from front to back. A docking tunnel extended from the crew compartment to the nose of the vehicle to allow the crew to enter the docking adapter through its axial port.

Within the command module were its attitude control and guidance systems, batteries, control and display panels for the command and service....

 


[22]

Service module [top left], Command module [top right], Docking adapter [bottom left], Airlock [bottom right]. [small picture- it's a link to a larger picture on a separate page]

Service module [top left], Command module [top right], Docking adapter [bottom left], Airlock [bottom right].

 

...module systems, the couches that supported the crew during launch, ascent, reentry, and landing, stowage compartments for consumables, and stowage provisions for equipment to be taken to or returned from Skylab.

The crew compartment was protected by a heat shield coated with material that burned away during reentry and dissipated the intense frictional heat.

The service module was about 13 feet in diameter and about 25 feet long. This unmanned vehicle contained the equipment and supplies that did not require direct crew accessibility during flight. These included the main command and service module propulsion system with its 20 OOO-pound thrust engine, a smaller reaction control system for maneuvering the spacecraft, [23] hydrogen and oxygen fuel cells for generation of electrical power, and radiators for cooling. The service module remained attached to the command module until near the end of the mission. Separation occurred just before atmospheric reentry, and the service module burned in the atmosphere.

The Skylab docking adapter, 17 feet long and 10 feet in diameter, was as large as many earlier spacecraft. It was the control center for solar, Earth observations, and metals and materials processing experiments. Many of the experiments and items of other equipment were stowed in the adapter.

Two docking ports were provided in the adapter. The primary port was axial and was located at the forward end. The alternate port, located on the side of the module, could have been used if a rescue became necessary. Cameras and Earth resources sensors were located adjacent to the alternate docking port; some were positioned at a window in the wall, others actually protruded through the wall. Vaults, for storage of film for the solar experiments, protected the film from the radiation experienced at orbital altitude.

The control and display console for the solar observatory was located at the rear of the docking adapter, where solar activities could be monitored by the astronauts on two television screens. This console also contained the instruments and controls for the attitude-control system and for the solar observatory electrical power system.

 


Workshop

Workshop.

 

The aft end of the docking adapter mated to the airlock module, which served as the environmental, electrical, and communications control center. It also contained the port through which the astronauts exited to perform extravehicular activity. The airlock contained a tunnel section through which Skylab crewmen could move between the workshop and the forward end of the airlock. It was encircled for part of its length at its aft end by the fixed airlock shroud, which had the same diameter as the workshop (22 feet) and was attached to the workshop's forward end. High-pressure containers for oxygen and nitrogen, which provided Skylab's atmosphere, were mounted in the annular space between the outside of the tunnel and the inside of the shroud. The forward end of the fixed airlock shroud was the base on which the tubular structure supporting the solar observatory was mounted.

Two hatches were provided to close off a section of the tunnel. A third hatch was located in the outer wall between these two hatches and was the opening through which the crew passed to perform tasks in space. A hatch was also located in the forward end of the workshop. Closing either the two airlock tunnel hatches or the forward airlock tunnel hatch and the workshop hatch prior to opening the hatch in the tunnel outer wall retained the atmosphere within the rest of the cluster.

The workshop was divided into two major compartments. The lower level provided crew accommodations for sleeping, food preparation and consumption, hygiene, waste processing and disposal, and performance of certain experiments. The upper level consisted of a large work area and housed water storage tanks, food freezers, storage vaults for film, the scientific airlocks, the mobility and stability experiment equipment, and equipment for other experiments. The compartment below the crew quarters was a container for liquid and solid waste and trash accumulated throughout the mission.

A solar array, consisting of two wings covered on one side with solar cells, was mounted outside the workshop to generate electrical power to augment the power generated by another solar array mounted on the solar observatory. Thrusters were provided at one end of the workshop for short-term control of the attitude of the space station.

The large size of the workshop made a reliable....

 


[24]

Solar Observatory

Solar Observatory.

 

....intercom system a necessity. Crewmen could talk to each other or to ground crews from any one of 12 locations. (Unaided voice communication between astronauts was difficult because of poor transmissibility caused by low atmospheric pressure in Skylab.)

 


Once in orbit, the protective aerodynamic shroud was jettisoned. For several orbits thereafter, the panels of the shroud trailed Skylab as it orbited.

Once in orbit, the protective aerodynamic shroud was jettisoned. For several orbits thereafter, the panels of the shroud trailed Skylab as it orbited.

 

The solar observatory was mounted on a truss structure extending outward from the forward end of the workshop and surrounding the airlock and docking adapter. Solar observatory experiments and related support equipment as well as items of equipment to support the basic laboratory were mounted on this structure.

The major element of the solar observatory was a cylindrical canister containing the experiments. It included a spar and two canister halves. The spar structure was insulated and had the experiments and rate gyroscopes installed on low conductance mounts. The canister halves were isolated from the spar and provided thermal and mechanical protection. Additional equipment carried in the solar observatory assembly included the sensors, momentum wheels, and computers for attitude control of the workshop.

Several additional assemblies played a major role in the Skylab program. These were the airlock shroud, the payload shroud, and the deployment assembly.

The payload shroud was both an environmental shield and an aerodynamic fairing. Attached to the forward end of the fixed airlock shroud, it protected the airlock, the docking adapter, and the solar observatory before and during launch. It also provided structural support for the solar observatory in the launch configuration. Once Skylab reached orbit, the payload shroud was jettisoned.

During the early part of the Skylab mission, observers on the ground often saw Skylab traveling across the sky followed by several bright objects. These were the jettisoned panels of the payload shroud and the second stage of the Saturn V.

The deployment assembly provided in-orbit structural support between the solar observatory and the fixed airlock shroud and deployed the solar observatory when Skylab reached orbit. It also served as a mounting fixture for some experiments, acquisition lights, VHF-ranging antenna and wire routing from the solar observatory to the workshop. It consisted of tubular truss members, a release operated by an explosive bolt system, a rotation system for moving the observatory into its orbital position, and latches to lock it there.

 

Skylab's Systems

Skylab's systems were designed to minimize the need for expendable supplies. Power, generated by the conversion of solar energy, was stored in [25] batteries. Spacecraft attitude was controlled by three large gyroscopes. Cooling was accomplished principally by radiating heat to space. The atmosphere was scrubbed of carbon dioxide by a reusable molecular sieve. Thus, except for the supplies specifically required by the astronauts, such as air, food, and water, Skylab's systems sustained operation over a long period with minimum replacement or maintenance.

Skylab's major systems controlled its attitude, generated and distributed electrical power, controlled its environment and temperature, and furnished communications capabilities.

The position of Skylab in space was controlled by an attitude and pointing control system. This function included rotating to predetermined orientations, holding the required orientation for as long as necessary, and providing precise pointing for the solar experiments.

To execute a change, the system recorded the desired attitude, checked the existing attitude and compared it with that desired, initiated the change maneuver, and terminated the maneuver once the desired attitude was reached.

A rate gyroscope system measured attitude rates which were used to derive the space station attitude. Reference attitude information was provided by a Sun sensor that indicated whether it was pointed at the Sun or not, and a star tracker that sensed the location of predetermined stars (Canopus and Achernar in the southern hemisphere, for example) and indicated their direction relative to Skylab's three axes.

The prime mechanisms for executing maneuvers were the control-moment gyroscopes, which were momentum storage devices. Three large gyroscope wheels (rotors) were mounted in gimbals with their axes mutually perpendicular like the edges of a box at a corner. To maneuver the Skylab, the astronaut entered the desired attitude into the digital computer, which compared the desired attitude with the existing attitude (derived from rate gyroscope data). If rotation was required, the axis of one or more of the control-moment gyroscopes was rotated to a new position by computer command; this caused a reactive force and rotation of the space station in the desired direction. When the desired attitude was achieved, momentum was transferred back to the gyroscopes, causing vehicle rotation to stop. The gyroscopes were then in approximately their original inertial orientation.

A second maneuvering system, the thruster attitude control system, consisted of six nitrogen gas expulsion nozzles mounted at the aft end of the workshop. By thrusting in the required direction, they rotated the vehicle to the desired position.

During orbital operation of Skylab, all the electrical power used was generated by two solar arrays. One array deployed in the form of two "wings," one on each side of the workshop; the other array consisted of four "wings" deployed from the solar observatory.

The Skylab orbit, however, took the vehicle out of sunlight for about one-third of the time. In order that the Skylab systems could operate during the periods of orbital darkness, batteries were charged from the solar arrays during sunlight periods.

An environmental and thermal control system was needed to provide a breathable atmosphere inside Skylab and to maintain the temperature of crew and equipment within tolerable limits. Before each crew arrived, Skylab was pressurized. Air purification and humidity control were achieved by passing the gases through carbon dioxide and odor removal filters and through water condensers.

Skylab was subjected both to intense heat and intense cold. Passive thermal control, in the form of insulation and thermal coatings on the workshop, airlock, and docking adapter, helped attenuate the effect of these thermal extremes on internal workshop temperatures.

To control temperature and humidity within Skylab, an active thermal control system was provided. This system provided heat through a combination of air-duct heaters and wall heaters. The heaters prevented condensation from forming and damaging instruments and equipment. Humidity control was achieved by passing air through heat exchangers that condensed the moisture. Cooling was provided by these heat exchangers and others which cooled air passing through them but did not remove moisture.

Heat-producing equipment was cooled by refrigerator-like cold plates. The temperature of these plates was maintained by a liquid coolant pumped to heat exchangers. The excess heat collected was dumped to space through radiators.

Thermal control of the solar observatory was provided by a system of passive control measures, radiant heaters, cold plates, and radiators similar to....

 


[26]

Assembled for a management meeting in the facilities of the Mc Donnell Douglas Astronautics Co., St. Louis, in April 1971, were, left to right: Eberhard Rees, Leland F. Belew, Kenneth S. Kleinknecht, William C. Schneider, and Kurt H. Debus.

Assembled for a management meeting in the facilities of the Mc Donnell Douglas Astronautics Co., St. Louis, in April 1971, were, left to right: Eberhard Rees, Leland F. Belew, Kenneth S. Kleinknecht, William C. Schneider, and Kurt H. Debus.


On hand for the

On hand for the "rollout" ceremonies for the orbital workshop at Huntington Beach, Calif., in September 1972, were, left to right: Willis H. Shapley, Casper W. Weinberger, James C. Fletcher, Rees, Walter Burke, and Dale D. Myers.


[27]

Inspecting the airlock trainer at St. Louis, in April 1970, were, left to right, Belew, James S. McDonnell, and George Radebush.

Inspecting the airlock trainer at St. Louis, in April 1970, were, left to right, Belew, James S. McDonnell, and George Radebush.



Skylab officials visiting the facilities of the Mc Donnell Douglas Astronautics Co., St. Louis, January 1972, donned special garments to enter clean rooms. Left to right: Fred J. Sanders, Rees, William K. Simmons, Jr., Myers, Belew, and E. T. Kisselberg.

Skylab officials visiting the facilities of the Mc Donnell Douglas Astronautics Co., St. Louis, January 1972, donned special garments to enter clean rooms. Left to right: Fred J. Sanders, Rees, William K. Simmons, Jr., Myers, Belew, and E. T. Kisselberg.


[28]

Life-support system. [small picture- it's a link to a larger picture on a separate page]

Life-support system.

 

....equipment from direct sunlight.

Spacecraft-to-ground communication was effected through the command module radio for talk between the Skylab crews and the mission controllers at Houston. In addition to voice communication, radios in Skylab transmitted scientific data to Earth and received and implemented commands sent from the Mission Control Center.

A TV system routed television signals from five cameras on the solar telescopes to the control and display panel. A portable color television camera provided views of internal activity and astronaut activity outside Skylab.

Measurement systems with sensors acquired and processed information on the active Skylab systems and experiments, including air pressure, temperatures, electrical power system measurements, experiment data, and crew biomedical information from sensors worn by the crewmembers. The instrumentation system processed all the measurement signals into a form suitable for transmission and transmitted them to Earth or recorded them on tape depending on the availability of ground communications contacts.

 

The Orbital Workshop

Skylab's three manned periods totaled 171 days in space, dictating a need to provide the crews with [29] comfortable living quarters and a healthy and safe living and working environment.

Although primary attention was given to functional layout of equipment and compartments for effective operations within the workshop, the design also carefully considered the astronauts' surroundings. Colors were selected for a pleasing appearance. Lighting was arranged to provide best visibility. Controls and displays were located for ease in operating the equipment.

Skylab's mission required that large quantities of supplies be stored. In all, more than 19 500 items were stored and cataloged in a number of preselected locations.

The air in Skylab was much like that on Earth, except that it was free of pollutants and the usual "trace elements" such as helium and argon. Oxygen and nitrogen were stored separately and supplied automatically to keep the breathing atmosphere a mixture of about 3 parts oxygen and I part nitrogen. This oxygen level was necessary to maintain the sea-level-equivalent oxygen pressure. (On Earth, because of the higher atmospheric pressure, the mixture of these gases is just the reverse-about three-fourths nitrogen and one-fourth oxygen.) Losses due to leakage or crew consumption of oxygen were automatically replenished. As long as the workshop remained manned, the pressure inside was maintained at 5 pounds per square inch.

Maintaining comfortable temperatures inside the orbiting workshop depended not only on the effectiveness of its environmental control systems but also upon the ability to shade the exterior of the workshop from the Sun's direct rays.

Skylab's design included a shield to shade the workshop and to protect the workshop from possible structural damage from the micrometeoroids which continuously travel through space at very great speeds. This thin aluminum structure was made of 16 long, rectangular panels hinged together. During launch, panels were held tightly against the outer skin of the workshop by a number of tension straps. Once Skylab was outside the Earth's atmosphere, torsion bars would rotate to separate the shield from the workshop and deploy it so that it was separated from the workshop by about 5 inches.

Since this shield, in effect, became the outside surface of the workshop, it was very important to the control of temperature.

 

New Requirements for Living in Space

Crew quarters were on the lower level of the workshop. This level housed the kitchen and dining room, bedrooms, an experiment work area, and the toilet.

In the wardroom or kitchen and dining room the crewmen chose their menus from a variety of frozen and dehydrated foods. Various kinds of meat, vegetables, cereals, and desserts were readily available. Foods that would stick to a spoon or fork were eaten with the usual table utensils, which were held in place on the table by magnets when not in use. Liquids were served in squeezable plastic containers.

All three crewmen could eat at the same time at a dining-room table designed so that each crewman could heat his food individually in a tray. This table also included the water chiller and the water heater.

The absence of gravity made it possible to eliminate things that we on Earth take for granted. For example, beds were not necessary. Instead, each astronaut was assigned a small closetlike enclosure equipped with a zippered sleeping bag.

 


The food on Skylab was a great improvement over that on earlier spaceflights. No longer was it necessary to squeeze liquefied food from plastic tubes. Skylab's kitchen was so equipped that each crewman could select his own menu and prepare it to his own taste.

The food on Skylab was a great improvement over that on earlier spaceflights. No longer was it necessary to squeeze liquefied food from plastic tubes. Skylab's kitchen was so equipped that each crewman could select his own menu and prepare it to his own taste.


[30]

Spaghetti and meat sauce came premixed and ready to be heated.

Spaghetti and meat sauce came premixed and ready to be heated.

 

One of the astronauts found that he preferred to sleep upside down with his head at the floor and his feet pointed toward the ceiling. He did this "to keep air from blowing up his nose," which annoyed him when he slept "right side up."

 

Problems of Waste Disposal

Getting rid of the garbage presented a unique challenge to the Skylab designers. Trash collected quickly and had to be stored securely out of the way to prevent its floating around. Medical experiments required that urine samples be collected and frozen and that solid human waste be dried before return to Earth for examination and analysis of mineral balance by the medical specialists.

Again, the lack of gravity severely complicated Skylab design problems. The system was required to sample, process, and store crew body wastes, including feces, urine, and vomit. Further, it had to provide a means for the crew to perform necessary fecal and urine eliminations, to sample and preserve the material for biomedical analysis upon return, and to dispose of the remainder.

The system finally designed consisted of a fecal-urine collector, collection and sample bags, sampling equipment, and odor-control filters. The fecal-urine collector used airflow to substitute for gravity in separating the waste material from the body. Urination could be performed in a standing position, and both elimination functions could be performed while the crewman was seated.

Some of the astronauts bathed in a cylindrical....

 


The disposal of body waste was a difficult problem for Skylab's designers. Airflow was used as a substitute for gravity, separating waste from the body and disposing of it in special containers. Samples of collected waste were preserved and returned to Earth for medical analysis.

The disposal of body waste was a difficult problem for Skylab's designers. Airflow was used as a substitute for gravity, separating waste from the body and disposing of it in special containers. Samples of collected waste were preserved and returned to Earth for medical analysis.


[31]

The collapsible cylindrical shower enclosure was attached to the floor. The astronaut drew it up around him for use. Water was driven into a collection system by airflow. Both water and soap were premeasured for economical use.

The collapsible cylindrical shower enclosure was attached to the floor. The astronaut drew it up around him for use. Water was driven into a collection system by airflow. Both water and soap were premeasured for economical use.

 

....shower, with water discharged through a hand-held showerhead. The floating water droplets were drawn into a water collection system by movement of air.

Both spring-wound and standard safety razors employing shaving cream were used for shaving.

Crew health and safety, always a major consideration in manned spaceflight programs, presented some particularly difficult design hurdles. Areas of special concern were the effects of radiation, contamination, and the selection of materials with potentially harmful properties such as flaking or the generation of undesirable gases.

 

Control of Radiation and Contamination

With a total mission of nearly 9 months, one of the most significant concerns was for the effects of exposure to prolonged space radiation on components, materials, sensors, measurements, but most especially on the crew. A radiation hazard analysis, performed with a computerized mathematical model to determine the expected radiation levels for the planned manned missions, showed that the maximum expected radiation doses were well within safe limits. Further analyses on equipment showed that, with the use of protective equipment such as vaults for film storage, the potential effects of radiation would probably be negligible.

Contamination had been a problem on many satellite and earlier manned space programs, degrading performance of critical experiment surfaces or even causing major system failures. Because of the expected long duration of the Skylab mission with its many sensitive optical experiments, and with man as one of the major contamination

 


[32]

The astronauts used both spring-wound and safety razors for shaving. Pilot Lousma is shown here.

The astronauts used both spring-wound and safety razors for shaving. Pilot Lousma is shown here.

 

....sources, a significant effort was required to keep contamination to a minimum.

The environment surrounding Skylab at its orbital altitude was composed of the very thin Earth atmosphere along with molecular and particulate matter produced by the space station itself. This induced environment was dynamic and resulted from materials outgassing and overboard venting from the operational activities.

Material from the induced atmosphere which deposited on Skylab surfaces altered surface characteristics and could have adversely affected sensitive instrumentation. Such deposited material could have also altered transmission and reflection characteristics of optical surfaces, changed the absorptivity and emissivity of thermal control surfaces, and altered the resistance of electrical connections.

As the sources of contamination were identified during the design phase and the effects on susceptible experiments and surfaces were understood, various control measures were established. Wherever possible the sources were eliminated, experiments and windows were kept covered when not in use, and the sequence of operational activities during the mission was planned to keep contamination-generating events from occurring when a sensitive instrument was exposed.

 

Skylab Materials

Materials used in the crew quarters and for the external Skylab structure were carefully selected to be compatible with the expected environments, including wide temperature ranges. The spacevacuum conditions required that the materials be stable from the standpoint of outgassing or volatility which could lead to contamination of optical apparatus and other experiments. The intensity of ultraviolet radiation from the Sun dictated use of protective thermal control coatings.

The high oxygen content in the crew quarters enhanced the flammability potential. For that reason, the use of flammable materials was severely restricted, and each specific use was identified and mapped. Special precautions were taken to insure that no ignition sources existed.

Many new nonflammable materials were developed during the Apollo and Skylab programs. Some were used for the first time in Skylab. Each material was rigidly screened to insure satisfactory....

 


[33]

Some areas on the Skylab exterior became discolored. Engineers attributed this to an interaction between contaminants and solar ultraviolet radiation.

Some areas on the Skylab exterior became discolored. Engineers attributed this to an interaction between contaminants and solar ultraviolet radiation.


 

[34] ...application with respect to outgassing, toxicity, odor, dimensional stability, and chemical stability.

 

Maintenance and Repair in Space

Initial planning for Skylab envisioned only a limited degree of inflight maintenance. As on previous manned spaceflight programs, dependence was to be placed on components of very high reliability and the use of redundant systems, where necessary. As the program evolved, however, the Skylab systems became increasingly complex. In addition, the manned periods were lengthened, and plans were developed to have the astronauts perform more and more tasks. It became obvious that, even with high reliability systems, failures could occur. And if they did, they could jeopardize mission completion.

Gradually, a concept was developed which called for considerable maintenance to be performed by the flight crew. This concept had certain restraints, however. No maintenance was to be performed during extravehicular activity except for film replacement and pinning open solar telescope aperture doors. This concept was later modified drastically, as extravehicular maintenance activity became necessary for the mission to continue.

Flight and ground crews, working together, demonstrated the wisdom of the provision for inflight maintenance. The extensive training of the flight crews and their knowledge of the Skylab systems enabled them to analyze problems and provide accurate technical data to engineering crews on the ground.

There were three categories of inflight maintenance: scheduled activities for normal cleaning and replacement tasks; unscheduled activities for anticipated repair and servicing of designated equipment; and a general capability for unexpected or contingency repairs.

Scheduled inflight maintenance included periodic cleaning or replacement of consumable, cycle-sensitive, or time-sensitive equipment. Such housekeeping tasks, scheduled in the daily flight plans, included the cleaning or replacement of such items as waste system and environmental control filters. Onboard tools, spares, and procedures were provided for such tasks.

Unscheduled inflight maintenance included replacing failed components, installing auxiliary and backup hardware, and servicing and repairing certain equipment. Spare components, tools, and procedures were provided for performing over 150 different unscheduled tasks, and the crew was trained to perform each. Task selection was based upon analysis of failure criticality, failure probability, failure effects on the mission and the crew, complexity of the required maintenance, support required, and time to perform the maintenance.

In addition to providing for scheduled and unscheduled maintenance, tools and materials were included for general repairs. Items such as tape, wire, C-clamps, pliers, vise, twine, hammers, and tweezers were included in the tool kit for this purpose. During the mission, additional tools and equipment were launched with the crews to troubleshoot and correct malfunctions for which onboard maintenance support was inadequate. Other contingency situations occurred that were resolved with the onboard support equipment, but required that step-by-step procedures be developed on the ground and transmitted to the crew.

 

Ground Support

The Mission Control Center, well known for its role in the Apollo program, also served as the control center for the Skylab mission. Engineers and technicians at the Marshall Space Flight Center provided technical support to Mission Control on systems and experiments they had developed. An operations support center at the Marshall center was manned around the clock by specialized engineering support groups involved in Skylab.

These technical groups were kept informed continuously. Data describing the condition of systems aboard Skylab as well as the results of scientific observations were transmitted regularly from the orbiting spacecraft to remote ground sites, and then to the NASA centers at Houston and Huntsville.

Debriefings of the crews also provided much valuable technical information. The astronauts were highly trained, technically knowledgeable men. They had been well schooled in operation of the Skylab systems, so they could quickly detect abnormalities and describe them to the ground crews. Frequent inflight debriefings included both live and recorded conversations, both in response to specific questions and simply to relate observations and experiences. And when each crew returned, the astronauts participated in a series of [35] extensive debriefings which provided still more valuable information on Skylab's operating condition.

The duration and complexity of the Skylab mission and unexpected problems which developed required continuing support from mission operations and engineering ground teams. Most of the NASA and contractor engineers were veterans of Apollo and earlier manned spaceflight programs, and their experience proved to be invaluable.

Daily flight plans were transmitted to the crew, identifying all activities to be performed, along with time allocations. But adjustments to daily activities were made when equipment problems occurred, when weather conditions precluded performance of a given experiment, or when other problems arose. Such additional tasks as observations of Comet Kohoutek were included. Crew motion sickness, experienced temporarily by some crewmembers, required some adjustments in planning. These and other factors dictated a need for great flexibility in ground support throughout the mission.

Mission operations support teams were located throughout the United States at NASA centers, contractor facilities, and universities. They were called upon to provide around-the-clock support for planning each day's activities and to provide technical analysis and coordination when problems occurred. The most dramatic example was the combined support of many Skylab participants working against time to solve the high temperature inflicted on Skylab with the loss of the meteoroid shield. But there were other problems that constantly were being analyzed throughout the entire mission and required total dedication of all involved to assure successful mission continuation. Such items as management of electrical power use as a result of the temporary loss of one of the two main sources, potential loss of attitude control gyroscopes, and the possible need of a rescue mission for the second crew when leakages occurred in the command and service module attitude control system presented a constant challenge to ground engineering personnel. Time was always a critical factor.

 

Skylab Crews

Nine astronauts lived and worked in Skylab, and six more astronauts were also involved as backup crewmen to the primary flight crews. The commander and pilot of each primary crew were trained spacecraft and aircraft pilots with strong engineering backgrounds. The scientist pilot was a rated jet pilot as well as a scientist.

The first crew consisted of Comdr. Charles Conrad, Jr., Pilot Paul J. Weitz, and Scientist Pilot Joseph P. Kerwin. Conrad was a U.S. Navy captain who had become an astronaut in 1962. He had been in space before on the Gemini 5 mission, in 1965, and the Gemini 11 flight, in 1966. In 1969, he became the third man to walk on the Moon as commander of the Apollo 12 mission. Weitz was a commander in the U.S. Navy, and he became an astronaut in 1966. He had not previously been in space. Kerwin, also a commander in the U.S. Navy, was a doctor of medicine who had been selected as an astronaut in 1965. He had not flown in space.

The commander of the second Skylab mission was Alan L. Bean, a captain in the U.S. Navy, who was named an astronaut in 1963. Earlier, he had flown in Apollo 12 as the lunar module pilot in 1969. Pilot Jack R. Lousma, a major in the U.S. Marine Corps, joined the astronaut ranks in 1966. Scientist Pilot Owen K. Garriott was a civilian who held a Ph.D. in electrical engineering and became an astronaut in 1965. Neither Lousma nor Garriott had flown in space.

None of the three members of the third crew had flown in space before. This crew was headed by Comdr. Gerald P. Carr, a lieutenant colonel in the U.S. Marine Corps, who had been appointed an astronaut in 1966. Pilot William R. Pogue, a lieutenant colonel in the U.S. Air Force, had become an astronaut in 1966. Scientist Pilot Edward G. Gibson, a civilian with a Ph.D. in engineering and physics, had been named an astronaut in 1965.

Assisting these astronauts during their training, and trained to take over for them in case something happened, were two backup crews.

For the first mission, the backup men were Russell L. Schweickart, a civilian, who had joined the astronauts in 1963. He had been the lunar module pilot for Apollo 9 in 1969. Schweickart was assisted by Bruce McCandless II, a lieutenant commander in the U.S. Navy, who had been appointed an astronaut in 1966. The third member of the team was Story Musgrave, a civilian and a doctor of medicine, who had been selected as an astronaut in 1967. Neither McCandless nor Musgrave had spaceflight experience.

 


[36]

The Skylab prime crews. [small picture- it's a link to a larger picture on a separate page]

The Skylab prime crews.

 

The second and third missions had the same backup crews, and none of them had previously been on a space mission. They were Vance D. Brand, a civilian who became an astronaut in 1966; Don L. Lind, a civilian, with a Ph.D. in physics, who joined the astronaut corps in 1966, and who also had a scientific experiment aboard Skylab; and William B. Lenoir, a civilian with a Ph.D. in electrical engineering, who became an astronaut in 1967.

 

Preparations for Launch

It was May 14, 1973.

Just 3 months earlier, the components standing on the launch pad had been housed in the giant Vehicle Assembly Building at the Kennedy Space Center. There they had been subjected to a series of tests before movement out to the pad. All possible tests were conducted within the enclosed building before moving Saturn and Skylab outside for special testing and servicing before launch.

Major elements of the Saturn V rocket and the Skylab had been brought to the Kennedy Space Center on Florida's east coast much earlier. Specially designed barges, with environmentally controlled hangarlike enclosures, transported the large Saturn stages. The Super Guppy, an awkward-looking airplane designed especially for the purpose, transported smaller, but still large by most standards, space station and Saturn V components.

The three Skylab prime crews and their backup...

 


[37]

Many of the Saturn and Skylab large components were transported to the launch center aboard special barges or in special modified aircraft.

Many of the Saturn and Skylab large components were transported to the launch center aboard special barges or in special modified aircraft.

 

.....crews had completed one of the most intensive training programs ever devised. Each had taken an active part in the development of their space station through a series of briefings and reviews, accompanied by individual study and trips to the contractors' plants. They were intimately familiar with the workshop and all its elements. They had undergone extensive training on Skylab systems. Each crewman had received practical training in the diagnosis of illnesses of an outpatient nature and had been schooled in therapeutic procedures for the treatment of illnesses and accidents. Full mission simulators, experiment task simulators, and various engineering development simulators had been used by the crews to rehearse and practice each procedure they would have to follow. Full-scale mockups had been employed extensively for experiment training, procedural and timeline development, conducting stowage exercises, performing procedures, and especially for performing tasks associated with extravehicular activities.

The neutral buoyancy tank at the Marshall Space Flight Center had been used for zero-gravity training, to prepare the crewmen to perform assigned extravehicular tasks, such as the installation and retrieval of film magazines. This training was to prove especially useful when it became necessary to repair the crippled space station.

Finally, as an added precaution, provisions had been made for rescue of a crew, if it had been needed. A rescue kit was available for the modification of a command and service module to receive the extra passengers and return them to Earth safely. And the Skylab crews had been given special training in the procedures necessary to effect safe recovery of their fellow astronauts. A number of significant problems were encountered, but the design of the Skylab systems, the reliability of the hardware in operation, the training and vast preparations carried out in preparation for the mission, and the skill and dedication of the flight and ground crews eliminated any need for rescue.

 


[38]

In October 1968, Fred J. Sanders, right, escorted Wernher von Braun through the Mc Donnell Douglas Astronautics Co. plant in St. Louis. Inspecting a mockup of the airlock also were Walter Haeussermann, standing, Jack L. Bromberg, left (behind von Braun), and John F. Yardley, behind Sanders.

In October 1968, Fred J. Sanders, right, escorted Wernher von Braun through the Mc Donnell Douglas Astronautics Co. plant in St. Louis. Inspecting a mockup of the airlock also were Walter Haeussermann, standing, Jack L. Bromberg, left (behind von Braun), and John F. Yardley, behind Sanders.


During his visit to the Marshall Space Flight Center in June 1967, Vice President Hubert H. Humphrey, as head of the National Aeronautics and Space Council, was briefed on the center's programs, including Skylab, by von Braun.

During his visit to the Marshall Space Flight Center in June 1967, Vice President Hubert H. Humphrey, as head of the National Aeronautics and Space Council, was briefed on the center's programs, including Skylab, by von Braun.


[39]

During his visit to the Marshall Space Flight Center in June 1967, Vice President Hubert H. Humphrey, as head of the National Aeronautics and Space Council, was briefed on the center's programs, including Skylab, by von Braun.

William A. Brooksbank used a model of the orbital workshop to explain its structure and operation to visitors from NASA Headquarters to the Marshall Space Flight Center in December 1967. Seated left to right are Leland F. Belew, James E. Webb, Charles W. Mathews, and von Braun.

In October 1968, von Braun, right, escorted Homer E. Newell through the Skylab mockup at the Marshall Space Flight Center.

.

NASA Administrator Thomas O. Paine visited the Marshall Space Flight Center in July 1970, for briefings on the developing Skylab program. Shown left to right are Belew, Samuel C. Philips, Harold T. Luskin, Paine, and Werner Kuers.

In October 1968, von Braun, right, escorted Homer E. Newell through the Skylab mockup at the Marshall Space Flight Center.

NASA Administrator Thomas O. Paine visited the Marshall Space Flight Center in July 1970, for briefings on the developing Skylab program. Shown left to right are Belew, Samuel C. Philips, Harold T. Luskin, Paine, and Werner Kuers.