Skylab's ultimate success contrasted sharply with its almost disastrous beginning.
Flawless and on-time launches of Saturn IB and Saturn V launch vehicles had come to be expected at the Kennedy Space Center. Neither of the rockets had ever experienced failure. Both had played key roles in America's manned space program.
The Skylab cluster which stood atop the Saturn V on the morning of May 14 was complex but thoroughly reliable. Each part was the result of an intensive design and development program, and the product of painstaking fabrication and test.
In the prelaunch tests, Skylab's systems had again been exercised and had performed as expected. The flight-readiness review was conducted to assure that any problems which had occurred in ground test were resolved and no open problems remained.
Now Skylab was ready. Provisioned with supplies for sustaining three crews as they lived and worked for weeks in the space environment, the giant laboratory was posed for flight.
Trouble Began Early for Skylab
Engineers manning the consoles in the control and support centers at the Kennedy Space Center in Florida, at the Johnson Space Center in Texas, and at the Marshall Space Flight Center in Alabama, checked off the key events almost routinely as the countdown continued. And the thousands of NASA and contractor management and technical personnel who had lived with Skylab as it evolved from drawing board to launch pad, followed each step, confident that the launch vehicle and the space station would perform as intended.
But this was not to be.
As the moment of launch neared, and the engines on the Saturn first stage thundered into life, no one could have predicted the bizarre series of events that would soon occur.
Precisely on time the huge rocket roared from the launch pad as NASA engineers carefully monitored flight perform ance. As the great rocket climbed into the atmosphere, all systems performed normally. But suddenly, 63 seconds into flight, engineers manning the consoles were startled to see an unexpected telemetry indication of micrometeoroid shield deployment and initiation of deployment of one of the solar-array beam fairings on the workshop. Also, abnormal micrometeoroid shield temperatures were seen. All other signals indicated a normal flight. Ten minutes after launch, the workshop separated as planned from the second stage. Eight seconds later, the workshop entered its nearly circular orbit above the Earth. Then, a planned sequence of deployment and activation procedures began.
The shield, which protected the refrigeration system radiator from exhaust gases from the rocket motors used during the separation sequence, was jettisoned. The workshop was then maneuvered so that its centerline pointed toward the center of the Earth. With the workshop in this position, the....
....radiator faced away from the Sun's hot rays. The refrigeration system was turned on. Then came jettisoning of the payload shroud, and Skylab was maneuvered to its "solar inertial" attitude.
In that attitude, both solar arrays, the solar observatory and one side of the workshop, always faced the Sun. The centerline of the workshop lay
in the orbital plane while the centerline of the solar observatory, when rotated to its normal position, pointed toward the Sun. Unlike Apollo, Skylab did not roll, but remained in this one position throughout the orbit unless the attitude needed to be changed so that particular experiments could be conducted.
 The next planned step in the sequence was to have been deployment of the workshop's winglike solar array, as well as the meteoroid shield which protected the workshop. But as Skylab began to go out of contact with ground tracking stations for the first time, the signal indicating that the micrometeoroid shield was in the deployed position still had not been received.
During the approximately 15 minutes in which there was no communication between ground stations and Skylab, engineers in the flight control centers waited and worried. When communication was resumed, signals should have indicated that the micrometeoroid shield and workshop solar array were in the fully deployed position. Neither of these signals was received. But temperatures on the outside of the workshop were rising rapidly.
As Skylab passed over Madrid on its second orbit, another command was sent to deploy the workshop solar array. Nothing happened. Later, as the workshop passed over Hawaii, another command was sent to deploy the shield. Again, there were no results.
At this point engineers had concluded, because of high temperatures on the outside of the workshop, and the signals recorded at 63 seconds after launch, that the micrometeoroid shield had been lost. Now the problem became one of protecting Skylab while determining what should be done to save it.
The micrometeoroid shield that was to have protected the workshop was also designed to serve as a heat shield. Black, white, and aluminum paints covered all external surfaces of the shield in a pattern carefully tailored to control heat losses and gains. The outside of the workshop was coated with gold foil, to maintain the required balance of absorption and emission of heat between the shield and the vehicle. Gold foil is a material highly absorbent to solar energy with very low heat loss from reradiation. When the shield was lost, the gold surface of the workshop was exposed to the Sun, and the workshop developed external temperatures about 200°F higher than it had been designed for.
The manned launch, scheduled for the following day, was postponed for 10 days to allow time for analysis of the problem and arrive at a means for overcoming it.
Ten days-and nights-seemed an incredibly short time to determine the exact problem and....
...devise a reliable means of correcting it so that the mission could continue as planned. But in that I O-day period, teams of engineers all over the country were to correctly assess the problem, design, build, test, and deliver the equipment and tools needed to save Skylab. Under usual conditions, this effort would have required many months.
Each of the participating NASA centers immediately initiated emergency activity. For almost 2 weeks, at these centers and at contractor locations, and at many universities throughout the country,  the lights burned continuously as engineers, scientists, and technicians worked around the clock.
Typical of their activities was a study to predict the effects of the conditions described by telemetered data. From measurements transmitted from Skylab to ground stations, engineers began calculations to determine the temperatures in the film vaults, the food lockers, and the medicine containers. They made investigations to determine the effect that high temperatures would have on the polyurethane foam insulation bonded to the workshop's inner wall. If the temperatures soared too high, they feared that the insulation might separate from the wall, begin disintegration, and give off toxic gases which could be harmful, even lethal, to the crew. High temperatures could also cause the stored food to spoil and the sensitive film to fog.
With no means of shading Skylab from the Sun, ground controllers maneuvered the space station to reduce the effect of the Sun's rays. But each maneuver to bring thermal relief also placed the solar array of the observatory in a position where it was no longer fully effective. The changing position also caused some auxiliary cooling systems to approach freezing temperatures.
It was found subsequently that one of the solar wings on the workshop had been torn away. The other had not deployed fully. All electrical power had to come from the solar array of the observatory. But the array produced full power only when it was perpendicular to the Sun's rays, and it was not possible to keep Skylab in this position because of the need to turn the workshop away from the Sun. Finally, after considerable maneuvering, ground controllers placed the orbiting workshop into a position where it was approximately 45 degrees from the Sun's rays. The solar power production decreased substantially, but temperatures in the workshop did not rise as rapidly.
Finally, temperature inside Skylab was stabilized at approximately 130°F and the power produced by the solar observatory array was about 2800 watts. This barely covered the requirements for operating essential systems such as the attitude control and communications systems. Before the men of Skylab could move in, considerably more power would have to be supplied, and temperatures would have to be reduced drastically.
Of the three kinds of food on board, the dried food was relatively insensitive to high temperatures. Frozen food in the deep freezers was not in danger, because the refrigeration system worked very well. But canned food could well be affected by high temperatures. However, the food could have been resupplied, if necessary, and preparations were made to replace some of the medicines.
The First 10 Days-A Rigorous Test
Skylab's first 10 days in orbit provided a rigorous test of its attitude and pointing control system.
Pointing control means developed for previous spacecraft helped greatly in the design and development of the Skylab attitude and pointing control system. But the size of Skylab, the long mission duration, and the great pointing accuracies required dictated the development of a new system. For example, the system needed would be required to point experiments on the Sun with less than 2.5-arc-second error for a minimum of 15 minutes. This accuracy is the equivalent of holding the sight of a rifle on a target the size of a period from a distance of 100 yards.
The principal device used for maneuvering and controlling the attitude of Skylab was a control-moment gyroscope.
Gyroscopes have been used for many years as error sensors in aircraft and for spacecraft stabilization and control. But large gyroscopes were used for attitude control for the first time on Skylab. These gyroscopes accepted commands from the controller or computer and applied torques to the spacecraft so that Skylab could change its position in orbit as needed.
Each Skylab control-moment gyroscope consisted of a motor-driven rotor, electronics assembly, and power inverter assembly. The 21-inch diameter rotor weighed 155 pounds and rotated at approximately 8950 revolutions per minute. Rotating the spin axis of the rotor caused the gyroscope to produce a torque or turning moment about an axis perpendicular to both the spin axis and the axis about which the spin axis was being driven. The torque generated was proportional to the rate at which the spin axis was rotated and to the angular momentum of the gyroscope (determined by the spin rate and mass).
Three such gyroscopes were used on Skylab. Any two could provide the torques needed. The third gyroscope added control capacity as well as being a backup, in case of failure of one of the...
...other two. This capability was to prove itself during the third manned period.
Skylab in orbit needed a reference direction in space to insure that it had the desired angular orientation as it passed any given point in its orbit. This function was performed by Sun sensors, rate gyroscopes, and star trackers. They sensed the angular position and rate of rotation of Skylab with respect to the Sun and selected stars.
Rate-gyroscope processors measured the rate of rotation of Skylab and sent signals to its digital computer. These signals were used in a mathematical computation to describe the space station orientation at any time.
Each of the rate-gyroscope processors consisted of a single rate-integrating gyroscope connected to electronic devices whose outputs were proportional to the precessional rate of the gyroscope about its input axis. Nine rate-gyroscope processors, three for each Skylab axis, were mounted on the solar observatory support structure. Two gyroscopes in each axis were averaged for control; the third was on standby to be used, if something happened to either of the others. An onboard digital computer monitored these gyroscopes to detect possible failures, isolate problems, and to select new combinations of gyroscopes, if necessary.
Updating, to correct for gyroscope drift, was accomplished by ground command through the onboard digital computer. Contrary to design...
...expectations, most of the rate gyroscopes drifted excessively and erratically at one time or another in the early part of the mission. Such drifts made it very difficult to hold the emergency positions commanded during the first 10 days. Sudden changes in drift rate, which occurred frequently, caused difficulties in Skylab attitude control until the new drift rate could be determined and appropriate compensation made. As the mission continued, the magnitude of the drift rate changes decreased. Eventually, three of the rate gyroscopes became stable.
Also, early in the Skylab mission, some of the  rate gyroscopes overheated and showed a tendency to oscillate. There was concern that the overheating might cause permanent damage, which, with continued use, would result in loss of control. Later, available spare gyroscopes were prepared for flight providing fresh hardware with changes to overcome the problems of overheating and excessive drift. These new units were carried aloft and installed in the docking adapter by the second Skylab crew and performed flawlessly.
In addition to the control-moment gyroscope system, a thruster control system, similar to that used in many of the previous manned spaceflight programs, provided backup control of Skylab's position. It also provided control of the space station during the time when the control-moment gyroscopes were being brought up to speed, normally during the first 10 hours of each mission, and controlled workshop position during docking of the command and service module to Skylab.
The thruster attitude control system had to provide a high thrust level of 50 pounds during separation of Skylab from Saturn V and 20-pound thrust for each of the dockings. The system used the same rate gyroscopes, Sun sensors, and computer as the control-moment gyroscopes.
Nitrogen gas had been used in many previous spacecraft control systems, so little development work was necessary to provide a system with a high degree of reliability.
Twenty-two titanium storage bottles, clustered in a ring around the aft end of the orbital workshop, held the nitrogen. This gas was supplied to six thruster nozzles arranged in two three-engine clusters opposite each other on the outside of the workshop. The thrusters received their commands from the onboard digital computers to open valves and release the nitrogen.
Each thruster was fired continuously at least I second during "full-on" firings, or in short bursts of from 40 to 400 milliseconds, depending upon the pressure in the nitrogen tanks.
During the first trying days of the mission, this system got a thorough workout. Nearly 50 percent of the nitrogen gas propellant provided for the entire mission was used before the first crew....
....occupied the workshop. Fortunately, because of weather conditions at the time of loading the propellant, about 25 percent more nitrogen was loaded than had been planned.
Energy From the Sun
Skylab's two separate solar-power generation systems were connected so that power could be transferred in either direction. Each system, when fully operational, was capable of providing 4000 watts of continuous power. While Skylab was unmanned, 3200 watts were required. During preparation for astronaut entry into Skylab and during the rendezvous and docking sequences, the total load requirement increased to 4000 watts. Upon activation of the Skylab by the astronauts, the electrical demand continued to increase until it reached an average of 5800 watts.
The solar observatory electrical power subsystem consisted of a four-wing solar array and 18 power conditioners. Each of the power conditioners included a nickel-cadmium battery, a battery charger, and a load regulator. Electrical energy from each power conditioner was supplied to the source buses in the power distributor, which contained the logic required to sequence the components in the power conditioners and to provide power to the 11 load distributors, for transmission to operating systems.
Some 165 000 silicon solar cells, each about the size of a postage stamp, were distributed on the surface area provided by the four deployable wings. The cells were divided into 18 groups, each group supplying energy to one of the 18 power conditioners.
To insure the integrity of the battery system for the thousands of charge-discharge cycles to which it would be subjected, it was necessary to limit the amount of energy removed from the battery during each cycle to no more than 30 percent of its capacity (6 ampere-hours). Since the cycle life of the batteries was also influenced by operating temperatures, thermostatically controlled electric heaters and radiant cooling measures were used to control battery temperatures.
The orbital workshop electrical power subsystem consisted of deployable solar wings, one on each side of the workshop, and eight power conditioners, consisting of batteries, battery chargers, and load regulators. Electrical energy from each conditioner was supplied to regulator buses, from which power was transmitted to each of the workshop load buses for final distribution to the loads. Circuit breakers were provided on the workshop control and display panels, as were switches to control load sequencing. A total of about 74 000 silicon solar cells of the same design used in the solar observatory system were arranged in eight groups on the surfaces of the two solar wings. Each group supplied power to one of the eight power conditioners. However, each group of solar cells could be switched to one alternate power conditioner to optimize the use of available power during contingency periods. The solar cell outputs were connected in parallel to the charger and load regulator, as they were in the solar observatory. The Skylab electrical load requirements were supplied as the first priority. The remaining power was used to recharge the batteries.
The eight batteries in the workshop electrical system were slightly larger than those of the solar observatory system. They were also limited to a discharge of no more than 30 percent (9.9 ampere hours), to insure adequate life to support the mission. Thermistors in each battery provided temperature sensing, load-meter compensation,....
 ...charge control, and protection against excessive temperatures. The cooling system in the airlock regulated the battery temperature. In addition to measurements of the currents, voltages, and temperature of each solar cell group and power conditioner, two state-of-charge meter readings were telemetered for each of the eight workshop batteries so that battery charge-discharge status could be monitored continuously.
Throughout the Skylab mission, the mission support engineering teams kept a close watch on the operation of the electrical power subsystems to detect possible malfunctions, to take immediate action to correct them, and to manage the available power. This involved monitoring scores of voltage, current, and temperature measurements as they were transmitted from the orbiting space station.
The two workshop solar-array wings, mounted on opposite sides of the workshop, consisted of solar panels hinged together in three sets, or wing sections, and folded for launch into a cavity in the underside of a supporting beam. The beam itself, ...
.....hinged at the forward end, folded for launch against the side of the workshop over the micrometeoroid shield. This beam protected the wing from aerodynamic forces during ascent and provided structural support during and after deployment.
Each of the two beams was held flush against the workshop's structural shell during launch and was freed from its attachments by a small explosive charge. The beam was extended into position by an actuator, which consisted of a spring wrapped around a hydraulic piston. Freeing the beam from its attachments allowed the spring to force the beam outward. A latch locked the beam in place when the hinge limit was reached.
Deployment of the solar wing followed. The three wing sections carried by each beam were made up of rectangular panels of silicon cells. Hinges between the panels permitted them to be folded accordion-fashion for storage during launch. Springs in the hinges caused the panels to unfold, extending the wing sections to their full length.
Protection of the Workshop Given Top Priority
This was how it was supposed to have worked, but now a means had to be devised for shading the workshop and protecting it from the heat generated by the merciless rays of the Sun, while Skylab was reoriented with its solar wings perpendicular to the Sun so that it could generate sufficient electrical power to carry out the mission.
Several schemes were proposed; the scheme selected for initial use involved a square thermal shield which operated like a parasol. This shield fitted into a small canister, originally developed to house an experiment which was to be deployed through a scientific airlock located in the side of the workshop normally facing the Sun. Once outside, the shield popped open like the familiar parasol, with four struts extending outward from a segmented center post. To deploy it, the crew pushed the center post outward a segment at a time, which extended the struts and opened the parasol.
Another concept was to let the crew rig a shield over the workshop while standing in the open hatch of the command module. They would attach ropes to the workshop and thus rig a sail-type shade. This scheme was simple, but it had a serious drawback. It required careful maneuvering to keep the command module close to Skylab while the....
....crew worked to avoid collision of the two. The uncertainty of the crew's ability to tie the shield led to the decision to retain this concept only as an alternative.
Another scheme was later used by the second crew. This "twin-pole" concept also required the astronauts to leave the workshop to hang a fabric awning from a twin-pole frame. The top of the frame was attached to an outrigger on the solar observatory, then 55-foot-long poles were extended down the side of the workshop, and the awning was stretched between them.
Still another proposal called for utilizing the same plastic material of which the Echo satellite was made. It would be formed into an umbrella held in place by inflated balloon ribs that were to be tied to the workshop's structure. Among other concepts suggested, but not used for various reasons, were painting of the workshop exterior, a shield held in place by plastic cords, and a shade produced by inflating a weather balloon.
One of the first methods considered for holding down workshop temperatures was to spray the unprotected side of the workshop with a special thermal control paint. The idea was abandoned because it provided a possible source of contamination.
Fabric awnings appeared to be the best answer. Fourteen different materials were tested. The investigations included the effects of ultraviolet radiation, tensile and peel characteristics, stickiness of the materials which might affect the capability to unfold the shield in space, weight changes, possible contamination, and others.
Extensive tests were also conducted on the special radiation-resistant rope to be used with the awning. Nothing was left to chance.
The limited storage space in the command module would accommodate only the three most feasible versions of the thermal shield. The choices were narrowed to the parasol, the twin-pole awning, and the screen deployed from the command module. Development continued, and the astronauts and engineers spent many hours in the neutral buoyancy simulator at Marshall training to deploy the two awnings.
Following a review of all the materials testing, failures, analyses, and deployment procedures associated with the design of the three thermal shields, the parasol was selected as the primary device, since it would not require the astronauts to....
....venture outside Skylab. The decision was made to deploy the twin-pole awning over the parasol at some later time. It was also to be stowed in the Apollo module as an alternate means of protection.
Meanwhile, a number of other very important problems also demanded immediate solution.
Procedures Developed to Free Solar Wing
NASA engineers were asked to determine what could be done to free the solar wing still pinned to the side of Skylab.
Since there was no way of determining from Earth what was preventing its deployment, all possibilities had to be investigated. One problem almost certainly involved the solar-wing beam's actuator-damper, which operated exactly like an automobile's hydraulic shock absorber. The beam was to be deployed immediately upon reaching orbit. Since that could not be done, the actuator cooled to some -60°F, which was near the freezing point of its hydraulic fluid. There was a high probability that the actuator-damper attachment would have to be broken to permit deployment.
The solar wing sections, which unfolded like an accordion from the beam, also had actuator-dampers. These actuators contained a less viscous fluid than the beam actuator, and they were mounted so that they could be exposed to the Sun after beam deployment. Thus, Skylab could be maneuvered so that the Sun could warm them enough for the wing sections to deploy.
Speculating that the debris holding the solar wing in place consisted of sheet metal and possibly bolts and small metal straps, engineers at Marshall Space Flight Center concentrated on devising tools which would be manipulated from as far away as 10 feet.
Long-handled tools used by telephone and power companies were adapted for use, and a two-pronged tool designed for prying and pulling was modified to help free the jammed wing. A pulley return mechanism was designed to replace the spring return system on the cable cutters.
The special tools were quickly fabricated and they were tested in the neutral buoyancy tank which simulated zero-gravity conditions.
On May 19, just 5 days following the Skylab launch, a section of the underwater Skylab mockup was rigged with fragments of metal wire bundles, bolts, and other items representative of the failed shield. This mockup, quickly dubbed "the junk pile," closely resembled conditions which engineers believed the astronauts would find when they reached Skylab.
The first flight crew-Astronauts Pete Conrad,....
....Joe Kerwin, and Paul Weitz-entered the tank to test the tools in the simulated weightless environment. They practiced prying the straps away from the wing, cutting straps with the cutting tools, and moving around the disabled wing safely while performing these operations.
The simulator proved an extremely valuable means for approximating zero gravity. Throughout the mission it was used by astronauts and engineers to train for extravehicular repairs and to develop procedures, and by astronauts and engineers during the missions to conduct "real time" experiments so that they could relay vital information to the flight crews.
The core of this simulator was a 1 300 OOO-gallon water tank 75 feet in diameter and 40 feet deep. The tank was large enough to accommodate full-size elements of the Skylab. The water was kept clean by a filter, much like that used in a large swimming pool. Integrated into the tank were special systems for underwater audio and video, pressure-suit environmental control, SCUBA support, and emergency rescue and treatment. Underwater lighting and provisions for communication and data acquisition were also provided.
To simulate weightlessness in the tank, the test subjects and all equipment had to be made neutrally buoyant. This required that the test subject and equipment be the same weight as the displaced water so that they were in a "neutral" state, neither rising nor sinking.
For Skylab extravehicular activity simulations, crewmen wore spacesuits. After the suit was pressurized to match spaceflight conditions, lead weights were then attached as needed to the upper torso, the forearms, and legs until the crewman was neutrally buoyant.
Tools and other equipment were made neutrally buoyant through the addition of flotation units placed so that the equipment retained its original  center of gravity and so that they would not interfere with equipment operation.
Possible Decomposition of Insulation a Concern
In addition to the loss of the micrometeoroid shield, the apparent loss of one workshop solar array wing, and the failure of the other to deploy, another serious problem arose. The workshop was insulated with a heavy layer of polyurethane foam bonded to its internal walls, a standard feature of the propulsive upper state. At temperature and pressure conditions similar to those that existed in the workshop, the decomposition of polyurethane creates gases which can be dangerous and even lethal. Extensive and accelerated tests were made to determine the decomposition that might occur at the workshop temperatures in question.
But tests showed that the insulation would not separate from the walls and that there would be no loose particles. However, it was found that appreciable amounts of gases were emitted from the insulation at 300°F. Updated information was obtained from flight data on heat exposures of the vehicle and retesting was begun. These tests showed that even though gas might be coming out of the walls, the volume of the workshop was sufficient to dilute this to acceptable levels.
As a further precaution, ground controllers repeatedly depressurized and repressurized the laboratory with nitrogen to flush overboard any toxic gases it might contain. This pressure cycling continued for 3 1/2 days. As a final precaution, plans were made for the crew to wear gas masks upon entering the workshop and to run gas analysis tests to provide full confidence in the safety of its atmosphere.
Hundreds of scientists, engineers, and technicians continued working around the clock. Many had to be ordered home for much-needed sleep. Meetings were held to determine what simulators and mockups were needed, which thermal models were to be used, when procedures and training facilities were required, which manufacturing personnel were needed, what computer facilities were required, and how crew participation should be scheduled, all in support of the problems being studied. Time went by rapidly. Testing proceeded. When the structural designs were completed, static and dynamic testing was performed. Extensive tests were carried out on workbenches and in the...
....neutral buoyancy simulator. Finally, difficult choices had to be made.
Besides the thermal shields and tools for releasing the solar-array wing, other new items were stowed in the command module, including additional cameras for the fly-around assessment, equipment for performing the extravehicular activity from the open command module hatch, and equipment for detecting poison gases and protecting the crew from them. Additional drugs, medications, and experiment film were stowed as replacements because of the possibility of damage from the high temperatures in the workshop.
Meanwhile, the schemes devised to hold temperatures down and electrical power at an acceptable level were working very well. Available power was strictly allocated, and, as far as possible, systems using it were turned off or operated intermittently. Heaters, one coolant pump, and telemetry transmitters, for example, were cycled on and off or were operated at reduced loads. The electrical power systems themselves were also managed to check out and protect the systems. The two major problems, high workshop temperatures and a general electricity shortage, still existed. But Skylab was still functioning as Conrad, Kerwin, and Weitz took their places in the Apollo....
... capsule atop the Saturn IB rocket on the morning of May 25.
The crew was confident that they could restore the damaged Skylab to full operating condition. The problems were staggering, and there were many unknowns. But the crew was experienced, well trained, and highly motivated.
"We can fix anything," they boasted, as the Saturn roared into space. This statement was soon to be tested.