Before Conrad and Kerwin completed freeing the workshop solar wing, trouble developed in the systems which cooled the spacesuits and the workshop.
Problems in Suit-Cooling Loop
While performing spacewalks, astronauts wore undergarments which were cooled by water from either of two supply loops. The water in each loop was cooled in a heat exchanger, which transferred the water's heat to a coolant flowing through the workshop's primary cooling system. Each of the loops had two pumps, a reservoir containing the water supply, and a separator whose function it was to remove gas from the circulating water.
Conrad and Kerwin were outside the spacecraft for 3 1/2 hours trying to free the solar wing. Each wore a spacesuit connected to a separate cooling loop. Before going outside, they had turned on valves in the primary coolant system. This action also activated heat exchangers to provide additional suit cooling. Apparently, this action caused solid particles to be flushed out of the heat exchangers and lodge in the temperature control valves, causing valves to stick. Temperatures in Conrad's suit loop decreased rapidly, and water apparently froze in the heat exchanger since water flow through his suit stopped completely.
At the time, the full extent of the problem was not realized since the secondary coolant loop appeared to be functioning adequately, and it was sufficient to provide adequate cooling. Conrad and Kerwin went on to complete the freeing of the solar wing. Once they were back inside the airlock, as they were disconnecting the second suit loop, they discovered that the valve in the secondary coolant loop was also stuck. They turned off the secondary coolant loop and tried the primary loop again. Temperatures dropped still lower. On the advice of the ground engineers, they switched back to the secondary coolant loop, which was still maintaining temperatures at a more acceptable level.
After the crew had gone to sleep, however, temperatures continued to drop in the secondary loop. Ground controllers woke the crew, and instructed them to connect the two liquid-cooled garments to the coolant system and to place the garments against a water storage tank which was relatively hot because it was on the Sun side of the workshop. This action added heat from the tank to the water in the loop. Temperatures rose to 40°F and stabilized there.
The crew went back to sleep, but the mission was still in jeopardy.
One of the loops in the primary coolant system was inoperative. Failure of the other loop, already operating erratically, would result in intolerably high workshop temperatures and overheating of electrical components.
The valves which controlled flow through these loops were located outside the airlock module. The only means of freeing them was through thermal....
.....cycling, which would cause the internal valve bellows to expand and contract. This action would move the valve first in one direction and then the other and dislodge any particles causing the valve to bind.
A time was selected for performing the operation when Skylab was in continuous contact with a ground tracking station. The plan was to turn on a pump in the primary loop while the crew and ground controllers carefully watched system performance. If the procedure was not successful, the pump would be turned off before damage could occur to the system.
The first attempt was unsuccessful, and the loop was shut down. Twelve hours later, the procedure was tried again. This time, temperatures stabilized at 47°F. The primary loop was now fully operational. Using the same procedure, the valve in the secondary loop was also freed.
A Home in Space
By this time, Conrad, Kerwin, and Weitz were seasoned space travelers. They had adjusted well to their new environment. The long hours spent in simulators and other exhaustive training had paid off handsomely.
"Mobility around here is super," Conrad reported. "Nobody has any motion sickness. Every kid in the United States would have a blast up here."
The cavernous workshop, 27 feet long and 22 feet in diameter, invited exploration. In the weightlessness of space, they soared around their home, embellishing their flights with flips, cartwheels, and inventive gymnastic exercises.
Skylab designers had provided recreational equipment to vary the routine of long hours in space. There were dart sets (without sharp points),...
 ....playing cards, balls, books, exercise equipment, and a tape player. But much of this went unused. Earth-gazing during orbital daylight and star watching during orbital night became principal diversions.
Conrad reported: "I've spent a lot of time in space before at 150 nautical miles, but this 237 is just unbelievable. You can really see the curvature of the Earth. As we came over the northern part of the United States east coast, we could see into Canada and clear down to the Keys."
Later, he said: "You can see the whole Bahama chain and all the shallow water and all the deep water in one big picture. It's really fantastic."
Kerwin also had kind words about the functioning of Skylab's toilet.
"We owe our greatest appreciation to the people who designed it," he said. "It has worked much better than anticipated, and it has been essentially trouble free and not terribly time consuming."
The Skylab toilet, designed to function in the weightless environment, bore little resemblance to that found in home bathrooms. It was designed so that crewmen could eliminate body wastes through the necessary acts of urination and defecation. But it also supported biomedical experiments by sampling and preserving certain body wastes and disposing of the remainder. The entire system included a fecal-urine collector, collection and sample bags, sampling equipment, odor control filters, and a fan. The toilet was mounted on the wall rather than the floor of the bathroom, in the crew quarters area.
Defecation in space was complicated by the absence of gravity to move waste material away from the body. On Skylab, a hinged, contoured seat provided access to the mesh liner into which the astronaut inserted a fecal collection bag. Air was drawn through the fecal bag from holes in the seat and exhausted through the bag's vapor port, through the mesh liner, into the fecal collection receptacle, and then through a filter, where odors were removed, before it was recirculated into the cabin by a fan.
To use the toilet for defecation, the crewman sat on the contoured seat, then fastened a belt across his lap to hold himself securely in position. Handholds and foot restraints allowed him to maintain a sufficiently tight seal on the seat, as airflow from the fan separated the fecal matter from his body and deposited it in the fecal collection bag. A separate fecal bag was used for each defecation.
The crewmen could urinate from either a standing or sitting position. A urine collector, located on the wall just below the fecal collector, also utilized airflow as a substitute for gravity to draw the urine through a receiver and hose into a urine collection bag. An alternate device incorporated a funnel-like attachment through which the bag could be filled by bladder pressure.
Feces and vomit were collected in bags and vacuum dried with heat, then stored for return to Earth or dumped into the waste tank. The return of body waste samples was necessary for chemical analysis to determine the effects of spaceflight on musculoskeletal metabolism to measure the daily gains or losses of pertinent biochemical substances. The drying process made the solid biological wastes inactive, a function performed on Earth by sewage-processing plants.
After the urine was collected, air was removed in a liquid-gas separator centrifuge. Then a sample was removed and frozen to prevent chemical changes prior to analysis on Earth. The remainder was disposed of in the waste tank. Urine and blood samples were returned for analysis to evaluate adaptation resulting from extended exposure to the space environment, to space diets, and to Skylab workloads.
The waste management area also included utility closets where supplies for personal hygiene and house cleaning were stored. Tissues, waste collection bags, soap, and utility wipes were among the items stored there. Utility wipes were used both as toilet tissue and for cleaning.
Skylab's zero-gravity shower compartment was collapsible. Located in the experiment and work area of the workshop, it was a cylindrical cloth enclosure that was folded flat when not in use. The bottom ring of the shower was fastened to the floor and contained foot restraints. The upper ring contained the shower head and hose. To use the shower, the astronaut filled a pressurized portable bottle with heated water and attached the bottle to the ceiling. A flexible hose connected the water bottle to a hand-held shower head. The astronaut pulled the cylindrical shower wall up into position and bathed, using liquid soap. Both soap and water were carefully rationed, having been premeasured for economical use.
Astronaut Weitz was the first to test the shower.
He reported that "it took a fair amount longer to use than you might expect, but you come out smelling good."
Each crewman had his own personal hygiene kit, which contained a razor, shaving cream, hand cream, toothpaste, toothbrush, comb, nail clippers, deodorant, and other personal items. When Conrad and his crew opened their kits, they found that the highly elevated workshop temperatures had caused some of the hand cream and toothpaste tubes to rupture but enough remained for their use during the time they occupied the workshop. The shaving cream container was intact, but the cream had hardened; water had to be added before it could be used. The second crew brought replacement kits with them.
Clothing worn by the crewmen was designed for comfort and safety. In all, more than 700 items of clothing were provided for the Skylab crewmen. Among these items were 39 jackets, 69 pairs of trousers, 126 shirts, 30 pairs of boots, 18 pairs of gloves, 4 union suits, 201 T-shirts, 45 half union suits, 85 jockey shorts, 112 boxer shorts, 54 knee shorts, 286 pairs of socks, and 24 constant-wear garments.
The gold-colored shirts, trousers, and jackets were made of a special fire-resistant fabric. The ankle-high boots and wrist-length gloves were lined with a fire-resistant fabric.
Towels and washcloths were provided both for personal hygiene and for general cleaning purposes. They were made of rayon terrycloth, and each was stitched with an identifying color coded for the individual crewman. In all, there were 840 reusable washcloths and 420 towels stowed in dispensers in the waste management compartment. Disposable wipes were also provided. Wet wipes were used principally for food cleanup and housekeeping. Dry utility wipes were used primarily as toilet tissue. Biocide wipes were used for housekeeping activities that required disinfection, such as cleaning up food spills and removing contamination in the fecal-urine system. General-purpose tissues were used for general housekeeping and personal use.
Inside the workshop, airflow was a limited substitute for gravity. Crewmen learned quickly to begin their search for missing items by looking on the surface of the air filters and screens, as loose objects usually found their way there. One screen duct became a favorite workbench, as the crewmen  found that tools and equipment could be held there by airflow against the screen.
As the result of many habitability studies and considerable experimentation, Skylab had been designed so that crewmen and equipment could be held securely in place, when necessary, or could be moved as needed. The walls and ceilings were a metal triangular - gridwork. Shoes worn by the astronauts had triangular plates fastened to the soles, which fitted through the triangular opening in the grid. By turning his foot slightly, the astronaut could hold himself as he worked. There were also other means of restraint. One was a set of straps similar to those on shower clogs. Three pairs of these were placed on the floor of the wardroom at the base of the food table, and another pair was located in the waste management compartment. Still another type of foot restraint, for use with spacesuits, consisted of toe bars and heel fittings which could be fastened to floors or walls.
Straps of varying lengths and elastic cords were stored on Skylab for holding objects securely in place. Rubber cups with a cross cut in the end were used to hold washcloths and towels. Adjustable universal mounts were provided for items such as cameras. These could be moved wherever they were needed and snapped into place. Throughout Skylab, there were provisions made to hold such temporary restraints as clips and snaps.
Handrails and handholds, colored blue for quick identification, were located throughout Skylab. A removable, collapsible "fireman's pole" extending from the workshop hatch to the floor of the forward compartment provided a means of rapid movement. However, the astronauts soon found that they could move about easily without using it, and it was removed and stowed.
Thigh restraints consisted of a round bar, with two crossbars. In use, the astronaut straddled the main bar with his legs between the crossbars. Such restraints were provided at the food table, but the astronauts preferred holding themselves in place with their shoes fastened to the floor.
The mobility aids and restraints aboard Skylab were very helpful. As the astronauts grew more familiar with their home in space, however, they became adept at restraining themselves by hooking their feet around any convenient protrusion, or wedging themselves between two pieces of equipment until they completed their tasks.
But sleeping crewmen did require restraints.
The bedroom was a small compartment divided into three separate modules, each about the size of a small walk-in closet. Each module was equipped with a bed, a locker, and a doorlike privacy curtain, and each had an adjustable vent through which air circulated.
The bed was a multilayered sleeping bag hung on a frame against the compartment wall. Ready for sleep, the astronaut zipped open his bed, selected the number of blankets he needed for warmth, eased himself between them, and then attached a body strap and closed the zipper. This enclosed him in the pillowed sleeping bag and kept him from floating around as he slept.
Despite sleeping in what would appear to be an upright position against the wall, and despite the absence of gravity, crewmen slept well. Some of the crewmen added their own variation to the sleeping position. Some slept with their heads nearer the floor, while others stretched their beds out like a hammock.
Skylab's interior lighting consisted of a combination of incandescent and fluorescent lights.
Seventy-eight fixed lights and five portable lights could be used in any combination to produce the lighting level required to support the astronaut activities. Portable high-intensity lights were used for filming experiments.
The size of the workshop and the necessity for crewmen to work in a number of different locations, as well as to perform extravehicular activity, demanded a reliable system of communications. Also, since the low pressure inside the workshop would not adequately support normal conversation beyond a few feet, audio aids were needed for crew communications.
The workshop intercommunication system was similar to a typical home intercommunication system which permits conversation between people in different rooms of the house. Conversation with the Mission Control Center was a typical two-way radio link.
Intercommunication stations were located at 13 positions within the workshop. Each station provided control for crewman communication as well as communication with the Mission Control Center. The station also included receptacles for a headset and controls which included microphone and transmitter keying, call channel and taperecorded selection, and volume adjustment, as well as audible indications from the caution and warning system.
Two types of headsets were provided for the crew. One type included two microphones and two earphones, and could be used in both suited and shirtsleeve operations. The second type contained a single microphone and earpiece and was used in the shirtsleeve mode.
Housekeeping, a Daily Requirement
Housekeeping demanded much of the astronauts' time. Floating around the workshop, tethered to a bracket, holding to a handrail, or with a foot locked around some piece of equipment, the astronaut carefully used a vacuum cleaner to remove such things as hair clippings from the air as well as to clean the workshop surfaces in the conventional manner.
As in most homes, trash disposal became an important housekeeping activity. Nonflammable, biologically inert trash was collected in cylindrical bags made of vented fabric. When filled, these bags were attached to cables inside the area adjacent to the waste tank beneath the crew compartment floor.
Flammable and biologically active trash was....
....collected in several specially designed types of bags, which were disposed of in the waste tank through the trash airlock.
Skylab's waste tank was part of the liquid oxygen tank located in the aft end of the propulsive stage. A bulkhead separated it from the living area. A network of fine-mesh screens was installed to prevent dumped solids and liquids from migrating into space. It was vented to prevent pressure buildup from the possible growth of bacteria.
The trash airlock extended into the experiment area. It provided a means of passing trash from the pressurized habitable area into the unpressurized waste tank.
Disposing of trash was a carefully executed procedure. The crewman opened a valve which brought the airlock to the same pressure as that within the workshop. He then opened the lid placed the bagged trash inside, and closed the lid and locked it. By turning the valve handle, he reduced the pressure within the airlock until it reached the vacuum of the waste tank. Another movement of the handle opened the door between the airlock and the waste tank. The crewman then operated an ejector handle, which caused a scissors-type mechanism to push the bagged trash from the airlock into the tank.
Scientific Observations and Experiments
Although the initial crew spent considerable time repairing their damaged space station and in readying the workshop for occupancy, they were also busy conducting scientific observations and experiments.
Early in the mission, Scientist Pilot Joe Kerwin had begun carrying out solar observations using the telescopes housed in the solar observatory.
The experiment canister in the solar observatory had four compartments, each of which housed two of the solar telescopes. Five of these telescopes viewed the Sun in its X-ray and ultraviolet wavelengths, observations that are impossible from Earth. One telescope created artificial eclipses so that the Sun's corona, or outer atmosphere, could be studied. The other two telescopes televised images of the Sun.
The acquisition Sun sensor provided coarse pointing attitude information, describing the space station's orientation relative to the line of sight from Skylab to the Sun.
Pointing large bodies such as Skylab with the extreme accuracies required for solar astronomy was beyond the capability of the control moment gyroscope system. In addition, astronaut activity within the space station caused disturbances in attitude that precluded meeting the required pointing accuracies. This made it necessary for the solar experiment canister to have a separate, highly accurate experiment pointing control system.
This experiment pointing control system consisted of four rate-gyroscope processors (two each  about the pitch-and-yaw axes of Skylab), redundant precise Sun sensors, a manual pointing controller, a roll positioning mechanism, pitch-and-yaw flex-pivot actuators, launch and orbital caging devices, and an analog computer for processing the rate and position sensor information and issuing commands to the actuators. The experiment canister was dynamically isolated from the solar observatory rack through the use of flex-pivot torque actuators in the pitch-and-yaw axes and ring gear in the roll axis. The actuators provided +2 degrees of movement in pitch and yaw and +120 degrees rotation in roll. The solar north pole was used as the canister roll position zero reference. The center of the solar disk was used for a pitch-and-yaw zero reference.
The mechanism which rotated the canister about the roll axis was controlled by the crew, using the manual pointing controller rate switches on the control and display console. During extravehicular activities, canister roll was controlled by the crew using the EVA rotation control panel, located at a work station on the solar observatory.
Four rate-gyroscope processors, identical to those used in the control-moment gyroscope system, were used for coarse mode canister rate sensing in the experiment pointing control system.
The precise Sun sensor provided the highly accurate information required for the "UP/ DOWN" and "LEFT/RIGHT" axes of the experiment pointing control system. Direction control for offset pointing was provided through either the manual pointing controller or the onboard digital computer.
The experiment pointing control system was used to point the experiment canister at selected targets on the solar disk with errors less than 2.5 arc-seconds. Using the manual pointing controller and television display on the control and display panel, astronauts were able to "home in" on selected targets on the solar disk with pointing errors of less than I arc-second. Stability of the experiment pointing control system was such that the canister deviation or drift from selected targets was no more than 1 arc-second in 15 minutes.
The control and display panel, located in the docking adapter, was the control center for carrying out solar experiments. It also contained the necessary lights, meters, and switches to operate and monitor certain systems throughout Skylab. From this central location, the astronauts sent....
....commands to experiments and systems with toggle and rotary switches, the manual pointing controller, and the digital address system. The manual pointing controller permitted the crew to point the solar experiment canister and position the star tracker. The two television monitors displayed the five solar experiment video pictures for the astronauts.
Earth Observations Begun
Observations of the Earth also received considerable attention from the first crew. Most Earth resources data are collected by ships and buoys, sounding rockets, balloons, aircraft, and satellites. Remote sensing of the Earth from orbital attitudes, together with photography in the visible and near-infrared spectral regions, provided valuable additional data. Observations from space offered the advantages of a broad field of view afforded by the increased altitude, periodic coverage of the same area, and coverage of areas otherwise inaccessible. Cameras, radar, and other precision instruments on board Skylab studied the surface of the Earth, surveyed crops, made precise terrain measurements, and detected the formation of storms.
Adjustments to the Space Environment
By mid-June, Conrad, Kerwin, and Weitz held a new space record. They had surpassed the 18-day duration of Soyuz 9. Their bodies had adjusted to weightlessness. Without the influence of gravity, their spines had stretched and they had grown about an inch taller. Their faces had become fatter, as body fluids migrated upward. Nevertheless, their physical condition remained excellent.
Their ability to diagnose problems and their skill.....
....in solving them underlined the importance of man in space. Some problems which arose could not have been solved without the crewmen performing some vital activity. An example was the failure of one of the solar observatory power conditioners, which controls energy received from the solar array. The power conditioner consisted of a battery charger, a battery, and a load regulator. Neither the regulator nor the charger would draw power. Ground analysis of the problem indicated that the solar-power contactor had failed in the open position.
Ground engineers who had worked on the system recalled that they had experienced similar problems during laboratory tests. They had observed that a mechanical shock of the contactor would sometimes correct the problem. They recommended that the power conditioner be rapped with a hammer in an attempt to close the contactor. Since the power conditioner was located on the solar observatory mounting structure, repairs would have to be made during a walk in space.
Working on the ground, engineers simulated the stuck contactor in the power conditioner and determined just where the power conditioner would have to be struck.
"Start at the upper right hand corner," they instructed Conrad, "come down three screws... turn to your left, and you go one screw. That's the one you pound on."
Weitz, outside the workshop with Conrad, reported Conrad's actions to Kerwin, manning the console inside the workshop.
"There it goes. Boy, is he hitting it."
Kerwin then relayed information to the ground controllers.
"He hit it with the hammer. I turned the charger on and I'm getting a lot of amps plus on the battery. "
While the solution to the problem was far from scientific, it worked.
Once again, experience and ground simulation, plus the presence of man, had solved a potentially difficult problem.
As the first manned period was nearing an end, Conrad and Weitz began retrieving the exposed film which had recorded the results of Skylab's experiments.
Film retrieval required that the suited astronauts work outside the space station for an extended period of time, one remaining just outside the airlock hatch at the airlock shroud work station with the other moving between the center, transfer, and Sun-end work stations to perform film replacement. Two film transfer booms were provided to transport the film magazines to and from the airlock shroud work station and the immediate  work area. Film was held to the booms by a special clamp.
Difficulties With Refrigeration
The refrigeration loop contained a valve which allowed the flow to pass through an external radiator when required by thermal conditions within the loop. The valve was automatically controlled and normally switched to the radiator flow mode for a portion of each orbit. During the deactivation period, the valve failed to operate properly when it was required to switch to the radiator flow mode. Signals received in Mission Control showed a sharp decrease in pressure across the pump and a reduction in temperature of the radiator surface during succeeding orbits. Temperatures in the frozen food compartments began to rise. The secondary loop was switched on automatically after temperatures increased within the loop, but it showed the same problems.
Engineers and technicians at the NASA centers and contractors' plants immediately began extensive ground testing to analyze the problem and to determine its effect on the mission. Tests showed up the most probable cause to be failure of the valve to close its bypass port completely.
The most logical cause, they determined, was particulate contamination of the valve seat. Moving the valve from one position to the other could possibly clear it. By ground command, both loops were cycled on and off. Cycling the secondary loop valve did not improve its performance. However, the primary loop valve opened enough to allow sufficient flow through the radiator to reduce the loop temperatures to the required values. Temperatures within the loop then remained within the specification limits during the remainder of the Skylab mission.
On June 22, with the command and service module checked out and working properly, and with all necessary equipment stowed for return, the crew undocked and carefully maneuvered their spacecraft about the Skylab, making final observations of its condition and photographing it from every angle. Then, they began their descent into the Earth's atmosphere and splashed down in the Pacific just 800 miles west of San Diego.
They had spent 28 days and 50 minutes orbiting the Earth, far longer than any men before them. During their 404 orbits, they had taken more than 25 000 photographs of the Sun and nearly 7500 photographs of Earth, a wealth of scientific data that would yield valuable information. Moreover, they had proved conclusively that man could live and work effectively in the space environment.