Medical experiments were one of the major justifications for the workshop from the outset, and Houston's medical researchers knew what they needed to investigate. The experiments defined in late 1966 sought answers to questions raised by experience in Mercury and Gemini: What changes does weightlessness produce in the human body ? How long do the changes go on? How does man adapt, if he does; and what can be done to counteract the changes if he does not?
Responsibility for developing the instruments to conduct these experiments lay with the Manned Spacecraft Center's Medical Research and Operations Directorate. Normally the physicians would have laid down the experiment requirements, while the Crew Systems Division and the Engineering and Development Directorate designed and built the hardware. But shortly after the medical program for Skylab was approved, the Apollo spacecraft fire threw all of Houston's arrangements askew. As one result, the medical experiments did not get coordinated attention from all Manned Spacecraft Center offices until 1969. Their development was plagued by technical problems-not unexpected, considering their complexity and novelty-that often threatened to delay Skylab's launch. Through a sometimes stormy four years, MSC and Marshall worked hard on these experiments; but the work paid off, for all of them functioned without major failure through all three manned missions.
Among the first experiments submitted for AAP missions were three medical studies: metabolic activities, cardiovascular function assessment, and bone and muscle changes. The first grew directly out of the unexpected difficulties the Gemini astronauts had with extravehicular activity and was designed to determine whether physical work was more demanding in zero g than on the ground. This experiment used a bicycle....
....ergometer, a highly instrumented version of an exercise bicycle, to measure the rate of energy expenditure during controlled exercise. The ergometer was to be used frequently during the missions so that trends with time could be detected, if they existed. The second study, cardiovascular function, assessed changes in the heart and circulatory system resulting from the absence of gravity. This required stressing the heart (which has less work to do in weightlessness and grows lazy) by subjecting the astronaut's lower body to a partial vacuum, simulating the effect of gravity in drawing blood into the legs. Changes in blood pressure, heart rate, and leg volume were telemetered to the ground, where physicians assessed the condition of the subject's heart and blood vessels. Supporting the medical experiments was a sophisticated system that supplied power, provided gases for the metabolic experiment and vacuum for the lower-body negative-pressure device, displayed certain critical data for the astronauts on board, and transmitted information from the experiment sensors to the ground.1 The third major experiment, bone and muscle changes, was the mineral-balance experiment described in chapter 7. At Headquarters and at MSC, aerospace medical experts spent much of 1967 defining the experiments in detail and selecting principal investigators for them. Not until November 1967 was the program organized, fully defined, and submitted to the Manned Space Flight Experiments Board for review.2
Engineering assistance was hard to come by at Houston in 1967 in the aftermath of the Apollo fire. Everything was subordinated to getting Apollo into shape and recovering time lost in the lunar landing schedule.
In these circumstances Dr. Charles A. Berry, director of Medical Research and Operations, was hard pressed to get the medical equipment built on time with the funds available. At a meeting of program officials at Kennedy Space Center in March 1968, Wernher von Braun suggested to Berry that Marshall could fabricate some of the equipment, saving time and money. Although von Braun carried away the impression that Berry welcomed such assistance, follow-up contacts indicated considerable reluctance. When von Braun formally proposed the arrangement, Gilruth s reply was polite and almost noncommittal. Berry had advised his chief that he was not convinced Marshall could meet MSC's requirements.3
Since everyone agreed that these experiments could easily become a pacing item for the program, Marshall wanted to help if possible. Talks continued into the fall, Marshall trying to get a commitment and MSC demanding detailed information as to how Marshall would conduct the project On 30 October 1968 the centers agreed that Marshall would build the ergometer (and the gas analyzer that went with it), the lower-body negative-pressure device, and the experiment support system. The dollar value of the project was not large (an estimated $4 million), but the engineering challenge was substantial and would extend Marshall's expertise into a new area. A task team from the Propulsion & Vehicle Engineering Laboratory, headed by Robert J. Schwinghamer, was established  and work got under way.4 The arrangement looked simple, but it turned out otherwise. It was hard for one center to direct another as it would a contractor, and during the next few years relations were occasionally strained. But in the afterglow of a successful program, most participants agreed that the strains had produced a creative tension that resulted in first-class equipment.5
While one group at Marshall worked on medical experiments, another group was coming to grips with a more complex problem: providing a system for waste management in the workshop. The problem had new dimensions in Skylab. Previous programs had required no more than a sanitary method of collecting and disposing of body wastes with a minimum of handling; but for Skylab, the medical experiments required collection, measurement, and return of both urine and feces for analysis. Gemini and Apollo systems would not do, even if-as they were not-they had been ideal from the user's point of view.6
The design of a system to collect and measure urine was driven by two considerations: the requirements of the mineral balance experiment and the astronauts' insistence on a system that was easy to use and failure-proof. As the medical requirements stood in late 1968, each urine void had to be measured with an accuracy of 1%, a sample ( 10%) of each void had to be collected and dried, the solid residues being combined daily. The system had to prevent contamination of one crewman's urine by another's. Each day's samples were to be tagged with identifying data: who, when, and how much. At the end of a 28-day mission, a Skylab crew would have something like 540 grams of neatly packaged urine solids to bring back to the labs.7
The engineering problems involved in collecting liquid, separating it from air, measuring it, and accurately sampling it, all in zero g, were formidable. Only two systems were available: one that the Fairchild Hiller Corporation had devised for the Air Force's Manned Orbiting Laboratory and one that the General Electric Company had developed for the Biosatellite program, where the subject was a seven-kilogram monkey. While GE's prototype could measure volumes within 0.2%, Fairchild Hiller's was designed for only rough volume measurements. Marshall believed the Fairchild Hiller system would be easier to develop in the time available, but MSC's medics did not think it could meet their requirements for volume measurement and sampling. They were willing to wait for comparative test results, but wanted the GE system kept under consideration. In spite of Houston's warnings, Marshall took the advice of McDonnell Douglas, prime contractor for the MOL as well as the Skylab workshop, and decided to adopt the Fairchild Hiller system.8
 By early 1969 the medical experimenters were reconsidering their requirements. In January word got back to Marshall that investigators wanted to collect all the urine for a 24-hour period, mix it, measure it, and take out a sample to be frozen. Pooling before sampling would reduce the chances for error in measurement; the change to freezing arose out of concern for the stability of some urine components. Organic compounds....
 ...(hormones and steroids) would be partially destroyed by the conditions of drying Marshall proposed to use (heating to 60° C under vacuum). Principal investigators feared their results would be challenged by other researchers unless the samples were preserved by a standard method, and freezing was the only accepted method.9
Since no freezer was planned for the workshop at that time, Marshall took strong exception to this costly and time-consuming change. Besides, Fairchild Hiller's medical consultants insisted that drying was perfectly adequate. MSC challenged this assertion vigorously at the preliminary requirements review for the habitability support system on 25 March 1969; Marshall proposed a study to prove the point, and MSC agreed. McDonnell Douglas was directed to compare drying with freezing to verify that vacuum drying would not alter the urine components- or if it did, to show that the changes were predictable. After MSC reviewed the contractor's test proposal, an independent analytical laboratory was picked to conduct the test. It was expensive and would take time, but Marshall engineers felt that if an independent study killed the requirement for a freezer, the time and money would be well spent.10
Houston was equally determined to establish freezing as the method for urine preservation. Early that summer, Bob Thompson emphasized to Belew that the only acceptable procedure was to chill the urine immediately after collection, sample it, and freeze the samples for return. When in July the centers agreed to provide for frozen food in the workshop McDonnell Douglas was directed to resume preliminary design studies on a urine freezer. Paul Rambaut, MSC's principal coordinating scientist for the urine experiments and deeply involved in both the waste management and food systems, saw considerable irony in this turn of events. While the scientists concerned with urine constituents unanimously agreed that urine samples must be frozen, nutritionists equally agreed that frozen food was not required. Yet the food freezer was accepted with little resistance from the engineers, while the urine freezer was strenuously opposed.11
Throughout the summer, Houston's medical directorate was skeptical of Marshall's intentions, suspecting that the effort to provide a urine freezer was not being pursued seriously. They continued to warn their center's Skylab office that even if the study showed drying to be acceptable, it was still "open to suspicion because it is not the standard approach used by the authorities in these fields of investigation." As far as other aspects of the Fairchild Hiller system were concerned, the medical experimenters had no confidence in its method of volume determination and they began to investigate an alternative technique using a chemical tracer.12
In late October 1969, Bill Schneider decided to try to resolve these questions. He called Headquarters and center program officials to  Huntsville on 21 November for a discussion of the issues. The test results on the two urine preservation methods were not yet available, but preliminary indications were that freezing was no better than drying. After examining the engineering tradeoffs, Schneider reaffirmed current plans, but allowed the freezer study to continue. Dismayed by this decision, MSC's medics asked for another review. In Houston on 18 December, Marshall reviewed the experiment requirements that MSC had established, pointing out that freezing was not specified. After reviewing the engineering considerations and test results, Marshall made its recommendations: stay with the present system (drying), stop all work on sampling and freezing, and go on with urine storage tests to establish the rate at which the heat-sensitive components were lost with time. Once more, Schneider saw no reason to change to freezing. All Houston could get was an agreement to have Fairchild Hiller's test results reviewed by an independent consultant and to study the impact of sampling and freezing on workshop systems. Directing Marshall to start this study, Schneider emphasized that if a change to freezing caused a schedule delay, Marshall was to find a way to work around the bottlenecks and keep the workshop on schedule. On 30 December Marshall ordered McDonnell Douglas to do the study.13
During the next three months, Fairchild Hiller and its subcontractor, Bionetics, Inc., of Bethesda, Maryland, completed the studies on drying versus freezing. MSC methodically pecked away at the results and statistical analysis. The test results seemed ambiguous. Fairchild Hiller's program manager admitted as much on submitting the final test report: "In effect the statistics are a draw." But MSC had run some tests of is own, which showed greater loss of hormones in dried samples than Bionetics had found. After the February meeting Paul Rambaut summarized the situation and recommended that the drying process be dropped once and for all. Severe and unpredictable deterioration of the heat-sensitive compounds did occur, and (once more) no recognized expert considered heat-drying to be acceptable for the proposed study. Acknowledging the engineering problems that Marshall faced in providing for freezing, Rambaut nonetheless saw nothing to be gained by further attempts to qualify the drying process for the Skylab missions.14
With the results in, Schneider convened one last meeting on 10 March to consider their implications. Though Huntsville stuck to its guns, it could not rebut Houston's arguments. (Marshall had not had time to do its own statistical analysis of the Bionetics results.) Houston's tactics and arguments finally prevailed, and Schneider ordered an immediate change in the urine processing system to provide for freezing the samples.15
In retrospect this was probably the most vigorously contested point in the entire workshop program. Stan McIntyre, Marshall's project  engineer for the urine system, later summarized his center's view. "We knew that when we went into the complexities of pulling samples, handling fluids m zero g was going to be a complex gray area that nobody had ever been in." Rather than tackle that job they elected to avoid it, and their contractor's scientific adviser assured them that drying would satisfy the medical objectives. Berry, on the other hand, insisted that MSC knew all along that the Fairchild Hiller system would not work, and he so warned von Braun. What irritated Berry most, however, was the engineers' insistence on arguing with medical experts about what was essentially a medical question. In the end, though Marshall accepted the change, Skylab engineers were not convinced. The workshop project manager at Huntsville commented four years later, "to my dying day I'll always say we should have dried the urine instead of freezing it.''16
With the freezing question settled, attention turned to volume measurement. The experimenters wanted the total daily urine output measured within 2%-a difficult goal, since liquids collected in zero g always entrap gas. Fairchild Hiller's system employed a synthetic membrane made up of microscopic fibers of liquid-repellent material, permeable to gases but not to liquids. A section of the urine collection bag was made of this material, and the company's engineers had designed the bag (so they assured McDonnell Douglas) so that surface tension would separate liquid from air. With the bag properly oriented, a squeezing device forced air out through the membrane while the urine was retained. The volume of liquid was measured by determining its thickness while the bag was confined in a box of fixed length and width. General Electric's system used a different principle; it separated air from urine with a centrifugal separator and used a peristaltic pump to measure volume and collect a proportional sample.17
In the spring of 1970 program officials began evaluating the two systems. McDonnell Douglas tried hard to sell the Fairchild Hiller system; Houston's medical team strongly backed the GE device, partly because they felt it offered better prospects for future development. Marshall's program officials might ordinarily have gone along with their prime contractor, but seemed skeptical of Fairchild Hiller's scheme; and they might have thought it prudent not to start another argument with Houston. At a review on 3 April, the GE system seemed to have clear technical advantages, but company representatives appeared reluctant to undertake development of the system for Skylab. McDonnell Douglas vigorously defended its subcontractor's system, asserting that it could "easily guarantee" an accuracy of 1% in volume measurement. MSC evidently could not persuade General Electric to compete, so in May the Fairchild Hiller system was selected for development and testing.18
When Fairchild Hiller's collection bag was tested in zero-g aircraft flights, however, it failed. The liquid-impermeable membrane did not  function after prolonged contact with urine, and the bag would have to store urine for a full day during operations. For all the confidence the company had in its analysis of the forces acting on liquids, urine might nevertheless come in contact with the filter. The small unbalanced forces always present during zero-g aircraft maneuvers were enough to cast doubt on the whole concept. The company proposed a number of remedies, but all would take time. 19
Center and contractor engineers spent a busy September trying to devise alternatives or to fix the system they had. Three major meetings during the month did nothing to raise confidence in it, and a proposal to use two bags, one for collection and another for measurement, created new problems. Headquarters, meanwhile, had learned that fluid-mechanics experts at Langley Research Center were working on gas-liquid separation in zero g using a centrifugal separator. Preliminary discussions between Langley and Marshall indicated that Langley's device was worth further examination.20
After reviews, meetings, and studies during October, Schneider, Belew, and Kleinknecht decided to continue working on three systems (the original one-bag design, a two-bag design, and the centrifugal separator) until one showed distinct advantages. Since the question of volume measurement was still in doubt, MSC was directed to report on the tracer method and to make recommendations for its possible use, either as a backup or as the primary method.21
Slowly, during the next several months, the centrifugal separator pulled ahead. Zero-g tests in November revealed that the two-bag system was seriously flawed. As 1971 began, Belew told Schneider that the one-bag system no longer seemed worth working on, and Houston decided that only the centrifugal separator would satisfy all major experimental and operational requirements. On 15 January, the three program offices agreed to drop the one-bag system and concentrate on the other two, which, they stipulated, must be interchangeable so as to simplify integration. Hamilton Standard, a firm that had worked with MSC in the Apollo program, was awarded a letter contract to develop the Langley separator. Belew notified Schneider that if neither system developed serious problems a decision would be made in September.22
By May, however, Stan McIntyre was convinced that the two-bag system was beyond salvage and recommended dropping it. In spite of changes in material and bag design, the filter was "basically unreliable and not suitable for Skylab." A review on 28 June showed that keeping the two-bag system, even as a backup, entailed a cost increase of at least $1.5 million. On 21 July Marshall ordered the workshop contractor to stop all work on the two-bag system. The centrifugal separator was selected in its place.23
Houston, meanwhile, had been working on the tracer method for  volume determination. The principle is simple: a known quantity of a substance not normally present in urine is placed in each collection bag before use; after the bag is filled and the tracer thoroughly mixed, a sample is taken; the fraction of the tracer found in the sample is the same as the fraction of the total urine volume represented by the sample. If the sample contains 1% of the tracer element, then the sample volume is 1% of the total volume. Lithium was chosen as the tracer element. A small amount of lithium chloride would be put in each collection bag. As part of the normal processing procedure, the contents of the full urine bag would be recirculated through the centrifugal separator, thoroughly mixing the tracer with the urine. Having satisfied themselves that the method gave the accuracy they required, MSC's medical experimenters adopted it as the backup method to verify volume measurements made in flight.24
Compared to the urine system, the design of a collector for solid waste was simple. All feces were to be collected, vacuum dried-heating was no problem in this case-and returned for analysis. Again, Fairchild Hiller had developed a system for the Manned Orbiting Laboratory; this one proved satisfactory for Skylab. The collector was a plastic bag fitted with a porous filter to allow passage of air. It was enclosed in a holder beneath a toilet seat; behind the holder was a blower that pulled a current of air through holes in the rim of the seat, carrying the feces into the bag. The air from the blower passed through a deodorizing filter and back into the workshop. The bag was then weighed, placed in a processor where the feces were heated under vacuum to remove moisture, and stowed for return.25
Since the problems of separating air from liquid and of volume measurement did not arise with solid wastes, the fecal collection system was in good shape by the end of 1969. Its principal problem arose out of the difficulty of conclusive testing in zero g. The zero-g condition could be maintained for only about 30 seconds in the KC-135 aircraft, and the device had to be tested in that short period. Urination could be successfully simulated by mechanical devices, and a urine-collecting device was easy to test; but defecation could not be simulated. Test subjects who could perform on cue were needed. The Huntsville program office was able to find a few people with this talent, and in November 1969 two days of aircraft testing produced nine good "data points" for the fecal collector.26
Still, aircraft testing was not absolutely conclusive, and in January 1970 Marshall's Skylab office started lobbying for a flight of the fecal collector on one of the Apollo missions. In July the Apollo program office agreed to a test flight on Apollo 14, only to reverse that decision later in the summer. The unofficial account that got back to Marshall was that MSC's Skylab office supported the test, the astronaut office was officially indifferent to it, and the commander of Apollo 14 flatly vetoed it. Marshall had to make do with aircraft testing.27
From the Marshall director's vantage point, building experiment hardware for MSC looked like a straightforward job. The Biomedical Task Team would fabricate some components in Marshall's shops (the ergometer frame and the shell for the lower-body negative-pressure device), contract for others, and assemble and test the final articles to Houston's specifications. The agreement hammered out by the two centers specified that Marshall would function "in the same manner as would any other contractor," with MSC managing the contract in the customary way. Missing, however, were the incentives and penalties that a NASA center could apply to a commercial contractor in a similar situation.28
Houston's medical directorate was responsible for management and technical direction of Marshall's task team, while the Skylab office retained "overall Center management including verification of requirements and resource management. " The medical directorate supplied technical direction and information; integration requirements were to be exchanged through the two center program offices. As events of the next two years would show, this arrangement was unwieldy. Lines of authority and supply were complex, and it was sometimes difficult to tell exactly who was in charge at MSC. Management problems thus complicated the technical snags that Marshall's task team encountered.29
The critical experiment was M171, metabolic activity, which measured the body's rate of energy production while physical work was being done. A bicycle ergometer provided several calibrated levels of resistance against which the astronaut could work, while his energy production was measured by the ratio of carbon dioxide exhaled to oxygen inhaled. Building the ergometer presented no special problems, but the system to measure respiratory gases did. It required accurate flowmeters, precision valves, and a high-speed gas analyzer-all of them at the leading edge of technology and all of them interacting with a specialized computer and data-transmission system.30
Faced with a short development schedule for a complex set of experiments, Houston's medical directorate wanted to look at more than one design. For the gas analyzer the medics had settled on a mass spectrometer, an electromagnetic instrument that sorts out gases according to their molecular weights and determines the percentage of each gas in a mixture. During 1969, Marshall's biomedical task team was evaluating one mass spectrometer design while Houston's Skylab office was discussing another with Martin Marietta. In September a third choice entered the picture when MSC's Biotechnology Division found that a mass spectrometer was being developed by another office for another purpose and recommended that it be adopted for the metabolic analyzer.31
While the medical experimenters tended to let developmental work continue in the hope that one design would show clear advantages over the  others, the Houston Skylab office had to meet a schedule. In April 1970 after the three designs had been compared, Houston program manager Kenneth Kleinknecht chose the design Marshall had been backing. Noting that this unit would meet the stated medical requirements and that a great deal of money had already been spent, Kleinknecht sought assurance that Marshall wanted to finish the job. When he got it, he stopped development work on the other two instruments.32
In early 1970 the other medical experiments were having a number of management difficulties. Marshall and Martin Marietta, the workshop integration contractor, could not agree as to who should integrate the Marshall-built medical experiments with the experiment support system, which was also a Marshall responsibility. Reporting to Huntsville's program office, Marshall's representative in Houston noted that the medical directorate and the Skylab program office at MSC were not communicating very effectively. And at Huntsville, Robert Schwinghamer's task team felt that the medical directorate was not coordinating its directions to them. Schwinghamer complained more than once that he was getting conflicting instructions from different people at MSC.33
Schedule pressures undoubtedly contributed to the confusion in the medical experiments program, because in July 1970 the medical directorate formally requested relief. As the schedule stood, development test units for the experiments-prototypes that would be tested to uncover faults in design or construction-had to be delivered in October 1971,13 months before launch. Flight units, modified as a result of these tests, were required a month later. That single month was certain to be inadequate to correct deficiencies. The unrealistic schedule might well force compromises in design and testing, degrading the value of the experiments. The medical investigators expected, under those circumstances, that sooner or later they would be told to fly the experiments in whatever shape they were in, simply because it was launch time. In their view, however, the schedule should yield to mission objectives; there was no point in launching hardware that gave less than complete results. When the medical directorate proposed a launch delay, it was disapproved; but the deadline for the metabolic analyzer-the biggest worry-was relaxed to allow necessary testing, so long as delivery of the completed workshop was not delayed. The workshop contractor would have to work around the missing experiment as best he could.34
Reviewing the state of the medical experiments that summer, medical director Charles Berry and center director Robert Gilruth decided that some engineers were needed to improve liaison with Marshall. In September, Gilruth announced the appointment of Richard S. Johnston as Berry's deputy director for biomedical engineering and acting chief of a newly formed Skylab Project Support Office. Johnston had been chief of the Crew Systems Division in the early days of AAP, then special  assistant to Gilruth for two years, and in 1970 was experiments manager for Apollo. After spending some time mastering the complexities of the management arrangements, Johnston brought in several engineers to expedite the translation of medical requirements into hardware. By the end of 1970, management problems were a much smaller annoyance than before.35
Marshall's first milestone was the production of design verification test units, which would be put through tests duplicating their expected use to discover deficiencies in design or construction. The verification testing was originally scheduled to begin in October 1970 and run until July 1971, but it actually began only in February 1971. In the next three months, six weeks of test activity were lost on account of failures in components supplied by MSC contractors. By mid-May Huntsville officials were expecting to resume tests shortly, but new requirements imposed by MSC promised to extend the test program into 1972.36
Assembly and testing continued through 1971, working toward a deadline of 15 January 1972 for delivery of all flight hardware to McDonnell Douglas. Troubles with electronic modules, however, continued to plague the project, notably the leg-volume measuring device manufactured by Martin Marietta. The metabolic analyzer, too, began acting up. By mid-summer 1971 only the bicycle ergometer and the lower-body negative-pressure device were comparatively trouble-free. In June, when MSC wanted two components removed from the metabolic analyzer test unit for examination by the manufacturer, Schwinghamer reported that this halted progress in the most successful test program to date.37
Late in September two "NASA alerts," agency-wide warnings about defective components, called attention to recently discovered malfunction of electronic parts, among them capacitors and integrated circuits similar to some already built into the metabolic analyzer. The capacitors were checked and replaced, but the integrated circuits-there were nearly 200 of them-completely stalled the program. Not enough acceptable replacements could be found anywhere in the country; delivery of new ones would take from 12 to 20 weeks. Testing went on with the units as built, but plans had to be made to replace the suspect components and retest the equipment further down the line. At year's end Huntsville notified McDonnell Douglas that flight articles would arrive 2 to 4 weeks late.38
Other factors now began to impinge on the medical experiments, particularly Houston's plans to simulate a 56-day Skylab mission, using the medical hardware. To be of any value, this had to be run well in advance of the first mission, and it required functioning experiment equipment. And at McDonnell Douglas's California plant, assembly and checkout of the workshop had reached a point where technicians were having to work around the missing medical hardware.
Late in January 1972, MSC requested authorization to postpone completion of tests and delivery of hardware as much as six weeks  Schneider approved the request in part. Deliveries might be put off, but he would not agree to delaying the test program and told the centers to find a way to complete it. By now Schneider was contemplating dropping the troublesome metabolic analyzer altogether and asked MSC to estimate the impact of such a step. Both the medics and the program office objected vigorously; all the experiments were mandatory, and the metabolic analyzer's problems could be solved. Evidently Schneider accepted their evaluation, for the subject was not raised again.39 Marshall found a way to substitute one metabolic analyzer unit for another so that the M171 equipment could be delivered in late February. Flight units of the medical equipment began arriving in California in February, the metabolic analyzer on 13 April. There was a lot of integration and testing yet to be done, but the hardest work was behind.40
Since 1968 Houston's medical directorate had been considering a full simulation of a 56-day Skylab mission. Primarily the doctors were worried about changes in the microbial population when three men were confined in close quarters; they wanted no flare-up of bacterial infection, either during a mission or after the crews returned. Besides, a properly conducted simulation would give them one-g data from the medical experiments, useful in assessing changes brought about by weightlessness, and would check out the experiment procedures and equipment. Early in 1970 MSC petitioned Headquarters for funds to conduct a full-dress mission simulation.41
Houston's plans, however, were too ambitious for Headquarters' purse, and after some months of discussions a modified plan was submitted. Instead of two flight-configured Skylab mockups, MSC agreed to use an existing altitude chamber equipped with flight-type medical hardware and waste-management systems and using flight food. The bacterial ecology question was dropped; the new plan was intended to check out the hardware, establish baseline medical data, and verify experiment procedures and data-handling systems.42
After getting approval for this proposal in February 1971, the medical directorate got busy organizing the Skylab Medical Experiments Altitude Test, known thereafter as SMEAT, a pronounceable if unintelligible acronym. SMEAT was to be the only mission-length simulation in Skylab's entire experiment program, and Houston organized it thoroughly. A steering committee chaired by Richard Johnston oversaw the entire operation; four test-project managers were responsible for various aspects of the test, and they worked with medical teams, principal investigators, and flight operations and crew training personnel.43
Crew Systems Division's altitude chamber, which approximated  Skylab's size and shape, was configured to duplicate the orbital workshop as nearly as possible. The lower level was laid out with the wardroom and food preparation area, the medical experiments, and the waste management compartment. The one-g environment imposed some limitations; crewmen could not sleep against the wall as they would in flight, and the waste collection module had to be on the floor, not on the wall as in the flight workshop. The upper level, occupied in Skylab by stowed equipment and experiments, was used as a study area during the simulation. Since the medical experiments did not take up all of the crew's time, they planned to occupy their off hours by studying Russian and reading.44
Outside the test chamber, medical operations personnel would monitor the performance of the medical experiments, taking data just as they would during the mission. Communication with the crew was intermittent, corresponding to the actual times that Skylab would be in touch with a ground station.45
In mid-1971 a SMEAT crew of two pilots and a scientist was picked. Lt. Cmdr. Robert L. Crippen, USN, and Lt. Col. Karol J. Bobko, USAF, both ex-MOL astronauts who joined NASA in September 1969, became commander and pilot; they were joined by scientist-pilot William E. Thornton, a physician and biomedical engineer from the scientist-astronaut group picked in August 1967. Of the three, only Thornton was directly involved in Skylab at the time; he was one of the principal investigators for the small-mass measurement device to be used for weighing specimens in flight.46
After a year of preparation, Crippen, Bobko, and Thornton were locked into the chamber on 26 July 1972 for their eight-week stay. Since both crew and operations personnel had much to learn, there was no lack of activity to fill the time. It took a few days to get routine working relationships established and straighten out procedures. As would happen with the flight crews a year later, the SMEAT crew found that they got along well enough with each other, but developed a certain "us versus them" feeling toward those outside. Most of their problems were normal and predictable: poorly-fitting medical sensors, lack of familiarity with some equipment, procedures that had to be modified; and these were ironed out. The crew found the environment tolerable if not luxurious, the food good if not exciting. There was plenty to do and no idle time to speak of, though they did find time for an hour or so of TV a day- commercial channels were available-and they could call family and friends on an outside telephone line.47
Though most of the problems in SMEAT were small and easily corrected, some very big ones proved the simulation's value. In the very first days the bicycle ergometer broke down and the metabolic analyzer was consistently erratic. Worse yet, the SMEAT crew uncovered faults in the urine collection system that threatened to require substantial redesign of the whole unit.48
 With launch only nine months away, MSC and Marshall immediately began troubleshooting the ergometer and the metabolic analyzer. The ergometer failure proved to be a mechanical design problem unique to the test unit; when this was corrected it functioned as intended. (Still, the other units-one of them already installed in the workshop-were torn down, examined, and rebuilt, and spare parts were included in the flight inventory.) The metabolic analyzer's problems were more complex, involving both mechanical and electronic failures. A meeting in late September prepared a list of essential changes and tests, and Marshall began reworking the units.49
Problems with the urine system were potentially very serious. The two-liter collecting bags were too small. Indications of this shortcoming showed up in pre-SMEAT activities; and during the simulation it turned out that one crewman's normal daily urine output was nearer three liters than two, and both of the others produced more than two liters occasionally.i This was not a problem for the SMEAT crew because they had other toilet facilities, but it was desperately serious for the engineers. The urine pooling bag and its mechanical accessories took up every cubic centimeter of the space allotted to it. Increasing its capacity looked all but impossible.50
A second SMEAT problem was, from the crew's point of view, even worse. The urine centrifuge leaked, and the collection unit could not be cleaned up completely. On six occasions, collection bags were torn in handling, dumping a liter or more of urine into the waste-collection unit, onto the floor, and onto the crewman. Astronauts were already concerned that the system seemed too complex and had not been adequately tested in zero g; these urine spills were very nearly the last straw. Pete Conrad, who would command the first Skylab mission and who was in training at the time, lost all confidence in the system. He began working with Houston engineers to adapt the system that was about to fly on Apollo 17 and indicated that he was quite prepared to abandon the Skylab system entirely. For a time, relations between engineers and crew representatives were strained.51
Meanwhile, tests at McDonnell Douglas had turned up an entirely unrelated defect in the urine system. The in-flight volume-measuring system, a complex device with a pressure plate and several mechanical linkages, did not meet the accuracy requirements. With launch now only six months away, the urine system seemed to need complete redesign, or the medical requirements had to be reconsidered-or both.52
 A week after SMEAT ended, a telephone conference between Headquarters, Houston, and Huntsville led to agreement on expanding the urine system's storage capacity to four liters. Three options for design modifications were defined for study, two of which bypassed the centrifuge entirely and relied on the Apollo 17 system. Two weeks later, however, a consensus developed for a two-way system, using a four-liter bag but giving the crew a choice of collecting devices, the Skylab centrifuge or the Apollo roll-on cuff. ii It was generally agreed that measurement of volume in flight could be dispensed with, since the lithium chloride tracer technique was adequate. These changes allowed the urine collection drawer to be simplified, leaving room for the larger bag as well as a protective metal box to enclose it. Mixing the 24-hour pooled urine, however, would have to be done by kneading the bag by hand rather than by recirculating its contents through the centrifuge. By 15 November, three and a half months after the problems came to light, an acceptable design was critically reviewed and modifications were going forward.53
Commenting on the significance of SMEAT at its conclusion, Dick Johnston expressed the conviction that it saved the program, since serious operational problems would have come up in flight with no way to solve them. Both he and Ken Kleinknecht acknowledged the problems to the press, but both were sure that they would be worked out. When the waste management system finally flew, the grueling four months of work after SMEAT paid off. The urine system and the medical hardware worked exactly as required. Redesign of the urine system was justified, because two crews had at least one member who consistently excreted more than two liters of urine a day. Experienced crewmen found the system a great improvement over what they had used before. The rookies, who had heard all the horror stories about waste management, were pleasantly surprised. And after all the tumult and shouting, Pete Conrad took particular care to compliment the engineers on an outstanding system. 54
i The bag size was based on physiological norms, not on measurements taken with crewmen. When the system was designed the crews had not been selected. Requests by medical investigators to measure 24-hour urine output for the astronauts were turned down by the astronaut office because it would interfere with training. Carolyn Leach interview, 3 Dec. 1976.
ii This was a rubber tube that functioned as an external catheter and was attached to a collecting bag. It amounted to a heavy condom. R. S. Johnston, L. F. Dietlein, and C. A. Berry, eds., Biomedical Results of Apollo, NASA SP-368 (Washington, 1975), p. 475.