How It All Turned Out: Results

How did it all turn out? All nine astronauts returned to Earth safely, and all but one are alive and well, over three decades later. The exception is Pete Conrad, who was healthy and vigorous until his tragic death in a motorcy­cle accident in 1999. But did the Skylab team accomplish their goals? Did they measure the right things and measure them accurately? Were they able to draw conclusions? And did they discover what’s needed to keep people well and effective in space?

First, all the equipment worked. Food was consumed, uneaten items logged, supplement pills taken. Urine was sampled and frozen; feces were proper­ly processed and dried; both were correctly returned. Exercise was accom­plished once it was learned how; oxygen consumption and vital signs were duly recorded. Lower body negative pressure and rotating chair devices did not fail. Nine men were measured as never before. And it’s a good thing they were because NASA remained conservative and skeptical till the end. Dur­ing the final flight, the NASA administrator required a weekly report—on Wednesdays, and in writing—that the crew was in good condition and cer­tified to go another week.

In spaceflight, the first symptom to show up is usually space motion sick­ness. The term was bowdlerized to “space adaptation syndrome” by some thoughtful researchers, but some irreverent crewmen called it dreaded space motion sickness, or “dsms” for short. It’s a lot like seasickness, and a severe case can make you miserable. A problem with treating motion sickness is that if you are already sick and take a pill, you’re likely just to throw it up. Shuttle crewmembers who get spacesick are now given injections to con­trol their symptoms. The drug, promethazine, is quite effective but makes you sleepy.

The odd thing is that a person’s susceptibility to motion sickness on Earth has no predictive value in space. You can be quite sensitive in boats or cars and never have a quiver while weightless, or the reverse. But repeated flights tend to diminish the severity of the illness. And after it goes away, usually in three or four days, zero-G is a lot of fun.

The Skylab I crew had no space adaptation syndrome during flight. Ker – win got seasick after splashdown and threw up in sickbay on the carrier, but seasickness was not unusual for him. The most surprising finding was that the rotating chair experiment showed that the crew was immune to motion sickness in flight once they had adapted. Kerwin said, “I think life on a rotating spacecraft will be easier than I thought.”

Once they learned how to ride the bicycle ergometer in zero-G, their per­formance matched their preflight levels. In between medical runs, Conrad exercised the most, Kerwin the least. In contrast with exercise, the lower body negative pressure experiment was much more stressful right from the

first run. Heart rates were higher, blood pressures dropped, and several runs were terminated early to make sure the subject didn’t pass out. Kerwin was the most susceptible. This was a concern early in the flight, but subsequent runs showed no further deterioration in performance.

Those three experiments were the main source of in-flight data on adap­tation — or deterioration—and the overall picture looked good. Also the crew ate well, slept well, and felt well. The physical work involved in their spacewalks gave them no trouble. Twenty-eight days in space seemed quite feasible. How would they react to gravity after landing?

Here are the basic findings. The crew had lost an average of 7.5 pounds of weight. They were unsteady and walked with feet wide apart. They were most comfortable lying down. Standing heart rate was 30 percent high­er than preflight. Ability to exercise on the treadmill was correspondingly lower; each of those heartbeats was moving less blood through their arter­ies. Treadmill performance on landing day did correlate with in-flight exer­cise; Conrad did best, while Kerwin was too tired to use the ergometer at all until the next morning. Response to the first lower body negative pres­sure test was just about the same as to the last in-flight test — worse than preflight. Blood tests showed that blood volume was down, and the num­ber of circulating red cells was smaller by 14 percent—the bone marrow was not producing them at all. Finally, postflight strength measurements on the arm and leg muscles showed big decrements.

Return to normal was relatively rapid. The crewmen ate and drank vig­orously after their first good night’s sleep, and much of the weight loss had been restored by the fifth day back. Performance on the lbnp and ergom­eter was close to normal preflight limits in a week, and completely normal in three weeks. Full leg strength returned more slowly, depending on what exercise the men chose to perform.

Some questions remained. Their bone marrow didn’t start to produce red cells again until about three weeks after landing. Imaging wasn’t sensi­tive enough to show visible bone loss, but examination of the returned urine and feces showed that they were losing calcium steadily with no sign of lev­eling off. The in-flight cardiovascular data from lbnp could be interpret­ed as “not yet steady state.” And the large losses in arm and especially leg strength were a sign that the crew hadn’t exercised enough. The next crew was strongly urged to do more.

Skylab 11, unlike their predecessors, faced space adaptation syndrome on Mission Day i. Lousma was most affected and vomited that evening. Bean and Garriott felt nausea; all three took Scop-Dex capsules on Day 2 to sup­press the symptoms, and Garriott and Lousma continued this medication on Day 3. Garriott and Bean tried making head movements to hasten their adaptation but decided they were not helpful. All were well enough for full duty by Day 4.

Initial adaptation issues aside, this crew’s in-flight experience was similar to that of the first crew. The big change was that they performed more exer­cise and did not allow exercise time to be preempted by other tasks as the first crew sometimes had. They launched with two additional exercise devic­es. After seeing the first crew’s strength losses, Bill Thornton got permission from Deke Slayton to add capability, with strict weight and volume limi­tations. (Exercise was still an operational responsibility.) Bill looked every­where for candidates, and found the Mini-Gym in John Rummel’s back room. He rebuilt it with help from center engineering and flight-qualified it. It was designed to produce “isotonic” loads on the back and legs, and was used faithfully by the crew during longer daily exercise periods. The other device was an “expander” from Sears, consisting of up to four springs with handles that could be used in various combinations. (The Russians cop­ied this device and used it in their Soyuz program for many years.) These devices largely solved the upper-body problem. The second crew also had a device to measure blood hemoglobin levels, to reassure the doctors that loss of red cells was not continuing.

Skylab II returned to Earth on 25 September 1973 at nineteen past one in the afternoon, and the Command Module was picked up by the uss New Orleans forty-four minutes later. Here’s some conversation between the crew­members and the crew Flight Surgeon, Dr. Paul Buchanan, as they pre­pared to egress:

Bean: “We’re going to have to be careful; as I said, I was dizzy. Better stick with me. But I feel like if I could move around, just sit up, and maybe the dizziness would go away.”

Garriott (who had already left his couch and taken the pulse of his crewmates): “I don’t think it will, Al. You ought to watch for it to increase slightly. It’s likely to increase, I think.”

Buchanan (to Garriott): “Are you doing all right standing?”

Garriott: “I’m doing fine, but I can tell that any sort of motion induces the sensation of pitching or rolling, a little dizziness.”

Bean: “That’s what I thought when I just leaned up. I thought that I didn’t feel like I was going to pass out, but I did feel like—that I would be unsta­ble. . . . Let’s not leave these guys standing out here too long.”

Bean (ten minutes later, in the medical lab): “I didn’t think we’d get back feeling this good.”

They did feel good, and they recovered rapidly from the effects of their flight—Garriott fastest. Their weight losses had been for Bean, 8.6 lbs. (5.5 percent); Garriott, 7.7 lbs. (5.7 percent); and Lousma, 9.25 lbs. (4.75 percent). By “r+5,” the fifth day after landing, their lower body negative pressure and exercise tolerance tests were “within normal limits”—that is, back with­in two standard deviations of their preflight results. That’s not 100 percent recovery, but it’s impressive. After R+9, Garriott and Lousma were returned to flight status in the T-38. Bean had strained his back on r+i (showing that muscles were a little more susceptible to injury after a long flight) and didn’t get back to flying for another week or so.

Loss of strength and endurance in the legs was virtually the same for this crew as for the first crew. That was a very encouraging finding and a worth­while payoff for the additional time this crew spent on exercise (about an hour a day each). But the decrements were still on the order of 20 percent, and Bean’s crew recommended to Carr’s that they increase exercise even more on their flight, then being extended to eighty-four days.

Although legs showed a decrement with their diminished use in weight­lessness, the arms were different. They were not only used for translation around the workshop, but there were two useful exercise machines available for heavy exercise. Jack was a consistent user of this hardware and his early postflight data show an average 15 percent increase in arm strength, while his two crewmates showed little change.

And that is when Dr. Bill Thornton, who was making the strength mea­surements, invented his “Thornton treadmill.” Faced with even more strin­gent limitations on what could be launched in the Command Module, Bill Thornton and engineering built the poor man’s treadmill from a strip of slippery Teflon, which could be fastened to the Skylab floor with fasten­ers already on board. The crew placed the Teflon near a side wall with a handrail to hold on to. Wearing cotton socks and the previously discarded

ergometer waist restraint, fastened to the floor with 180 pound-force bun­gees, they canted their bodies about thirty degrees forward and “ran,” feet slipping on the Teflon surface. It was much harder work than running, but it did the trick.

The Skylab ill crew lived longer in space than anyone had before—a lot longer—and spent more time and concentration thinking about the lack of gravity and its effect on their body and their performance. For the first month they felt rushed and behind and didn’t get enough sleep. After that they settled into a productive routine. How did they feel about it? Here is what they shared during the medical debrief:

Question: “When did you think you were in control of things and every­thing was ok?”

Ed: “Somewhere between four and six weeks. At four weeks we were over the hill and I think had started to settle down and by six weeks I felt locked in solid.”

Jerry: “If you drew a graph from launch day, you would have a fully steep slope and the graph would bottom out the day the three of us bombed out on M092 (for Jerry, that was on Mission Day 16, i December). And from then on, you can chart a gradual increase with a fairly reasonable slope until prob­ably Day 45, and then you could throw a gentle knee into it. Again there’s a positive slope, and we were on the increase all the way to the end.”

How stressful was the lower body negative pressure experiment? All three men came near to fainting on tests run during the tenth to sixteenth flight day. For these tests another astronaut was always assigned as an observer, able to watch the subject’s signs and terminate the tests if warranted. The test involved subjecting the subject’s lower body to a partial vacuum. There were three steps of increasing vacuum: minus thirty, forty, and fifty milli­meters of mercury, the latter estimated to pull blood into the legs about as much as standing quietly upright in normal gravity. These tests were ter­minated early, before the end of the minus fifty exposure—probably mak­ing both crew and experimenters a little doubtful that they’d go the whole three months. But things got better from there. Gibson had only one more test stopped, on Day 71; Carr and Pogue had none. Here are some of their comments:

Ed: “I would say that thirty up there was like fifty down here. . . the amount of sleep, amount of water intake and amount of salt intake were significant [variables] for me. If I felt dehydrated or overtired, I knew I would have a problem with lbnp. . . . I’ve always felt a craving for salt on this diet.”

Bill: “And related to that, perhaps equivalent, was the time of day. . . ear­lier in the day, you felt better.”

These men could feel the fluids shift within their bodies. During lbnp they would feel less fullness in the head as their legs became engorged—and sometimes that would be followed by cold sweat and faintness. Exercise also shifted fluid into muscles, but it felt much better. So did eva.

Jerry: “But the times when I could feel the fluid shifts the most were dur­ing exercise. As soon as you got on the bike and started pedaling, your head immediately began to clear up. And by the time you finished pedaling and the blood had shifted to your muscles, you felt great. Your nose was clear, the pressure was off your sinuses, and you felt good; tired from the work, but you felt clear.

Ed: “I recall that on the first eva it felt good to get outside and do some physical work for a long period of time. It was comfortable to have a heart rate above nominal for the duration of the eva.”

In contrast, they felt periods of dullness or sleepiness during times of less activity:

Jerry: “I think that during a period of adjustment my stamina, reserve, or whatever you want to call it, was gone. I found myself essentially living from meal to meal, what we call a lowering of blood sugar, when you’re get­ting really hungry and you start feeling fatigued and tired and dull. I don’t know what it is. I call it a lowering of the blood sugar. That’s what we felt up there, but as soon as we got a meal in us we would feel much better. You feel a little drowsy after the meal, but shortly after that you feel better. But then it only takes about two to three hours for you to become tired again. The old reserve and the stamina is gone and by 3:30 in the afternoon we were hungry again, feeling bad.”

Voice: “Did all three of you feel that?”

Bill: “I feel that way, but I would have liked to snack all the time I was up there; candy bars to eat periodically. I could have used those through­out the mission.”

Jerry: “I wish I could tell you where the calories go when you’re up there.”

Ed: “I felt the same effect as Jerry mentioned. I would have liked snacks. I would have liked three meals and then snacks in between, some high-ener­gy food like Bill mentioned.”

Question: “Listening to you, I get the impression that one might suggest shorter days or naps, recharging in that manner as well as eating.”

Ed: “A siesta right about noon time would have been great.”

Question: “Could you appreciate that your legs had diminished in size?

Ed: “You could see it and I think I could feel it in my calves, after I had worked the Thornton device, for example. That really was an excellent device. I’m glad we had it along. When did we start using it, around two weeks into the mission?”

Jerry: “Yes, somewhere between Day Ten and Fourteen is when we final­ly got time to set it up and start using it.”

Ed: “And from then on, we started to turn around.”

Jerry: “I felt pre-flight that the lbnp could be used. . . to maintain con­dition. I always hoped that you would take one of us as a control and put us in it every day as part of exercise. . . use it as an exercise tool and not require. . . all the instrumentation. Just get in it every day for five or ten minutes then see what you ended up with, compared to the other two guys.”

Question: “Which of you would have volunteered to be the no-exercise, no-LBNP control?”

Jerry: “Oh, I didn’t say no exercise (laughter). We had already decided that there would be no volunteers for no exercise.”

To summarize the crew’s opinion, the lbnp didn’t do much for them, but exercise was essential. And the postflight findings certainly bore them out.

They all adapted well to the topsy-turvy world ofweightlessness. As Carr related: “The first two-thirds of the mission, my dreams were one – G dreams, and I shifted to zero-G dreams about the last third. It really surprised me that I had some zero-G dreams.” They struggled a little bit to describe the feeling of carrying one’s personal “up” and “down” around in space:

Jerry: “Looking out the window at the Earth, sometimes the horizon would be upside-down. It was convenient just to flip (my own body) upside

down and look out the window. . . [but then] every once in a while you’d look inside at one of the other guys ‘upside-down with his feet locked in the ceiling’ and he looked funny that way. And the table was upside down. It was very strange.”

Jerry: “The normal mode of moving was just to go head first, whistling right down through the dome hatch all the way to the trash airlock. [But] if I ever decided to go through the other way, feet first, I had a very distinc­tive impression that I was very high and sure didn’t want to fall and hurt myself. It’s just because I had my feet out in front of me and all of a sudden there was a reference that connoted high.”

The following table compares data from the three Skylab crews.



Food / Day

(cal /kg.)



Weight Loss Percentage *

Leg Strength % decrease

Arm Strength % decrease

28 days



4.2% (1.7%)



59 days



5.3% (1.0%)



84 days



1.6% (0.0%)



Data Comparisons of Three Skylab Crews * Figure in parentheses is additional loss during prelaunch quarantine.

Those averages hide some sizeable individual variations. On Skylab I Con­rad exercised almost twice as much as Kerwin and munched many more cal­ories per kilogram than either of his crewmates. On Skylab II Lousma was a tiger for exercise, but Garriott ate the most. And on the final mission Carr set a record by losing essentially no weight (only two tenths of a pound) in nearly three months aloft. He was only the second astronaut ever not to lose weight in space. The first was Alan Shepard, not on his fifteen-minute Mer­cury flight but on his Apollo 14 journey to the moon.

But the averages do tell the story. The story is, “Feed them, exercise them hard, and they’ll do well in space.” Or, to quote Dr. Bill Thornton: “The conclusion is that muscle in space is no different from muscle on Earth; if it is properly nourished and exercised at reasonable load levels, it will main­tain its function.”

Based on the Skylab findings, here’s a combined narrative of what you could expect to happen to your body if you took a big “grand tour” flight to Mars.

When the rattle of the booster stops and you’re in orbit, that strange feel­ing of floating will occupy your attention fully. Your head feels full, as if you had a cold. You’ve been briefed to be very slow and careful with head and body movements. You will take this good advice and feel ok—but the per­son in the next seat will suddenly feel nauseated and reach for the sick bag. The flight attendant (all are trained nurses, as in the early days of commer­cial aviation) will give your neighbor an injection, and he’ll feel a little bet­ter in the morning and be back to normal in three days or so.

Your vestibular system adapts slowly to the absence of “down” — that constant acceleration of gravity. The same absence causes body fluids to migrate from the lower extremities up into your chest and abdomen; the body responds by decreasing thirst and effectively losing fluid. Your blood becomes a little more concentrated, with a higher red cell count. Your bone marrow notices this and stops producing new red cells.

You won’t get space motion sickness, but your appetite won’t be very good for the first several days, and learning to move, eat, go to the bath­room, and sleep while floating may seem hard. On the morning of day eight you’ll wake up thinking, “Wow! I feel great today!” But you’ll have lost six pounds since the day before launch. Your legs look ridiculously skinny. The chief flight attendant now puts you on a strict exercise program for the dura­tion of the flight.

Unused muscles atrophy; exercise is needed to keep them fit, and you have to keep doing it faithfully. A treadmill keeps your heart and lungs in order and provides some leg exercise; other devices simulate weight lift­ing and tone the other big muscle groups. The compression also helps your bone retain calcium, slowing the gradual thinning of bone structure that is another feature of zero-G.

Your flight goes on for several months. Your workload is light. The novelty of looking out the window at the stars slowly wears off; you become bored. Small habits and mannerisms of one of your fellow passengers, “Herb,” begin to irritate you. Psychological stress — “cabin fever”—is definitely a risk of long spaceflights as it is of any long isolation with a small group of people. Skylab didn’t experience much of that, because the crews had been so care­fully selected and extensively trained. We hope that your Mars flight has a compatible crew and good leadership. Talk to the flight surgeon about your problems with “Herb.”

You make it through the flight with flying colors. As reentry day gets clos­er, everyone becomes excited and upbeat. You and “Herb” exchange e-mail addresses. You’ve almost forgotten what gravity feels like. Now you are about to be reminded! You survive the parachute landing at the Space Recovery Field and are helped out of the spacecraft. You don’t feel very good. Every time you move your head the world moves too, a severe vertigo. You feel as if you weigh three hundred pounds, and you walk unsteadily, with feet wide apart. Your pulse races. You feel dizzy, tired, light-headed, and thirsty.

First your vestibular system needs to readapt to the long-absent gravity vector. Your weight is only a few pounds less than when you left, but you are low on body fluids and red cells in the blood—almost as though you had bled a pint or two from a wound. And your muscles, despite the exercise (did you slack off a little the last few weeks?) are weak. A very light landing day and a very long night’s sleep start you on the road to recovery. Next morning you feel like someone getting up after a bout with the flu—a little light-headed still, but good. A period of rehabilitation, with careful, supervised exercis­es, will be prescribed for three weeks to get you back to normal.

The red cell count will be normal in a month or so. Most of the calci­um lost from your bones will eventually return. You’ll have been exposed to radiation during your trip, including cosmic rays; the amount will deter­mine whether any future threats to health exist. The lifetime limit is prob­ably one Mars trip per person.

The Skylab medical data set rigorously quantified all these changes and allowed the causes of many of them to be understood. It demonstrated the safety of three-month spaceflights sufficiently to allow NASA to plan and build the International Space Station—and incidentally to allow the Soviet Union to plan and build Mir. Both the United States and Russia have built on this data and now routinely fly for up to six months. But the strict quan­titative metabolic balance study Skylab accomplished has never been repeat­ed. It did the job. And repeating it would drive the astronauts nuts.