From an engineering standpoint, the flights were to demonstrate the reliability of complex launch and landing systems, space capsule and life support systems. Each successive flight would demonstrate the reliability of these systems through a progressive buildup of tests and equipment.
A bioinstrumentation system was worn by astronauts to measure body temperature, respiration rate, heart rate, and during later flights, blood pressure. Electrodes attached at strategic locations on the astronaut recorded the physiologic data. Biomedical monitoring commenced with entrance into the spacecraft and ended with the loss of signal after landing. Data were transmitted by telemetry channels to ground monitoring stations, and the identical data were recorded by a tape recorder on board the spacecraft. Inside the spacecraft, a camera operating at 6 frames per second provided visual information. Voice transmissions throughout the flight were used to obtain subjective information regarding the astronaut's physical and mental status during the mission. Comments regarding body function, such as spatial orientation, eating, urination, and task performance, were regarded as significant. Inflight information was used primarily to determine the astronaut's well-being during flight and to make postflight detailed analyses of medical aspects of each mission for analytic, comparative and predictive purposes.
Respiration rate was measured by a thermistor kept at 200 degrees Fahrenheit and placed on the microphone pedestal inside the astronaut's helmet. The microphone was directed to register either nasal or oral breathing. In cases where the respiration thermistor did not function, respiratory rates per minute were estimated by using variations in the height of the ECG R-wave. During the Mercury Atlas 8 (MA-8) and MA-9 missions, respiration rate was measured by impedance pneumograph that was more accurate than the microphone-mounted system.
Heart rate and rhythm were recorded by the ECG. ECG electrodes were placed at two axillary and two sternal chest positions to minimize interference from muscle movement. This particular electrode placement was different from the method used in clinical monitoring at the time, but quickly became the standard due to the accuracy of the measurements.
During the Mercury Redstone 3 (MR-3) and MR-4 missions, the astronaut's heart rate was plotted at approximately 5-minute intervals during the early part of countdown by counting the rates for a 30-second interval. As lift-off time approached, heart rates were counted at 15-second intervals for 10-second duration. This procedure continued during the flight. Respiration rates were charted at approximately 5-minute intervals for 30-second durations during the countdown and at 30-second intervals during the flight. During the MA-6, MA-7, MA-8 and MA-9 missions, ECG, heart rate, blood pressure, respiration rate, body temperature, and space suit temperature were recorded throughout the entire mission. Heart and respiration rates were determined by counting the rates for 30 seconds every 3 minutes until 10 minutes prior to liftoff when 30-second duration counts were made each minute. These minute heart rate calculations continued through liftoff and took place again at reentry. During the mission, heart rate was calculated at 30 second intervals every 3 minutes.
A blood pressure recording system for use in flight was not developed until the MA-6 mission. As early as the MR-3 flight, however, a fully automatic blood pressure measuring system (BPMS) was under development. An early version of the BPMS, requiring manual cuff inflation, was used on the MA-6 mission. Beginning with the MA-7 mission, the manual BPMS contained in the bioinstrumentation harness was the replaced with a semiautomatic system. This system would inflate automatically, but required the astronaut to manually stop the inflation at the desired point.
Beginning with the MA-6 mission, calibrated exercise was performed using an exercise device designed for space flight. The device consisted of a short plastic handle attached to expandable bungee cords that was fixed within the spacecraft near the astronaut's feet. Exercise was accomplished by holding the device stationary at the feet and pulling on the handles for 30 repetitions in as near 30 seconds as possible. Blood pressure was recorded before and after the exercise test.
During the MA-9 mission, a tilt table procedure was performed postflight to study cardiovascular responses to position changes immediately after flight. A head-up tilt of 70 degrees from the horizontal was obtained in 3 to 4 seconds. Heart rate, blood pressure, respiration rate, and ECG were measured before, during and after table tilt.
Body temperature was measured continuously by a rectal thermistor during the first five missions. A change was made from continuous rectal to intermittent oral body temperature measurement for the 34-hour MA-9 mission due to the increased duration of the mission and a desire for more comfort.
A number of blood enzymes were studied preflight and postflight to evaluate variations of muscle or liver activity resulting from acceleration followed by a weightlessness period or from the prolonged semi-immobilization of the astronaut. These included transaminases, acetylcholine esterase, leucylamino peptidase, aldolase, and isomerase phosphohexose. The dehygrogenases examined included lactic, malic, succinic, alpha-ketoglutaric, inosine, isocitric, and beta-glutamic. L-glutamic and alkaline phosphatase and lactic acid were measured beginning with MR-4. Cholesterol and reduced diphosphopyridine nucleotide (DPNH) oxidation (non-specific enzyme activity) were added beginning with the MA-6 mission. No blood samples were obtained during flight, and every attempt was made to combine the various blood requirements so as to minimize the number of venipuncture, both preflight and postflight.
Urine was collected in flight beginning with the MA-6 flight to determine how the skeletal system and muscular system adapted to microgravity. The astronauts of MA-6, MA-7 and MA-8 voided in a simple urine collection bag strapped to the thigh inside the space suit. The entire void was returned to Earth for analysis. However, this method of urine collection became unworkable as the mission duration increased. By the end of Project Mercury, a urine collection device was developed for MA-9 that made it possible to collect separate urine samples during the flight.
Postflight, routine blood and urine samples were collected immediately on arrival at the debriefing area, and again at various times after the flight. The samples were processed, frozen, and transported to the various participating laboratories.
Nutrition and Metabolism
Beginning approximately three days before flight, each astronaut was placed on a low-residue diet to minimize the need to defecate during the mission. The ability to consume food in flight was tested for the first time during the MA-6 mission. Based on the success of each subsequent mission, additional solid and liquid food items were tested using a variety of food preparation techniques. A xylose tolerance test was performed in flight during MA-6 and MA-7 to measure intestinal absorption. This test required the astronaut to ingest a 5.0-gram xylose (sugar) tablet while weightless, followed by urination just before returning to 1-g.
Orientation and Behavior
Beginning with MA-6, two vestibular labyrinthine tests were conducted preflight and postflight to measure the effect of space flight and weightlessness on the human vestibular apparatus. The first labyrinthine test was a modified caloric test that was considered to be a valid and finely discriminating index of semicircular canal function. The subject's ear was irrigated for 45 seconds with water below body temperature that could be warmed or cooled under precise control. The times of onset and duration of nystagmus (fine eye jerk) were recorded. The highest water temperature that caused nystagmus was regarded as the threshold value. Usually this was 3 to 5 degrees centigrade below body temperature.
During the second labyrinthine test, astronauts were timed and scored on their ability to maintain balance while walking on narrow rails, similar to the rails of a railroad track. They were required to stand and walk heel-to-toe and to keep their arms folded on the chest. These challenges allowed scientists to study how space flight altered balance control. The standing tests were carried out first with the eyes open, then with the eyes closed. In addition, this test represented a quantitative method for evaluating neuromuscular mechanisms related to balance.
During MA-8 and MA-9, the two astronauts performed a specific test of orientation. At three different times during the mission, the astronaut would close his eyes and attempt to touch three different instruments with his index finger. The nine responses were recorded as either "direct hits" or "near misses." The purpose of the test was to determine if visual perception varied during flight.
As knowledge was gained from each successive Mercury mission, new tests were added in addition to the basic medical monitoring to further evaluate the physiological responses of the astronaut in microgravity. The MA-8 and MA-9 astronauts wore special radiation dosimeters attached to their helmet and the underwear of the space suit to measure radiation exposure. Retinal photography was performed pre- and postflight to identify any changes to the retina caused by radiation exposure and the weightless condition.
Project Mercury provided incremental exposures to microgravity that successively increased information on which to predict the physiological responses of more prolonged exposure. The astronauts uniformly reported that space flight was extremely pleasant and restful. Most thought that it was the only time they were comfortable in a pressure suit.
Voice transmissions throughout the flight were of excellent quality. The astronauts demonstrated coherent and appropriate communications that were on schedule during all flight phases. Inflight photography and television proved of little value in medical monitoring because of the poor positioning of the cameras and the varied lighting conditions that resulted from the operational situation.
Examination of the ECG waveforms recorded during flight varied in quality from mission to mission, but overall ECG trace quality from both sternal and axillary leads was quite satisfactory. The value of having two ECG leads, even though they differed from the standard clinical leads, was repeatedly shown. This allowed easier determination of artifacts and was most helpful in determining the valid sounds on the blood pressure trace by comparison with the remaining ECG lead. Changes noted in the ECGs included alterations in the pacemaker activity with wandering pacemakers and aberrant rhythm including atrio-ventricular nodal beats and rhythm, premature atrial and ventricular contractions, sinus arrhythmia, sinus tachycardia, sinus brachycardia, premature atrial fusion beats, atrial rhythm, and atrio-ventricular contraction. These rare irregularities were considered normal physiological responses when related to the dynamic situation in which they were encountered and did not compromise the work performance of any astronaut.
Data showed that the peak physiological responses were closely related to critical inflight events. As was expected, heart rate rose during periods of increased stress. The most significant elevations occurred at lift-off, during launch-vehicle engine cutoff and the spacecraft separation maneuver, retrorocket firing, reentry and descent. Heart rate responses to the microgravity flight period were somewhat erratic depending of the level of activity, but there was a general downward trend just prior to the onset of reentry.
The peak heart rates during the launch phase usually occurred at engine cut-off. This peak value ranged from 96 to 162 beats per minute. The peak rates obtained on reentry ranged from 104 to 184 beats per minute. This peak usually occurred immediately after obtaining peak reentry acceleration, or on drogue parachute deployment. Heart rates values obtained during weightlessness flight varied from 50 to 60 beats per minute during the sleep periods to 56 to 160 beats per minute during the normal waking periods. The elevated rates during weightless flight could usually be related to flight-plan activity.
The MA-9 astronaut consumed 5 mg of dextro-amphetamine sulfate orally prior to reentry. This measure was taken when it became evident that the astronaut had undergone a long and rigorous work schedule from which he might be expected to experience considerable fatigue, even assuming ideal environmental conditions and full benefit from restful sleep. The astronauts heart rate rose gradually with rather marked swings in rate levels as high as 140 beats per minute and lows of about 80 beats per minute throughout the remainder of the flight. A significant change in heart rate occurred at retrofire when the heart rate rose to 166 beats per minute for no longer than 20 seconds. The heart rate during reentry varied between 120 and 140 beats per minute until parachute deployment when it spiked to 184 beats per minute. It then gradually declined to 164 beats per minute at sensor disconnect subsequent to main parachute deployment.
Respiratory rates ranged from 30 to 40 breaths per minute at engine cut-off, from 8 to 20 breaths per minute during weightless flight, and from 20 to 32 breaths per minute at reentry. In-flight, blood-pressure values and body temperature readings were all within the physiologically normal range.
Calibrated exercise was performed without incident on board all missions beginning with MA-6. Heart rate increased moderately during each exercise period but returned to resting values within 1 minute after completion. The heart rate response to this nominal exercise demonstrated a reactive cardiovascular system. Analysis of the data did not show any striking differences between the exercise periods on Earth and in microgravity.
Symptoms of orthostatic hypotension were observed after the last two Mercury flights. Immediately following the MA-8 mission, it was noted that the astronaut's dependent leg veins were engorged; the feet and legs rapidly took on a dusky, reddish-purple color following standing. There was an orthostatic rise in heart rate accompanied by a fall in blood pressure that persisted between 7 and 19 hours after landing. This postflight condition was investigated by tilt table studies. There were no unusual color changes in the feet of the MA-9 astronaut, as had been noted following the MA-8 flight. The astronaut did not have any subjective complaints; however, objective changes in heart rate and blood pressure were noted. In both instances, these changes were present up until the astronaut retired for the night and always disappeared by the time of the first check after the astronaut was awakened. Thus, orthostatic changes lasted no longer following the 34-hour MA-9 mission than for the shorter 9-hour MA-8 flight. In both instances, blood pressure and heart rate returned to normal while the astronaut was at bedrest.
Inflight body temperature readings for all subjects were within the normal physiological range. The astronauts' body temperatures were observed to gradually increase throughout the flight, which was believed to have resulted in part from an increased temperature within the space suit. Body temperature gradually returned to normal after the flight.
Variations in the cabin and space suit temperatures caused discomfort on occasion but were not limiting factors during any of the missions. The temperature inside the space suit had a tendency to increase slowly during flight with a more rapid rise after reentry and during parachute descent; this resulted in increased sweating. One consequence of the high temperature was mild postflight dehydration and subsequent weight loss. The most significant weight loss came from the MA-7 astronaut who lost 6 ± 1 pounds after a flight of less than 5 hours. Attempts to regulate fluid and electrolyte balance in flight by increasing fluid intake was moderately successful. For all astronauts, normal fluid levels returned within 24 hours following space flight. Researchers learned that thermal control in the environmental system was of critical importance to regulating changes in body fluid dynamics associated with increasing exposure to microgravity.
Blood calcium levels were slightly increased for all astronauts in the immediate postflight period, but returned to preflight levels or decreased slightly within 14-48 hours after landing. Researchers hypothesized that the increases may have resulted from a number of causes, including dehydration, normal physiologic variation, and laboratory variation.
Generally, blood sodium and potassium levels were unchanged or slightly decreased in all astronauts 1-3 hours after landing. Levels for both electrolytes stabilized at or near preflight levels within 24-45 hours after landing. Blood chloride levels were mildly increased postflight in all six astronauts. Within 45 hours, chloride levels returned to within normal ranges.
There was no significant change in transaminase, acetylcholine esterase or aldolase activity in the MR-3, MR-4 and MA-6 astronauts. Only lactic dehydrogenase showed any appreciable change throughout the first three flights. Lactic acid showed an increase in the MA-6 astronaut. Increases were also noted in the leucylamino peptidase activity and in phosphohexose isomerase for the first three flights. Due to the consistency of the results, the number and type of enzyme studies were modified beginning with the MA-7 flight in order to obtain the maximum amount of useful information from a minimum number of determinations. The enzymes studied included leucylamino peptidase, phosphohexose isomerase, malic and lactic dehydrogenase, and cholesterol.
Many of the postflight blood enzyme increases for the MA-8 astronaut were near or above normal range. The reason for these elevations could have been attributed to the fact that this individual was of a lean body-mass type, as were the other Mercury astronauts. Further analysis of the enzyme results, especially heat-stable lactic dehydrogenase, suggested that these postflight elevations were the result of muscular activity rather than the visceral pooling of blood. Postflight decreases included leucylamino peptidase and phosphohexose isomerase.
Urination occurred quite normally in timing and volume. Bladder sensation and function were normal and unchanged from that of the customary 1-g environment. No abnormal gastrointestinal symptoms were reported during the missions, and there was no evidence of difficulty in intestinal absorption in the microgravity state. During missions MA-6, MA-7 and MA-8, all urine was collected in a single container within the space suit. Analysis of the urine specimens collected on MA-6 and MA-7 showed no abnormalities specifically attributable to space flight. Urinary calcium was elevated after MA-7 during the first two days after flight. The fact that the potassium excretion was also elevated in the same period of time suggested that this increased calcium output was a result of a variation in kidney activity rather than just calcium mobilization alone. The stability of the blood potassium values, moreover, indicated that the loss of potassium was well compensated.
The urine specimen was not recovered after the MA-8 mission due to leakage of the container, thus it was impossible to establish any abnormality in the urine. The last mission (MA-9) utilized a urine collection and transfer system that collected five separate and complete urine samples for later evaluation. This system worked properly but required a considerable amount of time and effort to transfer the urine to the storage bags manually. After the MA-9 flight, there was no indication of increased urinary calcium excretion. Sodium and chloride retention the first two days after flight were consistent with the period of restoration of fluid balance following the dehydration that occurred in flight. All other values were within the normal ranges for the subject.
Nutrition and Metabolism
The dietary program for the Mercury astronauts was satisfactory. Inflight food consisted of bite-size and semi-liquid tube food on missions MA-6 through MA-8. On the last mission, freeze-dehydrated food items were carried on board that used a specially deigned water nozzle to reconstitute the food containers. Problems with crumbling were encountered during MA-7 with the bite-size food, and difficulty in rehydrating the freeze-dehydrated food was encountered on the MA-9 mission. Once in the mouth, however, chewing and swallowing of both solids and liquids were accomplished without difficulty. Taste and smell were also normal. At the end of Project Mercury, it was apparent that additional work would be required to assure palatable food, as well as development of proper containers and practice in their use. Also deemed necessary was the scheduling of food and water intake on the flight plan and ensuring that it was properly accomplished.
Orientation and Behavior
No disturbing body sensations were reported as a result of weightless flight. Voluntary, violent head maneuvers within the limited mobility of the helmet were performed several times in every direction without symptoms of vertigo. Distances were estimated by the relative size of objects. Tactile (touch) approximation with the eyes closed was the same as that on the ground; there was no tendency to overshoot or under-reach control switches on the spacecraft instrument panel. Somatic sensations were normal, and there was no evidence of motion sickness in any of the astronauts. The inflight orientation tests demonstrated no impairment of performance. Hearing was adequate throughout the flights according to astronaut reports and voice responses. Near and distant visual acuity and color vision appeared to be normally retained. No disturbances in spatial orientation and no symptoms suggesting vestibular disturbances during the flight were reported. The astronauts' were always oriented with respect to the spacecraft, but at times lost orientation with respect to the Earth. When the horizon was not in view, it was difficult to distinguish up and down positions, but this was never of immediate concern to the astronauts.
Retinal photography revealed no significant changes from the preflight values. The radiation dose received by the astronauts was considered medically insignificant.
In conclusion, Project Mercury demonstrated that individuals could survive and function well in the space environment without undesirable reactions or detriment to normal body functions for periods as long as 34 hours. Other medical knowledge gained included the fact that there had been no evidence of abnormal sensory, psychiatric or physiological response to an orbital space flight of up to 1.5 days. Sleep during flight proved to be possible and subjectively normal. Other than an orthostatic rise in heart rate and fall in blood pressure and heart rate as previously mentioned, no other clearly significant changes were found in the comprehensive preflight and postflight physiological examination.
Certain basic problems in space medicine remained unresolved. What would be the effects of prolonged weightlessness and combined stressors upon the astronaut? What would be the effects of space radiation? Would toxins within the spacecraft endanger the astronaut? Some basic biological questions had to be answered. How would human beings survive for extended periods of time in a closed ecological system? Could food and wastes be recycled and regenerated? Problems of biotechnology, too, were still unsolved. However, investigators were now in a much better position to utilize improved biomedical instrumentation and to establish experimental designs having greater potential for solving these problems. While these problems had been identified years before in aviation medicine, Project Mercury had provided the first step in answering them. Simulation and testing on centrifuges could provide a partial answer, but only through actual experience in orbiting space laboratories could the larger answers be provided. As Project Mercury drew to a close, the scientific community looked forward with confidence to meeting that challenge.
|Mission||Launch/Start Date||Landing/End Date||Duration|
|Mercury 3||05/05/1961||05/05/1961||15 minutes, 22 seconds|
|Mercury 4||07/21/1961||07/21/1961||15 minutes, 37 seconds|
|Mercury 6||02/20/1962||02/20/1962||4.9 hours|
|Mercury 7||05/24/1962||05/24/1962||4.9 hours|
|Mercury 8||10/03/1962||10/03/1962||9 hours, 13 minutes|
|Mercury 9||05/15/1963||05/16/1963||1.5 days|