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MAN-SYSTEMS INTEGRATION STANDARDS
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MAN-SYSTEMS INTEGRATION STANDARDS Print this page Click to print the page

Volume I, Section 4

4 HUMAN PERFORMANCE CAPABILITIES

{A} For a description of the notations, see Acceleration Regimes.

This section contains the following topics:Skip Section listing

4.1    Introduction
4.2    Vision
4.3    Auditory System
4.4    Olfaction and Taste
4.5    Vestibular System
4.6    Kinesthesia
4.7    Reaction Time
4.8    Motor Skills (Coordination)
4.9    Strength
4.10  Workload
4.11  Effects of Deconditioning

See the video clips associated with this section.

4.1 INTRODUCTION

{A}

The user must keep in mind that much is still unknown about the over-all, long term effects of various space environments on performance capabilities. The data included here were derived from past experience with high-performance aircraft, and the relatively limited experience, particularly with respect to long orbital stays, with past space programs. A lot of the information in this chapter has been derived from one-g data to which trend information from the sources cited above was applied. Although less than perfect or complete data were compiled for this chapter, it is the best information in this field known to exist at this time.

This chapter is based on the premise that designers and mission planners will do a better job if they are familiar with the capabilities of the people for whom they are designing. When people go into space their performance capabilities may change in important ways. The purpose of this chapter is to document these changes.

The voluminous data that exists on human performance capabilities under 1-G (Earth) conditions are not included here. This material is covered in other sources (see refs. 4, 19, 143, and especially 336).

 

4.2 VISION

{A}

4.2.1 Introduction

{A}

This section discusses aspects of visual performance that are, or are likely to be, modified by space travel. For more general information on vision, consult the references provided in Paragraph 4.1.

4.2.2 Vision Design Considerations

{A}

Space-related factors that may affect visual perception as listed below.

a. Acceleration - The effects of acceleration on vision depend on the direction of the force vector.

(Refer to Paragraph 5.3, Acceleration, for additional information on the affects of acceleration.)

1. +Gz acceleration (eyeballs down) results in dimming of vision, followed by tunnel vision loss of sight which begins on the periphery and gradually narrows down until only macular (central) vision remains. This is followed by total blackout and then loss of consciousness.

2. +Gx acceleration (eyeballs in) results in loss of peripheral vision. This typically occurs at slightly over 4-G (based on a rate of onset of 1-G per second). Complete loss of vision varies between individuals, and with physical conditioning, training, and experience.

3. -Gz acceleration (eyeballs up) results in diminished vision, red-out (red vision), an increase in the time for the eyes to accommodate, and a blurring or doubling of vision.

4. When exposed to -Gx acceleration (eyeballs out), crewmembers will experience visual symptoms associated with -Gz acceleration (see 3" above).

5. Visual reaction time may be defined as the interval between the onset of a stimulus and the initiation of the crewmember's response. This interval is, in general, lengthened by increased G level.

6. Visual tracking is moderately degraded by increased G level.

b. Vibration - If vibration is sufficiently severe, visual performance will be degraded. The severity depends on the frequency and amplitude of the vibration along with the resonance frequency of the body part involved. Unfortunately, the times when vibration is most likely to be encountered (e.g., liftoff and landing) also tend to be times when vision is important. Displays that must be read during projected periods of high vibration should be designed accordingly. Design techniques to be considered should include display characters which are sufficiently large to be perceived even when blurred and sufficient illumination to avoid scotopic vision which results in a lower Critical Flicker Fusion Frequency.

(Refer to Paragraph 5.5.2.3, Human Response to Vibration, and reference 19 for additional information.)

c. Light in Space - Differences in light transmission and reflectance in space result in some significant differences in available perceptual cues in the extravehicular environment as compared to earth atmosphere.

1. Light Scatter - Atmospheric light scatter does not exist in space due to the lack of particulate and gaseous material. Thus, aerial perspective cues are absent. Figure-ground contrast is increased and shadows appear darker and more clearly defined. Loss of these cues along with other environmental consequences discussed below can degrade perception of object shape, distance, location and relative motion.

2. Luminance Range (Contrast) - The extravehicular environment is marked by a wider range of light intensities than normally encountered on Earth. Shifting gaze from a brighter to a substantially dimmer scene will require time for the eyes to adapt to the lower light level. For example, problems arise on EVA missions when crewmembers go from working in sunlight to working in shadows.

In Figure 4.2.2-1, adaptation time requirements are shown for shifting gaze from a brighter to a dimmer environment. For comparison, Figure 4.2.2-2 indicates luminance values for some typical visual stimuli.

Figure 4.2.2-1 Dark Adaptation Thresholds

Line graph showing dark adaption thresholds (microtrolands to minutes in dark)

Reference: 338, p. 187; NASA-STD-3000

Figure 4.2.2-2 Luminance Values for Typical Visual Stimuli

Example Scale of Luminance (millilamberts) Effect
Sun's Surface at noon 109 Damaging
108
107 Phototopic
Tungsten Filament 106
105
White paper in sunlight 104
103
102
Comfortable reading 10
1 Mixed
10-1 Scotopic
White paper in moonlight 10-2
10-3
White paper in starlight 10-4
10-5
Absolute threshold 10-6

Reference: 337, p. 26; NASA-STD-3000 194

d. Absence of Other Earth Cues:

1. Absence of a Fixed Vertical Orientation - Recognition of familiar objects, faces, and areas (e.g., workstation) is poor when viewed from an orientation significantly different from the established vertical. The viewer must be oriented within approximately 45 degrees of this vertical to perceive the surroundings in a relatively normal fashion. This fact argues for the establishment of a local vertical for each living and working area within a space module.

2. Absence of Fixed Horizon and its accompanying foreground and background cues can be expected to degrade extravehicular perception of object shape, distance, location and relative motion.

3. Absence of a fixed, overhead sun position and its effects on shadow cues is expected to have similar effects as those in 2 (above).

e. Light Flashes - The perception of light flashes has been reported by many crewmembers during periods of darkness at specific orbital locations. The cause is thought to be cosmic rays and/or heavy-particle radiation traversing the head or eyes and triggering a neural response that results in these perceptions.

f. Potential deficits - While visual perception in space is normal in many respects, there are reports of various changes in vision (some of them contradictory) that point out the complex consequences of the above factors. These include Soviet reports of a shift in perceived colors and a reduction in contrast sensitivity, along with a seemingly contradictory report indicating improved visual acuity for distant objects. Some U.S. astronauts have indicated a reduction in near acuity with no apparent change in far acuity, while some crewmembers who wear reading glasses on Earth found they were more dependent on them while in space. Clearly, more research is needed before we can say more about these effects.

4.3 AUDITORY SYSTEM

{A}

4.3.1 Introduction

{A}

There is no evidence that human auditory functioning changes in space. However, there are several factors (e.g., the effects of noise) that should be considered in designing the space habitat.

(Requirements pertaining to acceptable noise levels are described in Paragraph 5.4.3, Acoustic Design Requirements.)

4.3.2 Auditory System Design Considerations

{A}

4.3.2.1 Auditory Response

{A}

Figure 4.3.2.1-1 shows human auditory responses as a function of frequency.

Figure 4.3.2.1-1 Human Auditory Response as a Function of Frequency

Graph Figure demonstrating Human threshold of feeling, conversational speech, and threshold of hearing

Table supplementing the graph above
Human Auditory Response Decibels (db)
Threshold of pain 140
Subway - local station with express passing 120
100
Average factory, large store, or noisy office 80
60
Average residence 40
Low whisper 1.5 m (5 ft) 20
0

Reference:  335; NASA-STD-3000 195

(Refer to Paragraph 5.4.3.2, Noise Exposure Limits, for additional information.)

c. Communication - Even low levels of noise can interfere with communication.

(Refer to Paragraph 5.4.3.2, Noise Exposure Limits, for additional information.)

d. Task Complexity - Noise can adversely affect performance, with the effects being greater for more complex asks.

e. Intermittent Noise - Intermittent noise has more adverse effects than steady-state noise.

f. Adverse Effects - General effects of a noisy environment include fatigue, distractibility, sleep disturbance, irritation, and aggressive behavior.

(Refer to Paragraph 5.4.3.2, Noise Exposure Limits, for additional information.)

g. Psychological Factors - The level of annoyance that noise produces depends on a number of factors. Sensitivity varies greatly among individuals.

1. People are generally less sensitive to noise related to their well-being.

2. People are more sensitive to unpredictable noise.

3. People are more sensitive to noise they feel is unnecessary.

4. People who are most sensitive to noise become increasingly disturbed as the noise persists, whereas the annoyance level of less sensitive individuals remains constant over time.

5. The perceived abrasiveness of certain sounds is subjective and varies considerably among individuals (e.g., consider the potential conflict between opera and rock music lovers).

h. Cabin Pressure - Reduced cabin pressure causes a reduction in sound transmission. This means that crewmembers have to talk louder to be heard which can potentially lead to hoarseness on the part of some crewmembers. The problem becomes more noticeable as the distance between individuals increases.

(Refer to Paragraph 5.4, Acoustics, for additional information.)

4.3.2.2 Noise Design Considerations

{A}

Noise can have many adverse effects on humans and must be considered when designing the human habitat. Considerations include:

a. Extreme Noise - Extreme noise can cause pain and temporary or permanent hearing loss. The adverse effects of pure tones occur at a level about 10 dB lower than for broad band noise.

b. Extended Exposure - Exposure to loud noise for extended periods of time can cause permanent hearing loss. The degree of exposure that will result in damage depends on intensity and individual susceptibility.

4.4 OLFACTION AND TASTE

{A}

4.4.1 Introduction

{A}

Changes in our senses of smell and taste might occur in space. These changes are described below.

4.4.2 Olfaction and Taste Design Considerations

{A}

4.4.2.1 Olfaction

{A}

Aspects of olfaction (smell) that could influence design are presented below.

a. Decreased Sensitivity - There are frequently reported problems with nasal congestion while living in the microgravity environment.

b. Adverse Effects - Unpleasant odors have been associated with a number of medical symptoms including nausea, sinus congestion, headaches, and coughing. Such odors also contribute to general annoyance.

c. Microgravity Odors - Because particulate matter does not settle out in a weightless environment, odor problems in a space habitat may be more severe than under similar Earth conditions. Circulation and filtering will influence the extent of the problem.

d. Visual Cues and Odors - Responses to odors can be accentuated by the presence of visual cues. This increased responsiveness applies to pleasant and unpleasant odors and is something that a designer could potentially put to good use.

4.4.2.2 Taste

{O}

Generally there is a decrement in the sense of taste in microgravity. This is probably caused by the upward shift of body fluids and accompanying nasal congestion. Reports indicate that food judged to be adequately seasoned prior to flight tasted bland in space. Given the important role that food is likely to play in maintaining morale on extended space missions, attention should be paid to this problem.

4.5 VESTIBULAR SYSTEM

{A}

4.5.1 Introduction

{A}

Microgravity results in two categories of vestibular side effects: spatial disorientation and space adaptation syndrome (space sickness), both of which can impair crewmember performance.

4.5.2 Vestibular System Design Considerations

{O}

4.5.2.1 Spatial Disorientation

{O}

Spatial disorientation is experienced by some crewmembers and should be considered in the design of hardware and the planning of missions.

a. Spatial Disorientation - Responses include postural and movement illusions and vertigo. For example, stationary crewmembers may feel that they are tumbling or spinning. These illusions occur with the eyes open or closed.

b. Frequency of Occurrence - The percentage of crewmembers who experience spatial disorientation varies from mission to mission, but averages approximately 50%. The conditions that determine the likelihood and intensity of this disorientation are not well understood.

c. Duration - Some crewmembers may experience spatial disorientation for the first 2 to 4 days of a mission.

d. Activity Schedule - While spatial disorientation need not cause any serious problems, it is advisable not to schedule activities that depend heavily on spatial orientation early in a mission.

4.5.2.2 Space Adaptation Syndrome

{O}

Aspects of space adaptation syndrome (SAS) relevant to the design of space modules and mission planning are presented below.

a. Symptoms - SAS symptoms range from stomach awareness and nausea to repeated vomiting. Symptoms also include pallor and sweating.

b. Incidence and Duration - It appears that approximately 50% of the crewmembers are affected by SAS. Symptoms last for the first 2 to 4 days of flight.

c. Performance Decrements - A highly motivated crewmember may be able to maintain a high level of performance despite the presence of mild SAS. However, if motion sickness is severe, some crewmembers will be unable to work until the symptoms lessen.

d. Cause - The leading theory as to the cause of SAS is the sensory conflict theory. This theory states that space sickness occurs when patterns of sensory input to the brain from different senses (vestibular, other proprioceptive input, vision) are markedly rearranged, at variance with each other, or differ substantially from expectations.

e. Volume Effects - The severity of SAS tends to increase as the motion which induces sensory conflict and sickness (particularly head movements in the pitch and roll modes) increases. It follows then that as the volume in which a crewmember is working becomes larger, the chances for this sickness inducing motion increases.

f. Space and Motion Sickness - It is assumed that the mechanism of SAS and 1-G motion sickness are similar, but are similar, but it is not possible to predict an individual's susceptibility to space sickness from their susceptibility to Earth motion sickness.

g. Space Sickness Countermeasures.

1. Drugs - Anti-motion sickness pharmaceuticals (usually Scopedex) have reduced the severity of SAS symptoms for some crewmembers, but have appeared to be ineffective for others. It is likely that they would be more universally effective if they were administered prophylactically, either by injection or orally. The drug should be taken before symptoms develop and absorption from the gut is severely hampered due to the cessation of propulsive motions of the stomach., If a swallowed drug becomes trapped in the stomach, little absorption will take place.

2. Head movements - In some cases restricting head movements has been found effective in reducing the incidence of, and ameliorating the symptoms of, space motion sickness.

4.6 KINESTHESIA

{A}

4.6.1 Introduction

{A}

Kinesthesia is the sense mediated by end organs located in muscles, tendons, and joints, and stimulated by body movements and tensions. Present knowledge of kinesthetic changes occurring when one enters microgravity is limited to estimation of mass and limb position sense.

4.6.2 Kinesthetic Design Considerations

{O}

One experiment has indicated that some kinesthetic sensitivity degradation occurs for a few crewmembers. The indications of this experiment are provided below.

a. Mass Versus Weight - In a weightless environment, increments in mass must be at least twice as large as weight increments in a 1-G environment before they can be discriminated (see Figure 4.6.2-1).

b. Barely Noticeable Differences - For two masses to be perceived as different under microgravity conditions, they must differ by at least 10% (see Figure 4.6.2-1).

c. Mass and Acceleration - Differential sensitivity for mass under microgravity conditions can be improved by increasing the acceleration force imposed on the object.

d. Mass Estimation - Absolute judgments of mass tend to be lower under microgravity than under 1-G.

Figure 4.6.2-1 Mean Difference Thresholds (DL) and Associated Standard Deviations (SD) Plotted for Each Standard Under Both Weight and Mass Conditions.

Graph depicting the mean difference thresholds and associated standard deviations plotted against weight (grams)

Reference: 78, p. 1-90; NASA-STD-3000 196

4.7 REACTION TIME

{A}

4.7.1 Introduction

{A}

There appears to be some slowing of reaction times in space, although little precise data are available.

The subject of this Section is Response Time. This time period consists of two phases: 1) Reaction Time which is the time between the presentation of a stimulus to a subject and the beginning of the response to that stimulus, and 2) the time during which the actual response to the stimulus is accomplished. It is believed that this section is actually referring to Response Time and the titles and references should be changed accordingly. However, Reaction Time should not be slowed in micro-gravity as it has more to do with motivation and the effects of microgravity on the subject's physiological and emotional states. A good definition of the difference between Response Time and Reaction Time would help in the solution of this dilemma.

4.7.2 Reaction Time Design Considerations

{O}

Information on reaction time that should be considered by designers is provided below.

a. Object Mass - The time required to move an object in microgravity increases as the mass of the object increases.

b. Control Operation - In microgravity, the speed of operating switches (pushbuttons, toggles, rotary switches) is significantly lower than in the 1-G condition.

(Refer to Reference 171 for more information on visual reaction times; and Reference 347, for 1-G muscular-reaction time information.)

4.8 MOTOR SKILLS (Coordination)

{O}

4.8.1 Introduction

{O}

There is a minor impairment of motor skills upon first entering microgravity. This decrement is reduced or eliminated after a short period of adaptation.

4.8.2 Motor Skills (Coordination) Design Considerations

{O}

Aspects of human motor skills in space that should be considered by individuals designing for space are provided below.

a. Adaptation Period - Motor skills are somewhat affected when crewmembers are first exposed to microgravity, although these effects tend to diminish or disappear with adaptation. During the period that the crew is adapting to microgravity, fine motor movements are more adversely affected than either medium or gross motor movements. Designers should minimize requirements for crewmembers to exercise fine motor control early in the mission. Switches should be easy to manipulate and care should be taken to preclude accidental activation.

During periods that motor coordination is adapted for the micro-g environment, short returns to an altered g-state (as in reentry, maneuvers, landings, etc.) may result in dyskinesia and dysmetria. This can cause undershooting when reaching for switches for buttons or applying force to control sticks, pedals, knobs, handles, etc.

b. Postural Changes - A change in body posture in microgravity results in a change in the relative position of body parts and can cause decrements in coordination until adaptation occurs. Changes in body posture result from the crewmembers assuming the increase in height due primarily to spinal column expansion.

Refer to Section 3, Anthropometric and Mobility, for additional information on microgravity posture.

c. Body Part Weight - When moving in microgravity, the muscular system does not have to compensate for the weight of body parts. This changes the muscular forces required for coordinated movement and requires the system to readapt.

d. Large Mass Handling - When properly planned, no difficulty has been encountered by crewmembers in moving large masses in a microgravity environment.

4.9 STRENGTH

{A}

4.9.1Introduction

{A}

Physical work can be divided into two parts: power and endurance (anaerobic and aerobic performance).

The next section addresses the first of these (power), and how it can influence the design of facilities and equipment to achieve optimal crewmember performance. (Endurance is addressed in Paragraph 4.10.2a).

4.9.2 Strength Design Considerations

{A}

Aspects of human strength that should be understood and considered in designing for the space environment are presented below.

a. Strength - Strength is the ability to generate muscular tension and to apply it to an external object through the skeletal lever system. Sheer muscle mass (thus, body size) is a significant factor, with cross-sectional area of the muscle fibers being a major determinant of the maximum force that can be generated. Maximum muscular force (strength) can be exerted for only a few seconds.

b. Muscular Endurance - Muscular endurance is the duration a submaximal force may be held in a fixed position (Isometric), or the number of times a movement requiring a submaximal force may be repeated (Isotonic). The duration that a fixed percentage of maximum can be held is reasonably constant across individuals.

c. Counterforces - Microgravity does not have certain counterforces that allow people to effectively perform physical work in 1-G. Traction which depends on body weight is absent, as are forces that result from using body weight for counterbalance.

d. Working While Restrained - Crewmembers' work capabilities while restrained can approach the efficiency experienced on Earth-based tasks, but only where workstation design (including fixed and loose equipment) and task procedures are optimized for the microgravity environment.

e. Working Without Restraints - Without proper restraints, a crewmember's work capabilities will generally be reduced and the time to complete tasks increased.

f. Improved Performance - There are situations where a crewmember can achieve improved strength performance in microgravity. These situations occur when the crewmember uses the greater maneuverability of microgravity to achieve a more efficient body position to be able to push off solid surfaces.

g. Deconditioning - Experience in space indicates that both the strength and aerobic power of load bearing muscles in crewmembers decreases during missions exposing them to microgravity. Exercise programs have been used to counter these deficits but to date have been only partially effective.

(Refer to Paragraph 7.2.3, Reduced Gravity Countermeasures, for information on maintaining strength in space.)

h. Kinematics - The linear motion of free-floating crewmembers can be described by relatively simple equations. The time crewmembers can exert force is governed by the distance they can push before losing physical contact. The force exerted during this time will typically vary as in Figure 4.9.2-1.

The important aspects of this curve are the impulse (Fdt, or the area under the curve), which will determine departure velocity; and the peak force, which will determine peak acceleration. In the simplest case, for a subject of mass m, an impulse I with a peak force F acting through the subject's center of mass will result in a velocity

v = I/mwhere v is in ft/x, I is in lbfs, and m is in slugs; or v is in m/x, I is in Ns, and m is in kg and a peak acceleration

a=F/m where a is in ft/s2, F is in lbf, and m is in slugs; or a is in m/s2, F is in N, and m is in kg.

In reality, of course, an impulse will rarely go exactly through the center of mass to produce pure linear motion. For any offset of the force from the center of mass, a percentage of the impulse will go toward producing angular (tumbling) motion, with a corresponding decrease in linear velocity. This percentage depends on the offset distance and the subject's moment of inertia. (Moment of inertia varies considerably with body position, and so is difficult to analyze parametrically, but there will be some tumbling in practically all cases.)

Figure 4.9.2-1 Representation of Force Generated by Free-Floating Crewmember Pushing Off

A parabolic curve demonstrating relationship between push-off force and time

NASA-STD-3000 350

Figure 4.9.2-2 shows the time that a particular force can be exerted as a function of the magnitude of the force exerted, the mass of the individual, and the distance pushed. The velocity that the crewmember will have as they lose contact with the surface is also given.

Figure 4.9.2-2 Force Application and Push-Off Velocity

Time of Force Application and Push-Off Velocity
(95th percentile American male -- 99.3 kg (219 lb))
Force N(lb) Time in sec. for 0.3 m (1 ft) push-off Push-off velocity m/sec (ft/sec) Time in sec. for 0.6 m (2 ft) push-off Push-off velocity m/sec (ft/sec)
4.45 (1) 3.66 0.16 (0.52) 5.18 0.23 (0.75)
22.25 (5) 1.64 0.37 (1.21) 2.31 0.52 (1.71)
44.50 (10) 1.16 0.52 (1.71) 1.64 0.73 (2.40)
89.00 (20) 0.82 0.73 (2.40) 1.16 1.04 (3.41)

 

Time of Force Application and Push-Off Velocity
(72.6 kg (160 lb individual))
Force N(lb) Time in sec. for 0.3 m (1 ft) push-off Push-off velocity m/sec (ft/sec) Time in sec. for 0.6 m (2 ft) push-off Push-off velocity m/sec (ft/sec)
4.45 (1) 3.12 0.19 (0.63) 4.42 0.27 (0.89)
22.25 (5) 1.40 0.42 (1.41) 1.98 0.61 (2.00)
44.50 (10) 0.99 0.61 (2.00) 1.40 0.86 (2.82)
89.00 (20) 0.70 0.86 (2.82) 0.99 1.21 (3.97)

 

Time of Force Application and Push-Off Velocity
(5th percentile Japanese Female -- 40.3 kg (89 lb))
Force N(lb) Time in sec. for 0.3 m (1 ft) push-off Push-off velocity m/sec (ft/sec) Time in sec. for 0.6 m (2 ft) push-off Push-off velocity m/sec (ft/sec)
4.45 (1) 2.33 0.26 (0.85) 3.30 0.36 (1.18)
22.25 (5) 1.04 0.57 (1.87) 1.47 0.81 (2.66)
44.50 (10) 0.74 0.82 (2.69) 1.04 1.15 (3.77)
89.00 (20) 0.52 1.15 (3.77) 0.74 1.63 (5.35)

Note: Please be aware that all of the above data was gathered under 1-g conditions.

Reference: 335; NASA-STD-3000 197

4.9.3 Strength Design Requirements

{A}

Strength data that shall be used to guide design work are provided below. The weakest crew member in the specified design population shall be accommodated.

(Refer to Reference 16 for additional data on 1-G strength.)

a. Grip Force:

1. Grip strength, as a function of the size of the gripped object, is provided for men in Figure 4.9.3-1.

2. Maximum grip strength for men (5th, 50th, and 95th percentile) is given in Figure 4.9.3-2.

3. Grip strength for females is shown in Figure 4.9.3-3.

b. Arm, Hand, and Thumb/Finger Strength - Figure 4.9.3-4 presents arm, hand and thumb/finger strength for fifth percentile males. These figures must be corrected for females (see Figure 4.9.3-5).

c. Male/Female Muscular Strength - Figure 4.9.3-5 provides a comparison of male and female muscular strength for different muscle groups. These data allow a more accurate extrapolation from male to female strength data than is provided by the old method of assuming females have two thirds the strength of men.

(Refer to Reference 16 for more detailed male/female comparison data.)

d. Static Push Force - Maximal static push forces for adult males are shown in Figure 4.9.3-6. While these data were collected in a 1-G situation, the fact that they do not depend on friction resulting from body weight makes them applicable to microgravity. Corrections will have to be made for females (see Figure 4.9.3-5).

e. Leg Strength - Leg strength for the 5th percentile male as a function of various thigh and knee angles is reported in Figure 4.9.3-7. Estimates of female leg strength can be made from these data using the correction factors provided in Figure 4.9.3-5.

f. Torque Strength - Maximum hand torque data are provided in Figure 4.9.3-8.

Figure 4.9.3-1 Male Grip Strength as a Function of the Separation Between Grip Elements

Graph displaying male grip strength as a function of the separation between grip elements

Note: 44 subjects, all pilots or aviation cadets

Reference: 1, p. 2.5-19; NASA-STD-3000 200

Figure 4.9.3-2 Grip Strength for Males

Population Percentiles, N (lb)
U.S. Air Force personnel, air crewmen 5th 50th or mean 95th Population S.D.
Right hand 467 (105) 596 (134) 729 (164) 80.1 (18.0)
Left hand 427 (96) 552 (124) 685 (154) 71.2 (16.0)

Reference: 1, p. 2.5-18; NASA-STD-3000 201

 

Figure 4.9.3-3 Grip Strength for Females

Population Percentiles, N (lb)
5th 50th or mean 95th Population S.D.
U.S. Navy personnel
Mean of both hands
258 (58) 325 (73) 387 (87) 39.1 (8.8)
U.S. Industrial workers:
Preferred hand
254 (57) 329 (74) 405 (91) 45.8 (10.3)

Reference: 1, p. 2.5 - 18; NASA-STD-3000 202

 

Figure 4.9.3-4 Arm, Hand, and Thumb/Finger Strength (5th Percentile Male Data)

Figure showing Arm, hand, and thumb/finger strength
(1) (2) (3) (4) (5) (6) (7)
Degree of elbow flexion (rad) Pull Push Up Down In Out
L** R** L R L R L R L R L R
π 222 231 187 222 40 62 53 75 58 89 36 62
5/6 π 187 249 133 187 57 80 80 89 67 89 36 67
2/3 π 151 137 116 160 76 107 93 116 89 98 45 67
1/2 π 142 165 98 160 76 89 93 116 71 80 45 71
1/3 π 116 107 96 151 67 89 80 89 76 89 53 76
Hand and thumb-finger strength (N)
(3) (9)
(10)
Hand grip Thumb-finger grip {Palmer} Thumb-finger grip {tips}
L R
Momentary hold 250 260 60 60
Sustained hold 145 155 35 35

Note:
*   Elbow angle shown in radians
** L=Left; R=Right

Arm Strength (lb)
(1) (2) (3) (4) (5) (6) (7)
Degree of elbow flexion (deg) Pull Push Up Down In Out
L* R* L R L R L R L R L R
180 50 52 42 50 9 14 13 17 13 20 8 14
150 42 56 30 42 15 18 18 20 15 20 8 15
120 34 42 26 36 17 24 21 26 20 22 10 15
90 32 37 22 36 17 20 21 26 16 18 10 15
60 26 24 22 34 15 20 18 20 17 20 12 17
Hand and thumb-finger strength (lb)
(3) (9) (10)
Hand grip Thumb-finger grip {Palmer} Thumb-finger grip {tips}
L R
Momentary hold 56 59 13 13
Sustained hold 33 35 8 8

Note: * L=Left; R=Right

Reference: 2, p. 113; NASA-STD-3000 203

Figure 4.9.3-5 Comparison of Female vs. Male Muscular Strength

Graph showing comparison of female vs. male muscular strength

Note:

Female strength as a percentage of male strength for different conditions. The vertical line within each shaded bar indicates the mean percentage difference. The end points of the shaded bars indicate the range.

Reference: 16, p. VII-50; NASA-STD-3000 204

Figure 4.9.3-6 Maximal Static Push Forces

Figures Force-plate (1) height Distances (2) Force, N (lbf)
Means SD
Both hands
Sketch of a man from side view pushing on a force plate
100 percent of shoulder height 50 583 (131) 142 (32)
60 667 (150) 160 (36)
70 983 (221) 271 (61)
80 1285 (289) 400 (90)
90 979 (220) 302 (68)
100 645 (145) 254 (57)
Preferred Hand
50 262 (59) 67 (15)
60 298 (67) 71 (16)
70 360 (81) 98 (22)
80 520 (117) 142 (32)
90 494 (111) 169 (38)
100 427 (96) 173 (39)
Percent of thumb tip reach*
Frontal sketch of man pushing against 2 walls 100 percent of shoulder height 50 369 (83) 138 (31)
60 347 (78) 125 (28)
70 520 (117) 165 (37)
80 707 (159) 191 (32)
90 325 (73) 133 (30)
Percent of span **
Side sketch of man pushing against wall with foot wedged against another wall 50 100 774 (174) 214 (48)
50 120 778 (175) 165 (37)
70 120 818 (184) 138 (31)
Percent of shoulder height 1-g applicable data

Notes:

(1) Height of the center of the force plate - 200 mm (8 in.) high by 254 mm (10 in.) long - upon which force is applied. (2) Horizontal distance between the vertical surface of the force plate and the opposing vertical surface (wall or footrest, respectively) against which the subject brace themselves.

*Thumb-tip reach - distance from backrest to tip of subjects thumb as thumb and fingertips are passed together.

**Span - the maximal distance between a persons fingertips as he extends his arms and hands to each side. (3) 1-g data

Reference: 1, pp. 2.5-5, 2.5-6; NASA-STD-3000 205

 

Figure 4.9.3-7 Leg Strength at Various Knee and Thigh Angles (5th Percentile Male Data)

Graph showing Leg strength at various knee and thigh angles

Reference: 1, p. 115; NASA-STD-3000 206

 

Figure 4.9.3-8 Torque Strength

Maximum Torque Strengths
Maximum Torque Type Unpressurized suit, bare handed
Mean
Nm (lb-in)
SD
Nm (lb-in)
Maximum Torque Supination
Sketch demonstrating suppination (right forearm rotates clockwise)
13.73 (121.5) 3.41 (30.1)
Maximum Torque Pronation
Sketch demonstrating pronation (right forearm rotates counter-clockwise)
17.39 (153.9) 5.08 (45.0)

Reference: 1, pp. 2.5 - 20; NASA-STD-3000 207

4.10 WORKLOAD

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4.10.1Introduction

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This section covers workload considerations including aerobic power, aerobic endurance, and aerobic efficiency, as well as design factors such as optimum workload, task selection, and task complexity.

4.10.2 Workload Design Considerations

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Workload related factors that should be considered when designing for optimum crewmember performance are presented below.

a. Endurance (Aerobic Power) - Two complex factors determine the limits of an individual's capacity to produce work and generate the requisite power. One of these is the capacity to sustain output over a period of time (this is a function of aerobic power). The second is strength (discussed in Paragraph 4.9).

1. Aerobic power - Aerobic power is the total power that an individual generates. It is related to usable power output by an efficiency factor (see 5" below). Aerobic power is expressed as volume of oxygen used per unit time. It is also commonly expressed in food calories oxidized per unit time, when referring to workload for a given task.

2. Resting metabolic rate - At rest (zero external workload), the ratio of oxygen consumed to body mass has been found to be quite consistent across individuals [3.5 mL/kg/min (0.1 in3/lb/min)] and is called the resting metabolic rate or 1 MET.

3. Maximum aerobic power - An individual's maximum aerobic power can range from two times the resting rate for an invalid to 23 times for a champion marathon. The average person will have a maximum aerobic power of 8 to 12 times resting metabolic rate. As with rest, the energy demands for a given workload are reasonably consistent across individuals. Thus, their ability to perform becomes a function of the ratio of their capacity to the demand.

4. Aerobic endurance - Aerobic endurance is a function of the individual's maximum aerobic power, and determines how long an individual can perform tasks of moderate to heavy intensity. Maximum effort can be maintained for only a few minutes, while up to 40% of maximum can be maintained over an 8-hr work shift with typical rest breaks (see Figure 4.10.2-1). Most people would judge work requiring 40% of their maximum aerobic capacity as moderate to heavy, but tolerable for 8 hours. Tasks that may be performed by any of a number of crewmembers should keep metabolic energy requirements 10 to 20% lower than that which would be considered tolerable by the least fit of the users.

Figure 4.10.2-1 Aerobic endurance: Duration and Workload

Percent of individual's VO2 max Duration2 Crewmember mass3 28 mL/kb/min kcal/hr4 (Btu/hr) 42 mL/kb/min kcal/hr4 (Btu/hr) 56 mL/kb/min kcal/hr4 (Btu/hr)
100 5 min 54 454 (1800) 680 (2700) 907 (3600)
74 622 (2470) 932 (3700) 1243 (4930)
90 30 min 54 409 (1620) 621 (2470) 815 (3240)
74 560 (2220) 839 (3330) 1119 (4440)
80 60 min 54 363 (1440) 544 (2160) 726 (2880)
74 498 (1980) 746 (2960) 994 (3950)
50 3.5 hr 54 227 (900) 340 (1350) 454 (1800)
74 311 (1230) 466 (1850) 622 (2470)
40 8.0 hr 54 182 (720) 272 (1080) 363 (1440)
74 249 (990) 373 (1480) 497 (1970)

Notes:

1. Vo2 = aerobic power (consumed volume of O2 per unit time)
    Exemplary fitness levels:
       28 mL/kg/min (0.78 in3 /lb/min) would be considered "fair" for the general female population and is below the average of the U.S. female astronauts selected to date.
       42 mL/kg/min (1.16 in3 /lb/min) would be considered "average" for males and approximates the average for the U.S. male astronauts selected to date.
       56 mL/kg/min (1.55 in3 /lb/min) would be considered "high" for the males and is well above average for the U.S. male astronauts selected to date.

2. Nominal durations that individuals can maintain aerobic power levels as percent of their maximums. Durations greater than one hour normally require 10 minutes rest per hour, greater than 4 hours, a "lunch (rest) break" of approximately one hour.

3. Upper values assume a person of 54 kb (120 lb) and lower values one of 74 kb (163 lb).

4. Rate of caloric expenditure (kcal/hr) that can be maintained as tolerable for the corresponding duration. (NOTE: EVA activities have averaged about 230 kcal/hr).

Reference: 351, NASA-STD-3000 208

5. Aerobic efficiency - In a shirtsleeve environment on Earth, human efficiency ranges from approximately 35% to below 10%, depending on specific movement patterns. In cycling, for example, the human has an efficiency of about 21%. Thus, the useful power output for an individual expending 500 kcal/hr cycling would be 122 W rather than the 581 W that would result from 100% efficiency. Most of the wasted energy results in metabolic heat that must be dissipated by the person.

b. Optimum Workloads - It is important to try to maintain work loads that are close to optimum for each individual. This is especially true on longer duration flights. Optimum work loads mean not only to avoid overloading the individual but also not to underload them. Both of these conditions have been shown to lead to decreased performance.

c. Biomedical Changes - Biomedical changes, such as diminished musculoskeletal strength and reduced cardiac activity, can adversely affect work capacity. In-flight decrements in exercise capacity approaching 10% have been observed in some astronauts. These effects are likely to be more severe on longer missions and should be controlled to the extent possible by in-flight countermeasures such as exercise and diet.

d. Workload Prediction - It should be noted that a preponderance of evidence from previous flight experience implies several mechanisms which contribute to the difficulty of predicting workloads and task times during missions. These mechanisms include:

1. Effects of Space Adaptation Syndrome. These tend to increase task times due to the tendency for affected crewmembers to limit head motions. The effects are particularly evident during activation phases involving unstowage and frequent movements within the spacecraft, and are less evident with fully adapted crewmembers after the first few days in orbit.

2. Effects of Inappropriate Workstation Design - As noted in paragraph 4.9.2.d, workstation design can either support or confound task performance microgravity, with task difficulties ranging from slightly easier to significantly more difficult than the same task performed in one-g, depending on the success of the workstation design.

3. Proficiency Loss - Depending on the criticality of a task and its occurrence within the mission timeline, the length of time since a particular task was last performed in a training exercise may be significantly greater than the time between training sessions leading up to launch.

4. Adaptation to Microgravity Operations - This is a steep but significant learning curve associated with living and working in microgravity which often results in greatly decreased task times for second and subsequent performances of similar tasks as compared with the initial performance.

These mechanisms act independently and together to increase task times, particularly during early portions of a mission. Designers and mission planners should anticipate these changes and should allow for task time increments of from 25% to 100% compared with one-g experience.

e. Task Complexity and Fatigue - Simple tasks can be performed effectively at much higher levels of fatigue than more complex tasks. Thus, in designing the daily schedules, it would be beneficial to place the complex tasks during periods of least fatigue.

4.11 Effects of Deconditioning

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4.11.1 Introduction

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4.11.2 Effects of Deconditioning Design Considerations

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4.11.3 Effects of Deconditioning Design Requirements

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Figure 4.11.3-1 presents design requirements and constraints for accommodating deconditioned crewmembers. In establishing these requirements, different levels of conservatism were applied to normal, and to backup/contingency activities. Activities normally required for safe return must assure success for highly deconditioned crews. Activities associated with off-nominal, low probability situations are based on more optimistic estimates of crew capability. In applying these requirements, the following must be observed:

a. Crew activities and implementation methods listed are not presented as requirements, but as a catalog of candidates for which the crew may be used if the associated requirements and constraints are met. If activities or implementation methods not listed herein are intended, they must be submitted to the emergency vehicle Project Office for approval and subsequent incorporation into this document.

b. For design purposes, deconditioning effects are assumed significant only during reentry and subsequent mission phases. For operations prior to entry interface (0.2g), other sections of this document are to be applied without derating for deconditioning.

c. All crewmembers will remain in their couches or seats appropriately restrained, throughout reentry and landing. After landing, the crew will not be required to leave their couches or seats or release their restraints until the vehicle is upright. For nominal mission, post landing activities must not require the crew to stand without assistance by ground personnel.

d. The crew shall not be required to perform any tasks during transient environments associated with parachute opening or disreefing, landing retrorocket firing, or landing impact.

e. Not accommodated as used in Figure 4.11.3-1 specifies that the crew shall not be required to perform the activity. This does not necessarily imply that the crew is not able to perform the activity.

f. Post Landing items 10 thru 14 are considered off-nominal/non-routine activities.

Figure 4.11.3-1 Capabilities of a Deconditioned Crew Re-entry Through Final Descent

Potential Crew Activity/Implementation Design Requirements/Constraints
Environment
-2 < Gx < 2 2 < Gx < 4
1. Monitor displays:
- Alpha-numeric
- Graphical
- Analog
- Discrete
a. Displays must be within eye and head movement limits of Fig. 9.2.4.2.2-2 with lateral head movement of ±30 degrees and viewing distance limits of para. 9.2.4.2.2.a.

b. Must not require lifting the head.

a. Displays must be within eye and head movement limits of Fig. 9.2.4.2.2-2 with lateral head movement of ± 30 degrees and viewing distance limits of para. 9.2.4.2.2.a.

b. Must not require lifting the head.

2. Read checklist data:
a. Computer screen
b. Hard copy
a. See 1.a., 1.b

b. Hardcopy must be within visibility limits of 2.a. and reach envelope of para. 3.3.3.3.1.a.

a. See 1.a., 1.b

b. Hardcopy must be within visibility limits of 2.a. and reach envelope of para. 3.3.3.3.1.a.

3. Actual discrete controls:
- Toggle
- Push button
- Keyboard
- Rotary

a. Controls must be within visibility limits of 1.a or meet the blind operation actuation requirements of para. 9.3.3.1.g and within reach envelope of para. 3.3.3.3.1.a

b. Keystroke requirements should be minimized.

a. Controls must be within visibility limits of 1.a or meet the blind operation actuation requirements of para. 9.3.3.1.g and within reach envelope of para. 3.3.3.3.1.a

b. Keystroke requirements should be minimized.

4. Actuate analog controls:
a. Rotary
b. Linear

a. See 3.a.

b. Specific applications must be approved.

a. Specific applications must be approved.

b. Specific applications must be approved.

5. Communicate with Mission Control & SAR:
a. Vox
b. PTT

a. No constraints.

b. See 3.a.

a. No constraints.

b. See 3.a.

6. Monitor physical cues:
a. Vehicle motion
b. Aural (alarms)
c. Aural (equipment operation)
d. Out the window (visual)
a. Not accommodated.

b. Aural alarms must meet the requirements specified in para. 9.4.4.

c. Specific applications must be approved.

d. Specific applications must be approved.

a. Not accommodated.

b. Aural alarms must meet the requirements specified in para. 9.4.4.

c. Not accommodated.

d. Not accommodated.

7. Monitor patient
a. Direct visual observation of patient
b. Monitor medical support equipment
a. Attendant must be able to directly view the full side view of the patient from the waist up within the head and eye movement specified in para. 9.2.4.2.2.c.

b. The medical support equipment must be visible within the field of view specified in para. 9.2.4.2.2.c.

a. Attendant must be able to directly view the full side view of the patient from the waist up within the head and eye movement specified in para. 9.2.4.2.2.c.

b. Not accommodated

NASA-STD-3000 460A

Figure 4.11.3-1 Capabilities of a Deconditioned Crew Post-Landing

Potential Crew Activity/Implementation Design Requirements/Constraints
Environment
1-G Upright 1-G Inverted
1. Monitor displays:
- Alpha-numeric
- Graphical
- Analog
- Discrete
a. Displays must be within eye and head movement limits of para. 9.2.4.2.2.c and viewing distance limits of para. 9.2.4.2.2.a. Rapid head movement should not be required a. Displays must be within eye and head movement limits of para. 9.2.4.2.2.c, and viewing distance limits of para. 9.2.4.2.2.a. Rapid head movement should not be required.
2. Read checklist data:
a. Computer screen
b. Hard copy
a. See 1.a.

b. Hardcopy must be within visibility limits of 2.a. and reach envelope of para. 3.3.3.3.1.a.

a. See 1.a.

b. Hardcopy must be within visibility limits of 2.a. and reach envelope of para. 3.3.3.3.1.a.

3. Actual discrete controls:
- Toggle
- Push button
- Keyboard
- Rotary
a. Controls must be within visibility limits of 1.a or meet the blind operation actuation requirements of para. 9.3.3.1.g and within reach envelope of para. 3.3.3.3.1.a a. Controls must be within visibility limits of 1.a or meet the blind operation actuation requirements of para. 9.3.3.1.g and within reach envelope of para. 3.3.3.3.1.a
4. Actuate analog controls:
a. Rotary
b. Linear
a. See 3.a.

b. Specific applications must be approved.

a. See 3.a.

b. Specific applications must be approved.

5. Communicate with Mission Control & SAR:
a. Vox
b. PTT
a. No constraint.

b. No constraint.

a. Crew must be restrained in couch or seat.

b. Crew must be restrained in couch or seat.

6. Monitor physical cues:
a. Vehicle motion
b. Aural (alarms)
c. Aural (equipment operation)
d. Out the window (visual)
a. Only inverted or upright attitude determination is accommodated.

b. Aural alarms must meet the requirements specified in para. 9.4.4. Crew must be able to discern cues from couch or seat.

c. Specific applications must be approved.

d. Specific applications must be approved.

a. Only inverted or upright attitude determination is accommodated.

b. Aural alarms must meet the requirements specified in para. 9.4.4. Crew must be able to discern cues from couch or seat.

c. Specific applications must be approved.

d. Specific applications must be approved. Crew must be able to discern cues from couch or seat.

7. Monitor patient
a. Direct visual observation of patient
b. Monitor medical support equipment
a. No constraint.

b. No constraint.

a. Attendant must be able to directly view the full side view of the patient from the waist up within the head and eye movement specified in para. 9.2.4.2.2.c.

b. Medical support equipment must be visible within the field of view specified in para. 9.2.4.2.2.c.

8. Adjust medical equipment and provide medical assistance to patient. a. No constraint.

b. Attendant may exit couch or seat to provide assistance. The crewmember must not be required to stand.

Not accommodated.
9. Assist patient in eating, drinking and personal hygiene. a. No constraint.

b. Attendant may exit couch or seat to provide assistance. The crewmember must not be required to stand.

Not accommodated.
10. Operate auxiliary equipment, retrieve supplies, and perform personal hygiene functions. a. Crew may exit couch or seat to perform activities.

b. Unrestrained mass should be less than 12 lbs.

c. Control actuation must meet the requirements specified in para. 9.3.3.

d. Crew strength capabilities should be as specified in para. 4.9.3.

e. Contingency operations which require the crew member to stand must be approved.

Not accommodated.
11. Reconfigure couches, seats or panels after landing, Operate lock/ release mechanism, raise or lower seat pan or equipment. a. Crew may exit couch or seat to perform activity.

b. Unrestrained mass should be less than:
- dynamic (water) envir. - 12 lbs.
- static (land) envir. - 20 lbs

c. Restrained loads should not exceed capabilities specified in para. 4.9.3.

d. Contingency operations which require the crew member to stand must be approved.

Not accommodated.
12. Open hatch / Operate latch mechanism a. Crew may exit couch or seat to perform activity.

b. No unrestrained mass.

c. Restrained loads should not exceed crew strength capabilities specified in para. 4.9.3.

Not accommodated.
13. Egress without outside assistance a. Crew may exit couch or seat to perform activity.

b. Crew is assumed to have the physical capability and strength of a normally conditioned crew as stated in para. 4.9.3..

Not accommodated.
14. Deploy survival equipment a. Single crew member should not be required to lift more than 20 lbs. overhead.

b. Mass of single package of survival equipment should not exceed 50 lbs.

Not accommodated.

NASA-STD-3000 460B

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