Your browser does not support javascript. Please use the navigation links below to the left.
NASA - National Aeronautics and Space Administration
Follow this link to skip to the main content
+ Contact NASA

Skip over menu links

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

Appendix C - Glossary

Skip Alphabetical Shortcut Links| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |


This appendix contains a listing of the terms used in the text and figures of Volume I. Scroll down through the list or use the alphabetical links below to go directly to the section where your word is located.

Numerical Skip to A

5th Percentile Japanese Female

Females falling at the 5th percentile based on the size of the Japanese female population. This is the smallest human size considered for design purposes.

95th Percentile Caucasian Male

Males falling at the 95th percentile based on the size of the Caucasian male population. This is the largest size considered for design purposes.

A Skip to B


The movement of a body segment away from the midline of the body or body part to which it is attached.


The rate of change of velocity with respect to time.


Reduction of alkali reserve due to excess of acid metabolites.

Actuation force

The force required to operate a mechanical device such as a tool, access door, or fastener.

Acute CO2 Toxicity

Condition of exposure to high-level concentrations of carbon dioxide; associated physiological response.

Adaptive Response

Change in structure, form, or behavior of an organism to suit a new environment.


The movement of a body segment or segment combination toward the midline of the body or body part to which it is attached.

Aerobic Power

Aerobic power is the total amount of power an individual generates. It is related to useable power output by an efficiency factor which varies with the task and the individual.

Alveolar Pressure

Gas pressure existing within alveoli.


The air-containing cells of the lungs.

Anatomical Position

A baseline posture for measuring joint motion range. The posture is standing upright, head facing forward, arms hanging down with the palms facing forward.


The sense of being troubled, irritated, or disturbed by unwanted noise.


Hypoxia especially of such severity as to result in permanent damage.


Anthropometry is the application of scientific physical measurement methods to human subjects for the development of engineering design standards and specific requirements and for evaluation of engineering drawings, mock-ups, and manufactured products for the purpose of assuring suitability of these products for the intended user population.


Nervous or fear reaction to perception of danger.


A defect of an optical system in consequence of which rays from a point fail to meet in a focal point resulting in a blurred and imperfect image.


Collapsed or airless state of all or part of the lung.


1. The mixture of gasses surrounding the Earth or filling the habitable volume of a spacecraft.

2. The pressure exerted by a column of mercury 760 mm high at 1 G, equal to 101.329 kilopascals.


B Skip to C


A periodic sound resulting from the interaction of two or more sounds of different frequencies.


See Decompression Sickness.

Binary Number System

A base 2 number system using only 1's and 0's. Well suited for electronic logic where the 1's and 0's can be represented by signal present and signal absent.


Of, relating to, or involving both ears.


Biomechanics is the interdisciplinary science (comprising mainly anthropometry, mechanics, physiology, and engineering) of the mechanical structure and behavior of biological materials. It concerns primarily the dimensions, composition, and mass properties of body segments; the joints linking the body segments together; the mobility in the joints; the mechanical reactions of the body to force fields, vibrations, and impacts; the voluntary actions of the body in bringing about controlled movements, in applying forces, torques, energy and power to external objects like controls, tools, and other equipment.

Bit-Mapped Graphics

The data that defines the pixel color which is behind the screen pixel.


See Graying of Vision.

Body Envelope

The volume envelope which just encloses the body and body motions during an activity.


Used in this document to designate mass of fecal discharge.


1. Gamma radiation emitted by an electron when it is deflected by the Coulomb field of an atomic nucleus of charge Z; the fraction of energy radiated as photons by an electron of initial energy E (Mev) is approximated numerically by ZE/1000.

2. The electromagnetic radiation produced by the sudden retardation of a charged particle in an intense electric field (as of an atomic nucleus); also : the process that produces such radiation.


The amount of light emitted or reflected from a surface.

Brightness Ratio

The ratio of the luminance of two areas or surfaces.

British Thermal Unit (Btu)

The amount of heat required to raise 1 lb of water 60 degrees F, 1 degree F.


C Skip to D


A structural housing into which drawers and shelves are installed. Generally, there is no utility connections between the cabinet and the items installed within it. See Housing.


Origin or production of cancer

Cardiac Arrhythmias

Periodic irregular heartbeat; an alteration in rhythm of the heartbeat either in time or force.

Cardiovascular System

Pertaining to the heart and blood vessels.


Vernacular descriptive of inertial resultant of human body to rotational acceleration around the x-axis. (Refer to Figure 5.3.1-1).


The formation of cataracts.

Central Acuity

Center part of the visual field.

Cerebral Hemodynamic Effects

Relating to or functioning in the mechanics of blood circulation in the brain.

Chassis Leakage Currents

Currents generated by such internal sources as filter capacitors terminated to accessible parts or ground, and capacitive and inductive coupling to accessible parts or ground. These currents can be conveyed form accessible parts and subsequently applied to a crew member.


Syndrome of chest pain, cough, and respiratory distress.

Chronic CO2Toxicity

Condition of exposure to long-term, low-level excess concentrations of carbon dioxide, associated physiological response.

Circadian Rhythms

Bodily functions rhythmically fluctuating with time. These functions include heart rate, blood pressure, body temperature, and respiratory volume. Generally, these metabolic functions slow for a period of time once during a 24 hour period. The most important activity geared to circadian rhythms is sleep.


Symptoms arising from cessation of exposure to excess CO2.

Color Saturation

Saturation is the extent to which an object has more or less color. Saturation is, therefore, relative colorfulness.


A state of profound unconsciousness caused by disease, injury, or poison.

Command Language (command set)

A set of terms, each with a precise function, used to control the operations of a computer.


The mucous membrane that lines the inner surface of the eyelids and is continued over the forepart of the eyeball.


Unwanted material or bacteria.

Continuous Noise

A noise with negligibly small fluctuations of level within the period of observation


The difference between the luminance of an object or figure C = [(Lc + Lr) - (Ld + Lr)] / (Lc + Ld + 2Lr)

and its immediate background.

C = Contrast

Lc = Object luminance

Ld = Background luminance

Lr = Reflected luminance


A manually operated hardware item used to operate or change the performance of a machine or system.

Core-Shell Concept

Concept of representing a human as a heat-producing core surrounded by a shell (skin) through which heat exchange with the environment takes place.

Coronary Occlusion

Occlusion of a branch of the arterial system that supplies blood to the heart muscle.

Coulomb Friction

Sliding or kinetic Friction.

Crew Station

Any location where a task or activity is performed. There are two basic types of crew stations: workstation and activity center.

Critical Flicker Fusion Frequency

The frequency at which a flashing light will appear as a steady state light - approximately 65 Hz.


A bluish or purplish discoloration (as of skin) due to deficient oxygenation of the blood.


D Skip to E

Dark Adaptation

Dark adaptation is the state of being adapted (sensitive) to low levels of ambient luminance (brightness). At any one time the visual system operates well within only a limited range of luminance levels. This range is centered about a particular adaptation level that is determined by the prevailing luminance. As the prevailing luminance changes the adaptation level will also change. The adaptation level shifts more quickly to higher than lower luminance levels.


An electrically conductive surface incapable of supplying sufficient energy under normal conditions to present a hazard (e.g., the output of a solid-state switch when in the "STANDBY" state).

Decompression Sickness

A sometimes fatal disorder that is marked by neuralgic pains and paralysis, distress in breathing, and often collapse and that is caused by the release of gas bubbles (as of nitrogen) in tissue upon too rapid decrease in air pressure after a stay in a compressed atmosphere; called also caisson disease, the bends.

Default Values

A value or option automatically provided by the computer system for use in processing when no alternative has been specified by the operator.


A condition of mental confusion, often with hallucinations.


The act of reducing dissolved nitrogen concentration in tissues, usually by breathing mixture devoid of nitrogen.

Dependent Elbow

The elbow being engorged with blood during acceleration.

Design Eye Volume

That volume of space in front of a workstation within which a user's head and eyes should be located to guarantee visual access to all display information. The design of displays and display layout may be guided by a specified design eye volume.


To peel off in scales.

Diluent Gas

Physiologically inert component of an atmosphere, purpose of which is to reduce oxygen partial pressure.

Direct Contact

The personal contact of a crewmember to electrically powered surfaces.

Direct Glare

Glare produced by a light source located within a person's field-of-view.


Hardware item used to present system information needed by the operator to make decisions for controlling the system.


Used in Section 8.0, Architecture, to denote a full opening body passageway. A door opening is closed with a door cover. A door cannot be sealed against a differential pressure.

Double Insulated Enclosure/Chassis

An enclosure/chassis which incorporates an insulation system comprised of basic insulation and supplementary insulation with the two insulations physically separated and so arranged that they are not subject to the same deteriorating influences (e.g., temperature, contaminants, and the like) to the same degree.


A hardware element designed to slide in and out of a cabinet, rack, or housing. See Equipment drawer.

Dry Bulb Temperature

Air temperature measured by a common thermometer.


Condition arising from differential pressures between gas pockets in body and ambient. In this document, considered to indicate greater pressure within body cavities.


A disease characterized by severe diarrhea with passage of mucus and blood and usually caused by infection.


Impairment of voluntary movements resulting in fragmented or jerky motions (as in Parkinson's disease).


Dysmetria is lack of coordination of movement typified by under- or over-shooting the intended position with the hand, arm or leg. Dysmetria of a hand can make writing and picking things up difficult or even impossible. Dysmetria that involves undershooting is called hypometria and overshooting is called hypermetria.


Difficult or labored respiration.


E Skip to f

Ear Clearing

Act of equalizing pressure between inner ear and ambient.


Vaporization of body fluids at body temperature and low barometric pressure.


An abnormal infiltration and excess accumulation of serous fluid in connective tissue or in a serous cavity (for example, Edematous Eyelids).

Edematous Eyelids

Excessive accumulation of fluid in eyelids due to the disturbances of fluid exchange.

Effective Temperature

Empirical sensory index accounting for temperature, humidity and air movement.

Electrical Shock

Sudden stimulation of the nerves and convulsive constriction of the muscles caused by the discharge of electricity through the body.


An abnormal particle such as an air bubble circulating in the blood. Compare to Thrombus.


Occlusion of a blood vessel. In the case of gas embolism, by a bubble of gas.


A condition characterized by air-filled expansions of body tissues; specifically : a condition of the lung marked by abnormal dilation of its air spaces and distension of its walls and frequently by impairment of heart action. See Mediastinal Emphysema.


The outer casing of an electrical/electronic device.

Enhancement Coding

Any of a variety of techniques used to enhance, or increase the salience of selected items of information (e.g., color coding. It is well suited for interactive computer applications.

Environmental Control

Control of ambient conditions to produce habitable environments.

Equipment Drawer

A drawer used to house subsystem components. The installed components are generally attached to the drawer using fasteners which require tools for attachment/detachment. It has utility connections to its housing's utility distribution system.


Abnormal redness of the skin due to capillary congestion.

EVA (Extravehicular Activity)

Activities performed by a space-suited crewmember in an unpressurized or space environment.

EVA Restraint

A means of stabilizing the EVA crewmember which requires physical ingress and egress by the crewmember.

EVA Workstation

Any area at which an EVA task is performed.

Exchange Rate

The increase in sound level (dBA) for which permissible exposure time is halved.

Exposure Limit

Maximum safe acceleration exposure limit as a function of vibration frequency and exposure time.


Straightening or increasing the angle between the parts of the body.


To pass by infiltration or effusion from a proper vessel or channel (as a blood vessel) into surrounding tissue.

Extravehicular Mobility Unit

An independent anthropometric space suit system that provides crewmembers with environmental protection, life support, mobility, communications, and visibility while performing various EVAs.

Eyeballs Down

Vernacular descriptive of inertial resultant of human body to linear acceleration in the upward + Gz vector. (Refer to Figure 5.3.1-1).

Eyeballs In

Vernacular descriptive of inertial resultant of human body to linear acceleration in the forward -Gx vector. (Refer to Figure 5.3.1-1).

Eyeballs Left

Vernacular descriptive of inertial resultant of human body to linear acceleration in the left yaw +Gy vector. (Refer to Figure 5.3.1-1).

Eyeballs Out

Vernacular descriptive of inertial resultant of human body to linear acceleration in the backward +Gx vector. (Refer to Figure 5.3.1-1).

Eyeballs Right

Vernacular descriptive of inertial resultant of human body to linear acceleration in the right yaw -Gy vector. (Refer to Figure 5.3.1-1).

Eyeballs Up

Vernacular descriptive of inertial resultant of human body to linear acceleration in the downward -Gz vector. (Refer to Figure 5.3.1-1).


F Skip to G


Equipment or equipment and the area dedicated to a specific crew activity. Similar to the term "Center," but "Facility" can refer to only equipment without specifying an area of use. Examples: Shaving Facilities, Recreation Facility.

Fatigue Decreased Proficiency Boundary

Acceleration boundaries as a function of vibration and exposure time for the preservation of working efficiency.


Bending or decreasing the angle between the parts of the body.


The visual movable indicator on a computer video screen that points to or marks the current position at which a character may be entered.

Foot Restraint

A restraint which stabilizes a crewmember by providing a platform for immobilizing the feet.


G Skip to H

Gas Exchange

The flow of gas through a membrane in the small air sacs in the lungs to the blood stream and vice versa.

Gas Tension

The partial pressure exerted by a gas.


A consequence of bright light sources in the visual field that cause discomfort and/or a decrease in visual functioning. The effect is worse the closer the light source is to the line of gaze. The amount of light scattering within the eye (which varies between individuals effects susceptibility to glare.

Globe Temperature

Physical composite of dry bulb temperature, radiation, and wind effects measured by placing a temperature sensing device in the center of a blackened sphere.


The elongated space between the vocal cords; also : the structures that surround this space.

Graying of Vision

Due to the draining of blood from the occipital region of the brain during acceleration, the vision begins to narrow (tunnel vision) and things appear less bright.


See Graying of Vision.

Grounded Enclosure/Chassis

An enclosure/chassis electrically connected to the ground return.

Gustatory Sensations

Pertaining to the sense of taste.


H Skip to I

Habitable Volume

Habitable volume is defined as free, pressurized volume, excluding the space required for equipment, fixtures, and stowage.

Handhold, Handrail

A handle or grasp area which is slightly larger than the hand and is used as a mobility aid, hand restraint, or as a hardware mounting surface.


An overtone having a frequency that is an integral multiple of a given primary tone.


Used in this document to denote a full body passageway. A hatch opening is closed with a hatch cover. A hatch can be sealed against a differential pressure.

Heart Arrhythmia

An alteration in rhythm of the heartbeat either in time or force. See Cardiac Arrhythmia.

Heat Exhaustion

(Also known as heat prostration) - A syndrome resulting from exposure to high temperatures; characterized by a moist, cold skin, poor circulation, a normal temperature but elevated rectal temperature, restlessness and anxiety.

Heat Stroke

The body temperature rises because of faulty heat dissipation due to high environmental temperature and humidity. Rectal temperatures may go from 106 - 100 deg F.


Blood producing. Hematopoiesis is the formation of blood or of blood cells in the living body.


Oxygen carrying cells of the blood.


Escape of blood from vessels.

Hexadecimal Number System

A base 16 number system used by computers in which each digit represents a power of sixteen. For each digit of a hexadecimal number four digits (24=16) of binary logic are required.

Hierarchical Menu

A set of embedded menus such that entries in all but the lowest level menu will produce another menu when selected.


A structure into which equipment is installed. See Cabinet, Rack.


Dealing with ambient pressures which are greater than the gas pressures in the body.


Oxygen excess condition arising when greater than normal oxygen partial pressures are encountered.


Dealing with ambient pressures which are less than the gas pressures within the body.


Abnormally low blood pressure.


Subnormal temperature of the body.


A deficiency of oxygen reaching the tissues of the body.


I Skip to J


A symbol that graphically resembles its intended meaning (e.g., a schematic drawing or a headlight on the control that is used to control an automobile's headlights).


The amount of light (luminance flux) falling on a surface. Measured in lumen/m2 lux = 0.093 ft-c. Illumination decreases with the square of the distance from a point source.

Impact Acceleration

Pulsed or short-duration accelerations of less than 1 second duration.

Impact Noise

See Impulse Noise.

Impulse Noise

A noise consisting of one or more bursts of sound energy, each of a duration less than about one second.

Inaccessible area

Any area with an opening that will accept a loose and floating object of 10mm (0.4in.) diameter and cannot be retrieved or captured by using a retrieval tool and/or crewmember reaching their hand and forearm into the area.


Tiny particles of foreign matter or air bubbles entrained in glass.


Unable to retain a bodily discharge (as urine) voluntarily. Inability to control the natural evacuation of the feces or urine; specifically, involuntary evacuation due to organic causes.


Sound at frequencies below the audibility range of the human ear, f 20 Hz.

Indirect Contact

The contact of a crewmember to electrically powered surfaces through an electrically conducting medium (e.g., probe, rod).

In-Line Circuit Leakage Currents

Unintentional currents which can flow in a conductor. These currents may result from the inability of solid-state electronics to reach an "infinite" impedance "OFF" state, as is the ability of a mechanical switch. The solid-state electronic device has a finite impedance which undesirably completes the input/output circuit thus providing a means for current to flow. Connections to in-line circuits are normally isolated from crewmember inadvertent contact by barriers and may be considered a hazard if accessible to inadvertent crewmember contact. In-line circuits with leakage currents are referred to as in "STANDBY" when placed in the high impedance state since a complete disconnect is not possible and the circuit output is still energized.

Intermittent Noise

A noise whose level suddenly drops to the level of the background noise several times during the period of observation, the time during which the level remains at a constant value, different from that of the ambient being of the order of magnitude of one second or more.

Ischial Tuberoscities

Two bony protuberances in the hip structure. These bones support a major portion of the seated body weight in 1-G conditions.

Isolated Patient Contact

A direct or indirect patient contact that is deliberately separated from the supply circuit and ground by virtue of spacings, insulation, protective impedance, or a combination thereof (e.g. intra-aortic pressure monitor).

Isometric Joystick

The isometric joystick, often referred to as a force joystick or a pressure joystick, is a lever that doesn't move. The output of the isometric joystick is a function of the amount of force applied to it.

Isotonic Joystick

The isotonic joystick, often referred to as a displacement joystick, provides an output which is proportional to the displacement of the joystick from the center.


J Skip to K



K Skip to L


Inflammation of the cornea of the eye. See Photokeratitis.

Keystone Effect

A distortion in the shape of a projected image resulting from the film plane and screen plane not being parallel. Usually, magnification will vary from top to bottom or right to left.

Kinesthetic System

Sensations originating in the sense organs of the muscles, tendons, and joints that provide us with a sense of relative body segment movement and position.


L Skip to M


The secretion of tears especially when abnormal or excessive.

Lateral Rotation

The turning away from the midline of the body.

Leakage Currents

Unconditional currents which can be applied to a crewmember.

Level Equivalent or Leq

Equivalent sound level or time-average sound level in dB. The level of steady sound which, in a stated time period and at a stated location, has the same A-weighted sound in dB energy as the time-varying sound.


A condition in which the number of white blood cells circulating in the blood is abnormally low.

Light scatter fraction

The ratio of scattered light to specular reflected light.

Line of sight

The optical axis extending from the observers eyes to the target viewed.

Line of sight deviation

The angle which the line of sight is redirected into the eye due to intervening optically refractive material (e.g., prism).

Linear Acceleration

The rate of change of velocity of a mass; the direction of movement of which is kept constant.

Local Vertical

Local vertical is achieved by a consistent arrangement of vertical cues within a given visual field to provide an definable demarcation at the crew station boundary within the visual field. A consistent local vertical within modules is highly desirable.

Long Term Mission

Any mission in which crewmembers are away from earth for a period greater than two weeks.


The photometric equivalent of the brightness of an area as viewed from a given direction. More technically, luminance flux per unit of projected area per unit solid angle. Measured in candela per square meter (cd/m2), foot-lamberts (ft-L, or millilamberts (mL). 1.0 cd/m2 0.31 mL = 0.29 ft-L. The luminance of a surface does not vary with the distance of the observer from the surface being viewed.

Luminance Ratio

The difference between the luminance of an object and its surroundings.


M Skip to N

Masking Noise

A background noise or signal with dynamic range in frequency and level sufficient to obscure another noise or signal from aural awareness.

Mean Perception

A mild shock perceived by 50% of the population.

Medial Rotation

The toning toward the midline of the body.


The space in the chest between the pleural sacs of the lungs that contains all the viscera of the chest except the lungs and pleurae; also: this space with its contents.

Mediastinal Emphysema

Accumulation of gas in the tissues of the chest, specifically in the Mediastinum. Compare to Emphysema.


A method for inputting information to a computer. The menu is a list of the available input options that may be selected.


Of, relating to, or situated on or along a meridian. A line or a plane which is normal to the line of sight.


Physiological activity involving utilization of foodstuffs and oxygen to produce tissues and provide for production of energy.


To urinate.

Minimal Passageway

A minimal passageway is a translation path which is only large enough to permit passage of a space suited crewmember with his or her long axis in the direction of travel.

Mobility Aid

A device (such as a handle) or a surface (padding which facilitates translation in a microgravity environment.


N Skip to o


A state of profound stupor, produced by toxic effect of certain substances, in diluent gas narcosis, by excessive partial pressure of diluent.

Narrow Band Noise

A simple or complex tone having intense and steady state frequency components, relative to wideband noise components, in a very narrow band (1, of the octave band or 5Hz, whichever is less) and is heard as a musical sound either harmonic or discordant.


Discomfort in stomach with aversion to food and tendency to vomit.

Neurocirculatory System

Concerned with both nervous and vascular systems.

Neutral Body Posture

The characteristic posture that the relaxed human body assumes in microgravity.

No Sensation

The level of perception only perceived by a fractional percentage of the population.

Noise Canceling

A technique to delete, neutralize, or counteract any unwanted electrical signal within a communication system that interferes with the sound or image being communicated.

Noise Shields

The physical coverings or shells used to protect or screen any unwanted electrical signal within a communication system that interferes with the sound or image being communicated.

Non-adaptive Response

Pathological response to a new environment which presents conditions beyond an organisms ability to adapt.


Having a normal level of oxygen.

Neurocirculatory collapse

R psychosomatic disorder characterized by dyspnea, palpitation, vertigo, faintness, fatigue. Tremor, caused by stress, fear, and violent exercise.


O Skip to P

Octal Number System

A base 8 number system in which each digit represents a power of eight. For each digit of an octal number three digits (23 = 8 of binary logic are required.

Octave Band

The band of frequencies where the highest frequency is twice that of the lowest frequency.

One-Third Octave Band

The band of frequencies In which the ratio of the extreme frequencies is equal to the cubic root of 2: i.e. fn/fe 1.260, where fn and fe are the highest and lowest cutoff frequencies of the band.

Orbital Replacement Unit (ORU)

A piece of equipment (a single item or module containing an assembly of components) which is designed for removal and replacement as a unit.

Ordinary Patient Connection

A direct patient contact that does not have the spacing, insulation, or protective impedance associated with an isolated patient connection (e.g., blood pressure cuff).

Orthostatic Intolerance

Difficulty in standing erect in a l-G environment. This could be due to any number of effects of exposure to microgravity (cardiovascular, muscular, skeletal, or coordination.

ORU Chassis Leakage Currents

Currents generated by such internal sources as filter capacitors terminated to accessible parts or ground, and capacitive and inductive coupling to accessible parts or ground. These currents can be conveyed from accessible parts to ground or other accessible parts and subsequently applied to a crewmember.

Overall SPL

Overall SPL (Sound Pressure Level) is interpreted as including all noise within the frequency range from 22.4 to 11,200 Hz.

Oxygen Atelectasis

Collapse of the expanded lung.

Oxygen Toxicity

Toxic effects of excess oxygen partial pressure.


P Skip to Q

Parallax Error

The perceived change in relative position of objects at different distances from an observer when viewed from different positions. Can cause errors in the reading of some instruments.


A sensation of tingling, crawling, or burning of the skin that has no objective cause.


A fit, attack, or sudden increase or recurrence of symptoms


A pass-through is a translation path which is only large enough to permit passage by an IVA clothed crewmember with his or her long axis in the direction of travel.


A pass-through area between non-adjacent modules or spaces.


A crewmember instrumented with electrical/electronic equipment.

Patient Connection Leakage Current

Leakage currents measured between patient leads at the patient interface, or between patient leads at the patient interface and ground.

Pattern Coding

A perceptual indicator used to differentiate areas of interest to the observer, or reduce operator search time.

Peak Pressure Level

Peak sound pressure for any specified time interval is the maximum absolute value of the instantaneous sound pressure in that interval.


A point on a scale indicating the percentage of persons within a population who have a body dimension of a certain size or smaller. The value of the statistical variable that marks the boundary between the consecutive intervals in a distribution of 100 intervals, each containing one percent of the total population.


The awareness of the elements of environment through physical sensation such as perceiving a mild shock.

Perfusional changes

Changes in the flow rate of blood in blood vessels.

Petechial Hemorrhages

A minute reddish or purplish spot containing blood that appears in skin, mucous membrane, serous membrane, or on a cross-sectional surf ace of an organ especially in some infectious diseases.


Photochemical injury to the cornea of the eye by ultraviolet exposure may result in photokeratoconjunctivitis. This painful condition may last for several days and is very debilitating; called also welders flash, snow blindness. See Conjunctiva.


Photokeratitis is essentially a reversible sunburn of the cornea resulting from excessive UV-B exposure. It occurs when someone spends hours on the beach or snow without eye protection. It can be extremely painful for one to two days and can result in temporary loss of vision. See Keratitis.

Physiologically Inert

Substance that does not Interact chemically with the body.


The organic processes and phenomena of an organism or any of its parts or of a particular bodily process.

Pixel Addressability

The capability to store or retrieve from, a specific location in memory, the basic unit or picture element that makes up the image displayed in a video screen.


The delicate serous membrane that lines each half of the thorax of mammals and is folded back over the surface of the lung of the same side. This membrane envelopes the lung and lining the thoracic cavity.


A condition in which air or other gas is present in the pleural cavity and which occurs spontaneously as a result of disease or injury of lung tissue or puncture of the chest wall or is induced as a therapeutic measure to collapse the lung

Postrun Headache

Headache that occurs after an event.

Predicted Four-hour Sweat Rate

Empirical index incorporating environment, work and clothing to predict sweat production.


The intentional alteration of the relative strengths of signals at different frequencies (as in radio and in disc recording) to reduce adverse effects (as noise) in the following parts of the system.

Primary Passageway

A primary passageway is a translation path which accommodates a space suited crewmember in an upright working position or neutral body posture.


A message or other signal displayed on a computer generated display advising the operator that he or she is expected to provide some specific response.


The rotation of the hand and forearm so that the palm faces backwards or downwards.


The study of the nature, degree, and effect of the spatial separation individuals naturally maintain (as in various social and interpersonal situations) and of how this separation relates to environmental and cultural factors.

Proximity Operations

Any space module related activity that is performed outside the space module and within a specified boundary.


Q Skip to S



R Skip to S

R value

Ratio of initial nitrogen partial pressure to the final total pressure.


A structure into which equipment drawers or other types of equipment mounting hardware is installed. A rack generally has a built-in utility distribution system that provides interfaces far connecting the installed equipment's utilities.

Random Noise

A sound whose instantaneous amplitudes occur, as a function of time, according to a normal (Gaussian) distribution curve. Random noise need not have a uniform frequency spectrum.

Reaction Time

The time between the presentation of a stimulus and the beginning of a response to that stimulus.

Reduced Comfort Boundary

Acceleration boundaries as a function of vibration and exposure time for the preservation of comfort.

Remote Operation

An operation which permits personnel to send and receive information or commands to a distant environment.

Replacement Unit

General term that includes Orbital replacement units (ORU), Line replacement units (LRU), and Shop replacement units (SRU).


The series of actions resulting in the supply of oxygen to tissues of the body.

Response Time

The time interval during which the actual response to the stimulus is accomplished.


A mechanism for restricting unwanted movements of an object or a person in microgravity environments. Restraints can be mechanical (such as a strap) or non-mechanical (magnetism or vacuum.

Reverberation Time

Time required for the average sound energy density in an enclosure to decrease to -60 d B of the initial value after the source has stopped.

Roentgen Equivalents, Man

The absorbed dose of any ionizing radiation which produces the same biological effects in crewmembers as those resulting from the absorption of 1 roentgen of x-rays.

Rotational Acceleration

The rate of change of the direction of a mass, the velocity of which is kept constant. In this regard, the rotational acceleration is directly proportional to the square of the velocity and inversely proportional to the radius of the turn.


S Skip to T

Sacrificial surfaces

A protective surface placed over a delicate surface which will absorb environmental damage.


An operation or facility of a VDT in which display elements make a continuous bottom-to-top vertical movement across the screen (or window) under control of the operator, with display lines appearing at the bottom edge and dropping off at the top.


A body segment is the largest dimensional mass which when moved will maintain a constant geometry.


Physical or emotional trauma; clinical manifestations of inadequate amount of circulating blood. See Impact Acceleration.

Shock - Electrical

See Electrical Shock

Shock Load

See Impact Acceleration

Signal-To-Noise Ratio

The ratio of the amplitude of the signal transmitted through an instrumentation system to the amplitude of the noise generated within the system.


Vernacular descriptive of inertial resultant of human body to rotational acceleration around the y-axis. (Refer to Figure 5.3.1-1).


1. Relating to the speed of sound in air (about 761 miles per hour or 1224 kilometers per hour) at sea level at 59°F (15°C).

2. Sound at frequencies with the human ear's audibility limit (between 20 Hz and 20KHz). See Ultrasonic, Infrasonic.

Space Module

An inhabited establishment away from the earth.

Space Motion Sickness

A malady occurring in approximately 50, of people initially exposed to microgravity. Symptoms are similar to that of motion sickness and last 2-4 days. To date, susceptibility to space motion sickness has not been predictable from responses In a l-G environment. Only limited success has been achieved in controlling space motion sickness.


Of, relating to, or having the qualities of a mirror.

Specular Glare

Glare which is created by the image of a light source reflecting off a surface within a person's field-of-view.

Specular Reflection

The reflected image of the light source corresponds very closely in size and shape to the original light source.

Speech Interference Level

The background or sound noise level in dB at frequencies between 150 and 7500 Hz that will result in the loss of intelligibility conversation.


Condition arising when gas pocket is compressed to a smaller size than its normal residual volume.


A high impedance state of an electronic device, usually to minimize the amount of energy consumed or supplied (e.g., the off state of an electronic switch).

Standard Passageway

A standard passageway is a translation path which accommodates an IVA clothed crewmember in an upright working position or neutral body posture.


Common term for apoplexy; hemorrhage into the brain, causing sudden onset of coma and neurological signs.

Subcutaneous Emphysema

Accumulation of gas under the surface of the skin.


1. To spread over or through in the manner of fluid or light.

2. A spreading or flow of any fluid of the body into surrounding tissue; an extensive superficial extravasation of blood.


The rotation of the forearm and hand so that the palm faces forward or upward and the radius lies parallel to the ulna


A character or graphic that stands for or represents - something else such as operations, quantities, elements, relations, or qualities.


The loss of consciousness resulting from insufficient blood flow to the brain.


T Skip to U


A remotely controlled mobility module which incorporates sensory and manipulative subsystems for the purpose of extending the human operator's skills and cognitive capabilities into hostile or remote environments.


A hook and lanyard which is used to attach a crewmember or a piece of hardware to a piece of hardware.

Thermal Comfort

That condition of mind which expresses satisfaction with the thermal environment. Specifically, when the core temperature is normal, and the rate of body heat storage is zero.


The production of heat, for example, muscular heat production by shivering.


Regulation of temperature, particularly self-regulation of body temperature.


Persistent decrease in the number of blood platelets that is often associated with hemorrhagic conditions.


A clot of blood formed within a blood vessel and remaining attached to its place of origin. Compare to Embolus.


A sensation of noise (as a ringing or roaring) that is caused by a bodily condition (as a disturbance of the auditory nerve or wax in the ear) and can usually be heard only by the one affected.


An aggregate of cells usually of a particular kind together with their intercellular substance that form one of the structural materials of a plant or an animal.

Touch Temperature

Temperature of objects in direct physical contact.


The quality of poison; the kind and amount of poison produced by a microorganism.

Tracheal Pressure

Gas pressure existing within the trachea (wind pipe).


To move from one place to another by use of reaction power.


The proportion of luminous flux which passes completely through a window to the eyes or sensor to the amount of luminous flux incident upon the outside of the window.


Retinal illuminance resulting from viewing a surface with a luminance of 1 cd/m2 through an artificial pupil with an area of lmm2.


A passageway which allows the crewmember to move only along his/her longitudinal axis.


Vernacular descriptive of inertial resultant of human body to rotational acceleration around the z-axis. (Refer to Figure 5.3.1-1).


U Skip to V


Sound at frequencies above the human ear's audibility limit of about 20,000 hertz -- used of waves and vibrations.


The canal that carries urine from the bladder.


V Skip to W


Narrowing of the blood vessels in order to decrease blood flow to the skin to preserve body heat.

Vasodilation (Variant: Vasodilatation)

Widening of the blood vessels to allow increased blood flow to the skin to promote heat loss.

Vestibular System

Located in the inner ear, the vestibular system is responsible for the sense of balance (and relative position of the body with respect to the environment). The vestibular system senses acceleration and direction of gravity.


A transparency located such that an observer can see from one compartment into another.

Visual acuity

Refers to the smallest resolvable detail an observer can see.

Visual Angle

The angle formed at the eye by two imaginary lines drawn to either side of the object in question.

Visual Clutter

Visual clutter results when the quantity of information in a visual display becomes great enough so that it starts to result in information overload. Accuracy and speed of performance will decline as visual clutter increases.

Visual Display Terminal

An electronic device used to present visual information - that is usually computer generated. They are used in conjunction width both the Input and output of information. Examples include: cathode ray tub (CRT), liquid crystal diode (LCD, light emitting diode (LED), plasma, and electro-luminescent (EL).


W Skip to X

Wavefront Deviation

Any change in the reflected wavefront of a set of rays as compared with the incident wavefront of the same set.

Wet Bulb Glove Temperature

Calculated refinement of globe temperature by weighting dry bulb and wet bulb temperatures with the standard globe temperature.

Wet/Dry Index

Calculated prediction of human stress temperature accounting for wet and dry bulb temperatures.

Wing Tab Connector

An electrical utilities or other connector with two opposed radial tabs to facilitate EVA connect or disconnect.


X Skip to Y


The axis of a plane Cartesian coordinate system parallel to which ordinates are measured. This refers to the direction of back to chest, anatomically.


Y Skip to Z


The axis of a plane Cartesian coordinate system parallel to which ordinates are measured. This refers to the direction of right to left side, anatomically.




The axis of a plane Cartesian coordinate system parallel to which ordinates are measured. This refers to the direction of foot or buttocks to head, anatomically.


FirstGov - Your First Click to the US Government Skip over links
+ Web Privacy Policy | Accessibility
+ Human Health & Performance Directorate
+ Johnson Space Center
NASA - National Aeronautics and Space Administration Skip over links
Curator: HHPIT AppDev Team
Content Manager: Jurine Adolf
NASA Official: Lucy Barnes-Moten
Last Updated: 02/27/2024
+ Contact Us