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- Mach = Mach
- Some writers use Mach as a unit of speed equivalent to a Mach number of
1.00, as a speed of Mach 3.1.
- Mach angle
- The angle between a Mach line and
the direction of movement of undisturbed flow. See Mach wave.
- Mach cone
- 1. The cone-shaped shock wave
theoretically emanating from an infinitesimally small particle moving at
supersonic speed through a fluid medium. It is the locus of the Mach Lines.
- 2. The cone-shaped shock wave generated by a sharp-pointed body, as at the
nose of a high-speed aircraft. See Mach wave.
- Mach indicator = Machmeter.
- machine error
- See error,
- machine language
- 1. A language,
occurring within a computer,
ordinarily not perceptible or intelligible to persons without special
equipment or training.
- 2. A translation or transliteration of sense 1 into more conventional characters
but frequently still not intelligible to persons without special training.
- machine word
- For a given computer, the
number of information characters
handled in each transfer. This number is usually fixed, but may be variable in
- Mach line
- A line representing a Mach wave; a
- An instrument that measures and indicates speed relative to the speed of
sound, i.e., that indicates the Mach
number. Also called Mach indicator.
- Mach number (symbols M, NMa)
- (Pronounced mock, after Ernst Mach, 1838-1916, Austrian scientist).
A number expressing the ratio of the speed of a body or of a point on a body
with respect to the surrounding air or other fluid, or the
speed of a flow, to the speed of
sound in the medium; the speed represented by this number. See Cauchy
- If the Mach number is less than 1, the flow is called subsonic
and local disturbances can propagate ahead of the flow. If the Mach number is
greater than 1, the flow is called supersonic and disturbances cannot
propagate ahead of the flow with the result that shock waves form.
authorities use mach number but engineering practice is to use a
capital M in all words and combinations employing Mach.
- Mach wave
- 1. A shock wave
theoretically occurring along a common line of intersection of all the
pressure disturbances emanating from an infinitesimally small particle moving
at supersonic speed through a fluid medium,
with such a wave considered to exert no changes in the condition of the fluid
passing through it.
- The concept of the Mach wave is used in defining and studying the realm
of certain disturbances in a supersonic field of flow.
- 2. A very weak shock wave appearing, e.g., at the nose of a very sharp
body, where the fluid undergoes no substantial change in direction.
- Maclaurin series
- See Taylor
- Large enough to be visible to the naked eye or under low order of
- The technology of sound at signal
amplitudes so large that linear
approximations are not valid.
- magic tee
- A compound waveguide or
coaxial tee with four arms which exhibits directional characteristics, when
properly matched, so that a signal entering one arm will be split between two
of the other arms but not the third. A signal entering
another arm is likewise split with half the energy entering one of the arms
common to the other input but not its second arm and the other half of the
energy entering the arm not used by the other input.
- The magic tee is used in radar as a transmitter-receiver duplexer.
- (A trade name, from magnetic + synchronous; often capitalized). An
electromagnetic device that transmits the direction of a magnetic
field from one coil to another, used to transmit measurements electrically
from a point of measurement to an indicator in
a remote-indicating system.
- A body which produces a magnetic
field around itself.
- 1. Of or pertaining to a magnet.
- 2. Of or pertaining to a material which is capable of being magnetized.
- 3. Related to or measured from magnetic north.
- magnetic bay
- A small magnetic disturbance whose magnetograph
resembles an indentation of a coastline.
- On earth, magnetic bays occur mainly in the polar regions and have
durations on the order of a few hours.
- magnetic binary core = binary
- magnetic character figure = C-index.
- magnetic core = binary
- magnetic crotchet
- A sudden change in the earth's magnetic
field due to an increase in the conductivity of the lower ionosphere. See
- magnetic current sheath
- See plasma
- magnetic declination (symbol D, )
- In terrestrial
magnetism; at any given location, the angle between the geographical meridian and
meridian; that is, the angle between true north and magnetic north. Also
called declination , and in navigation, variation.
- Declination is either east or west according as the
compass needle points to the east or west of the geographical meridian. Lines
of constant declination are called isogonic lines and the one of zero
declination is called the agonic line.
- magnetic deviation
- The angle between the magnetic
meridian and the axis of a compass card, expressed in degrees east or west
to indicate the direction in which the northern end of the compass card is
offset from magnetic
north. Also called deviation. Compare variation.
- magnetic dip (symbol i)
- The angle between the horizontal
and the direction of a line of force of the earth's magnetic
field at any point. Also called magnetic inclination, magnetic
latitude, inclination, dip.
- magnetic dipole moment = magnetic
- magnetic disturbance daily variation (symbol
- A periodic variation of the earth's magnetic
field that is in phase with solar (local) time. It is the difference
between the solar daily variation (or the disturbed-day solar daily variation)
and the quiet-day solar daily variation. This variation is primarily an effect
of enhanced electromagnetic radiation during increased solar activity.
- magnetic disturbed-day solar daily variation (symbol
- The solar
daily variation of the earth's magnetic field obtained from the 5 most
disturbed days of the month.
- magnetic double refraction
- The splitting, into two components, of a radio wave
traveling in a region of free
electrons. This is due to the interaction of the earth's magnetic
field and the alternating field of the radio wave. Except for waves near
the components of the split wave, the ordinary ray and the extraordinary ray,
will travel with slightly different velocities and be reflected at different
heights. See magneto-ionic
- magnetic drum
- A memory device used in computers; a
rotating cylinder on which information may be stored as magnetically polarized
areas, usually along several parallel tracks around the periphery.
- magnetic element
- 1. In terrestrial magnetism, any of the following measurements: the vector
magnetic field, also called total field (symbol ); the scalar intensity of the total field (
symbol F); declination, also called variation (
symbol D); the intensity of the horizontal component of
the earth's field ( symbol H); the intensity of the
vertical component ( symbol Z), taken as positive
downward; the inclination or dip ( symbol I); the
angle between and H; the intensity of the
component of the horizontal field in the geographic north direction (
symbol X); and the intensity of the component of the
horizontal field in the geographic east direction.
- 2. That part of an instrument producing or influenced by magnetism.
- magnetic equator
- That line on the surface of the earth connecting all points at which the
dip is zero. Also called aclinic line. See geomagnetic
- magnetic equivalent amplitude indices
- A linear measure of geomagnetic disturbance activity, based on the
K-indices that gives an equivalent amplitude of the magnetic disturbance for
the 3-hour period denoted by a. A daily index
A is defined as the average of the
a value over the 8 values of the day. See magnetic
- magnetic field
- 1. A region of space wherein any magnetic dipole would
experience a magnetic force or torque; often represented as the geometric
array of the imaginary magnetic
lines of force that exist in relation to magnetic poles.
- 2. = magnetic
- magnetic field intensity
- The magnetic force exerted on an imaginary unit magnetic
pole placed at any specified point of space. It is a vector quantity. Its
direction is taken as the direction toward which a north magnetic pole would
tend to move under the influence of the field. If the force is measured in
dynes and the unit pole is a cgs unit pole, the field intensity is given in oersteds. Also
called magnetic intensity, magnetic field, magnetic field strength.
- Prior to 1932 the oersted was called the gauss; but the latter
term is now used to measure magnetic induction (within magnetic materials),
whereas oersted is reserved for magnetic force. By definition, one magnetic
line of force per square centimeter (in air) represents the field intensity of
- magnetic field strength = magnetic
- magnetic giant pulsations
- Magnetic micropulsations having large amplitudes.
- magnetic inclinations = magnetic
- magnetic induction
- A measure of the strength of a magnetic field existing within a magnetic
- The relation between the magnetic induction and magnetic field
intensity is such that the magnetic induction within a small mass of material
of magnetic permeability µ is, except for possible hysteresis effects,
µ times greater than the external magnetic field intenstiy. Whereas
magnetic field intensity is measured in oersteds,
magnetic induction is measured in gausses.
- magnetic intensity = magnetic
- magnetic K-indices
- An approximately logarithmic measure of geomagnetic disturbance activity
based on the range of the most disturbed magnetic
element during each 3-hour interval of the day. The K-indices are assigned
integers from 0 to 9.
- The K-indices averaged over the observatories of the earth are called
planetary indices K and divided into 28
- magnetic latitude = magnetic
- See geomagnetic
- magnetic lines of force
- Imaginary lines so drawn in a region containing a magnetic
field to be everywhere tangent to the magnetic
vector if in vacuum or nonmagnetic material, or parallel to the magnetic
induction vector if in a magnetic medium. See electric
lines of force.
- As so defined, these lines of force are merely convenient artifices for
delineating the geometry of a magnetic field. They are given quantitative
significance in magnetic theory by associating one line of force per square
centimeter normal to the force for every oersted of field intensity (in
vacuum), for every gauss of magnetic induction (in magnetic media).
- magnetic lunar daily variation (symbol L)
- A periodic variation of the earth's magnetic
field that is in phase with the transit of the moon.
- This variation is essentially a tidal effect. The amplitude of this
variation changes with the phase of the moon, the seasons, and the sunspot
- magnetic memory
- 1. The ability of a material to retain magnetism after the magnetizing
force is removed.
- 2. = magnetic
- magnetic meridian
- The horizontal line which is oriented, at any specified point on the
earth's surface, along the direction of the horizontal component of the
field at that point; not to be confused with isogonic
line. Also called geomagnetic meridian. Compare isoclinic
- magnetic micropulsations
- Oscillations in magnetic records having periods of
between a fraction of a minute and a few minutes, lasting for an hour or so.
- magnetic mirror
- A magnetic
field so arranged that it will theoretically confine a hot plasma.
- magnetic moment
- 1. The quantity obtained by multiplying the distance between two magnetic
poles by the average strength of the poles.
- 2. A measure of the magnetic flux set up by the
gyration of an electric charge in a magnetic
field. The moment is negative, indicating it is diamagnetic, and equal to
the energy of rotation divided by the magnetic field.
- 3. (symbol m). In atomic and nuclear physics, a moment, measured in
magnetons, associated with the intrinsic spin of the particle and with the
orbital motion of the particle in a system. Also called magnetic dipole
- magnetic north
- The direction north at any point as determined by the earth's magnetic
lines of force; the reference direction for measurement of magnetic
- magnetic pole
- 1. Either of the two places on the surface of the earth where the magnetic
dip is 90 °, that in the Northern Hemisphere (at, approximately, latitude
73° 8 N, longitude, 101° W in 1955) being designated north magnetic pole
, and that in the Southern Hemisphere (at, approximately, latitude, 68° S,
longitude, 144° E in 1955) being designated south magnetic pole. Also
called dip pole. See geomagnetic
- 2. Either of those two points of a magnet where the
magnetic force is greatest.
- 3. In magnetic theory, a fictitious entity analogous to a unit electric
charge of electrostatic theory. In nature only dipoles, not
isolated magnetic poles, exist.
- magnetic pressure
- The energy density associated with a magnetic
- In a very real sense, there is energy stored in a magnetic field, and
since energy per unit volume is equivalent to force per unit area or pressure,
one may speak of the pressure exerted by a magnetic field. For plasma
containment in a thermonuclear device, the magnetic pressure must be greater
than the kinetic pressure of the plasma. See beta
factor. A pressure of 1 atmosphere corresponds approximately to 5,000
gausses, and the pressure is proportional to the square of the field.
- magnetic quiet-day solar daily variation (symbol
- The magnetic
solar daily variation obtained from the 5 most quiet days of the month.
- magnetic solar daily variation (symbol S)
- A periodic variation of the earth's magnetic
field that is in phase with solar (local) time.
The primary source of this variation is the ionizing effect of solar
electromagnetic radiation on the atmosphere coupled with the earth's rotation.
The amplitude of this variation changes with the seasons and the sunspot
- magnetic storage
- In computer terminology, any device which makes use of the magnetic
properties of materials for the storage of information.
- magnetic storm
- A worldwide disturbance of the earth's magnetic
field. See M-region.
- Magnetic storms are frequently characterized by a sudden onset, in
which the magnetic field undergoes marked changes in the course of an hour or
less, followed by a very gradual return to normality, which may take several
days. Magnetic storms are caused by solar disturbances, though the exact
nature of the link between the solar and terrestrial disturbances is not
understood. They are more frequent during years of high sunspot number.
Sometimes a magnetic storm can be linked to a particular solar disturbance. In
these cases, the time between solar flare and onset of the magnetic storm is
about 1 or 2 days, suggesting that the disturbance is carried to the earth by
a cloud of particles thrown out by the sun.
When these disturbances are
observable only in the auroral zones, they may be termed polar magnetic
- magnetic storm-time variation (symbol
- A nonperiodic variation determined from the onset of a magnetic
storm. This variation is characterized by a rapid increase of the magnetic
horizontal intensity above the normal value, remaining so for a few hours and
then rapidly decreasing to below the normal value and remaining so for periods
up to several days. The intensity then returns slowly to the normal value.
- magnetic tape
- A ribbon of paper, metal, or plastic, coated or impregnated with magnetic
material on which information may be stored in the form of magnetically polarized
- magnetic variation
- 1. Variation,
- 2. Change in a magnetic
- magnetic wire
- Wire made of magnetic
material on which information may be stored in the form of magnetically polarized
- Of or pertaining to electricity produced by or associated with magnetism.
- Electromagnetic pertains to magnetism produced by or associated with
- magnetoelectric transducer
- A transducer
which measures the electromotive force generated by the movement of a
conductor relative to a magnetic
- magnetofluiddynamics = magnetohydrodynamics.
- magnetogasdynamics = magnetohydrodynamics.
- The trace of an instrument recording variations in the geomagnetic
- magnetohydrodynamics (abbr MHD)
- The study of the interaction that exists between a magnetic
field and an electrically conducting fluid. Also
called magnetoplasmadynamics, magnetogasdynamics, hydromagnetics.
- magnetohydrodynamic wave = Alfvén
- magnetoionic theory
- The theory of propagation of electromagnetic
radiation through a medium containing ions in the
presence of an external magnetic
- It applies to the propagation of radio waves in the ionosphere, and
provides theoretical relationships among such aspects of the subject as the
index of refraction, radiofrequency, free-electron density, electron collision
frequency, the earth's magnetic field (components relative to the direction of
propagation), the nature of polarization, etc. See magnetic
- magnetoionic wave component
- Either of the two elliptically polarized wave components into which a
linearly polarized electromagnetic
wave, incident of the ionosphere,
is separated because of the earth's magnetic
- An instrument used in the study of geomagnetism
for measuring a magnetic
- See Bohr
- magnetoplasmadynamics = magnetohydrodynamics.
- The region of the earth's atmosphere where ionized gas plays an important
part in the dynamics of the atmosphere and where the geomagnetic field,
therefore, plays an important role. The magnetosphere begins, by convention,
at the maximum of the F layer at
about 350 kilometers and extends to 10 or 15 earth radii to the boundary
between the atmosphere and the interplanetary plasma.
- 1. The phenomenon wherein ferromagnetic materials experience an elastic
strain when subjected to an external magnetic
- 2. The converse of sense 1 in which mechanical stresses cause a change in
induction of a ferromagnetic material.
- magnetostrictive delay line
- In electronic computers, a device in which a wave is induced by the
characteristic, possessed by nickel and certain other materials, of shortening
in length when placed in a magnetic field. The wave travels at the speed of
sound through the material. See delay line.
- An electron
tube characterized by the interaction of electrons with the electric field
of a circuit element in
crossed steady electric and magnetic fields to
produce alternating-current power output.
- magnitude (symbol m)
- 1. The relative luminance of
a celestial body. The smaller (algebraically) the number indicating magnitude,
the more luminous the body. Also called stellar magnitude. See absolute
- The ratio of relative luminosity of two celestial bodies differing in
magnitude by 1.0 is 2.512, the fifth root of 100.
Decrease of light by a
factor of 100 increases the stellar magnitude by 5.00; hence, the brightness
objects have negative magnitudes (Sun: -26.8; mean full moon: -12.5; Venus at
brightest: -4.3; Jupiter at opposition: -2.3; Sirius: -1.6; Vega: 0.2;
Polaris: 2.1). The faintest stars visible to the naked eye on a clear dark
night are of about the sixth magnitude (though on a perfectly black background
the limit for a single luminous point approaches the eighth magnitude). The
faintest stars visible with a telescope of aperture a (in inches) is
one approximately of magnitude . The
magnitude of the faintest stars which can be photographed with the 200-inch
telescope is about +22.7.
The expression first magnitude is often
used somewhat loosely to refer to all bodies of magnitude 1.5 or brighter,
including negative magnitudes.
- 2. Amount; size; greatness. See order of
- main bang
- The transmitted pulse, within a
- main stage
- 1. In a multistage rocket, the stage that
develops the greatest amount of thrust, with or
- 2. In a single-stage
rocket vehicle powered by one or more engines, the period when full thrust
(at or above 90 percent) is attained.
- 3. A sustainer
engine, considered as a stage after booster engines have fallen away, as
in the main stage of the Atlas.
- major axis
- The longest diameter of an ellipse or ellipsoid.
- major lobe
- See lobe.
- major planets
- The four largest planets:
Jupiter, Saturn, Uranus, and Neptune.
- Improper functioning of a component,
causing improper operation of a system.
- man-machine integration
- The matching of the characteristics and capabilities of man and machine in
order to obtain optimum conditions and maximum efficiency of the combined system. See man-machine
- man-machine system
- A system
in which the functions of the man and the machine are interrelated and
necessary for the operation of the system.
- Of a vehicle
occupied by one or more persons who normally have control over the movements
of the vehicle, as in a manned aircraft or spacecraft, or who perform some
useful function while in the vehicle.
- An instrument for measuring pressure of gases and vapors both above and
pressure. See vacuum
- manometric equivalent
- The length in millimeters of a vertical column of a given liquid at
standard room temperature equivalent to 1 millimeter of mercury at 0° C.
- many-to-few matrix = decoder.
- map-matching guidance
- 1. The guidance of a
rocket or aerodynamic vehicle by means of a radarscope
film previously obtained by a reconnaissance flight over the terrain of the
route, and used to direct the vehicle by aligning itself with radar echoes received
during flight from the terrain below.
- 2. Guidance by stellar
- March equinox = vernal
- mare (pl. maria)
- Latin for sea. The large, dark, flat areas on the lunar surface, thought
by early astronomers to be bodies of water. The term is also applied to less
well-defined areas on Mars.
- Mariotte law = Boyle-Mariotte
- marmon clamp
- A ring-shaped clamp, consisting of three equal length segments held
together by explosive
bolts, used to couple the main subsections of a rocket vehicle.
- marriage = mating.
- See planet, table.
- An amplifier
utilizing the principle of microwave amplification by
stimulated emission of radiation. Emission of
energy stored in a molecular or atomic system by a microwave
power supply is stimulated by the input
- mass (symbol m)
- A quantity characteristic of a body, which relates the attraction of this
body toward another body. Since the mass of a body is not fixed in magnitude,
all masses are referred to the standard kilogram, which is a lump of platinum.
- Mass of a body always has the same value; weight changes with change in
the acceleration of gravity.
- mass-charge ratio
- The ratio of the mass number
of an element to the number of electronic
gained or lost in ionization.
- mass-density (symbol )
- Mass per
- mass-energy equivalence
- The equivalence of a quantity of mass m and
a quantity of energy E,
the two quantities being related by the mass-energy relation, .
- This relation was proposed by Einstein as a consequence of his
restricted (or special) theory of relativity; it has subsequently received
abundant experimental confirmation and is regarded as the conversion factor
relating units of energy and mass; various useful forms of this factor are:
= (2.998 X
1010) centimeters per second = 8.987 X
1022 ergs per gram = 931.1 million electron volts per atomic mass
- mass flow rate per unit area (symbol G)
- In aerodynamics,
the product of fluid density
and the linear velocity of the fluid v or
G = pvp = lower case Rho
- mass number
- The whole number nearest the value of the atomic mass of an element as
expressed in atomic
- The mass number is assumed to represent the total number of protons and
neutrons in the atomic nucleus of the element and is therefore equal to the
atomic number plus the number of the neutrons. The mass number of an atom is
usually written as a superscript to the element symbol, as in O18,
an isotope of oxygen with mass number 18.
- mass ratio
- The ratio of the mass of the propellant
charge of a rocket to the
total mass of the rocket when charged with the propellant.
- mass-velocity ratio
- A quantity mv /mr expressing the relativistic
variation of mass with velocity.
mv is moving mass, mr is rest mass,
v is velocity, and c is the velocity of light.
- This ratio becomes important only at speeds approaching the speed of
- master station
- In a hyperbolic
navigation system, such as loran, that
transmitting station which controls the transmissions of another station or of
other stations. See hyperbolic navigation, slave
- Mate (abbr)
- Modular automatic test equipment.
- To fit together two major components
of a system.
Also called marry.
- material coordinates = Lagrangian
- material derivative = individual derivative.
- In general, the substances of which rockets and space vehicles are
composed; specifically, the metals, alloys, ceramics, and plastics used in
structural, protective, and electronic functions.
- 1. The act of fitting together two major components
of a system
as mating of a launch vehicle and a spacecraft. Also called marriage.
- 2. = interface.
- 1. Any rectangular array of elements composed of rows and columns;
specifically, such an array consisting of numbers or mathematical symbols
which can be manipulated according to certain rules.
- 2. In electronic computers, any
logical network whose
configuration is a rectangular array of intersections of its input-output
leads, with elements connected at some of these intersections. The network
usually functions as an encoder or decoder .
Loosely, any encoder, decoder, or translator.
- Matts (abbr) = multiple
airborne target trajectory system.
- maximum energy density
- See sound
- maximum evaporation rate
- The maximum rate at which molecules
could emerge from a surface, deduced from measurements of saturated vapor
pressure at the same temperature. Also called Knudsen rate of
evaporation or Langmuir rate of evaporation.
- maximum sound pressure
- For any given cycle of a
the maximum absolute value of the instantaneous sound
pressure, without regard to sign, occurring during that cycle. The unit is
- In the case of a sinusoidal sound wave, the maximum sound pressure is
also called the pressure amplitude.
- maximum usable frequency (abbr MUF)
- For a given distance from a transmitter,
the highest frequency at
waves can be received.
- Maxwellian distribution
- The velocity distribution, as computed in the kinetic
theory of gases, of the molecules of a gas in thermal equilibrium.
- This distribution is often assumed to hold for neutrons in
thermal equilibrium with the moderator
- McLeod gage
- A liquid-level vacuum gage
in which a known volume of gas, at the pressure to be
measured, is compressed by the movement of a liquid column to a much smaller
known volume, at which the resulting higher pressure is measured.
- Particular designs are named after the inventors or by various trade
- A plot of values of M-units (modified
index of refraction) as a function of height in an atmosphere. M-curves
are frequently used in ray tracing
- MCW (abbr) = modulated
- In radar, a display in which target distance is determined by moving an
along the baseline until it coincides with the horizontal position of the target signal
deflections. The control which moves the blip is calibrated in distance. Also
called M-scan, M-scope, M-indicator.
- mean = arithmetic
- mean anomaly
- See anomaly.
- mean center of moon
- A central point for a lunar coordinate system; the point on the lunar
surface intersected by the lunar radius that is directed toward the earth's
center when the moon is at the mean ascending node and when the node coincides
with the mean perigee or mean apogee.
- mean deviation = average
- mean distance = semimajor
- mean equinox
- A fictitious equinox whose position is that of the vernal
equinox at a particular date with the effect of nutation
removed. Also called mean equinox of date.
- mean equinox of date = mean
- mean error = root-mean-square
- mean free path (symbol l, , L)
- 1. Of any particle, the
average distance that a particle travels between successive collisions with
the other particles of an ensemble.
In vacuum technology, the ensemble
of particles of interest comprises only the molecules in the gas phase.
- 2. Specifically, the average distance traveled by the molecules of
gas between consecutive collisions with one another. It may be determined
roughly from either of the formulas
where l is the mean free path; u (lower case
Mu) is the dynamic viscosity; v is the kinematic viscosity; p
(lower case Rho) is the density; c is the molecular speed (a function
of the gas temperature); n is the number of molecules per unit volume;
and d is the molecule diameter.
- Given the mean free path l0 at a level where the pressure is
p0 , the temperature is T0 (°K), and the acceleration of
gravity is g0, then its value at any other level is
l = l0 p0 Tg / pT0 g0
where p, T, and g are the pressure, temperature, and acceleration of
gravity, respectively, at the new level. See mixing
- 3. For any process the reciprocal of the cross
section per unit volume for that process.
- mean motion (symbol n, µ)
- Of an object in orbit, a measure of angular velocity,
n = / P where
P = period.
- mean noon
- The instant the mean sun is over the upper branch of the reference
meridian; twelve o'clock mean time.
- mean position
- Of a star, the position on the celestial
sphere computed from past observations plus known proper
motion but not corrected for short term variations. See Besselian
- mean sea level
- The average height of the surface of the sea for all stages of the tide
over a 19-year period, usually determined from hourly height readings.
- Mean sea level is the datum from which heights are measured. In this
sense sometimes shortened to sea level. See geoid.
- mean sidereal time
time adjusted for nutation to
eliminate slight irregularities in the rate.
- mean solar day
- The duration of one rotation of
the earth on its axis, with respect to the mean sun.
- The length of the mean solar days is 24 hours of mean solar time or 24
hours 3 minutes 56.555 seconds of mean sidereal time. A mean solar day
beginning at midnight is called a civil day; and one beginning at noon,
12 hours later, is called an astronomical day. See calendar
- mean solar second
- Prior to 1960 the fundamental unit of time, equal to 1/86,400 of the mean solar
day. Now replaced by the ephemeris
- mean solar time
- See solar
- mean square
- Referring to the arithmetic
mean of the squares of the values under consideration, as mean-square
amplitude, mean-square error.
- mean-square error
- The quantity whose square is equal to the sum of the squares of the
individual errors divided
by the number of those errors.
- mean sun
- A fictitious sun conceived to move eastward along the celestial
equator at a rate that provides a uniform measure of time equal to the
time; the reference for reckoning mean time, zone time,
etc. See dynamical
- mean time
- Time based upon the rotation of
the earth relative to the mean sun.
- Mean time may be designated as local or Greenwich as the
local or Greenwich meridian is the reference. Greenwich mean time is also
called universal time. Zone, standard, daylight saving or summer, and
war time are also variations of mean time, specified meridians being used as
the reference. Mean time reckoned from the upper branch of the meridian is
called astronomical time. Mean time was called civil time in
U.S. terminology from 1925 through 1952. See equation
of time, mean
- A physical quantity, force, property or condition which is to be measured.
Also called stimulus.
- mechanical equivalent of heat (symbol J) = Joule
- mechanical system
- In the study of vibration, an
aggregate of matter comprising a defined configuration
of mass, mechanical stiffness, and mechanical resistance.
- A nerve ending that reacts to mechanical stimuli, as touch,, tension, and
- The middle term of a series, or the interpolated value of the two middle
terms if the number of terms is even. Compare mean.
- median lethal dose
- The amount of radiation
required to kill, within a specified period, 50 percent of the individuals of
a group of animals or organisms.
- medium frequency (abbr MF)
- See frequency
- mega (abbr M)
- A prefix meaning multiplied by 106.
- megacycle (abbr Mc, mc)
- One million cycles; one thousand kilocycles.
- The term is often used as the equivalent of one million cycles per
- One million parsecs. See parsec.
- A unit of acoustic
pitch. By definition, a simple tone of frequency
1000 cycles per second, 40 decibels above a listener's threshold, produces a
pitch of 1000 mels. The pitch of any sound that is judged by the listener to
be n times that of a 1-mel tone is n mels.
- membrane structure
- A shell structure, often pressurized,
that does not take wall bending or compression loads.
- The component of a computer,
control system, guidance system, instrumented satellite, or the like, designed
to provide ready access to data or instructions previously recorded so as to
make them bear upon an immediate problem, such as the guidance of a physical
object, or the analysis and reduction of data.
- memory capacity
- See storage
- memory device
- See storage.
- Men, Mens
- International Astronomical Union abbreviations for Mensa. See constellation.
- Mensa (abbr Men, Mens)
- See constellation.
- See planet, table.
- mercury memory
- The retention of information by the propagation of a sound wave
in liquid memory.
- A north-south reference line, particularly a great
circle through the geographical poles of the earth. The term usually
refers to the upper
branch, that half, from pole to pole, which passes through a given place,
the other half being called the lower branch. See coordinate,
- A terrestrial meridian is a meridian of the earth. Sometimes designated
true meridian to distinguish it from magnetic meridian, compass
meridian, or grid meridian, the north-south lines relative to magnetic,
compass, or grid direction, respectively. An astronomical meridian is a line
connecting points having the same astronomical longitude. A geodetic meridian
is a line connecting points of equal geodetic longitude. Geodetic and
sometimes astronomical meridians are also called geographic meridians.
Geodetic meridians are shown on charts. The prime meridian passes through
longitude 0°. A fictitious meridian is one of a series of great circles or
lines used in place of a meridian for certain purposes. A transverse or
inverse meridian is a great circle perpendicular to a transverse equator. An
oblique meridian is a great circle perpendicular to an oblique equator. Any
meridian used as a reference for reckoning time is called a time meridian. The
meridian through any particular place or observer, serving as the reference
for local time, is called local meridian, in contrast with the
Greenwich meridian, the reference for Greenwich time. A celestial sphere,
through the celestial poles and the zenith.
- meridian angle
- Angular distance east or west of the local celestial
meridian; the arc of the celestial
equator, or the angle at the celestial pole, between the upper
branch of the local celestial meridian and the hour circle
of a celestial
body, measured eastward or westward from the local celestial meridian
through 180°, and labeled E or W to indicate the direction of measurement. See
- meridian transit
- See transit.
- Referring to a meridian.
- A set of branches
forming a closed path in a network,
provided that if any one branch is omitted from the set, the remaining
branches of the set do not form a closed path.
- The term loop is sometimes
used in the sense of mesh.
- In the classification of a subatomic
particles by mass, the second lightest of such particles. Its mass is
intermediate between that of the lepton and the
- Mesons are highly unstable, very short-lived particles; they carry
positive, negative, or no charge, and, in a vacuum, move with velocities
approaching the speed of light. All of these particles have extremely short
lifetimes and the heavier more unstable mesons tend to decay into lighter
- The base of the inversion at the top of the mesosphere,
usually found at 80 to 85 kilometers. See atmospheric
- The temperature maximum at about 50 kilometers in the mesosphere.
- 1. The atmospheric
shell, in which temperature generally decreases with heights, extending
from the stratopause
at about 50 to 55 kilometers to the mesopause at
about 80 to 85 kilometers.
- 2. The atmospheric shell between the top of the ionosphere
(the top of this region has never been clearly defined) and the bottom of the
(This definition has not gained general acceptance.)
- 1. An ordered selection from an agreed set of symbols, intended to
- 2. The original modulating
wave in a communication system.
- The term in sense 1 is used in communication theory; the term in sense
2 is often used in engineering practice.
- metabolic reserves
- The energy source stored in chemical form, such as carbohydrates, that can
be efficiently mobilized and utilized by the body, particularly for muscular
activity and work beyond the normal level of activity of an individual.
- Pertaining to the chemistry of subatomic
- The entire system of galaxies including the Milky Way.
- metallic fuels
- Of or pertaining to nuclear
fuels which are a mixture, a pressed powder, or an alloy of a fissionable
material, such as uranium-235 or plutonium-239, and a metal such as aluminum,
zirconium, or stainless steel.
- metastable atom
- An atom
with an electron excited to an energy
level where simple radiation is forbidden and thus the atom is momentarily
stable. See forbidden
- The presence of these metastable atoms in a discharge is the cause of
several anomalous effects since in essence they are storing energy which can
be released to other particles upon collision. The Penning
effect is a result of the presence of metastable atoms.
- metastable compound
- A chemical compound of comparative stability which, however, becomes
unstable under a particular set of conditions.
- metastable propellant
- A metastable
compound used as a propellant.
- Nitromethane (CH3NO2), for example, may be used
as a monopropellant at chamber pressure above 500 pounds per square inch. At
lower pressure, it requires an oxidizer for stable combustion.
- In particular, the light phenomenon which results from the entry into the
earth's atmosphere of a solid particle from space; more generally, any
physical object or phenomenon associated with such an event. See meteoroid.
- Of or pertaining to meteors and meteoroids.
- Any meteoroid
which has reached the surface of the earth without being completely vaporized.
- Of or pertaining to meteorites.
- The study of meteorites
and meteoric and
- A solid object moving in interplanetary space, of a size considerably
smaller than an asteroid and considerably larger than an atom or molecule.
- meteorological optics = atmospheric
- meteorological rocket
- A rocket
designed primarily for routine upper
air observation (as opposed to research) in the lower 250,000 feet of the
atmosphere, especially that portion inaccessible to balloons, i.e., above
100,000 feet. Also called rocketsonde.
- The study dealing with the phenomena of the atmosphere.
This includes not only the physics, chemistry, and dynamics of the atmosphere,
but is extended to include many of the direct effects of the atmosphere upon
the earth's surface, the oceans, and life in general.
- A distinction can be drawn between meteorology and climatology, the
latter being primarily concerned with average, not actual, weather conditions.
Meteorology may be subdivided, according to the methods of approach and the
applications to human activities, into a large number of specialized sciences.
The following are of interest to space science: aerology, aeronomy, dynamic
- meteor path
- The projection of the trajectory
of a meteor
in the celestial sphere as seen by the observer.
- meteor shower
- A number of meteors with
approximately parallel trajectories.
- meteor stream
- A group of meteoric bodies with nearly identical orbits.
- meteor trail = meteor
- meteor train
- Anything, such as light or ionization, left along the trajectory of the
meteor after the head of the meteor has passed.
- meteor wake
train phenomena of very short duration, in general much less than a
- 1. (abbr m) The basic unit of length of the metric
system, defined as 1,650,763.73 wavelengths in vacuum of the unperturbed
transition 2p10 - 5d5 in krypton.
- Effective 1 July 1959 in U.S. customary system of measures, 1 yard =
0.9144 meter, exactly, or 1 meter = 1.094 yards = 39.37 inches. The standard
inch is exactly 25.4 millimeters.
- 2. A device for measuring, and usually indicating, some quantity.
- metering jet
- A jet in a
- method of attributes
- In reliability testing, measurement of quality by noting the presence or
absence of some characteristic (attribute) in each of the units in the group
under consideration and counting how many do or do not possess it.
- An example of this method is go and no-go gaging of a dimension.
- method of characteristics
- See characteristics.
- method of small perturbation = perturbation
- Metonic cycle
- A period of 19 years, after which the various phases
of the moon fall on approximately the same days of the year as in the
- The Metonic cycle is the basis for the golden numbers used to determine
the data of Easter. Four such cycles form a Callippic cycle.
- metric photography
- The recording of events by means of photography (either singly or
sequentially), together with appropriate coordinates,
to form the basis for accurate measurements.
- metric system
- The international decimal system of weights and measures based on the meter and the kilogram.
- The use of the metric system in the United States was legalized by
Congress in 1866 but was not made obligatory.
- metric wave
- See frequency
- The science of dimensional measurement; sometimes includes the science of
- Mev = million
- Mic, Micr
- International Astronomical Union abbreviations for Microscopium.
- Michaelson actinograph
- A pyrheliometer
of the bimetallic type used to measure the intensity of direct
solar radiation in terms of the angular deflection of a blackened
bimetallic strip exposed to the direct solar beams.
- International Astronomical Union Abbreviation for Microscopium. See
- micro (abbr)
- 1. (abbr µ). A prefix meaning divided by 106.
- 2. A prefix meaning very small, as in micrometeorite.
- microbar (abbr µb)
- The unit of pressure in the CGS system
and equal to 1 dyne per square centimeter; the unit of sound
- In British literature the term barye has been used.
bar properly denotes a pressure of 106 dynes per square
centimeter. Unfortunately, the bar was once used in acoustics to mean 1 dyne
per square centimeter, but this is no longer correct.
- The environment
created and maintained within a very small space, such as a pressurized
capsule or space suit, and sufficient to support life in a reasonably normal
- A satellite telemetry
system which uses phase-lock
techniques in the ground receiving equipment to achieve extreme sensitivity.
- A manometer
capable of measuring very small pressure changes or differences.
- A very small meteorite or
particle with a diameter in general less than a millimeter.
- micrometeorite penetration
- Penetration of the thin outer shell (skin) of space vehicles by small
particles traveling in space at high velocities.
- One of a class of instruments for making precise linear measurements in
which the displacements measured correspond to the travel of a screw of
accurately known pitch.
- micron (abbr µ)
- 1. A unit of length equal to one-millionth of a meter or one-thousandth of
- The micron is a convenient length unit for measuring wavelengths of
infrared radiation, diameters of atmospheric particles, etc.
- 2. = micron of
- micron liter
- One liter of gas at a pressure of
one micron of
- micron of mercury (abbr µ of Hg or µ Hg)
- A unit of pressure equal
to a pressure of 1/1000th of 1 millimeter of mercury pressure at ° C and the
standard acceleration of gravity; a millitorr (10-3 torr
approximately). See torr.
- An electroacoustic
transducer which receives an acoustic
signal and delivers a corresponding electric signal.
- Microscopium (abbr Mic, Micr)
- See constellation.
- microsecond (abbr µsec)
- One-millionth of a second.
- A unit of pressure equal to 10-6 torr. See torr.
- Of, or pertaining to, radiation in the microwave
- microwave refractometer
- A device for measuring the refractive
index of the atmosphere at microwave frequencies - usually in the
- microwave region
- Commonly, that region of the radio spectrum between approximately 1000
megacycles and 300,000 megacycles. See frequency
- Corresponding wavelengths are 30 centimeters to 1 millimeter. The
limits of the microwave region are not clearly defined but in general it is
considered to be the region in which radar operates.
- microwave turbulence
- Irregular and fluctuating gradients of microwave refractive
index in the atmosphere. See optical
- Microwave turbulence may be due either to blobby distribution of water
vapor, or to thermal turbulence.
- A two-object trajectory
measuring system whereby two complete Cotar antenna systems and two sets
of receivers at each station, with the multiplexing done after phase
comparison, are utilized in tracking more than one object at a time.
- midcourse guidance
- Guidance of a
the end of the launching phase to some arbitrary point or at some arbitrary
time when terminal
guidance begins. Also called incourse guidance. See guidance.
- Midot (abbr) = multiple
interferometer determination of trajectories.
- Mie particle
- See Mie
- Mie scattering
- Any scattering
produced by spherical particles without special regard to comparative size of
radiation wavelength and particle diameter. See Mie theory.
- Mie theory
- A complete mathematical-physical theory of the scattering
radiation by spherical particles, developed by G. Mie in 1908. In contrast
scattering, the Mie theory embraces all possible ratios of diameter to
- The Mie theory is very important in meteorological optics, where
diameter-to-wavelength ratios of the order of unity and larger are
characteristic of many problems regarding haze and cloud scattering.
Scattering of radar energy by raindrops constitutes another significant
application of the Mie theory.
- 1. One-thousandth of an inch.
- 2. A unit of angular measurement, 1/6400 of a circle.
- A unit of distance. See statute
- military grid
- Any grid
specified for use on a particular map, or series of maps, by military
- Milky Way
- The galaxy to which
the sun belongs.
- As seen at night from the earth, the Milky Way is a faintly luminous
belt of faint stars.
- milli (abbr m)
- A prefix meaning multiplied by 10-3.
- A unit of pressure equal to 1000 dynes per square centimeter, or 1/1000 of
- The millibar is used as a unit of measure of atmospheric pressure, a
standard atmosphere being equal to 1,013.25 millibars or 29.92 inches of
- A unit of acceleration
equal to 1/1000 of a gal, or 1/1000
centimeter per second per second.
- This unit is used in gravity measurements, being approximately
one-millionth of the average gravity at the earth's surface.
- millimeter (abbr mm)
- One-thousandth of a meter; one-tenth of a centimeter; 0.039370 U.S. inch.
- millimeter of mercury (abbr mm Hg)
- A unit of pressure corresponding to a column of mercury exactly 1
millimeter high at 0° C under standard acceleration of gravity of 980.665
centimeters per second square. See torr.
- By mercury at 0° C is meant a hypothetical fluid having an
invariable density exactly 13.5951 grams per cubic centimeter.
- millimetric wave
- See frequency
- millimicron of mercury (abbr mµ Hg)
- A unit of pressure equal to 10-6 millimeters of mercury or
- millimicrosecond (abbr mµsec) = nanosecond.
- million electron volt (abbr Mev)
- A unit of energy equal to 1.603 X 10-8 ergs.
- millisecond (abbr msec)
- One-thousandth of a second.
- A proposed new unit of pressure equal to 10-3 torr. See torr.
- A satellite of Saturn orbiting at a mean distance of 186,000 kilometers.
- M-indicator = M-display
- A contraction of miniature used in combination, as in
minicomponent, miniradio, minitransistor.
- Used attributively in reference to equipment, such as gimbals, gyroscopes,
computers, etc., made small to fit into confined spaces, as within an earth
satellite or rocket vehicle.
- See miniaturize.
- To construct a functioning miniature of a part or instrument. Said of
telemetering instruments or parts used in an earth satellite or rocket
vehicle, where space is at a premium. Hence, miniaturized, miniaturization.
- minimum deviation
- The least total refraction
experienced by radiation
passing through a prismatic refractive medium.
- It is important to note that the refractive deviation is minimal, in
general, only with respect to adjacent light paths, for there may exist a
number of path directions through a single object, each one of which yields a
local minimum deviation. When radiation has undergone minimum deviation, the
angular difference in path directions before and after total refraction is
termed the angle of minimum deviation.
- minimum ionizing speed
- The speed with which a free
electron must move through a given gas to be able to ionize gas atoms
or molecules by collision. In air at standard conditions, this speed is about
107 centimeters per second. See electron
- A satellite tracking system consisting of a field of separate antennas and
associated receiving equipment interconnected so as to form interferometers
which track a transmitting beacon in the payload itself.
- minor axis
- The shortest diameter of an ellipse or ellipsoid.
- minor lobe
- See lobe.
- minor planet = asteroid.
- See planet.
- minute (abbr min or ´ )
- 1. The sixtieth part of an hour.
- 2. The sixtieth part of a degree of arc.
- 1. (Optics) definition submitted by Andy Young, June 30, 1997
apparently reflected image of an object, caused by abnormal atmospheric refraction.
The most commonly seen is the inferior mirage over heated surfaces, which
often looks like a pool of water because it reflects the sky. Superior
mirages, which appear above the direct image of the object, are due to strong
thermal inversions above eye level. Other mirage-like images can be produced
by thermal inversions below eye level, and by hot air adjacent to a wall
heated by the Sun (lateral mirage).
- 2. (Radar) A refraction phenomenon in the atmosphere
wherein an image of some object is made to appear displaced from its true
position. See radio duct,
Simple mirages may be any one of three types, the inferior
mirage, the superior mirage, or the lateral mirage, depending, respectively,
on whether the spurious image appears below, above, or to one side of the true
position of the object. Of the three, the inferior mirage is the most common,
being usually discernible over any heated street in daytime during summer. The
abnormal refraction responsible for mirages is invariably associated with
abnormal temperature distributions that yield abnormal spatial variations in
the refractive index.
- Miran (abbr) = missile
- A satellite of
Uranus orbiting at a mean distance of 124,000 kilometers.
- mirror altitude
- The altitude above the earth at which electrically charged corpuscular
radiation impinging upon the earth is reflected by the geomagnetic
- mirror ratio
- See magnetic
- mirror reflection = specular
- Any object thrown, dropped, fired, launched, or otherwise projected with
the purpose of striking a target. Short for ballistic missile, guided
- Missile should not be used loosely as a synonym for rocket or
- missile ranging (abbr Miran)
- A trajectory
measuring system that measures loop ranges from a
transmitter to a beacon to remote slave stations and back to the transmitter
through comparison of time differences of pulses.
- The transmitter interrogates at 600 megacycles and the beacon replies
at 580 megacycles.
- The art or science of designing, developing, building, launching,
directing, and sometimes guiding a rocket missile; any
phase or aspect of this art or science.
- This term is sometimes spelled missilery, but is then pronounced as a
- An error,
usually large, resulting from a human failing or an equipment malfunction.
- mixed-base notation
- A system of positional
notation used in computers in
which two or more bases are arranged
according to a plan. See biquinary
- mixed-flow compressor
- A rotary compressor
through which the acceleration of fluid is partly radial and partly axial.
- mixed icing
- Mixed aircraft icing is composed of both glaze and
Typically the ice will be clear near the stagnation line of the wing with the
remainder rime. It represents about 15% of icing reports.
- mixed reflection = spread
- mixing length
- A mean length of travel, characteristic of a particular motion in a fluid
over which an eddy maintains its
identity; analogous to the mean free
path of a molecule.
- Physically, the idea implies that mixing occurs by discontinuous steps,
that fluctuations which arise as eddies with different characteristics wander
about, and that the mixing is done almost entirely by the small eddies.
- mixing ratio
- In a system of moist air, the dimensionless ratio of the mass of water vapor
to the mass of dry air. For many purposes, the mixing ratio may be
approximated by the specific
humidity. In terms of the pressure p and vapor pressure e,
the mixing ratio w is
w = (0.6222 e) / (p - e) Compare absolute
humidity, dew point.
- mixture ratio
- In liquid-propellant
rockets, the relative mass flow
rates to the combustion chamber of oxidizer and
- MKSA system
- A system of units based on the meter, kilogram, second, and ampere. Also
- MKS system
- A system of units based on the meter, the kilogram, and the second.
- 1. The average velocity or drift
velocity that a charged particle in a plasma will
acquire in response to a unit applied electric field when restrained by
collisions with other particles.
- 2. = drift
- 3. = Hall
- In general the electron mobility is considerably larger than any ion
- mock test
- An operational test of a complete rocket system
without actually firing a rocket.
- A full-sized replica or dummy of something, such as a spacecraft, often
made of some substitute material such as wood, and sometimes incorporating
actual functioning pieces of equipment, such as engines.
- A functioning position or arrangement that allows for the performance of a
- Said of a spacecraft,
which may move, for example, from a cruise mode to an encounter
mode; or said of controls that permit the selection of a mode, such as a
- model atmosphere
- 1. Any theoretical representation of the atmosphere,
particularly of vertical temperature distribution. See adiabatic
barotropic model, barotropic
- 2. = standard
atmosphere, sense 1.
- mode of vibration
- In a system undergoing vibration, a
characteristic pattern assumed by the system in which the motion of every
particle is simple harmonic with
the same frequency.
- Two or more modes of vibration may exist concurrently in a
- A material that has a high cross
section for slowing down fast
neutrons with a minimum of absorption, e.g., heavy water, beryllium, used
- Moderators are used to improve the neutron utilization by slowing the
neutrons to low energies, thereby increasing the probability of fission
capture in the nuclear fuel.
- mode shape = mode of
- modified index of refraction
- An atmospheric index
of refraction mathematically modified so that when its gradient is applied
to energy propagation over a hypothetical flat earth it is substantially
equivalent to propagation over the true curved earth with the actual index of
refraction. Also called refractive modulus, modified refractive index.
index of refraction.
- The modified index of refraction is usually expressed in M-units;
is the index of refraction at a point in the atmospheric; h is the height
above mean sea level of that point; a is the radius of the earth; and N is the
index of refraction in N-units. In ray tracing problems, the vertical gradient
dM/dh can be used directly to obtain a ray path curvature that is relative to
the curvature of the earth, i.e.,
is a value by which the earth's radius is multiplied to get the radius of
curvature of the ray path; ka is called the effective earth radius.
- modified refractive index = modified
index of refraction.
- modulated continuous wave (abbr MCW)
- A form of emission in
which the carrier is
modulated by a constant audiofrequency
- modulated wave
- A wave
which varies in some characteristic in accordance with the variations of a
modulating signal. Compare
wave. See modulation.
- modulating wave
- See modulation.
- 1. The variation in the value of some parameter characterizing a periodic
- 2. Specifically, variation of some characteristic of a radio wave,
called the carrier wave, in accordance with instantaneous values of
another wave, called the modulating wave.
- Variation of amplitude is amplitude modulation, variation of
frequency is frequency modulation, and variation of phase is phase
modulation. The formation of very short bursts of a carrier wave, separated
by relatively long periods during which no carrier wave is transmitted, is
- modulation index = ratio
- A device to effect the process of modulation.
- 1. A self-contained unit of a launch
vehicle or spacecraft
which serves as a building block for the overall structure. The module is
usually designated by its primary function as command module, lunar landing
- 2. A one-package assembly of functionally associated electronic parts,
usually a plug-in unit, so arranged as to function as a system or
subsystem; a black box.
- 3. The size of some one part of a rocket or other
structure, as the semidiameter of a rocket's base, taken as a unit of measure
for the proportional design and construction of component parts.
- modulus (plural moduli)
- 1. A real, positive quantity which measures the magnitude of
some number, as the modulus of a complex number is the square root of the
sum of squares of its components.
- 2. A coefficient
representing some elastic property of body, such as the modulus of
elasticity or the modulus of resilience.
- modulus of elasticity (symbol E) = Young
- Mögel-Dellinger effect = fadeout.
- moist adiabatic lapse rate = saturation
adiabatic lapse rate.
- Pertaining to a mole, or measured
- See tektite.
- mole (abbr mol)
- The amount of substance containing the same number of atoms as 12 grams of
pure carbon12 (C12).
- The gram-mole or gram-molecule is the mass in grams numerically equal
to the molecular weight.
- molecular drag gage
- A vacuum
gage in which tangential momentum is
transported (viscous transport) by gas molecules from a rapidly rotating
member (usually in the form of a disk or cylinder) to a nearby movable member
restrained by a restoring torque which can be correlated with gas pressure.
Also called molecular gage, rotating disk gage, rotating cylinder gage.
- molecular effusion
- The passage of gas through a
single opening in a plane wall of negligible thickness where the largest
dimension of the hole is smaller than the mean free
- molecular flow
- The flow of gas through a duct under conditions such that the mean free
path is greater than the largest dimension of a transverse section of the
- molecular flux
- The net number of gas molecules
crossing a specified surface in unit time, those having a velocity component
in the same direction as the normal to the surface at the point of crossing
being counted as positive and those having a velocity component in the
opposite direction being counted as negative.
- molecular gage = molecular
drag gage .
- molecular scale temperature (symbol TM
- An atmospheric parameter defined by TM = (M0 /
M)T where M0 is the mean molecular weight at sea level,
M is the mean molecular weight at altitude, and T is air
temperature at altitude.
- Up to an altitude of about 90 kilometers, the molecular composition of
air is constant; thus M0 / M = 1 and T M = T. Above 90
kilometers, M0 / M is greater than unity, and T M is
greater than T.
- molecular weight
- The weight of a given molecule
expressed in atomic
- An aggregate of two or more atoms of a
substance that exists as a unit.
- Moll thermopile
- A thermopile
used in some types of radiation instruments. Alternate junctions of
series-connected thermocouples are imbedded in a shielded nonconducting plate
having a large heat capacity. The remaining junctions, which are blackened,
are exposed directly to the radiation. The voltage developed by the thermopile
is proportional to the intensity of radiation. See solarimeter.
- moment (symbol M)
- A tendency to cause rotation about
a point or axis, as of a control surface about its hinge or of an airplane
about its center of gravity; the measure of this tendency, equal to the
product of the force and the perpendicular distance between the point of axis
of rotation and the line of action of the force.
- moment of inertia (symbol I)
- Of a body about an axis, , where m is the mass of a particle of the body and r
is its distance from the axis.
- Quantity of motion.
- Linear momentum is the quantity obtained by multiplying the mass of a
body by its linear speed. Angular momentum is the quantity obtained by
multiplying the moment of inertia of a body by its angular speed.
momentum of a system of particles is given by the sum of the momentums of the
individual particles which make up the system or by the product of the total
mass of the system and the velocity of the center of gravity of the system.
The momentum of a continuous medium is given by the integral of the
velocity over the mass of the medium or by the product of the total mass of
the medium and the velocity of the center of gravity of the medium.
- momentum thrust = thrust.
- momentum-transport hypothesis
- The hypothesis that momentum is
conserved in turbulent eddy transfer.
- This hypothesis is to be compared with the vorticity transport
hypothesis, the respective results being identical only if the eddy viscosity
- Mon, Mono
- International Astronomical Union abbreviations for Monoceros. See
- To observe, listen in on, keep track of, or exercise surveillance over by
any appropriate means, as, to monitor radio signals; to monitor the flight
of a rocket by radar; to monitor a landing approach.
- Monoceros (abbr Mon, Mono)
- See constellation.
- Pertaining to a single wavelength,
or, more commonly, to a narrow band of wavelengths.
- A type of construction, as of a rocket body, in which all or most of the
stresses are carried by the skin.
- A monocoque may incorporate formers but not longitudinal members such
- A rocket
propellant consisting of a single substance, especially a liquid, capable
of producing a heated jet without the addition of a second substance.
- Used attributively in phrases, such as monopropellant rocket engine
or motor, monopropellant rocket fuel, monopropellant system, etc.
- monostatic reflectivity
- The characteristic of a reflector which reflects energy only along the
line of the incident
e.g., a corner reflector. See bistatic
- 1. The period of the revolution
of the moon around the earth.
- The month is designated as sidereal, tropical, anomalistic,
dracontic, or synodical, according to whether the revolution is
relative to the stars, the vernal equinox, the perigee, the ascending node, or
- 2. The calendar month, which is a rough approximation to the synodical
- month of the phases = synodical
- 1. The natural satellite of the earth.
- 2. A natural satellite of
any planet. See planet table.
- The crossing of the visible horizon by the
limb of the ascending moon.
- The crossing of the visible horizon by the
limb of the descending moon.
- MOPTAR (abbr) = multiple
object phase tracking and ranging.
- The act, process, or instance of change of position. Also called
movement, especially when used in connection with problems involving
the motion of one craft relative to another.
- Absolute motion is motion relative to a fixed frame of reference.
Actual motion is motion of a craft relative to the earth. Apparent
or relative motion is change of position as observed from a
reference point which may itself be in motion. Diurnal motion is the
apparent daily motion of a celestial body. Direct motion is the
apparent motion of a planet eastward among the stars; retrograde
motion, the apparent motion westward among the stars. Motion of a celestial
body through space is called space motion, which is composed of two
components: proper motion, that component perpendicular to the line of sight;
and radial motion, that component in the direction of the line of
- motion sickness
- The syndrome of pallor, sweating, nausea, and vomiting which is induced by
- See engine.
- Oscillation in a system or component, usually manifested by a succession
occurring at a subaudio or
low-audio repetion frequency.
- moving target indicator (abbr MTI)
- A device which limits the display of radar information
primarily to moving targets.
- See M-region
magnetic storm, note.
- M-region magnetic storm
- A magnetic storm that is independent of visible solar disk features; it
begins gradually and shows a strong tendency to recur within a period of 27
- The hypothetical region on the solar disk assumed to be the source of
the incident corpuscular radiation is called the M-region.
- M-scan = M-display.
- M-scope = M-display.
- MTI (abbr) = moving
- MUF (abbr) = maximum
- multi (combining form)
- More than one. Used in contexts where a category of two or more is
distinguished from a category of one, as in a multipropellant fuel system
is more complicated than a monopropellant system.
- A device for connecting several receivers to
and properly matching the impedances of the receivers and the antenna.
- multipath = multipath
- multipath transmission
- The process, or condition, in which radiation
travels between source and receiver via
more than one path. Since there can be only one direct path, some
process of reflection,
must be involved. See fading, Fresnel
zone. Also called multipath.
- multiple airborne target trajectory system (abbr Matts)
- A long-baseline angle-measuring system consisting of two crossed-baseline
angle-measuring-equipment (AME) stations. Each AME station simultaneously
tracks three airborne targets by means of frequency sharing.
- multiple-degree-of-freedom system
- A mechanical system for which
two or more coordinates
are required to define completely the position of the system at any instant.
- multiple interferometer determination of trajectories (abbr
- A trajectory
measurement system with multiple-object-tracking capability utilizing two
or more short-baseline stations and a data output consisting of a series of
amplitude nulls that represent direction
cosines at given times in the flight.
- multiple object phase tracking and ranging (abbr Moptar)
- A short-baseline continuous-wave phase comparison, trajectory
measuring system, similar to the Cotar which consists of a
crossed-baseline angle-measuring-equipment (AME) system and a
distance-measuring-equipment (DME) system, wherein time sequencing of the
ground station and transponders
is used to track multiple targets.
- multiple scattering
- In contrast to primary scattering, and scattering
in which radiation is scattered more than once before reaching the eye,
antenna, or other sensing element.
- multiple-stage compressor = multistage
- multiple-stage rocket = multistage
- multiple-unit steerable antenna
- See musa
- A mechanical or electrical device for time sharing or a circuit.
- The simultaneous transmission of two or more signals within
a single channel.
- The three basic methods of multiplexing involve the separation of
signals by time division, frequency division, and phase division.
- 1. A device which has two or more inputs and whose
output is a
representation of the product of the quantities represented by the input signals.
- 2. = multiplier
- multiplier phototube
- A phototube
with one or more dynodes between
and the output electrode.
- A rocket
propellant consisting of two or more substances fed separately to the combustion
chamber. See bipropellant.
- multistage compressor
- An axial-flow
compressor having two or more, usually more than two, stages of rotor and
stator blades; a radial-flow compressor having two or more impeller
wheels. Also called a multiple-stage compressor.
- multistage rocket
- A vehicle having two or more rocket units,
each unit firing after the one in back of it has exhausted its propellant.
Normally, each unit, or stage, is jettisoned after completing its firing. Also
called a multiple-stage rocket or, infrequently, a step rocket.
- A two-stage regenerative
circuit with two possible states and an abrupt transition characteristic. See
- Multivibrators are used in digital computer for computation in binary
- See modified
index of refraction.
- muon = mu meson.
- See meson.
- Mus, Musc
- International Astronomical Union abbreviations for Musca. See constellation.
- musa antenna
- A multiple-unit steerable antenna consisting of a number of stationary
antennas, the composite major lobe of which can
be aimed electrically.
- Musca (abbr Mus, Musc)
- See constellation.
- A prefix meaning multiplied by 104.
- myriameter = ten-thousand meters.
- myriametric wave
- See frequency