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- The aggregate crosstalk
from a large number of communications channels.
- Babinet point
- One of the three commonly detectable points of zero polarization
sky radiation, neutral points, lying along the vertical
circle through the sun; the other two are the Arago point
- The Babinet point typically lies only 15° to 20° above the sun, and
hence is difficult to observe because of solar glare. The existence of this
neutral point was discovered by Babinet in 1840.
- Any effect in a sensor or other apparatus or system above which the
phenomenon of interest must manifest itself before it can be observed. See background
- background counts
- In radiation counters, responses of the counting system caused by radiation
coming from sources other than that to be measured.
- background luminance
- In visual-range theory, the luminance
(brightness) of the background against which a target is viewed. Compare adaptation
- background noise
- 1. In recording and reproducing, the total system noise independent
of whether or not a signal is present. The signal is not to be included as
part of the noise.
- 2. In receivers, the noise in the absence of signal modulation on the
noise detected, measured, or recorded with the signal part of the
background noise. Included in this definition is the interference resulting
from primary power supplies, that separately is commonly described as hum.
- background return
- See clutter.
- Dead space or unwanted movement in a control
- An undoing of things already done during a countdown,
usually in reverse order.
- back pressure
- Pressure exerted backward; in a field of fluid flow, a pressure exerted
contrary to the pressure producing the main flow.
- back radiation = counterradiation.
- back scatter = backward
- back scattering = backward
- back-scattering cross section
- See scattering
- back-to-chest acceleration
- See physiological
- 1. An item kept available to replace an item which fails to perform
- 2. A redundant component in a system which is not the normally active (or
prime, primary) component. Also known as second-string.
- backward scatter
- The scattering
of radiant energy into the hemisphere of space bounded by a plane normal to
the direction of the incident radiation and
lying on the same side as the incident ray; the opposite of forward
scatter. Also called back scattering .
- Atmospheric backward scatter depletes 6 to 9 percent of the incident
solar beam before it reaches the earth's surface.
In radar usage,
backward scatter refers only to that radiation scattered at 180° to the
direction of the incident wave.
- backward wave
- In traveling-wave
tubes, a wave whose group
velocity is opposite to the direction of electron-stream motion.
- A plate, grating, or the like used especially to block, hinder, or divert
a flow or to hinder the passage of something, as: (a) A plate used to conduct,
or help to conduct, a flow of cooling air around an engine cylinder. (b) A
plate, wall, or the like in a fuel tank or other liquid container, used
especially to prevent sloshing of the contents. (c) A ridge or wall on the top
of a piston in a two-stroke-cycle engine, used to deflect the incoming mixture
upward and divert it from the exhaust port. (d) A plate in the forward section
of a pitot tube, used to reduce turbulence in the tube and to prevent dirt,
moisture, etc., from entering the system.
- bailout bottle
- A personal supply of oxygen usually contained in a cylinder under pressure
and utilized when the individual has left the central oxygen system as in a
- The degassing of
surfaces of a vacuum system by heating during the pumping process.
- 1. The equilibrium attained by an aircraft, rocket, or the like when
forces and moments are
acting upon it so as to produce steady flight, especially without rotation
about its axes; also used with reference to equilibrium about any specified axis, as, an
airplane in balance about its longitudinal axis .
- 2. A weight that counterbalances something, especially on an aircraft
control surface, a weight installed forward of the hinge axis to
counterbalance the surface aft of the hinge axis.
- balanced amplifier
- An amplifier circuit in which there are two identical signal branches
connected so as to operate in phase opposition and with input and output
connections each balanced to ground. Also called push-pull amplifier .
- balanced circuit
- A circuit, the
two sides of which are electrically alike and symmetrical with respect to a
common reference point, usually ground.
- balanced detector
- A demodulator
for frequency-modulation systems. In one form the output consists of the
rectified difference of the two voltages produced across two resonant
circuits, one circuit being tuned slightly above the carrier
frequency and the other slightly below.
- balanced modulator
- A device in which the carrier and
modulating signal are so introduced that, after modulation takes place, the
output contains the two sidebands
without the carrier.
- ballistic body
- A body free to move, behave, and be modified in appearance, contour, or
texture by ambient conditions, substances, or forces, as by the pressure of
gases in a gun, by rifling in a barrel, by gravity, by temperature, or by air
- A rocket with a self-contained propulsion unit is not considered a
ballistic body during the period of its guidance or propulsion.
- ballistic camera
- A ground-based camera using multiple exposures on the same plate to record
of a rocket.
- ballistic condition
- A condition affecting the behavior of a vehicle in flight.
- Ballistic conditions include the velocity, weight, shape, and size of
the vehicle; likewise the density and temperature of the ambient element, the
magnetic field, etc.
- ballistic density
- A representation of the atmospheric density actually encountered by a
projectile in flight, expressed as a percentage of the density according to
- Thus, if the actual density distribution produced the same effect upon
a projectile as the standard density distribution, the ballistic density would
be 100 percent .
- ballistic missile
- A missile designed to operate primarily in accordance with the laws of ballistics.
- A ballistic missile is guided during a portion of its flight, usually
the upward portion, and is under no thrust from its propelling system during
the latter portion of its flight; it describes a trajectory similar to that of
an artillery shell.
- ballistic recovery
- Nonlifting reentry.
- The science that deals with the motion, behavior, and effects of
projectiles, especially bullets, aerial bombs, rockets, or the like; the
science or art of designing and hurling projectiles so as to achieve a desired
- ballistic temperature
- That temperature (in° F) which, when regarded as a surface temperature and
used in conjunction with the lapse rate of the standard
artillery atmosphere, would produce the same effect on a projectile as the
actual temperature distribution encountered by the projectile in flight.
- ballistic trajectory
- The trajectory
followed by a body being acted upon only be gravitational forces and the
resistance of the medium through which it passes.
- A rocket without lifting surfaces is in a ballistic trajectory
after its engines cease operating.
- ballistic vehicle
- A nonlifting vehicle; a vehicle that follows a ballistic
- ballistic wind
- That constant wind which would produce the same effect upon the trajectory
of a projectile as the actual wind encountered in flight. Ballistic winds can
be regarded as made up of range wind
components. See zone wind.
- ball lightning
- A relatively rare form of lightning, consisting of a reddish, luminous
ball, of the order of 1 foot in diameter, which may move rapidly along solid
objects or remain floating in midair. Hissing noises emanate from such balls,
and they sometimes explode nosily but may also disappear noiselessly. Also
called globe lightning .
- It has been suggested that ball lightning is a temporarily stable
- balloon-type rocket
- A liquid-fuel rocket, such as
Atlas, that requires the pressure of its propellants
(or other gases) within it to give it structural integrity.
- A cross between a balloon and a parachute, used to brake the free fall of
- 1. = frequency
- 2. = absorption
- 3. A group of tracks on a magnetic
- 4. = auroral
band. See aurora.
- band-elimination filter
- A wave
filter that attenuates one frequency
band, neither the critical nor cutoff frequencies being zero or infinite.
- band of position
- An area extending to either side of a line of
position of imperfect accuracy, within which a craft is considered to be
- band-pass filter
- A wave
filter that has a single transmission band extending from a lower cutoff
frequency greater than zero to a finite upper cutoff frequency.
- bands with ray structure (abbr R.B.)
- See aurora.
- 1. In an antenna, the
range of frequencies
within which its performance, in respect to some characteristic, conforms to a
- 2. In a wave, the least
frequency interval outside of which the power
spectrum of a time-varying quantity is everywhere less than some specified
fraction of its value at a reference frequency.
- 3. The number of cycles per second between the limits of a frequency
- Sense 2 permits the spectrum to be less than the specified fraction
within the interval. Unless otherwise stated, the reference frequency is that
at which the spectrum has its maximum value.
- 4. In information theory, the information-carrying capacity of a
- bang-bang control
control, especially as applied to rockets.
- Bang-bang in this term is imitative, arising from the noise made by
control mechanisms slamming first to one side, then to the other, in this sort
- A unit of pressure equal
to, 1000 millibars, 29.53 inches of mercury. See torr.
- Some writers have used bar as equivalent to barye (1 dyne per square
- A commercial trade name for a type of carbon dioxide absorber, a mixture
of calcium hydroxide and barium hydroxide.
- Bárány chair
- (After Robert Bárány, 1876-1936, Swedish physician). A kind of chair in
which a person is revolved to test his susceptibility to vertigo.
- bare core
- A reactor
core without a reflector.
- barn (Abbr b)
- A unit of area for measuring a nuclear
cross section. One barn equalssquare
- barocline = baroclinic.
- Of, pertaining to, or characterized by baroclinity.
Sometimes called barocline.
- baroclinicity = baroclinity.
- The state of stratification in a fluid in which surfaces of constant
pressure (isobaric) intersect surfaces of constant density (isosteric). The
number, per unit area, of isobaric-isosteric solenoids
intersecting a given surface is a measure of the baroclinity. Also called
baroclinicity, barocliny .
- Barotropy is
the state of zero baroclinity. Since the presence of solenoids (baroclinity)
complicates the dynamics of the fluid, there has been much investigation of
the extent to which an atmosphere,
though obviously a baroclinic fluid, can be dynamically treated as barotropic.
- barocliny = baroclinity.
- An instrument used to measure atmospheric
- barometric altimeter = pressure
- barometric pressure = atmospheric
- barometric wave
- Any wave in
the atmospheric pressure field. The term is usually reserved for short-period
variations not associated wit cyclonic-scale motions or with atmospheric
tides. See pressure
wave, sense 2.
- The atmosphere below the critical
level of escape.
- (From barometric switch). 1. Specifically, a pressure-operated switching
device used in a radiosonde.
In operation, the expansion of an aneroid capsule causes an electrical contact
to scan a radiosonde commutator composed of conductors separated by
insulators. Each switching operation corresponds to a particular pressure
level. The contact of an insulator or a conductor determines whether
temperature, humidity, or reference signals will be transmitted. 2. Any switch
operated by a change in atmospheric
- Of, pertaining to, or characterized by a condition of barotropy.
- barotropic disturbance
- 1. An atmospheric wave in a two-dimensional nondivergent flow, the driving
mechanism for which lies in the variation of vorticity of
the basic current and/or in the variation of the vorticity of the earth about
the local vertical. When the basic current is uniform, the wave is a Rossby
wave . Also called barotropic wave .
- 2. An atmospheric wave of cyclonic scale in which troughs and ridges are
- barotropic model
- Any of a number of model
atmospheres in which some of the following conditions exist throughout the
motion: coincidence of pressure and temperature surfaces; absence of vertical
shear; absence of vertical motions; absence of horizontal velocity
divergence; and conservation of the vertical component of absolute
- barotropic vorticity equation
- The vorticity equation in the absence of horizontal divergence and
vertical motion, so that the absolute
vorticity of a parcel is conserved:
where is the relative
vorticity and f is the coriolis
- This equation may also be interpreted as governing vertically averaged
flow in which divergence is present but wind direction is constant with
height. See equivalent
- barotropic wave = barotropic
- The state of a fluid in which surfaces of constant density (or
temperature) are coincident with surfaces of constant pressure; it is the
state of zero baroclinity.
Mathematically, the equation of barotropy states that the gradients of the
density and pressure fields are proportional:
is the density; p is the pressure; and B is a function
of thermodynamic variables, called the coefficient of barotropy.
- With the equation
of state, this relation determines the spatial distribution of all state
parameters once these are specified on any surface. For a homogeneous
atmosphere, B=0; for an adiabatic
B = c v / cp RTwhere
cv and cp are the specific heats at
constant volume and pressure, respectively; R is the gas constant; and
T is the Kelvin temperature; for an isothermal
atmosphere, B = 1/RT.
- The center of mass of a system of masses, as the barycenter of the
earth-moon system .
- barycentric elements
elements referred to the center of
mass of the solar system.
- The pressure unit of the centimeter-gram-second
system of physical units; equal to one dyne per square centimeter (0.001
millibar). Sometimes called bar or microbar.
- A quantity, the powers of which are assigned as the unit value of columns
in a numeric
system; for example, two is the base in binary notation, and
ten in decimal
notation. Also called radix . See logarithm, binary
- base drag
- Drag owing
to a base
pressure lower than the ambient pressure. It is a part of the pressure
- base line
- 1. Any line which serves as the basis for measurement of other lines, as
in a surveying triangulation, measurement of auroral heights, etc.
- 2. The geodesic
line between two stations operating in conjunction for the determination
of a line of position, as the two stations constituting a loran rate.
- 3. In radar, the line traced on amplitude-modulated
indicators which corresponds to the power level of the weakest echo
detected by the radar. It is retraced with every pulse transmitted by the
radar, but appears as a nearly continuos display on the scope.
- Target signals show up as perpendicular deviations from the base line;
range is measured along the base line; signal strength is indicated by the
magnitude of the deviations; and the type of target usually can be determined
by the appearance of the deviations.
- base point
- In computer terminology, the character, or the location of an implied
symbol, which separates the integral part of an expression in positional
notation from the fractional part; the point which marks the place between
the zero and negative powers of the base. Also called radix point . See
- base pressure
- In aerodynamics, the pressure
exerted on the base, or extreme aft end, of a body, as of a cylindrical or
boattailed body or of a blunt-trailing-edge wing, in a fluid flow.
- base-timing sequencing
- (abbr BT sequencing)
- The control of the time sharing of a single transponder
between several ground transmitters through the use of suitable coded timing
- basic thermal radiation
- Thermal radiation from a quiet sun.
- A unit of signaling speed. The speed in bauds is the number of code elements per
- Baumé scale (abbr Be)
- Either of two scales sometimes used to graduate hydrometers;
one scale is for liquids heavier than water, the other for liquids lighter
- Bayard-Alpert ionization gage
- A type of ionization
vacuum gage using a tube with an electrode structure designed to minimize
X-ray induced electron emission from the ion collector.
- Bayer letter
- The Greek (or Roman) letter used in a Bayer name.
- Bayer name
- The Greek (or Roman) letter and the possessive form of the Latin name of a
used as a star name. Examples are Cygni (Deneb), Orionis (Rigel), and Ursae Majoris (Alkaid). See navigational
- In radar, a rectangular display in
which targets appear
as blips with
indicated by the horizontal coordinate and distance by the vertical
coordinate. Also called B-scan or B-scope .
- 1. A light, group of lights, electronic apparatus, or other device that
guides, orients, or warns aircraft, spacecraft, etc. in flight.
- 2. A structure, building, or station where such a device is mounted or
located. See radar
- beacon delay
- The amount of inherent delay within a beacon, i.e.,
the time between the arrival of a signal and the response of the beacon.
- beacon skipping
- A condition where transponder
return pulses from a beacon are
missing at the interrogating radar.
- Beacon skipping can be caused by interference, overinterrogation of
nulls, or pattern minimums.
- beacon stealing
- Loss of beacon
tracking by one radar due to (interfering) interrogation
signals from another radar.
- beacon tracking
- The tracking of a
moving object by means of signals emitted from a transmitter or transponder
within or attached to the object.
- See lunar
- 1. A ray or collection of focused rays of radiated energy. See beam width,
- 2. A beam (sense 1) of radio waves used as a navigation aid.
- 3. =electron
- 4. A body, one of whose dimensions is large compared with the others,
whose function is to carry lateral loads (perpendicular to the long dimension)
and bending movements.
- beam angle= beam width.
- beam-climber guidance= beam-rider
- beam rider
- A craft following a beam, particularly
one which does so automatically, the beam providing the guidance.
- beam-rider guidance
- A system for guiding aircraft or spacecraft in which a craft follows a
radar beam, light beam, or other kind of beam along the
desired path. Also called beam-climber guidance . See guidance.
- beam splitter
- A partially reflecting mirror which permits some incident light
to pass through and reflects the remainder.
- beam-switching tube
- A trochotron
in which an electron
beam can be formed and switched to any one of several (usually 10)
- beam width
- A measure of the concentration of power of a directional
antenna. It is the angle in degrees subtended at the antenna by arbitrary
power-level points across the axis of the beam. This power
level is usually the point where the power
density is one-half that which is present in the axis of the beam at the
same distance from the antenna (half-power points). Also called beam angle
- The beam width of a radar determines the minimum angular separation
which two targets can have and still be resolved. Roughly speaking, two
targets at the same range whose angular separations at the radar antenna
exceeds one-half of the beam width between half-power points will be resolved
or distinguishable as two individual targets. The smaller the beam width, the
greater the annular resolving power. Beam width may be at different locations
through the axis depending upon the shape of the antenna reflector.
- The horizontal direction of an object or point, usually measured clockwise
from a reference line or direction through 360°.
- A bearing is often designated as true, magnetic, compass, grid,
or relative as the reference direction is true, magnetic, compass, or
grid north, or heading, respectively.
At one time bearing was
restricted to reference to the direction of a terrestrial object or point as
distinguished from azimuth which referred to the direction of a
celestial body. This distinction has been blurred by usage.
- bearing angle
- Horizontal direction measured from 0° at the reference direction clockwise
or counterclockwise through 90° or 180°. Compare bearing.
- Bearing angle is labeled with the reference direction as a prefix and
the direction of measurement from the reference direction as a suffix. Thus,
bearing angle N 37° W is 37° west of north, or bearing 323°.
- 1. One complete cycle of the
variations in the amplitude of
two or more periodic phenomena of different frequency which mutually react.
frequency. 2. To produce beating.
- beat-beat Dovap = Dovap
- beat frequency
- The frequency
obtained when two simple harmonic
quantities of different frequencies .
- A wave
phenomenon in which two or more periodic quantities of different frequencies
produce a resultant having pulsations of amplitude.
- This process may be controlled to produce a desired beat
frequency. See heterodyne
- beavertail antenna
- A type of radar antenna which
forms a beam having a greater beam width
in azimuth than in elevation, or vice versa. In physical dimensions, its long
axis lies in the plane of smaller beam width.
- See tektite.
- Beer law = Bouguer
- The way in which an organism, organ, body, or substance acts in an environment
or responds to excitation, as the behavior of steel under stress , or
the behavior of an animal in a test .
- The fundamental division of a logarithmic
scale for expressing the ratio of two amounts of power, the number of bels
denoting such a ratio being the logarithm to the base 10 of this ratio.
- Bemporad formula
- A formula for the optical air mass m in terms of the zenith
distance z of the sun or other celestial body:
m = R/58.36 sec sin zwhere R is astronomical
refraction, seconds of arc.
- For values of z less than about 70°, the Bemporad formula can be
replaced by the simpler approximate formula,
m = sec z
- 1. Pains in the extremities, abdomen, and chest caused by aeroemphysema
and in some instances by aeroembolism
resulting from the reduction of ambient air pressure.
- 2. Popularly used as synonymous with aeroembolism (sense 2).
- Bernoulli law or Bernoulli theorem
- (After Daniel Bernoulli, 1700-1782, Swiss scientist).
- 1. In aeronautics, a law or theorem stating that in a flow of
incompressible fluid the sum of the static
pressure and the dynamic
pressure along a streamline
is constant if gravity and frictional effects are disregarded.
- From this law it follows that where there is a velocity increase in a
fluid flow there must be a corresponding pressure decrease. Thus an airfoil,
by increasing the velocity of the flow over its upper surface, derives lift
from the decreased pressure.
- 2. As originally formulated, a statement of the conservation
of energy (per unit mass) for a nonviscous fluid in steady motion. The
specific energy is composed of the kinetic energy u2/2,
where u is the speed of the fluid; the potential energy gz,
where g is the acceleration of gravity and z is the height above
an arbitrary reference level; and the work done by the pressure forces of a
compressible fluid v dp, where p is the pressure, v is the specific
volume, and the integration is always with respect to values of p and
v on the same parcel. Thus, the relationship
= Constant along a streamline
is valid for a
compressible fluid in steady motion, since the streamline is also the path. If
the motion is also irrotational, the same constant holds for the entire fluid.
- Besselian star numbers
- Constants used in the reduction of a mean
position of a star to an apparent
position (used to account for short-term variations in the precession,
- Besselian year = fictitious
- Bessel fictitious year = fictitious
- beta decay
- Radioactive transformation of a nuclide in
which the atomic
number changes by ±1 with the emission of a beta
particle and the mass number
remains unchanged. Also called beta disintegration .
- Increase of atomic number occurs with negative beta particle emission,
decrease with positive beta particle (positron) emission or upon electron
- beta disintegration = beta decay.
- beta factor, -factor
- In plasma
physics, the ratio of the plasma kinetic pressure to the magnetic
- If is less than 1, the magnetic field has a chance to contain the
plasma providing there are no instabilities. If is larger than 1, there is no possible chance of containment.
- beta particles
- See betatron,
- beta ray, -ray
- A stream of beta
- A particle
accelerator in which magnetic induction is used to accelerate electrons.
- Betatron refers to the accelerated particles, electrons, which are
identical with beta
- bias error
- A measurement error that remains constant in magnitude for all
observations. A kind of systematic
- An example is an incorrectly set zero adjustment.
- bidirectional transducer
- A transducer
device capable of measuring input in both a positive and a negative direction
from a reference zero or rest position.
- bilateral transducer
- A transducer
capable of transmission simultaneously in both directions.
- billiard-ball collision = elastic
- See tektite.
- bimetallic strip gage
- A thermal conductivity vacuum gage
in which deflection of a bimetallic strip with changing temperature indicates
the changes in pressure.
- 1. Involving the integer two (2). See binary
- 2. =binary
- 3. =binary
- binary cell
- Any device or circuit that can be placed in either of two stable states to
store a bit of
binary information. Often called a binary .
- binary chain
- A cascaded series of binary
- binary code
- A code composed of a combination of entities each of which can assume one
of two possible states. Each entity must be identifiable in time or space.
- binary counter
- A counter with
two distinguishable states.
- binary device = binary
- binary digit
- A digit (0
or 1) in binary
notation. See bit.
- binary magnetic core
- A ferromagnetic material which can be caused to assume either of two
stable magnetic states and thus can be used in a binary
- binary notation
- A system of positional
notation in which the digits are
coefficients of power of the base 2 in same way as the digits in the
conventional decimal system are coefficients of power of the base 10.
- Binary notation employs only two digits, 1 and 0, therefore is used
extensively in computers where the on and off positions of a switch or storage
device can represent the two digits. In decimal notation
- binary number system
- See binary
- binary point
- The base
point in binary
- binary star
- A system of two stars revolving about their barycenter.
- The smaller star of the system is referred to as the companion
Visible binaries are those which can be resolved into
two stars by a telescope.
Spectroscopic binaries are those which
cannot be resolved by a telescope by show temporary displacement and doubling
of the lines in their spectra.
- binding energy
- 1. The force which holds molecules, atoms, or atomic particles together;
specifically, the force which holds an atomic nucleus
- 2. The energy required to break chemical, atomic, or molecular bonds.
- The study of biological, behavioral, and medical problems pertaining to astronautics.
This includes systems functioning in the environments
expected to be found in space, vehicles designed to travel in space, and the
conditions on celestial bodies other than on earth.
- Chemistry dealing with the chemical processes and compounds of living
- The study of the relations of climate and life, especially the effects of
climate on the health and activity of human beings (human bioclimatology) and
on animals and plants.
- The study of the effects of dynamic processes (motion, acceleration,
etc.) on living organisms.
- The study of systems, particularly electronic
systems, which function after the manner of, or in a manner characteristic of,
or resembling, living systems.
- A container for housing a living organism in a habitable environment
and for recording biological functions during space flight.
- An artificial satellite
which is specifically designed to contain and support man, animals, or other
living material in a reasonably normal manner for an adequate period of time
and which, particularly for man and animals, possesses the proper means for
safe return to the earth. See ecological
- A sensor
used to provide information about a life process.
- That transition zone between earth and atmosphere
within which most forms of terrestrial life are commonly found; the outer
portion of the geosphere and
inner or lower portion of the atmosphere. See hydrosphere.
- The application of engineering and technological principles to the life
- The remote measuring and evaluation of life functions, as, e.g. in spacecraft
and artificial satellites.
- A test
chamber used for biological research within which the environmental
conditions can be completely controlled, thus allowing observations of the
effect of variations in environment
on living organisms.
- A rocket propellant
consisting of two unmixed or uncombined chemicals (fuel and oxidizer) fed
to the combustion chamber separately.
- bipropellant rocket
- A rocket
using two separate propellants
which are kept separate until mixing in the combustion
- biquinary notation
- A numerical system in which each decimal
digit is represented by a pair of digits consisting of a coefficient of
five followed by a coefficient of one.
- For example, the decimal digit 7 is represented in biquinary notation
by 12 [(1 x 5) + (2 x 1)], and the decimal quantity 3648 is represented by 03
11 04 13.
The abacus is based on biquinary notation.
- A colloquial term for a rocket, satellite, or
- bistable elements
- In computer terminology, a device which can remain indefinitely in either
of two stable states.
- bistable multivibrator
- A multivibrator which can exist indefinitely in either of two stable
states. Also called flip-flop .
- bistatic reflectivity
- The characteristic of a reflector
which reflects energy along a line, or lines, different from, or in addition
to, that of the incident
- For example, any reflector that scatters the
- 1. An abbreviation of binary
- 2. A single character of a language employing only two distinct kinds of
- 3. A quantity of intelligence which is carried by an identifiable entity
and which can exist in either of two states.
- 4. A unit of storage
capacity; the capacity in bits of a storage device is the logarithm to the
base two of the number of possible states of the device.
- 5. A quantum of
- 6. Loosely, a mark.
- bit rate
- The frequency derived from the period of time required to transmit one bit.
- black body, blackbody (symbol b used as a
- 1. An ideal emitter which radiates energy at the maximum possible rate per
unit area at each wavelength for any given temperature. A black body also
absorbs all the radiant energy in the near visible spectrum incident upon it.
- No actual substance behaves as a true black body, although platinum
black and other soots rather closely approximate this ideal. However, one does
speak of a black body with respect to a particular wavelength interval. This
concept is fundamental to all the radiation
laws, and is to be compared with the similarly idealized concepts of the
body and the gray body. In
accordance with the Kirchhoff
law, a black body not only absorbs all wavelengths, but emits at all
wavelengths and does so with maximum possible intensity for any given
- 2. A laboratory device which simulates the characteristics of a black body
(sense 1). See hohlraum.
- black-body emission= black-body
- black-body radiation
- The electromagnetic
radiation emitted by an ideal black body;
it is the theoretical maximum amount of radiant energy of all wavelengths
which can be emitted by a body at a given temperature.
- The spectral distribution of black-body radiation is described by Planck law
and the related radiation
laws. If a very tiny opening is made into an otherwise completely enclosed
space (hohlraum), the
radiation passing out through this hole when the walls of the enclosure have
come to thermal equilibrium at some temperature will closely approximate ideal
black-body radiation for that temperature.
- black box
- 1. In engineering design, a unit whose output is a
specified function of the input, but for
which the method of converting input to output is not necessarily specified.
- 2. Colloquially, any unit, usually an electronic device such as an
amplifier, which can be mounted in, or removed from, a rocket, spacecraft, or
the like as a single package.
- 1. A fadeout of
radio communications due to ionospheric disturbances.
- Blackouts are most common in, but are not restricted to, the arctic. An
arctic blackout may last for days or even weeks during periods of intense
auroral activity. Past experiments with high-altitude nuclear detonations have
produced blackouts and artificial auroras over the subtropics .
- 2. A fadeout of radio and telemetry transmission between ground stations
and vehicles traveling at high speeds in the atmosphere caused by signal
attenuation in passing through ionized boundary layer (plasma
sheath) and shock wave regions generated by the vehicle.
- 3. A vacuum tube characteristic which results from the formation of a dielectric
film on the surface of the control grid.
- A negative charge, accumulated on the film when the grid is driven
positive with respect to the cathode, affects the operating characteristics of
- 4. A condition in which vision is temporarily obscured by a blackness,
accompanied by a dullness of certain of the other senses, brought on by
decreased blood pressure in the eye and a consequent lack of oxygen, as may
occur, e.g., in pulling out of a high-speed dive in an airplane. Compare grayout, redout.
- 1. (a) An arm of a propeller; a rotating wing. (b) Specifically,
restrictive, that part of a propeller arm or of a rotating wing from the shank
outward, i.e., that part having an efficient airfoil shape and that cleaves
the air. See blade shank.
- 2. A vane (in sense 2), such as a rotating vane or stationary vane in a
rotary air compressor, or a vane of a turbine wheel.
- To blank out or obscure weak radio signals by a stronger signal.
- blank-off pressure
- See ultimate
- 1. The brief and rapid movement of air or other fluid away from a center
of outward pressure, as
in an explosion.
- 2. The characteristic instantaneous rise in pressure, followed by a sudden
decrease, that results from this movement, differentiated from less rapid
- 3. To take
off from a launching pad or stand. Said of a rocket in reference to the
blast effects caused by rapid combustion of fuel as the rocket starts to move
- This term is commonly used for explosion, but the two terms should be
distinguished. In space, an explosion could take place, but no blast would
- blast chamber
- A combustion
chamber, especially a combustion chamber in a gas-turbine engine, jet
engine, or rocket engine.
- blast deflector
- A device used to divert the exhaust of a rocket fired
from a vertical position.
- A missile launch (Slang).
- blast vane = jet vane.
- Blaton formula
- In meteorology, an expression relating the curvature of the trajectory
Ki of a fluid parcel
to the streamline
where v is the parcel speed, is the local change of wind direction, is the wind angle, and t is time. The curvatures and change
of wind direction are positive for cyclonic flow.
- To let a fluid, such as air or liquid oxygen, escape from a pipe, tank, or
- bleed off
- To take off a part or all of a fluid from a tank or line, normally through
an escape valve or outlet, as in to bleed off excess oxygen from a tank
- A spot of light or deflection of the trace on a
radarscope, loran indicator, or the like, caused by the received signal, as
from a reflecting object. Also called a pip or echo .
- A fairly small-scale temperature and moisture inhomogeneity produced by turbulence
within the atmosphere.
- The abnormal gradient of the index
of refraction resulting from a blob can produce a radar echo of the
type known as angels.
- In computer operations, a group of machine
words considered as a unit.
- blockhouse, block house
- 1. A reinforced concrete structure, often built underground or half
underground, and sometimes dome shaped, to provide protection against blast,
heat, or explosion during rocket launchings or related activities;
specifically, such a structure at a launch site
that houses electronic control instruments used in launching a rocket.
- 2. The activity that works in such a structure.
- blocking oscillator
- A regenerative circuit which generates pulses of short
- Blocking oscillators are used in digital
- blowdown tunnel
- A type of wind tunnel
in which stored compressed gas is allowed to expand through a test section to
provide a stream of gas or air for model testing.
- The downstream side may or may not be reduced in pressure to provide
greater expansion potential.
- blowdown turbine
- A turbine
attached to a reciprocating
engine which receives exhaust gases separately from each cylinder,
utilizing the kinetic energy of the gases.
- The action of applying an explosive force and separating a package section
away from the remaining part of a rocket
vehicle or reentry
body, usually to retrieve an instrument or to obtain a record made during
early flight. See fallaway
- blue-sky scale = Linke
- bluff body
- A body having a broad, flattened front, as in some reentry
- bluntness (symbol B)
- A parameter of a conic related to
e, of the conic in the following way:
B = 1/(1-e2)
For hyperbolas and prolate ellipses,
- The rear portion of an elongated body, as a rocket, having decreasing
cross-sectional area toward the rear.
- Fluctuation of the strength of a radar echo, or its
indication on a radarscope,
due to alternate interference and reinforcement of returning reflected waves.
- 1. The main part or main central portion of an airplane, airship, rocket,
or the like; a fuselage or hull.
- 2. In a general sense, any fabrication, structure, or other material form,
especially one aerodynamically or ballistically designed, as, an airfoil is
a body designed to produce an aerodynamic reaction.
- body angle
- The angle which the longitudinal
axis of the airframe makes
with some selected line.
- body axis
- Any one of a system of mutually perpendicular reference axes fixed in an
aircraft or similar body and moving with it. See axis.
- body of revolution
- A symmetrical body having the form described by rotating a plane curve
about an axis
in its plane.
- 1. A supporting and aligning wheel or roller on the inside of an endless
track, used, e.g., in certain types of landing
- 2. A type of landing-gear unit consisting of two sets of wheels in tandem
with a central strut.
- Bohr magneton, electronic Bohr magneton (symbol
- A constant equivalent to the magnetic moment of an electron, erg/gauss. See physical
- Bohr magneton is sometimes used as a synonym for nuclear
- Bohr radius (symbol a0)
- The smallest possible radius of an electron orbit in the Bohr model of the
- boilerplate model
- A metal copy of a flight vehicle, the structure or components of which are
heavier than the flight model.
- boiling point (abbr bp)
- The temperature at which the equilibrium
vapor pressure between a liquid and its vapor is equal to the external
pressure on the liquid. Compare ice point.
- The vaporization of a liquid, such as liquid oxygen or liquid hydrogen, as
its temperature reaches its boiling
point under conditions of exposure, as in the tank of rocket being readied
- A brilliant meteor,
especially one which explodes; a detonating fireball.
- The record obtained from a bolometer.
- An instrument which measures the intensity of radiant energy by employing
a thermally sensitive electrical resistor; a type of actinometer.
Also called actinic balance . Compare radiometer.
- Two identical, blackened, thermally sensitive electrical resistors are
used in a Wheatstone bridge circuit. Radiation is allowed to fall on one of
the elements, causing a change in its resistance. The change is a measure of
the intensity of the radiation.
- bolometric magnitude
- 1. The magnitude of
a star for the entire electromagnetic
spectrum without atmospheric absorption.
- The magnitude measured within the earth's atmosphere by a bolometer is
the radiometric magnitude.
- 2. Loosely = radiometric
- Boltzmann constant (symbol k)
- The ratio of the universal
gas constant to Avogadro
number; equal to
called gas constant per molecule, Boltzmann universal conversion factor
- Boltzmann universal conversion factor = Boltzmann
- Bond albedo
- The ratio of the amount of light reflected from a sphere exposed to
parallel light to the amount of light incident upon it. Sometimes shortened to
- The Bond albedo is used in planetary astronomy.
- 1. Specifically, a system of connections between all metal parts of an
aircraft or other structure forming a continuos electrical unit and preventing
jumping or arcing of static electricity.
- 2. Gluing or cementing together for structural strength.
- Boo, Boot
- International Astronomical Union abbreviation for Bootes. See constellation.
- Boolean algebra
- The study of the manipulation of symbols representing operations according
to the rules of logic.
- Boolean algebra corresponds to an algebra using only the numbers 0 and
1, therefore can be used in programming digital computers which operate on the
- 1. Additional power, pressure, or force supplied by a booster, as,
hydraulic boost, or extra propulsion given a flying vehicle during lift-off,
climb, or other part of its flight as with a booster engine.
- 2. Boost
- 3. To supercharge.
- 4. To launch or to
push along during a portion of flight, as to boost a ramjet to flight speed
by means of a rocket, or a rocket boosted to altitude with another rocket
- 1. Short for booster
engine or booster
- 2. = launch
- booster engine
- An engine, especially a booster
rocket, that adds its thrust to the thrust of the sustainer
- booster pump
- A pump in a fuel system, oil system, or the like, used to provide
additional or auxiliary pressure when needed or to provide an initial pressure
differential before entering a main pump, as in pumping hydrogen near the
- booster rocket
- 1. A rocket
motor, either solid or liquid, that assists the normal propulsive system
engine of a rocket or aeronautical vehicle in some phase of its flight.
- 2. A rocket used to set a vehicle in motion before another engine takes
- In sense 2 the term launch vehicle is preferred.
- booster vehicle = launch
- boostglide vehicle
- A vehicle
designed to glide in the atmosphere following a rocket-powered phase. Portions
of the flight may be ballistic,
out of the atmosphere.
- boost pressure
- Manifold pressure greater than the ambient atmospheric
pressure, obtained by supercharging. Often called boost.
- Bootes (abbr Boo, Boot)
- See constellation.
- 1. Referring to a self-generating or self-sustaining process;
specifically, the operation of liquid-propellant rocket engines in which,
during main-stage operation, the gas generator is fed by the main propellants
pumped by the turbopump, and the turbopump in turn is driven by hot gases from
the gas generator system.
- Such a system must be started in its operation by outside power or
propellants. When its operation is no longer dependent on outside power or
propellant the system is said to be in bootstrap operation.
- 2. In computer operations, the coded instructions at the beginning of an
input tape which together with manually inserted instructions, initiate a routine.
- 3. = leap-frog.
- boresight camera
- A camera mounted in the optical axis of a tracking
radar to photograph rockets being tracked while in camera range and thus
provide a correction for the alignment of the radar.
- boresight error
- The linear displacement between two parallel lines of sight.
- In radio the process of aligning a directional
antenna system by an optical procedure.
- Bose-Einstein statistics
- Formulas relating to equations
of state and partition of kinetic
energy when the wave functions are symmetric.
- Bouguer law
- A relationship describing the rate of decrease of flux density of a
plane-parallel beam of monochromatic
radiation as it penetrates a medium which both scatters and absorbs at that
wavelength. This law may be expressed
where I is the flux density of the radiation; is the attenuation
coefficient (or extinction coefficient) of the medium at wavelength ; is the flux density at the source; and x is the distance from
the source. Sometimes called Beer law, Lambert law of absorption . See
- bounce table
- A testing device which subjects devices and components
to impacts such as might be encountered in accidental dropping.
- boundary conditions
- A set of mathematical conditions to be satisfied, in the solution of a
differential equation, at the edges or physical boundaries (including fluid
boundaries) of the region in which the solution is sought. The nature of these
conditions usually is determined by the physical nature of the problem. See boundary-value
- boundary layer
- The layer of fluid in the
immediate vicinity of a bounding surface; in fluid mechanics, the layer
affected by viscosity of the fluid, referring ambiguously to the laminar
boundary layer, turbulent boundary layer, planetary boundary layer, or surface
boundary layer .
- In aerodynamics the boundary-layer thickness is measured from the
surface to an arbitrarily chosen point, e.g., where the velocity is 99 percent
of the stream velocity. Thus, in aerodynamics, boundary layer by selection of
the reference point, can include only the laminar boundary layer or the
laminar boundary layer plus all, or a portion of, the turbulent boundary
- boundary-value problem
- A physical problem completely specified by a differential equation in an
unknown, valid in a certain region of space, and certain information (boundary
condition) about the unknown, given on the boundaries of that region. The
information required to determine the solution depends completely and uniquely
on the particular problem. See initial-value
- Boussinesq approximation
- The assumption (frequently used in the theory of convection)
that the fluid is incompressible except insofar as the thermal expansion
produces a buoyancy, represented by a term gaT (a is equivalent to
alpha), where g is the acceleration
of gravity; a is the coefficient of thermal expansion; and T is the
- bow wave
- A shock
wave in front of a body, such as an airfoil, or apparently attached to the
forward tip of the body.
- Boyle law = Boyle-Mariotte
- Boyle-Mariotte law
- The empirical generalization that for many so-called perfect gases, the
product of pressure p and volume V is constant in an isothermal
process: pV = F(T) where the function F the temperature T
cannot be specified without reference to other laws (e.g., Charles-Gay-Lussac
law). Also called Boyle law, Mariotte law .
- brake parachute = deceleration
- braking ellipses
- A series of ellipses, decreasing in size due to aerodynamic drag, followed by
in entering a planetary atmosphere.
- In theory, this maneuver will allow a spacecraft to dissipate the heat
generated in entry without burning up.
- braking rocket = retrorocket.
- 1. In an electrical circuit, a portion of a network
consisting of one or more two-terminal elements in series.
- 2. The point in a computer
program at which the machine will proceed with one of two or more possible routines
according to existing conditions and instructions.
- branch point = node.
- Brayton cycle
- (After George B. Brayton, American engineer). Same as Joule
- Joining metals by flowing a thin-layer capillary thickness of nonferrous
filler metal into the space between them.
- Bonding results
from the intimate contact produced by the dissolution of a small amount of
base metal in the molten filler metal, without fusion of the base metal.
Sometimes, the filler metal is put in place as a thin solid sheet or as
cladding and the composite is heated as in furnace brazing.
The term brazing is used where the temperature exceeds some
arbitrary value, such as 800°F; the term soldering is used for
temperatures lower than the arbitrary value.
- 1. An assembly of preliminary circuits or parts used to prove the
feasibility of a device, circuit, system, or principle without regard to the
final configuration or packaging of the parts.
- 2. To prepare a breadboard , sense 1.
- The action of a boundary
layer separating from a surface.
- breakaway phenomenon
- See breakoff
- breakdown potential = dielectric
- breakoff = breakoff
- breakoff phenomenon
- The feeling which sometimes occurs during high-altitude flight of being
totally separated and detached from the earth and human society. Also called
the breakaway phonomonon.
- break point
- In computer operations, a point at which a break-point
instruction inserted in the routine will
cause the machine to stop, upon a command from the operator, for a check of
- break-point instruction
- In computer operations, an instruction which, in conjunction with a
manually operated control, causes the machine to stop.
- bremsstrahlung (German, braking radiation).
radiation produced by the rapid change in the velocity of an electron or
another fast, charged particle as it
approaches an atomic nucleus and is
deflected by it. See bremsstrahlung
- bremsstrahlung effect
- The emission of electromagnetic
radiation as a consequence of the acceleration of charged elementary particles,
such as electrons, under the influence of the attractive or repulsive force
fields of atomic nuclei near which the charged particle moves.
- In cosmic-ray shower production, bremsstrahlung effects give rise to
emission of gamma rays as electrons encounter atmospheric nuclei. The emission
of radiation in the bremsstrahlung effect is merely one instance of the
general rule that electromagnetic radiation is emitted only when electric
charges undergo acceleration.
- brennschluss (German, combustion termination ).
- The cessation of burning in a rocket,
resulting from consumption of the propellants, from deliberate shutoff, or
from other cause; the time at which this cessation occurs. See burnout, cutoff.
- Brewster point
- One of the three commonly detectable points of zero polarization of diffuse
sky radiation, neutral points, along the vertical circle through the sun;
the other two are the Arago point
- This neutral point, discovered by Brewster in 1840, is located about
15° to 20° directly below the sun; hence it is difficult to observe because of
the glare of the sun.
- 1. The attribute of visual perception in accordance with which an area
appears to emit more or less light.
- 2. = luminance.
- In sense 2 luminance is preferred.
- brightness level = adaptation
- brightness temperature
- 1. In astrophysics, the temperature
of a black
body radiating the same amount of energy per unit area at the wavelengths
under consideration as the observed body. Compare effective
- 2. The temperature of a nonblack body determined by measurement with an
- Brinell hardness number (abbr Bhn)
- A parameter describing the hardness of a material as the ratio of pressure
on a standard sphere used to indent the material to be tested to the area of
the indentation produced.
- British candle = international
- British thermal unit (abbr Btu)
- The amount of heat required to raise 1 pound of water at 60 degrees F, 1°
- This unit is defined for various temperatures, but the general usage
seems to be to take the Btu as equal to 252 15° gram-calories or 1055 joules.
- broadside array
- An antenna
array whose direction of maximum radiation is perpendicular to the line or
plane of the array according as the elements lie on a line or plane. A uniform
broadside array is a linear
array whose elements contribute fields of equal amplitude and
- brush discharge = corona
- B-scan = B-display.
- A cathode-ray indicator in which a signal appears as a spot with bearing
as the horizontal coordinate and distance as the vertical coordinate. Also
called B-display .
- In loran,
the designation applied to the transmitting station of a pair, the signal of
which always occurs more than half a repetition period after the next
succeeding signal and less than half a repetition period before the next
preceding signal from the other station of the pair, designated an A- station.
- The second trace of an oscilloscope
having more than one, as the lower trace of a loran indicator.
- Btu (abbr)
- 1. An unstable state of equilibrium of a thin-walled body stemming from
compressive stresses in the walls.
- 2. The lateral deflection of a thin-walled body resulting from such
- In computers: 1. An isolating circuit used to
avoid reaction of a driven circuit on the corresponding driving circuit.
- 2. A storage device
used to compensate for a difference in rate of flow of information or time or
occurrence of events when transmitting information from one device to another.
- buffer storage
- In computer operations, storage used to
compensate for a difference in rate of flow or time of occurrence when
transferring information from one device to another.
- The beating of an aerodynamic structure or surfaces by unsteady flow,
gusts, etc.; the irregular shaking or oscillation of a vehicle component owing
to turbulent air or separated flow.
- Of a radiant energy signal, to increase, often temporarily, in received signal
strength without a change of receiver controls.
- The opposite is fade.
- A wall, partition, or similar member in a rocket, spacecraft, airplane
fuselage, or similar structure, at right angles to the longitudinal
axis of the structure, and serving to strengthen, divide, or help give
shape to the structure.
- bulk modulus
- The reciprocal of the coefficient
- See potential
index of refraction.
- A separation or breakdown of the laminar
flow past a body; the eddying or turbulent
flow resulting from this.
- Burble occurs over an airfoil operating at an angle of attack greater
than the angle of maximum lift, resulting in a loss of lift and an increase of
drag. See compressibility
- burble angle = burble
- burble point
- A point reached in an increasing angle of
attack at which burble begins.
Also called burble angle.
- burner = combustion
- burn-in = debug.
- burning rate (symbol r)
- The velocity at which a solid
propellant in a rocket is
- Burning rate is measured in a direction normal to the propellant
surface and is usually expressed in inches per second.
- burning rate constant (symbol a )
- A constant, related to initial grain temperature, used in calculating the
rate of a rocket propellant grain.
- burning-rate exponent (symbol n)
- The exponent n in the equation
r = ap where
r is burning
rate, p is chamber
pressure; and a and n are constants.
- The value of n varies with the propellant.
- 1. An act or instance of fuel or oxidant depletion or, ideally, the
simultaneous depletion of both; the time at which this occurs. Compare cutoff.
- In the United Kingdom all burnt is preferred to burnout.
- 2. An act or instance of something burning out or of overheating;
specifically, an act or instance of a rocket combustion chamber, nozzle, or
other part overheating so as to result in damage or destruction.
- burnout velocity
- The velocity of a rocket,
rocket-powered aircraft, or the like at the time the fuel or oxidant or both
are depleted. Also called burnt velocity.
- burnt velocity = burnout
- 1. In a reactor, the
percentage of fissionable
atoms that have been fissioned. 2. Depletion of reactor fuel by fission.
- 1. A single pulse of radio
energy; specifically such a pulse at radar
- 2. = solar
- 3. = cosmic ray
- burst disk
- A diaphragm designed to burst at a predetermined pressure differential;
sometimes used as a valve, e.g., in a liquid-propellant line in a rocket. Also
called a rupture disk .
- In computer operations, a main circuit, channel, or part for the transfer
of information. Also called trunk .
- Busch lemniscate
- The locus in the sky, of all points at which the plane of polarization of
diffuse sky radiation is inclined 45° to the vertical. Also called neutral
- 1. In supersonic
diffuser aerodynamics, a nonsteady shock motion and airflow associated
with the shock system ahead of the inlet, very rapid pressure pulsations are
produced which can affect downstream operation in the burner, nozzle, etc.
- 2. Sustained oscillation of an aerodynamic control surface caused by
intermittent flow separation on
the surface, or by a motion of shock waves
across the surface, or by a combination of flow separation and shock-wave
motion on the surface.