- appointment
- approach path
- archive flag
- area code
- arithmetic term
- array antenna
- array declaration
- array index
- array pitch
- arrival direction
- arriving signal
- artificial variable
- ascent path
- astrodynamics
- astronomical refraction
- asymmetric signal
- asymmetrical effect
- asymptotical relation
- asynchronous mode
- approach speed
- approximate error
- approximate rendezvous
- approximation
- arc tunnel
- arcing monitor
- area coverage
- area ratio
- areal velocity
- argument passing
- arithmetic conversion
- arithmetic sort
- armouring
- ARQ circuit
- array
- array blanket
- array description
- artefact
- arithmetic relation
- arithmetic step
- arithmetic technical
- ARQ apparatus
- array identifier
- artificial antenna
- artificial comet
- artificial dispersal
- ascent acceleration
- asecndingnode
- assembler directive
- assembly instruction
- assignment instruction
- associate expert
- ascent
- ascent stage
- assembler operator
- assembling building
- assembling phase
- assembly code
- assembly routine
- assignment channel
- assignment statement
- associated picture
- astrometry
- astronomical time
- asymptotic speed
- asynchronous communication
- asynchronous transmission
- athermanous
- atmospheric gradient
- atmospheric path
- atmospheric subsidence
- atmospheric transmittance
- atmospheric window
- atmospherics
- atomic gyro
- attach header
- arabic numerals
- area exchange
- argument principle
- arithmetic exception
- arming circuit
- arriving waveform
- artificial gravity
- artificial selection
- assembly listing
- assembly pattern
- assigned band
- asteroid belt
- astronomy satellite
- asymmetrical mode
- atmospheric emission
- atmospheric friction
- atmospheric model
- atmospheric noise
- atmospheric sounder
- attach fitting
- attached device
- attachment feature
- attention field
- attenuation curve
- attenuation equalizer