Basics of Space Flight Glossary
- A
- Acceleration.
- Å
- Angstrom (0.0001 micrometer, 0.1 nm).
- AAAS
- American Association for the Advancement of
Science.
- AACS
- Attitude and Articulation Control Subsystem
onboard a spacecraft.
- AAS
- American Astronomical Society.
- AC
- Alternating current.
- ALT
- Altitude.
- ALT
- Altimetry data.
- AM
- Ante meridiem (Latin: before midday), morning.
- am
- Attometer (10
m).
- AMMOS
- Advanced Multimission Operations System.
- AO
- Announcement of Opportunity.
- AOS
- Acquisition Of Signal, used in DSN operations.
- Aphelion
- Apoapsis in solar orbit.
- Apoapsis
- The farthest point in an orbit from the body
being orbited.
- Apogee
- Apoapsis in Earth orbit.
- Apojove
- Apoapsis in Jupiter orbit.
- Apolune
- Apoapsis in lunar orbit.
- Apselene
- Apoapsis in lunar orbit.
- Argument
- Angular distance.
- Argument of periapsis
- The argument (angular distance) of
periapsis from the ascending node.
- Ascending node
- The point at which an orbit crosses the
ecliptic plane going north.
- Asteroids
- Small bodies composed of rock and metal in
orbit about the sun.
- Attometer
- 10
meter.
- AU
- Astronomical Unit, mean Earth-to-sun distance,
approximately 150,000,000 km.
- AZ
- Azimuth.
- Barycenter
- The common center of mass about which two or
more bodies revolve.
- BOT
- Beginning Of Track, used in DSN operations.
- BPS
- Bits Per Second, same as Baud rate.
- c
- The speed of light, 299,792 km per second.
- Caltech
- California Institute of Technology.
- Carrier
- The main frequency of a radio signal generated by
a transmitter prior to application of modulation .
- C-band
- A range of microwave radio frequencies in the neighborhood of 4 to 8 GHz.
- CCD
- Charge Coupled Device, a solid-state imaging
detector.
- C&DH
- Command and Data Handling subsystem on board a
spacecraft, similar to CDS.
- CCS
- Computer Command subsystem on board a spacecraft,
similar to CDS.
- CDS
- Command and Data Subsystem onboard a
spacecraft.
- CDU
- Command Detector Unit onboard a spacecraft.
- Centrifugal force
- The outward-tending apparent force of a body
revolving around another body.
- Centimeter
- 10
meter.
- Centripetal acceleration
- The inward acceleration of a body
revolving around another body.
- CIT
- California Institute of Technology, Caltech.
- CMC
- Complex Monitor and Control, a subsystem at
DSCCs.
- CNES
- Centre National d'Études Spatiales,
France.
- Coherent
- Two-way communications mode wherein the
spacecraft generates its downlink frequency based upon the frequency of
the uplink it receives.
- Coma
- The cloud of diffuse material surrounding the
nucleus of a comet.
- Comets
- Small bodies composed of ice and rock in various
orbits about the sun.
- CRAF
- Comet Rendezvous / Asteroid Flyby mission,
cancelled.
- CRT
- Cathode ray tube video display device.
- DC
- Direct current.
- DEC
- Declination, the measure of a celestial body's
apparent height above or below the celestial equator.
- Descending node
- The point at which an orbit crosses the
ecliptic plane going south.
- Downlink
- Signal received from a spacecraft.
- DSCC
- Deep Space Communications Complex, one of three
DSN tracking sites at Goldstone, California; Madrid, Spain; and Canberra,
Australia; spaced about equally around the Earth for continuous tracking
of deep-space vehicles.
- DSN
- Deep Space Network, JPL's worldwide spacecraft
tracking facility.
- DSS
- Deep Space Station, the antenna front-end equipment
at DSCCs.
- Dyne
- A unit of force equal to the force required to
accelerate a 1-g mass 1 cm per second per second (1cm/sec
).
Compare with
Newton.
- E
- East.
- Earth
- Third planet from the sun, a terrestrial planet.
- Eccentricity
- The distance between the foci of an ellipse
divided by the major axis.
- Ecliptic
- The plane in which Earth orbits the sun.
- EDR
- Experiment Data Record.
- EHz
- ExaHertz (10FM
Hz)
- EL
- Elevation.
- Ellipse
- A closed plane curve generated in such a way that
the sums of its distances from the two fixed points (the foci) is
constant.
- ELV
- Expendable launch vehicle.
- EOT
- End Of Track, used in DSN operations.
- Equator
- An imaginary circle around a body which is
everywhere equidistant from the poles, defining the boundary between the
northern and southern hemispheres.
- ERT
- Earth-received time, UTC of an event at DSN receive-
time, equal to SCET plus OWLT.
- ESA
- European Space Agency.
- ET
- Ephemeris time, a measurement of time defined by
orbital motions. Equates to Mean Solar Time corrected for irregularities
in Earth's motions.
- eV
- Electron volt, a measure of the energy of subatomic particles.
- F
- Force.
- FDS
- Flight Data Subsystem.
- FE
- Far Encounter phase of mission operations.
- Femtometer
- 10
meter.
- Fluorescence
- The phenomenon of emitting light upon
absorbing radiation of an invisible wavelength.
- fm
- Femtometer (10
m)
- FM
- Frequency modulation.
- FY
- Fiscal year.
- G
- Giga (billion).
- g
- Gram, a thousandth of the metric standard
unit of mass (see kg). the gram was originally based
upon the weight of a cubic centimeter of water.
- Gal
- Unit of gravity field measurement corresponding to a
gravitational acceleration of 1 cm/sec.
- Galaxy
- One of billions of systems, each composed of
numerous stars, nebulae, and dust.
- Galilean
- The four large satellites of Jupiter so named
because Galileo discovered them when he turned his telescope toward
Jupiter: Io, Europa, Ganymede, and Callisto.
- Gamma rays
- Electromagnetic radiation in the neighborhood of 100 femtometers
wavelength.
- GCF
- Ground Communications Facilities, provides data and
voice communications between JPL and the three DSCCs.
- GDS
- Ground Data System, encompasses DSN, GCF,
MCCC, and project data processing systems.
- GEO
- Geosynchronous Earth Orbit.
- Geostationary
- A geosynchronous orbit in which the spacecraft is constrained to a
constant
latitude.
- Geosynchronous
- A direct, circular, low inclination orbit
about the Earth having a period of 23 hours 56 minutes 4 seconds.
- GHz
- Gigahertz (10
Hz).
- GLL
- Galileo spacecraft.
- GMT
- Greenwich Mean Time, similar to UTC but not
updated with leap seconds.
- Gravitation
- The mutual attraction of all masses in the
universe.
- Great circle
- An imaginary circle on the surface of a sphere
whose center is at the center of the sphere.
- GSSR
- Goldstone Solar System Radar, a technique which
uses very high-power X and S-band transmitters at DSS 14 to illuminate
solar system objects for imaging.
- GTL
- Geotail spacecraft.
- GTO
- Geostationary (or geosynchronous) Transfer
Orbit.
- Gravitational waves
- Einsteinian distortions of the space-time medium predicted by general relativity
theory
(not yet detected as of November 1995).
- Gravity waves
- Certain atmospheric waves within a planet's atmosphere.
- HA
- Hour Angle, the angular distance of a celestial object
measured westward along the celestial equator from the zenith crossing.
In effect, HA represents the RA for a particular location and time of
day.
- Heliopause
- The boundary theorized to be roughly circular
or teardrop-shaped, marking the edge of the sun's influence, perhaps 100
AU from the sun.
- Heliosphere
- The space within the boundary of the
heliopause, containing the sun and solar system.
- HGA
- High-Gain Antenna onboard a spacecraft.
- Horizon
- The line marking the apparent junction of Earth
and sky.
- h
- Hour.
- Hz
- Hertz, cycles per second.
- ICE
- International Cometary Explorer spacecraft.
- Inclination
- The angular distance of the orbital plane from
the plane of the planet's equator, stated in degrees.
- Inferior planet
- Planet which orbits closer to the Sun than
the
Earth's
orbit.
- Inferior conjunction
- Alignment of Earth, sun, and an inferior planet on the same
side
of the sun.
- Ion
- A charged particle consisting of an atom stripped of
one or more of its electrons.
- IPC
- Information Processing Center, JPL's computing
center on Woodbury Avenue in Pasadena.
- IR
- Infrared, meaning "below red" radiation. Electromagnetic radiation in the
neighborhood
of 100 micrometers wavelength.
- IRAS
- Infrared Astronomical Satellite.
- ISOE
- Integrated Sequence of Events.
- Isotropic
- Having uniform properties in all directions.
- IUS
- Inertial Upper Stage.
- JGR
- Journal Of Geophysical Research.
- Jovian
- Jupiter-like planets, the gas giants Jupiter, Saturn,
Uranus, and Neptune.
- JPL
- Jet Propulsion Laboratory, operating division of the
California Institute of Technology.
- Jupiter
- Fifth planet from the sun, a gas giant or Jovian
planet.
- k
- Kilo (thousand).
- K-band
- A range of microwave radio frequencies in the neighborhood of 12 to 40
GHz.
- kg
- Kilogram, the metric standard unit of mass, based on the mass of a metal
cylinder kept in France. See g (gram).
- kHz
- kilohertz.
- Kilometer
- 10
meter.
- km
- Kilometers.
- KSC
- Kennedy Space Center, Cape Canaveral, Florida.
- KWF
- Keyword file of events listing DSN station
activity.
- LAN
- Local area network for inter-computer
communications.
- Laser
- Light Amplification by Stimulated Emission of
Radiation.
- Latitude
- Circles in parallel planes to that of the equator
defining north-south measurements, also called parallels.
- L-band
- A range of microwave radio frequencies in the neighborhood of 1 to 2 GHz.
- Leap Year
- Every fourth year, in which a 366th day is added
since the Earth's revolution takes 365 days 5 hr 49 min.
- LECP
- Low-Energy Charged-Particular Detector onboard a
spacecraft.
- LEO
- Low Equatorial Orbit.
- LGA
- Low-Gain Antenna onboard a spacecraft.
- Light
- Electromagnetic radiation in the neighborhood of 1 nanometer wavelength.
- Light speed
- 299,792 km per second, the constant c.
- Light time
- The amount of time it takes light or radio
signals to travel a certain distance at light speed.
- Light year
- The distance light travels in a year.
- LMC
- Link Monitor and Control subsystem at the SPCs.
- Local time
- Time adjusted for location around the Earth or
other planets in time zones.
- Longitude
- Great circles that pass through both the north
and south poles, also called meridians.
- LOS
- Loss Of Signal, used in DSN operations.
- LOX
- Liquid oxygen.
- M
- Mass.
- M
- Mega (million).
- m
- Meter (U.S. spelling; elsewhere metre), the international standard of linear
measurement..
- Major axis
- The maximum diameter of an ellipse.
- Mars
- Fourth planet from the sun, a terrestrial planet.
- Maser
- Microwave Amplification by Stimulated Emission of
Radiation.
- MC-cubed
- Mission Control and Computing Center.
- MCCC
- Mission Control and Computing Center.
- MCT
- Mission Control Team, Section 391 project
operations.
- Mean solar time
- Time based on an average of the
variations
caused by Earth's non-circular orbit.
- Mercury
- First planet from the sun, a terrestrial planet.
- Meridians
- Great circles that pass through both the north
and south poles, also called lines of longitude.
- MESUR
- The Mars Environmental Survey project at JPL,
the
engineering prototype of which is called MESUR Pathfinder.
- Meteor
- A meteoroid which is in the process of entering
Earth's
atmosphere.
- Meteorite
- Rocky or metallic material which has fallen to
Earth or to
another planet.
- Meteoroid
- Small bodies in orbit about the sun which are
candidates for falling to Earth or to another planet.
- MGA
- Medium-Gain Antenna onboard a spacecraft.
- MGN
- Magellan spacecraft.
- MHz
- Megahertz (10
Hz).
- Micrometer
- µm, 10
meter.
- Micron
- Obsolete
terms for micrometer, µm (10 m).
- Milky Way
- The galaxy which includes the sun and
Earth.
- Millimeter
- 10
meter.
- MIT
- Massachusetts Institute of Technology.
- mm
- millimeter (10 m).
- MO
- Mars Observer spacecraft.
- Modulation
- The process of modifying a radio frequency by
shifting its phase, frequency, or amplitude to carry information.
- Moon
- A small natural body which orbits a larger one. A
natural satellite.
- MOSO
- Multimission Operations Systems Office at JPL.
- µm
- Micrometer (10
m).
- N
- Newton, a unit of force equal to the force required to
accelerate a 1-kg mass 1 m per second per second (1m/sec).
Compare with
dyne.
- N
- North.
- Nadir
- The direction from a spacecraft directly down
toward the center of a planet. Opposite the zenith.
- NASA
- National Aeronautics and Space Administration.
- NE
- Near Encounter phase in flyby mission operations.
- Neptune
- Eighth planet from the sun, a gas giant or Jovian
planet.
- NIMS
- Near-Infrared Mapping Spectrometer onboard the
Galileo spacecraft.
- nm
- Nanometer (10
m).
- nm
- Nautical Mile, equal to the distance spanned by one
minute of arc in latitude, 1.852 km.
- Nodes
- Points where an orbit crosses a plane.
- Non-coherent
- Communications mode wherein a spacecraft
generates its downlink frequency independent of any uplink frequency.
- Nucleus
- The central body of a comet.
- OB
- Observatory phase in flyby mission operations
encounter period.
- One-way
- Communications mode consisting only of
downlink received from a spacecraft.
- Oort cloud
- A large number of comets theorized to orbit the
sun in the neighborhood of 50,000 AU.
- OPCT
- Operations Planning and Control Team,
"OPSCON."
- OSR
- Optical Solar Reflector, thermal control component
onboard a spacecraft.
- OSSA
- Office Of Space Science and Applications,
NASA.
- OTM
- Orbit Trim Maneuver, spacecraft propulsive
maneuver.
- OWLT
- One-Way Light Time, elapsed time between Earth
and spacecraft or solar system body.
- PAM
- Payload Assist Module upper stage.
- Parallels
- Circles in parallel planes to that of the equator
defining north-south measurements, also called lines of latitude.
- Pathfinder
- The Mars Environmental Survey (MESUR)
engineering prototype.
- PDS
- Planetary Data System.
- PDT
- Pacific Daylight Time.
- PE
- Post Encounter phase in flyby mission operations.
- Periapsis
- The point in an orbit closest to the body being
orbited.
- Perigee
- Periapsis in Earth orbit.
- Perihelion
- Periapsis in solar orbit.
- Perijove
- Periapsis in Jupiter orbit.
- Perilune
- Periapsis in lunar orbit.
- Periselene
- Periapsis in lunar orbit.
- Phase
- The angular distance between peaks or troughs of
two waveforms of similar frequency.
- Phase
- The particular appearance of a body's state of
illumination, such as the full phase of the moon .
- Photovoltaic
- Materials that convert light into electric
current.
- PHz
- Petahertz (10
Hz).
- PI
- Principal Investigator, scientist in charge of an
experiment.
- Picometer
- 10
meter.
- PIO
- JPL's Public Information Office.
- Plasma
- Electrically conductive fourth state of matter
from solid, liquid, and gas, consisting of ions and electrons.
- PLL
- Phase-lock-loop circuitry in telecommunications
technology.
- Pluto
- Ninth planet from the sun, sometimes classified as a
small terrestrial planet.
- pm
- Picometer (10
m).
- PM
- Post meridiem (Latin: after midday), afternoon.
- PN10
- Pioneer 10 spacecraft.
- PN11
- Pioneer 11 spacecraft.
- PST
- Pacific Standard Time.
- PSU
- Pyrotechnic Switching Unit onboard a spacecraft.
- RA
- Right Ascension, the angular distance of a celestial
object measured in hours, minutes, and seconds along the celestial
equator eastward from the vernal equinox.
- Radian
- Unit of angular measurement equal to the angle at
the center of a circle subtended by an arc equal in length to the radius.
Equals about 57.296 degrees.
- RAM
- Random Access Memory.
- Red dwarf
- A small star, on the order of 100 times the
mass of Jupiter.
- Refraction
- The deflection or bending of electromagnetic
waves when they pass from one kind of transparent medium into
another.
- RF
- Radio Frequency.
- RFI
- Radio Frequency Interference.
- ROM
- Read Only Memory.
- RPIF
- Regional Planetary Imaging Data Facilities.
- RTG
- Radioisotope Thermo-Electric Generator onboard a
spacecraft.
- RTLT
- Round-Trip Light Time, elapsed time roughly equal
to 2 x OWLT.
- S
- South.
- SA
- Solar Array, photovoltaic panels onboard a
spacecraft.
- SAF
- Spacecraft Assembly Facility, JPL Building 179.
- SAR
- Synthetic Aperture Radar.
- Satellite
- A small body which orbits a larger one. A
natural or an artificial moon. Earth-orbiting spacecraft are called
satellites. While deep-space vehicles are technically satellites of the sun
or of another planet, or of the galactic center, they are generally called
spacecraft instead of satellites.
- Saturn
- Sixth planet from the sun, a gas giant or Jovian
planet.
- S-band
- A range of microwave radio frequencies in the neighborhood of 2 to 4
GHz.
- SC
- Steering Committee.
- SCET
- Spacecraft Event Time, equal to ERT minus
OWLT.
- SCLK
- Spacecraft Clock Time, a counter onboard a
spacecraft.
- Sec
- Second.
- SEDR
- Supplementary Experiment Data Record.
- SEF
- Spacecraft event file.
- SEGS
- Sequence of Events Generation Subsystem.
- Semi-major axis
- Half the distance of an ellipse's
maximum diameter, the distance from the center of the ellipse to one
end.
- Shepherd moons
- Moons which gravitationally confine ring
particles.
- Sidereal time
- Time relative to the stars other than the
sun.
- SIRTF
- Space Infrared Telescope Facility.
- SOE
- Sequence of Events.
- SNR
- Signal-to-Noise Ratio.
- SP-100
- JPL's Space Power-100 Project developing
nuclear reactors for use in space.
- SPC
- Signal Processing Center at each DSCC.
- SSA
- Solid State Amplifier in a spacecraft
telecommunications subsystem, the final stage of amplification for
downlink.
- SSI
- Solid State Imaging Subsystem, the CCD-based
cameras on Galileo.
- SSI
- Space Services, Inc., Houston, manufacturers of the
Conestoga launch vehicle.
- STS
- Space Transportation System (Space Shuttle).
- Subcarrier
- Modulation applied to a carrier which is itself
modulated with information-carrying variations.
- Superior planet
- Planet which orbits farther from the sun
than Earth's orbit.
- Superior conjunction
- Alignment between Earth and a
planet on the far side of the sun.
- SWG
- Science Working Group.
- TAU
- Thousand AU Mission.
- TCM
- Trajectory Correction Maneuver, spacecraft
propulsive maneuver.
- TDM
- Time-division multiplexing.
- Three-way
- Coherent communications mode wherein a DSS
receives a downlink whose frequency is based upon the frequency of an
uplink provided by another DSS.
- THz
- Terahertz (10
Hz).
- TOS
- Transfer Orbit Stage, upper stage.
- Transducer
- Device for changing one kind of energy into
another, typically from heat, position, or pressure into a varying
electrical voltage or vice-versa, such as a microphone or speaker.
- Transponder
- Electronic device which combines a
transmitter and a receiver.
- TRC
- NASA's Teacher Resource Centers.
- TRM
- Transmission Time, UTC Earth time of uplink.
- True anomaly
- The angular distance of a point in an orbit
past the point of periapsis, measured in degrees.
- TWNC
- Two-Way Non-Coherent mode, in which a
spacecraft's downlink is not based upon a received uplink from DSN.
- Two-way
- Communications mode consisting of downlink
received from a spacecraft while uplink is being received at the
spacecraft. See also coherent.
- TWT
- Traveling Wave Tube, downlink power amplifier in a
spacecraft telecommunications subsystem, the final stage of
amplification for downlink (same unit as TWTA).
- TWTA
- Traveling Wave Tube Amplifier, downlink power
amplifier in a spacecraft telecommunications subsystem, the final stage
of amplification for downlink (same unit as TWT).
- µm
- Micrometer (10
m).
- ULS
- Ulysses spacecraft.
- Uplink
- Signal sent to a spacecraft.
- Uranus
- Seventh planet from the sun, a gas giant or Jovian
planet.
- USO
- Ultra Stable Oscillator, in a spacecraft
telecommunications subsystem.
- UTC
- Universal Time, Coordinated.
- UV
- Ultraviolet (meaning "above violet") radiation. Electromagnetic radiation in
the
neighborhood
of 100 nanometers wavelength.
- Venus
- Second planet from the sun, a terrestrial planet.
- VGR1
- Voyager 1 spacecraft.
- VGR2
- Voyager 2 spacecraft.
- VLBI
- Very Long Baseline Interferometry.
- W
- Watt, a measure of electrical power equal to potential
in volts times current in amps.
- W
- West.
- Wavelength
- The distance that a wave from a single
oscillation of electromagnetic radiation will propagate during the time
required for one oscillation .
- WWW
- World-Wide Web.
- X-band
- A range of microwave radio frequencies in the neighborhood of 8 to 12
GHz.
- X-ray
- Electromagnetic radiation in the neighborhood of 100 picometers
wavelength.
- Z
- Zulu in phonetic alphabet, stands for GMT.
- Zenith
- The point on the celestial sphere directly above the
observer. Opposite the nadir.
