Basics of Space Flight Glossary of  NASA

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A
Acceleration.
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 (10m).
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
1meter.
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
10-2 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'╔tudes 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 gr(gram).
kHz
kilohertz.
Kilometer
10+3 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+6 Hz).
Micrometer
Ám, 10-6 meter.
Micron
Obsolete terms for micrometer, Ám (10-16 m).
Milky Way
The galaxy which includes the sun and Earth.
Millimeter
10-3 meter.
MIT
Massachusetts Institute of Technology.
mm
millimeter (10-3 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.
Ám
Micrometer (10.-6 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/sec2). 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 (10-9 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+12 Hz).
PI
Principal Investigator, scientist in charge of an experiment.
Picometer
10-12 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 (10-12 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+12 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).
Ám
Micrometer (10-6 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.

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