Glossary
2 centimeters
Approximately 1 inch.
2.5 centimeters
Approximately 1 inch.
3 centimeters
Approximately 1 inch.
3 or 4 centimeters
Approximately 1 to 2 inches.
4.0 centimeters
Approximately 1.6 inches.
4.3 centimeters
Approximately 1.7 inches.
5 centimeters
Approximately 2 inches.
10 centimeters
Approximately 4 inches.
20 centimeters
Approximately 8 inches.
30 centimeters
Approximately 12 inches.
32 centimeter
Approximately 13 inches.
50 centimeter
Approximately 20 inches.
84 degrees Fahrenheit
9 degrees Celsius.
5 grams per square centimeter
Equivalent to approximately 1.14 ounces of force at nominal gravity per square inch.
2169.4 kilograms
Equivalent to approximately 4782.7 pounds of force at nominal gravity.
2388.4 kilogram
Equivalent to approximately 5265.5 pounds of force at nominal gravity.
2600 kilogram
Equivalent to approximately 5,732 pounds of force at nominal gravity.
1 kilometer
Approximately .62 miles.
1336 kilometer
Approximately 830 miles.
20,200 kilometer
Approximately 12,600 miles.
1.3 meters
Approximately 4.3 feet.
1.5 meters
Approximately 4.9 feet.
2.5 meters
Approximately 8.2 feet.
2.6 meters
Approximately 8.5 feet.
3 meters
Approximately 10 feet.
3.3 meters
Approximately 11 feet.
5.5 meters
Approximately 18 feet.
6.6 meters
Approximately 22 feet.
8.89 meters
Approximately 29.2 feet.
10 meters
Approximately 33 feet.
11.5 meters
Approximately 37.7 feet.
58 meters
Approximately 190 feet.
15 meters per second
Approximately 49 feet per second or 33 miles per hour.
1 newton
Approximately .225 pounds of force.
22 newtons
Approximately 4.95 pounds of force.
29.4 square meters
Approximately 317 square feet.
accuracy
The measure of how close an instrument's readings are to the true value.
algorithm
A series of steps used to process data.
altimeter
A device for measuring distance. For TOPEX/Poseidon, the height of the spacecraft above the surface of the ocean.
altimetric
Pertaining to measurements made by an altimeter.
ampere-hour
The quantity of electricity carried past any point of a circuit in one hour by a current of one ampere.
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anomaly
A deviation from what is expected or predicted.
Arianespace
A company owned by the French government responsible for building and operating the Ariane launch vehicle.
atmosphere
The mass of air surrounding a planet. For the earth, the mass per unit area of the atmosphere is approximately 10,200 kg/m(squared). This is equivalent to an atmosphere with a thickness of 8.4 km and uniform density of 1.21 kg/m(squared).
attitude
The orientation of a spacecraft relative to the earth.
biogeochemical
Chemical composition of and chemical changes in the solid matter of the earth and how these changes relate to plant and animal life.
bow
The forward part of a ship or spacecraft.
buoy
A free-floating or moored instrument platform at sea that provides measurements that may include tides, currents, wind, salinity, etc.
canted
Set at an angle.
circulation
The flow of a fluid that follows a circuit and eventually returns to its staring point. For the earth, the oceans and atmosphere circulate due to heating and cooling effects and to the rotation of the earth.
CNES
France's space agency, the Centre National d'Etudes Spatiales.
concentric
Having a common center.
consumables
Resources, such as propellants, aboard a spacecraft which are depleted during a mission and cannot be replaced.
corner-cube
A geometrical shape consisting of the corner of a cube. Light entering the face reflects off the inner surfaces of the cube and exits along the same path that it entered.
Doppler shift
A change in the frequency of waves (usually sound or radio) from a given source when the source and the observer are moving with respect to each other. The frequency is higher than normal as they approach each other and lower as they part.
DORIS
Doppler Orbitography and Radiopositioning Integrated by Satellite.
Deep Space Network
A set of 26 meter antennas used to observe earth satellites. The primary DSN stations are located in Goldstone California, Madrid Spain, and Canberra Australia. The locations of these 3 stations allow uninterrupted tracking of spacecraft regardless of its location.
dual-frequency
Using two separate radio frequencies.
electromagnetic bias
A term used to describe the fact that electromagnetic waves, in this case the radar signal, appear to be reflected from a surface that is lower than sea-level. The bias gets larger as the ocean waves get higher and the winds stronger.
electrostatic discharge
Discharge of built up static electricity.
ephemeris
Position and velocity of planets and satellites at a particular time.
free electrons
Electrons that are not bound to a nucleus.
geocentric
Measured as if observed from the earth's center.
geodesy
A branch of applied mathematics concerned with the determination of the size and shape of the earth and the exact positions of points on its surface with respect to the geoid.
geodetic
Relating to or determined by the size and shape of the earth and the exact positions of points on its surface with respect to the geoid.
geodynamics
A branch of mechanics that deals with forces within the earth and their relation to the motion and equilibrium of the solid earth.
geoid
Average sea-level of an ocean at rest.
geophysical
Dealing with the physics of the earth including the fields of meteorology, hydrology, oceanography, seismology, volcanology, magnetism, radioactivity and geodesy.
gigahertz
One billion cycles per second.
gimbal joint
Joints that allow rotational movement around one axis (much like an elbow joint).
gravitational
Information relating to gravity.
greenhouse gas
Gasses, primarily water vapor, in the atmosphere that trap infrared radiation and thereby increase the earth's temperature.
ground track
The trace of a satellite's nadir path on the earth's surface.
gyro
A device consisting of a heavy spinning disk mounted on gimbals which allow it to remain in a fixed orientation, regardless of the orientation of the spacecraft.
hydrazine
A highly toxic liquid fuel typically used in attitude control thrusters on spacecraft. Hydrazine is typically not ignited to produce thrust, but rather is rapidly decomposed in a chemical reaction.
hypergolic
Propellants that will ignite upon contact of their components without external aid such as a spark.
inclination
The angle between the satellite orbit plane and the earth's equatorial plane.
ionosphere
The part of the earth's atmosphere beginning at an altitude of about 30 miles and extending outward 300 miles or more. The ionosphere contains a large quantity of positively and negatively charged particles or ions (a neutral plasma). 95% of the ionoshpere is below the orbit of the TOPEX/Poseidon spacecraft.
ionospheric delay
The apparent increase in the path length of an electromagnetic signal due to the slowing of the signal in the ionosphere.
JPL
NASA's Jet Propulsion Laboratory.
kb/s
One thousand bits per second.
laser beam
A coherent beam of light.
limb
The outer edge of the apparent disk of a planet or satellite.
lithosphere
The outer part of the solid earth, composed of rock, and considered to be about 50 miles in thickness.
low-gain
A radio-antenna system which has a low efficiency relative to a directional or "pointable" system. The advantage of a low-gain system is that the antenna does not need to be aimed at a receiver. The disadvantage is that since the radio signal is transmitted in all directions, most of the power is lost.
magnetic torquer bars
Electromagnets used to push against the magnetic field of the earth, causing the spacecraft to turn.
magnetometers
An instrument used to detect the presence of a metallic object or to measure the intensity of a magnetic field.
magnitude
Brightness quality of a star according to an established scale.
mantle processes
Activities occurring in the part of the interior of earth that lies beneath the lithosphere and above the central core.
margin
Extra capability allowing for contingencies or special situations.
mathematical models
A set of equations and boundary conditions used to simulate the natural environment.
Mb
Megabits - One million bits.
meteorologists
Individuals who study the atmosphere and its phenomena, especially weather and weather forecasting.
microwave signal
A comparatively short electromagnetic wave, about 1 millimeter to 1 meter in length.
MMS
Multimission Modular Spacecraft.
mono-propellant
A rocket propellant containing both the fuel and the oxidizer in a single substance.
nadir
The direction pointing from the satellite to the center of the earth, directly opposite the zenith.
nadir column
A cylinder of air extending from the satellite to the surface.
NASA
National Aeronautics and Space Administration.
ocean topography
The difference between the sea-surface height and the ocean geoid.
oceanographers
Individuals who study the oceans.
oceanographic
Pertaining to the measurement of oceanic processes.
oceanography
A science that deals with the oceans including the delineation of their extent and depth, the physics and chemistry of their waters, and the plants and animals contained in them.
omnidirectional
In all directions.
orbit maintenance maneuvers
Controlled variation in the velocity of the spacecraft with the purpose of correcting orbit decay and restoring the satellite to the nominal reference orbit.
parabolic dish
Bowl shaped.
payload
Spacecraft equipment related directly to the purpose of the flight as opposed to equipment necessary for its operation.
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port
The left side of a ship or spacecraft looking forward.
precision
The measure of an instrument's ability to obtain consistent readings.
protons
A positively charged elementary atomic particle which, along with neutrons, is a constituent of all other atomic nuclei.
pyrotechnic device
Explosive mechanical mechanism usually used to release a deployable appendage.
radial position
The location of the spacecraft with respect to the center of the earth.
radiation
The process of emitting radiant energy in the form of waves or particles.
radiometer
An instrument for measuring the intensity of electromagnetic radiation.
range delay
Delay observed in the radar signal path. The apparent increase in the path length of an electromagnetic signal.
safe-hold mode
Backup state of the spacecraft. A spacecraft will usually switch itself to a safe-hold, or protected state if a fault is detected. Various levels of backup states have been defined to cover different situations.
sea-surface height
The height of the sea surface relative to the center of the earth.
sea-surface humidity
Humidity of the atmosphere at sea level.
sequences
An ordered set of commands transmitted to a spacecraft that provide instructions for functions to be performed, such as observations or maneuvers.
single-frequency
Using one frequency channel.
skewed
Set at an angle to all three of the major axis of the spacecraft.
SLR
Satellite Laser Ranging.
solid-state
Relying on solid semiconductors instead of electron tubes.
SRB
Solid Rocket Booster.
starboard
The right side of a ship or spacecraft looking forward.
stern
The back end of a ship or spacecraft.
subtropical
Near but not in the tropics.
TDRSS
Tracking Data Relay Satellite System.
telemetry
Data and system-health related information transmitted by radio from a satellite to a ground system.
tide gauges
Instruments used to measure the alternate rising and falling of the surface of the ocean. These changes are primarily due to the gravitational interaction of the sun and moon with the fluid earth.
time-tagged signals
Transmissions from satellites that include a time reference used to calculate the difference between the time the signal is sent and when it is returned.
TLC
Tender Loving Care.
topographic
Height variations in the earth's surface, usually reckoned to the geoid.
transponder
Transmitter and receiver aboard the satellite that receives and re transmits the ground signal for purposes of tracking the satellite.
tropical
Within the region of the earth bounded on the north by the Tropic of Cancer (23.5 N latitude) and on the south by the Tropic of Capricorn (23.5 S latitude).
tropospheric delay
The apparent increase in the path length of an electromagnetic signal due to slowing of the signal through the air.
watt
The amount of energy, in joules, expended per second. The typical incandescent light bulb is rated at about 100 watts.
zenith
The direction pointing from the center of the earth upward through the satellite, directly opposite the nadir.
zenith hemisphere
The area above and directly to the sides of the spacecraft.