Glossary - C

C band
frequency band between 4 and 8 GHz, normally 6 GHz is used for uplinks to the satellite and 4 GHz is used for the downlink
(satellite communications)

Cable head
common receiving equipment in a cable television network which receives terrestrial and satellite transmissions for distribution across the network
(broadcasting)

Call drop-out
unintentional disconnection of a call by a mobile terminal, usually as a result of the loss of signal strength at the terminal
(communications)

Canadarm, Canadarm2, Canadarm3
a series of robotic manipulator arms used on the Space Shuttle (Canadarm) and on the International Space Station (Canadarm2) and intended to be used on the Lunar Gateway (Canadarm3)
(human spaceflight)

Carrier
1: a radio or microwave signal transmitted from one earth station, through the satellite, to one or more earth stations
(satellite communications)

Carrier
2: holder of a telecommunications carrier licence
(regulations)

Carrier
3: a continuous electromagnetic wave which can be modulated by a signal to carry information
(communications)

Cassegrain
a reflector antenna and telescope geometry employing a primary parabolic reflector (dish or mirror) and a secondary convex hyperbolic reflector placed close to the main reflector''s focus
(technology)

Centre fed dish
reflector antenna with the focal point of the dish on the axis of the dish in front of the reflector; the feed is located at the focus
(technology)

Channel
the one-way simplex path from one earth station, through the satellite, to another earth station
(satellite communications)

Chromosphere
the second layer of a star's outer atmosphere located between the photosphere and the corona
(solar physics, astrophysics)

Circuit
a two-way duplex path from one earth station, through the satellite, to another earth station - equivalent to two channels or two half-circuits
(satellite communications)

Circuit switched network
network that establishes a physical circuit temporarily, until it receives a disconnect signal
(communications)

Circuit switching
a networking technique in which a physical connection is established between the sender and receiver for the duration of the transmission
(communications)

Cislunar
the region of space between the Earth and the Moon
(orbits)

Clarke orbit
an archaic expression for the geostationary orbit, so named because it was first suggested by Arthur C Clarke in 1945
(orbits)

Closed user group
group of users which operate a private network
(communications)

Cluster
in a VSAT system an outbound and its associated inbounds
(satellite communications)

Co-location
the technique of using the same orbital position for two or more communication satellites
(satellite communications)

Coma
a cloud of gas and dust surrounding the nucleus of a comet
(planetary science)

Combined access TDMA
is a synchronised multi-access protocol with both contention and fixed assigned access
(communications)

Comet
small bodies (usually 1 to 50 km diameter) composed of ice (both water ice and frozen gases) and rock which orbit a star; when comets in the solar system approach the Sun they can develop a coma and a tail of dust and plasma which is typically 1 to 10 million km long
(planetary science)

Communications satellite
a spacecraft intended to primarily provide communications and broadcast services
(satellite communications)

Conditional access
the technique of encrypting broadcasts and restricting the provision of decoders and keys to those authorised to receive the transmissions
(communications)

Conformal array
an antenna that is contoured to the surface of the structure carrying it, for example an antenna built into the skin of an aircraft
(earth station technology)

Conjunction
the alignment of two celestial bodies in which they have their least apparent angular separation
(astronomy)

Constellation
a group of similar satellites which operate together to provide a regional or global service
(technology)

Contention TDMA
a variant of Aloha (slotted Aloha) in which packet transmissions occur in predefined, and centrally synchronised, time slots; at the transmitting earth station, packets of data are transmitted in the next time slot; in the event of a collision, the data is retransmitted
(communications)

Conus
contiguous US - all the states of the USA except for Hawaii and Alaska
(satellite communications)

Coordination area
the area associated with an earth station outside of which another earth station sharing the same frequency band neither causes nor is subject to interference greater than a specified level
(regulations)

Corona
the outer layer of a star's atmosphere present in most stars (F, G, K and M class stars) consisting of of very high temperature, very low density plasma
(solar physics, astrophysics)

Coronal mass ejection (CME)
a large ejection of plasma (mainly protons and electrons) embedded in a magnetic field from a star's corona
(solar physics, astrophysics)

Cosmic rays
high energy particles (primarily protons and atomic nuclei) moving through space at near light speed, originating from stars (such as the Sun), supernovas and active galactic nuclei; when cosmic rays impact with a planetary atmosphere they produce showers of secondary particles
(astrophysics)

Cross modulation
signal distortion in which the modulation from one or more RF carriers modulates another carrier, generally when passing through a non linear unit such as a power amplifier
(communications)

Cross strapping
uplinking in one frequency band and beam type and downlinking in another frequency band and beam type
(satellite communications)

Cross talk
interference caused by the unwanted leakage of signal between two independent channels
(communications)