Glossary - S

Sample return
a space mission to a planet, moon, asteroid or comet which collects surface samples and returns them to the Earth for analysis
(planetary science, space exploration)

Satellite
1: a small body which orbits a larger one
(astronomy, planetary science)

Satellite
2: a natural or artificial moon
(astronomy, planetary science, space technology)

Satellite
3: spacecraft placed in a stable orbit around the Earth
(spacecraft technology)

Satellite link
a radio link between a transmitting earth station and a receiving earth station through a satellite, consisting of an uplink and a downlink
(communications)

Satellite news gathering
technique of using a small transportable earth station to relay news items (usually television) directly from the site where the newsworthy event has occurred to a television studio for incorporation into news programmes
(broadcasting)

S band
frequency band from 2 to 4 GHz
(communications)

Scalar feed
a type of horn antenna feed which uses a series of concentric rings to capture signals
(technology)

Service area
a geographical area that is served by a specific gateway in a mobile satellite system
(satellite communications)

Service link
the transmission link between a satellite and end-users' mobile transceivers
(satellite communications)

Set top box
decoder (which is often placed on top of a television - hence the name) which decodes and decompresses digital signals to enable them to be viewed on a television; usually also incorporates some form of conditional access
(broadcasting)

Shepherd moon
a moon which gravitationally confines particles in a ring system around a planet
(astronomy, planetary science)

Short term fade
a fade whose duration is less than the round trip delay
(communications)

Sideband
the band of frequencies on either side of a carrier produced during the process of modulation
(communications)

Sidelobe
secondary beam of an antenna at an angle to the main beam
(technology)

Sidereal time
time determined relative to the reference frame of the fixed stars, rather than by the Earth’s orbit around the Sun
(astronomy)

Slant range
distance between the satellite and the ground station
(communications)

Small Magellanic Cloud (SMC)
the smaller of two small satellite galaxies which orbit the Milky Way; only visible from the southern hemisphere
(astronomy)

Soft handoff
in a mobile satellite system the process of transferring a circuit from one beam or satellite to another without interruption of the call
(satellite communications)

Soft landing
a near zero velocity landing of a spacecraft on the surface of a planet, moon, asteroid or comet
(space exploration)

Solar array
several solar panels which are connected together to generate electrical power for a spacecraft; the panels are usually connected by hinges so that the array can be folded to fit inside the launcher shroud during launch
(spacecraft technology)

Solar cell
device which converts light from the sun into electrical power
(technology)

Solar flare
in the Sun’s atmosphere which can last from a few minutes to several hours
(solar physics)

Solar outage
an increase in sky noise caused by the sun being within the receive antenna beam and which swamps the wanted signal
(communications)

Solar panel
a panel covered on one side with solar cells for generating electrical power; usually attached to the body of the spacecraft or to several other solar panels to form a solar array
(spacecraft technology)

Solar sail
a sail consisting of several large sheets of very thin, lightweight material stretched between rigid spars which uses radiation pressure from sunlight for spacecraft propulsion
(spacecraft technology)

Solar wind
a continuous stream of charged particles (mainly electrons, protons and alpha particles) which escape from the Sun’s corona and which then travel out across the solar system
(solar physics)

Solid propellant
the rubber or plastic like material used in solid rocket motors; solid propellants contain a fuel (ie aluminium powder) and an oxidiser (ie ammonium perchlorate); solid propellants give a very high thrust for a short time
(rocketry)

Solid state power amplifier (SSPA)
a type of RF and microwave output amplifier using solid state electronics instead of, for example, travelling wave tubes for amplification (which are now obsolete for many applications)
(technology)

Spaceport
a facility for launching spacecraft into space and for spacecraft returning from space
(spaceflight)

Space segment
the part of a satellite system consisting of the satellite and the ground support facilities for the satellite including telemetry, telecommand and ranging
(technology)

Space station
ITU terminology for the repeaters and antennas forming a communications payload on a satellite
(regulations)

Space tourism
orbital and suborbital flights by non-professional passengers in which the cost of the flight is not paid by the passenger’s employer, a government or a space agency
(human spaceflight)

Specific impulse
the change in momentum per unit mass of a rocket fuel, usually given in seconds, which is used as a measure of the efficiency of rocket engines
(rocketry)

Spectrometer
a scientific instrument used to separate and measure the spectral components of a physical phenomenon
(technology)

Spectrometer
a scientific instrument (optical spectrometer) used to split light into a spectrum, measuring the wavelength and intensity of spectral lines in the spectrum
(technology)

Spillover
satellite signals that fall outside the beam pattern's defined edge of coverage
(communications)

Spin stabilisation
a form of satellite stabilisation and attitude control in which the exterior of the spacecraft is spun about an axis at a fixed rate
(spacecraft technology)

Splitter
a passive device which divides a signal between two or more paths
(technology)

Spot beam
a narrow satellite antenna beam covering a small geographical area
(communications)

Spread spectrum
a transmission technique which uses a much wider bandwidth than would normally be required
(communications)

Star network
a network configuration in which a major hub is connected to many nodes which are not connected to each other except through the hub
(communications)

Stationkeeping
minor orbital adjustments that maintain the satellite within the defined parameters of its orbit
(spacecraft technology)

Static fire test
a rocket test in which the rocket is ignited when attached to a test stand or launch pad, but is not released and does not fly as part of the test; static fire tests are used as part of the pre-launch test sequence of some launch vehicles
(launcher technology)

Statistical multiplexing
form of multiplexing which allocates time or bandwidth only to active channels
(communications)

Stratosphere
the second lowest layer of the Earth’s atmosphere above the troposphere and below the mesosphere
(atmospheric physics)

Sub satellite point
the point on the earth's surface immediately below a satellite
(orbital geometry)

Subscriber communicator
small data terminal uses to send and receive packets of data to and from Orbcomm satellites
(satellite communications)

Sunspot
dark areas on the Sun’s photosphere that last for a few weeks, caused by concentrations of magnetic flux which reduce convention
(solar physics)

Sun Synchronous Orbit (SSO)
an orbit in which the satellite retains the same direction in relation to the sun; the satellite, therefore, always passes over the equator at the same location at the same local time; this orbit is generally used by Earth observation satellites
(orbits)

Superior conjunction
an alignment in which the Earth, Sun and another planet lie on a straight line, with the other planet being behind the Sun as seen from Earth
(astronomy)

Superior planet
a planet which orbits the Sun outside of the orbit of the Earth (ie Mars, Jupiter, Saturn, Uranus and Neptune)
(planetary science)

Supermassive black hole
a black hole with a mass greater than 100,000 solar masses
(astrophysics)

Supernova
a powerful and very bright stellar explosion occurring when a massive star reaches the end of its life or when a white dwarf undergoes runaway nuclear fusion
(astronomy, astrophysics)

Synthetic Aperture Radar (SAR)
a radar imaging technique which processes multiple images from a moving linear receive array to create a high resolution image
(Earth observation)