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Space and Solar Glossary / Terms / Dictionary

Space and Solar Definitions - S

S-band - A range of microwave radio frequencies in the neighborhood of 2 to 4 GHz.

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.

SC - Steering Committee.

SCET - Spacecraft Event Time, equal to ERT minus OWLT.

SCLK - Spacecraft Clock Time, a counter onboard a spacecraft.

Sec - Second.

Sector Boundary - In the solar wind, the area of demarcation between sec- tors, which are large-scale features distinguished by the predominant direction of the interplanetary magnetic field, toward or away from the sun.

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.

SFOF - Space Flight Operations Facility, Buildings 230 and 264 at JPL.

SFOS - Space Flight Operations Schedule, product of SEGS.

Shepherd moons - Moons which gravitationally confine ring particles.

Short Wave Fade (Swf) - A particular ionospheric solar flare effect under the broad category of sudden ionospheric disturbances (sids) whereby short-wavelength radio transmissions, vlf, through hf, are absorbed for a period of minutes to hours.

SI - The International System of Units (metric system).

Sidereal time - Time relative to the stars other than the sun.

SIRTF - Space Infrared Telescope Facility.

SMC - Small Magellanic Cloud, the smaller of two small galaxies orbiting nearby our Milky Way galaxy, which are visible from the southern hemisphere.

Smoothed Sunspot Number - An average of 13 monthly ri numbers, centered on the month of concern.

SNR - Signal-to-Noise Ratio.

SOE - Sequence of Events.

Solar Coordinates. Central Meridian Distance (Cmd) - The angular distance in solar longitude measured from the central meridian.

Solar Cycle - The approximately 11-year quasi-periodic variation in frequency or number of solar active events.

Solar Maximum - The month(s) during the solar cycle when the 12-month mean of monthly average sunspot numbers reaches a maximum. The most recent solar maximum occurred in july 1989.

Solar Minimum - The month(s) during the solar cycle when the 12-month mean of monthly average sunspot numbers reaches a minimum. The most recent minimum occurred in September 1986.

Solar Sector Boundary (Ssb) - The apparent solar origin, or base, of the interplanetary sector boundary marked by the larger-scale polarity inversion lines.

Solar wind - Flow of lightweight ions and electrons (which together comprise plasma) thrown from the sun.

SPC - Signal Processing Center at each DSCC.

Spectrum - A range of frequencies or wavelengths.

Sporadic E - A phenomenon occurring in the e region of the ionosphere, which significantly affects hf radiowave propagation. Sporadic e can occur during daytime or nighttime and it varies markedly with latitude.

Spotnil - Spotless disk

SSA - Solid State Amplifier in a spacecraft telecommunications subsystem, the final stage of amplification for downlink.

SSI - Space Services, Inc., Houston, manufacturers of the Conestoga launch vehicle.

SSIS - Solid State Imaging Subsystem, the CCD-based cameras on Galileo.

STD - Space Transportation System (Space Shuttle).

STS - Space Transportation System (Space Shuttle).

Subcarrier - Modulation applied to a carrier which is itself modulated with information-carrying variations.

Sudden Commencement (Sc, Or Ssc For Storm Sudden Commencement) - An abrupt increase or decrease in the northward component of the geomagnetic field, which marks the beginning of a geomagnetic storm.

Sudden Impulse (Si+ Or Si-) - A sudden perturbation of several gammas in the northward component of the low-latitude geomagnetic field, not associated with a following geomagnetic storm. (an si becomes an sc if a storm follows.)

Sudden Ionospheric Disturbance (Sid) - Hf propagation anomalies due to ionospheric changes resulting from solar flares, proton events and geomagnetic storms.

Sun synchronous orbit - A spacecraft orbit that processes, wherein the location of periapsis changes with respect to the planet's surface so as to keep the periapsis location near the same local time on the planet each orbit. See walking orbit.

Sunspot - An area seen as a dark spot on the photosphere of the sun. Sunspots are concentrations of magnetic flux, typically occurring in bipolar clusters or groups. They appear dark because they are cooler than the surrounding photosphere.

SUNSPOT GROUP CLASSIFICATION (Modified Zurich Sunspot Classification).

A - a small single unipolar sunspot or very small group of spots without penumbra.

B - bipolar sunspot group with no penumbra.

C - an elongated bipolar sunspot group one sunspot must have penumbra.

D - an elongated bipolar sunspot group with penumbra on both ends of the group.

E - an elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 10 deg. But not 15 deg.

F - an elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 15 deg.

H - a unipolar sunspot group with penumbra.

Sunspot Number - A daily index of sunspot activity (r), defined as r = k (10 g + s) where s = number of individual spots, g = number of sunspot groups, and k is an observatory factor.

Superior conjunction - Alignment between Earth and a planet on the far side of the sun.

Superior planet - Planet which orbits farther from the sun than Earth's orbit.

Surge - A jet of material from active regions that reaches coronal heights and then either fades or returns into the chromosphere along the trajectory of ascent.

SWG - Science Working Group.

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