The

Global Geospace Science Global Geospace science program (GGS) is designed to improve greatly the understanding the flow of energy, mass and momentum in the solar-terrestrial environment with particular emphasis on geospace. GGS has primary scientific objective of its own: ...

(GGS) ''Polar'' satellite was a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

science spacecraft designed to study the polar

magnetosphere In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior Dynamo ...

and

aurora An aurora ( aurorae or auroras), also commonly known as the northern lights (aurora borealis) or southern lights (aurora australis), is a natural light display in Earth's sky, predominantly observed in high-latitude regions (around the Arc ...

e. It was launched into orbit in February 1996, and continued operations until the program was terminated in April 2008. The spacecraft remains in orbit, though it is now inactive. ''Polar'' is the sister ship to GGS ''Wind''.

Launch

It was designed and manufactured by

Lockheed Martin The Lockheed Martin Corporation is an American Arms industry, defense and aerospace manufacturer with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta on March 15, 1995. It is headquartered in North ...

, and launched at 11:23:59.997 UTC on February 24, 1996, aboard a

McDonnell Douglas McDonnell Douglas Corporation was a major American Aerospace manufacturer, aerospace manufacturing corporation and defense contractor, formed by the merger of McDonnell Aircraft and the Douglas Aircraft Company in 1967. Between then and its own ...

Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas, and sometimes known as the Thorad Delta 1. Delta II was part of the Delta rocket family, derived directly from the Delta 3000, and entered service in ...

7925-10 rocket from launch pad 2W at

Vandenberg Air Force Base Vandenberg may refer to: * Vandenberg (surname), including a list of people with the name * USNS ''General Hoyt S. Vandenberg'' (T-AGM-10), transport ship in the United States Navy, sank as an artificial reef in Key West, Florida * Vandenberg S ...

Lompoc Lompoc ( ; Chumashan ) is a city in Santa Barbara County, California, United States. Located on the Central Coast, its population was 43,834 as of July 2021. Lompoc has been inhabited for thousands of years by the Chumash people, who called t ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

, to study the polar

. The spacecraft was placed into a highly elliptical orbit with

apogee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

at 9 Earth radii and

perigee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

at 1.8 Earth radii (geocentric), 86 degrees inclination, with a period of around 18 hours. The apogee was initially over the northern polar region, but has since been precessing south at about 16° per year.

Operations

Sensors on the spacecraft gathered multi-wavelength imaging of the

, and measured the entry of plasma into the polar magnetosphere and the geomagnetic tail, the flow of plasma to and from the

ionosphere The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...

, and the deposition of particle energy in the ionosphere and upper

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

. The nominal mission duration was two years, but was extended several times. ''Polar'' Mission Operations were finally terminated on April 28, 2008, after the spacecraft depleted its remaining fuel.

Characteristics

''Polar'' is a cylindrical satellite of 2.4 meters in diameter and 1.8 meters in height built by the "Astro Space" division of Martin Marietta. WIND is a stabilized satellite rotation at a speed of 10 rpm about its axis which is maintained perpendicular to the plane of the ecliptic. A platform that serves as support for certain instruments (including imaging) require that their field of view is fixed is fixed to the top of the satellite and rotates in the opposite direction. Satellite walls are covered with solar cells that provide 440 watts of electricity including 186 W are used by the scientific instruments. The satellite has a mass of 1297 kg, including 269 kg of propellant and 264 kg payload. It is designed for a minimum lifetime of 2 years. Scientific data are stored on a digital recorder with a capacity of 1.3

gigabits The bit is the most basic unit of information in computing and digital communication. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented as ...

and transmitted at a rate between 56 and 512 kb. ''Polar'' is the twin satellite of ''

Wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

''.

Scientific instruments

''Polar'' carried 11 scientific instruments totaling a mass of 264 kg: Five instruments studying the local

electromagnetic field An electromagnetic field (also EM field) is a physical field, varying in space and time, that represents the electric and magnetic influences generated by and acting upon electric charges. The field at any point in space and time can be regarde ...

s at

low frequency Low frequency (LF) is the ITU designation for radio frequencies (RF) in the range of 30–300 kHz. Since its wavelengths range from 10–1 km, respectively, it is also known as the kilometre band or kilometre waves. LF radio waves ...

: * MFE (

Magnetic Field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

Experiment) * EFI (

Electric Field An electric field (sometimes called E-field) is a field (physics), physical field that surrounds electrically charged particles such as electrons. In classical electromagnetism, the electric field of a single charge (or group of charges) descri ...

s Instrument) * PWI ( Plasma Wave Instrument) * HYDRA (Hot Plasma Analyzer Experiment) * TIDE/PSI (Thermal Ion Dynamics Experiment / Plasma Source Investigation) Three instruments responsible for studying populations of particles associated with electromagnetic fields: * TIMAS (Toroidal Imaging Mass Angle

Spectrograph An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mate ...

) * CAMMICE (Charge and Mass Magnetospheric Ion Composition Experiment) * CEPPAD (Comprehensive Energetic Particle-Pitch Angle Distribution) Three imagers responsible for providing a comprehensive view of the processes that interact with the upper atmosphere: * UVI (

Ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

Imager) * VIS ( Visible Imaging System) * PIXIE (''Polar''

Ionospheric The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

Imaging Experiment)

Results

''Polar'' collected images of auroras in multiple

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

s. It also measured the amount of plasma used in the polar regions of the magnetosphere, the flow of the latter in the ionosphere and the entry of other charged particles in it and in the upper atmosphere. For the first time the entire sequence of events initiated by magnetic substorms to the generation of the

was observed in detail. Analysis of the collected data determined that solar storms deposited such an amount of energy in the ionosphere that it stretched to fill the magnetosphere completely. ''Polar'' instruments were used during the primary mission of the

THEMIS In Greek mythology and religion, Themis (; ) is the goddess and personification of justice, divine order, law, and custom. She is one of the twelve Titan children of Gaia and Uranus, and the second wife of Zeus. She is associated with oracles a ...

satellite between January and April for his study of magnetic tail.

References

External links

''Polar'' website
at NASA.gov
Old ''Polar'' website
at NASA.gov {{DEFAULTSORT:Polar (satellite) Spacecraft launched in 1996 NASA satellites orbiting Earth Spacecraft launched by Delta II rockets Geospace monitoring satellites