Polar (satellite)

The Global Geospace Science (GGS) Polar satellite was a NASA science spacecraft designed to study the polar magnetosphere and aurorae. 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.

Polar
Polar is the second of NASA's Global Geospace Science program
NamesGGS/Polar, ISTP/Polar, Polar Plasma Laboratory
Mission typeEarth observation
OperatorNASA
COSPAR ID1996-013A
SATCAT no.23802
Websitehttp://pwg.gsfc.nasa.gov/polar/
Mission durationPlanned: 2 years
Final: 12 years, 2 months, 3 days
Spacecraft properties
ManufacturerLockheed Martin Astro Space
Launch mass1,297 kg (2,859 lb)[1]
Dry mass1,028 kg (2,266 lb)[1]
Payload mass264 kg (582 lb)[1]
Dimensions2.4 × 1.8 m (7.9 × 5.9 ft)[1]
Power440 watts[1]
Start of mission
Launch dateFebruary 24, 1996, 11:24 (1996-02-24UTC11:24) UTC[2]
RocketDelta II 7925-10 D233
Launch siteVandenberg SLC-2W
End of mission
DisposalDecommissioned
DeactivatedApril 28, 2008 (2008-04-29)[3]
Orbital parameters
Reference systemGeocentric
RegimeHighly elliptical
Semi-major axis35,490.94 km (22,053.05 mi)
Eccentricity0.701992
Perigee altitude4,198.46 km (2,608.80 mi)
Apogee altitude54,027.15 km (33,570.91 mi)
Inclination78.63°
Period1,109.02 minutes
RAAN260.60°
Argument of perigee306.12°
Mean anomaly7.84°
Mean motion1.30°
EpochAugust 19, 2018, 04:42:45 UTC[4]
Revolution no.10,771
 

Launch

It was designed and manufactured by Lockheed Martin, and launched at 11:23:59.997 UTC on February 24, 1996 aboard a McDonnell Douglas Delta II 7925-10 rocket from launch pad 2W at Vandenberg Air Force Base in Lompoc, California, to study the polar magnetosphere.

The spacecraft was placed into a highly elliptical orbit with apogee at 9 Earth radii and perigee 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 aurora, and measured the entry of plasma into the polar magnetosphere and the geomagnetic tail, the flow of plasma to and from the ionosphere, and the deposition of particle energy in the ionosphere and upper atmosphere.

The nominal mission duration was two years, but was extended several times. Polar Mission Operations were finally terminated on April 28, 2008.[5][3]

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

Scientific instruments

Polar carried 11 scientific instruments totaling a mass of 264 kg:

Five instruments studying the local electromagnetic fields at low frequency:

  • MFE (Magnetic Field Experiment)
  • EFI (Electric Fields 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)
  • 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:

Results

Polar collected images of auroras in multiple wavelengths. She 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 aurora was observed in detail. The collected data and 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 satellite between January and April for his study of magnetic tail.[1]

A time-lapse animation of aurorae over both Earth poles shows symmetries and simultaneous changes - the long-suspected aurora mirroring – in images from the Visible Imaging System (VIS).
This composite image contains the first picture of the Earth in X-rays, taken in March 1996 by Polar.

References
  1. "Polar". eoPortal. European Space Agency. Retrieved August 19, 2018.
  2. "Polar". NASA Space Science Data Coordinated Archive. NASA. March 21, 2017. Retrieved April 28, 2018.
  3. Layton, Laura (April 28, 2008). "'Broken Heart' Image the Last for NASA's Long-Lived Polar Mission". NASA. Retrieved August 19, 2018.
  4. "Polar - Orbit". Heavens-Above. August 19, 2018. Retrieved August 19, 2018.
  5. Nelson, Buddy (April 30, 2008). "Long-Lived NASA Polar Satellite, Built by Lockheed Martin, Ends Service After 12 Productive Years". Lockheed Martin. Archived from the original on January 4, 2009.
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