Polar (satellite)

{{Short description|NASA science spacecraft which studied the polar magnetosphere until 2008}} {{italic title}} {{Infobox spaceflight |auto=all | name = Polar | names_list = GGS/Polar, ISTP/Polar, {{nowrap|Polar Plasma Laboratory}} | image = Polar line drawing.jpg | image_caption = ''Polar'' is the second of NASA's [[Global Geospace Science]] program | image_size = 230px

| mission_type = [[Earth observation]] | operator = [[NASA]] | COSPAR_ID = 1996-013A | SATCAT = 23802 | website = http://pwg.gsfc.nasa.gov/polar/ | mission_duration = Planned: 2 years <br /> Final: {{time interval|24 February 1996 11:24|28 April 2008|show=ymd|sep=,}}

| manufacturer = [[Lockheed Martin Space Systems|Lockheed Martin Astro Space]] | launch_mass = {{convert|1297|kg|abbr=on}}<ref name="eoPortal">{{cite web |url=https://directory.eoportal.org/web/eoportal/satellite-missions/p/polar |title=Polar |work=eoPortal |publisher=European Space Agency |access-date=August 19, 2018}}</ref> | dry_mass = {{convert|1028|kg|abbr=on}}<ref name="eoPortal" /> | payload_mass = {{convert|264|kg|abbr=on}}<ref name="eoPortal" /> | dimensions = {{convert|2.4|xx|1.8|m|ft|abbr=on}}<ref name="eoPortal" /> | power = 440 watts<ref name="eoPortal" />

| launch_date = {{start-date|February 24, 1996, 11:24}} UTC<ref name="nssdc.orbit">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1996-013A |title=Polar |work=[[NASA Space Science Data Coordinated Archive]] |publisher=NASA |date=March 21, 2017 |access-date=April 28, 2018}}</ref> | launch_rocket = [[Delta II]] 7925-10 D233 | launch_site = [[Vandenberg Air Force Base|Vandenberg]] [[Vandenberg AFB Space Launch Complex 2|SLC-2W]] | launch_contractor = | entered_service =

| disposal_type = Decommissioned | deactivated = {{end-date|April 28, 2008}}<ref name="nasa20080428">{{cite web |url=https://www.nasa.gov/topics/earth/features/polar_heart.html |title='Broken Heart' Image the Last for NASA's Long-Lived Polar Mission |publisher=NASA |first=Laura |last=Layton |date=April 28, 2008 |access-date=August 19, 2018 |archive-date=June 24, 2017 |archive-url=https://web.archive.org/web/20170624133838/https://www.nasa.gov/topics/earth/features/polar_heart.html |url-status=dead }}</ref> | decay_date =

| orbit_reference = [[Geocentric orbit|Geocentric]] | orbit_regime = [[Highly elliptical orbit|Highly elliptical]] | orbit_semimajor = {{convert|35490.94|km|mi|abbr=on}} | orbit_eccentricity = 0.701992 | orbit_periapsis = {{convert|4198.46|km|mi|abbr=on}} | orbit_apoapsis = {{convert|54027.15|km|mi|abbr=on}} | orbit_inclination = 78.63° | orbit_period = 1,109.02 minutes | orbit_RAAN = 260.60° | orbit_arg_periapsis = 306.12° | orbit_mean_anomaly = 7.84° | orbit_mean_motion = 1.30° | orbit_epoch = {{nowrap|August 19, 2018, 04:42:45 UTC<ref name="heavens-above">{{cite web |url=https://heavens-above.com/orbit.aspx?satid=23802 |title=Polar - Orbit |work=[[Heavens-Above]] |date=August 19, 2018 |access-date=August 19, 2018}}</ref>}} | orbit_rev_number = 10,771 | apsis = gee

| instruments_list = {{Infobox spaceflight/Instruments | acronym1 = MFE | name1 = Magnetic Field Experiment | acronym2 = EFI | name2 = Electric Fields Instrument | acronym3 = PWI | name3 = Plasma Wave Instrument | acronym4 = HYDRA | name4 = Hot Plasma Analyzer Experiment | acronym5 = TIDE/PSI | name5 = Thermal Ion Dynamics Experiment/Plasma Source Investigation | acronym6 = TIMAS | name6 = Toroidal Imaging Mass-Angle Spectrograph | acronym7 = CAMMICE | name7 = Charge and Mass Magnetospheric Ion Composition Experiment | acronym8 = CEPPAD | name8 = Comprehensive Energetic-Particle Pitch Angle Distribution | acronym9 = UVI | name9 = Ultraviolet Imager | acronym10 = VIS | name10 = Visible Imaging System | acronym11 = PIXIE | name11 = Polar Ionospheric X-ray Imaging Experiment }}

| programme = [[International Solar-Terrestrial Physics Science Initiative]] | previous_mission = ''[[Wind (spacecraft)|Wind]]'' | next_mission = ''[[Solar and Heliospheric Observatory|SOHO]]'' }}

The [[Global Geospace Science]] (GGS) '''''Polar''''' satellite was a [[NASA]] science spacecraft designed to study the polar [[magnetosphere]] and [[aurora]]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 [[Wind (spacecraft)|GGS ''Wind'']].

==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 (astronomy)|aurora]], and measured the entry of [[Plasma (physics)|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, after the spacecraft depleted its remaining fuel.<ref>{{cite web |url=http://www.lockheedmartin.com/news/press_releases/2008/4-30-polarsat.html |title=Long-Lived NASA Polar Satellite, Built by Lockheed Martin, Ends Service After 12 Productive Years |publisher=Lockheed Martin |first=Buddy |last=Nelson |date=April 30, 2008 |archive-url=https://web.archive.org/web/20090104024248/http://www.lockheedmartin.com/news/press_releases/2008/4-30-polarsat.html |archive-date=January 4, 2009}}</ref><ref name="nasa20080428" />

==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 [[kilobit|kb]]. ''Polar'' is the twin satellite of ''[[Wind (spacecraft)|Wind]]''.

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

Five instruments studying the local [[electromagnetic field]]s at [[low frequency]]:

* '''MFE''' ([[Magnetic Field]] Experiment) * '''EFI''' ([[Electric Field]]s Instrument) * '''PWI''' ([[Plasma (physics)|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:

* '''UVI''' ([[Ultraviolet]] Imager) * '''VIS''' ([[Light|Visible]] Imaging System) * '''PIXIE''' (''Polar'' [[Ionospheric]] [[X-ray]] Imaging Experiment)

==Results== ''Polar'' collected images of auroras in multiple [[wavelength]]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 [[aurora]] 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]] satellite between January and April for his study of magnetic tail.<ref name="eoPortal" />

{{multiple image |align=left |total_width=450 |image1=Aurora mirroring Polar 2.gif |caption1=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). |image2=Earthxray polar.jpg |caption2=This composite image contains the first picture of the Earth in X-rays, taken in March 1996 by ''Polar''. }} {{clear}}

==References== {{reflist}}

==External links== {{Commons category|Polar (satellite)}} {{Portal|Spaceflight}} * [https://pwg.gsfc.nasa.gov/polar/ ''Polar'' website] at NASA.gov * [https://www-istp.gsfc.nasa.gov/istp/polar/ Old ''Polar'' website] at NASA.gov

{{DEFAULTSORT:Polar (satellite)}} [[Category:Spacecraft launched in 1996]] [[Category:NASA satellites orbiting Earth]] [[Category:Spacecraft launched by Delta II rockets]] [[Category:Geospace monitoring satellites]]