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The Akebono satellite, also known as EXOS-D previous to its launch and 1989-016A for international design code, is a satellite designed to study the Earth’s magnetosphere and aurora (polar lights). Akebono was developed by the Japanese national research organization of astrophysics: Institute of Space and Astronautical Science (ISAS). The satellite operates through eight instruments on board as well as additional facilities to assist the operation of the instruments. With the main focus of investigating aurora phenomena, Akebono has made discoveries in respect of plasmas [the cause of aurora].

Origin
The satellite was first launched on February 22, 1989 at 8:30 (JST) by the M-3SII-4 launch vehicle from the Uchinoura Space Center (USC).The shape can be described as an octagonal cylinder with four solar-array paddles, two sets of 60 m tip-to-tip wire antennas, a height of 100cm and 126cm from face to face, weighing approximately 295kg.

Akebono was launched into a highly elliptical orbit, covering the region from the polar cap to the equator, and a status of:


 * Inclination: 75 degrees
 * Initial apogee (highest point):10,482km
 * Initial perigee (nearest to Earth): 272 km
 * Orbital period: 211 minutes
 * Orbit covers: 500 to 10,500 kilometers
 * Spin axis direction: Always towards sun
 * Spin-Stabilisation: 7.5rpm spin rate

Akebono, meaning “the dawn”, is the fourth satellite within the EXOS series of satellites launched by ISAS to investigate Earth’s upper atmosphere.The satellite’s purpose is to study the mechanism of auroral particle acceleration and the related physical phenomena of the magnetosphere. For maximum data coverage, four ground stations track Akebono’s path:
 * The Kagoshima Space Center (Japan)
 * Esrange Space Center (Sweden)
 * Prince Albert Satellite Station (Canada)
 * Syowa station (Antarctica)

Termination
Akebono's operation was terminated on April 23, 2015 at 15:59 p.m. due to built up radiation damaging instruments and deteriorating the electric system onboard the spacecraft. The damage led to reduced flight altitude and made it incapable to collect sufficient observation data for operation. 25 years past the expected target life,The Japan Aerospace Exploration Agency (JAXA) stopped sending and receiving radio waves to and from Akebono.

Mechanics
There are eight instruments contributing to the operation of Akebono including: Electric Field Detector (EFD), Magnetic Field Detector (MGF), Very Low Frequency Plasma Wave Detectors (VLF), Plasma Wave Detectors in High Frequency Range and Sounder (PWS), Low Energy Particle Spectra Analyzer (LEP), Suprathermal Mass Spectrometer (SMS), Thermal Electron Detectors (TED), and an Auroral Television Camera (ATV) for capturing images. The components contribute to a direct observation of particle acceleration regions above the auroral region.

Electric Field Detector (EFD)
The satellite includes two electric field detector systems, (EFD-B) and (EFD-P), to measure both the static and quasi-static vector electric field though two techniques: standard double probe and ion beam, which was developed specifically for the Akebono satellite. The electric field has three components, through the standard double probe technique (EFD-P), the field is measured as the possible differences between three orthogonal [intersecting at right angles] pairs of sensors, the sensors are separated and later divided by the distance between their separation. For quality measurement of the electric field, the satellite's surface is conductive [allowing heat or electricity to travel through] to minimize electrical disturbances surrounding Akebono.

Magnetic Field Detector (MGF)
Akebono carries both triaxial [three directions] search coil and triaxial fluxgate magnetometers [a device used to measure magnetic fields]. The fluxgate is mounted on a 5-m extendable mast and used for vector magnetic fields, collecting data at an altitude of 3,000-10,000 km. Search coils are mounted on a 3-m extendable mast and measure low frequency magnetic field fluctuations and waves, the measurements are collected with a frequency response of up to 800 Hz.

(VLF) and (PWS)
(VLF) and (PWS) are used for investigation of plasma waves in the magnetosphere, (PWS) has a frequency range of 20 kHz to 5.1 MHz and (VLF) has 3.16 Hz to 17.8 kHz. . (PWS) consists of three sub-systems:

(NPW)
For natural plasma wave observations, the sub-system contains three components: a) dynamic spectra observation b) polarization observation and c) poynting vector observation

(SPW)
For stimulated plasma wave experiments, five different modes are utilized for measurements.

(NEI)
The instrumentation for measurement of plasma density is created by a swept frequency impedance probe. Fixed frequency impedance allowed for accurate measurements of the electric field component.

(LEP) and (SMS)
Measuring magnetospheric phenomena requires the measurement of ion components of hot plasma, (LEP) and (SMS) are utilized for these measurements. (LEP) is designed in a keV energy range and (SMS) in thermal and suprathermal range.(SMS) is a radio frequency type mass spectrometer with a fast scan mode, thermal mode and a retarding potential analyzer (RPA) (sensor used to measure ion energy distribution of a plasma). The large dynamic range helps to regularly measure major and minor components of high latitude auroral plasma.

Thermal Electron Detectors (TED)
To support (LEP) and (SMS), Akebono carries a device, (TED) to measure the temperature and energy distribution of the plasma.

Observations
Throughout operation, Akebono has contributed to several observations, some include:

Electromagnetic Ion Cyclotron Waves
In April 1989, Akebono observed a change in intensity of characteristic frequency of electromagnetic ion cyclotron waves (EMIC) [waves generated by fundamental plasma instability]. The decrease in intensity was observed in the area surrounding the geomagnetic equator [between the geomagnetic poles] along the satellite's trajectory.

Plasma Wave Enhancement
Akebono's PWS and VLF plasma wave spectra were utilized to indicate the enhancement of plasma waves in a frequency range from 3 Hz to 50 kHz.

Ion cyclotron whistler waves
Below 10,500km altitude, Akebono observed ion cyclotron waves, leading to the study of distribution of the M/Q=2 ion in the inner magnetosphere.