Overview

Kyokko (EXOS-A) was an aurora observation satellite developed by the Institute of Space and Aeronautical Science at the University of Tokyo (currently ISAS/JAXA) to observe the density, temperature, and composition of space plasma, to study the energy and spectrum of auroral electrons, to take ultraviolet images of the aurora, and to participate in the International Magnetospheric Sounding (IMS) project.
It was launched by the M-3H rocket No.2 from the Kagoshima Space Center (currently Uchinoura Space Center) on February 4, 1978, and completed its operation on August 2, 1992.

Weighing 126 kg, with a cylindrical shape of 95 cm in diameter and 80 cm in height, it orbited at an altitude of 630 km at perigee and 3,970 km at apogee in a quasi-polar (elliptical) orbit with an inclination of 65 degrees at a speed of 134 minutes per revolution.

DARTS archives raw telemetry and orbit data from Kyokko. However, data processing and analysis software is not archived, which may limit the ability to support scientific data analysis.

Observation Instruments

UV Auroral Television Camera (ATV)

ATV is a device that captures the aurora borealis in the ultraviolet region.
It is a TV camera that consisted of an image-memory tube with a slow-scan readout. The photoelectric surface is potassium bromide with a magnesium fluoride faceplate, that made it sensitive to photons around 1300 A. A pair of spherical mirrors produced an image on the photoelectric surface. The number of pixels in an image frame is 178x198 and the camera field of view is 60 deg.
An auroral pattern was measured every 128 s when the satellite was over the Arctic.

Electron Energy Spectrometer (ESP)

ESP is an instrument that measures the energy spectrum of auroral electrons.
It consisted of two spherical electrostatic analyzers, one mounted at the front and one at the back of the spacecraft to view the electrons streaming either down the magnetic field line or toward the equator. Each analyzer covered the energy range from 4.5 eV to 11.3 keV in nine energy channels.

Atmospheric UV Glow Spectrometer (AUV)

AUVs are spectrometers used to observe ultraviolet emission.
It consisted of a grating spectrograph with a resolution of 10 A and vibrating slit. The spectrum is scanned in a bandwidth of plus or minus 1.5 nm around the following spectral lines: 30.4 nm (He⁺)、58.4 nm (He)、83.3 nm (O⁺)、121.6 nm (H, Lyman-α)、130.4 nm (O).
Five-channel multipliers, one for each spectral line, are used to measure intensity.
The UV emissions from the atmosphere, magnetosphere, and interplanetary space were observed.

Ion Mass Spectrometer (MSP)

MSP is an instrument that measures the mass of ions in space plasma.
It measured upper-atmosphere positive ions in the ranges 1 to 4 and 14 to 16 atomic mass units and consisted of a quadrupole mass filter and a channel electron multiplier. The ion inlet is located on the forward end of the spacecraft main body.
MSP was used to understand the composition and dynamics of plasma by analyzing the mass and distribution of ions.

Plasma Wave Experiment (ESW)

ESW is an instrument that observes electromagnetic waves in plasma.
Two Faraday cups are employed to pick up electrostatic waves, while a dipole antenna is used to receive radio waves.
The dipole antenna consisted of a pair of thin wires 1.9 m long and is attached along the extendable stabilization booms.
One Faraday cup is mounted to look parallel to the spin axis, and the other, perpendicular to the spin axis.
Waves in the 0.4 to 30 kHz range are received by wideband receivers and telemetered in analog form.
The wave strength in the 0.045 to 3 MHz range is measured in 11 bands.
This instrument was used to analyze the properties of plasma waves and improve understanding of the plasma environment.

Langmuir Electron Probe (NEL)

NEL is a Langmuir probe for measuring the electron density and temperature in plasma. This instrument measures electron density and temperature in real time, enabling detailed analysis of the plasma state.

Electron Temperature Probe (TEL)

TEL is an RF-rectifier type probe that measures the electron temperature in plasma. This device is used to analyze the electron temperature distribution in detail and understand the energy state of plasma.

Achievements

Kyokkou was the first in the world to capture ultraviolet aurora images, and discovered plasma turbulence and strong electromagnetic radiation in the sky when the aurora appears. These observational results were important in understanding the mechanism by which auroras occur and the characteristics of space plasma.