Geotail

Geotail satellite (artist's concept)
Mission type	Earth observation
Operator	ISAS / NASA
COSPAR ID	1992-044A
SATCAT no.	22049
Website	www.stp.isas.jaxa.jp/geotail/
Mission duration	30 years, 4 months, 4 days
Spacecraft properties
Launch mass	980 kg (2,160 lb)
Power	273.0 watts
Start of mission
Launch date	24 July 1992, 14:26:00 (1992-07-24UTC14:26Z) UTC
Rocket	Delta II 6925
Launch site	Cape Canaveral LC-17A
End of mission
Disposal	Decommisioned
Deactivated	28 November 2022
Orbital parameters
Reference system	Geocentric
Regime	HEO
Semi-major axis	127,367.75 km (79,142.65 mi)[1]
Eccentricity	0.5469845[1]
Perigee altitude	51,328 km (31,894 mi)[1]
Apogee altitude	190,664 km (118,473 mi)[1]
Inclination	10.51 degrees[1]
Period	7539.86 minutes[1]
Epoch	15 January 2015, 13:40:53 UTC[1]

Geotail was a satellite that observed the Earth's magnetosphere. It was developed by Japan's ISAS in association with the United States' NASA, and was launched by a Delta II rocket on 24 July 1992 from Cape Canaveral Air Force Station.

The primary purpose of the mission was to study the structure and dynamics of the tail region of the magnetosphere with a comprehensive set of scientific instruments. For this purpose, the orbit has been designed to cover the magnetotail over a wide range of distances: 8 R_🜨 to 210 R_🜨 from the Earth. This orbit also allowed it to study the boundary region of the magnetosphere as it skims the magnetopause at perigees. In the first two years the double lunar swing-by technique was used to keep apogees in the distant magnetotail. This involved 14 lunar flybys.^[2]

In 1993 the computer that controls the Low Energy Particles experiment locked up.^[2] Attempts to reset it failed.^[2] This problem was solved by changing the trajectory of the craft during a lunar flyby that took place on 26 September 1993 so that it passed through the shadow of the Moon.^[2] Power from the batteries was cut while this took place.^[2] When the craft left the shadow of the Moon, power returned and the computer started working again.^[2]

The apogee was lowered down to 50 R_🜨 in mid November 1994 and then to 30 R_🜨 in February 1995 in order to study substorm processes in the near-Earth tail region. The present orbit is 9 R_🜨 × 30 R_🜨 with an inclination of -7° to the ecliptic plane."

Geotail instruments studied electric fields, magnetic fields, plasmas, energetic particles, and plasma waves.^[3]

In 1994 the principal investigator of the Plasma Wave Instrument (PWI), the experiment complement, was Professor Hiroshi Matsumoto of Kyoto University, with co-investigators from NASA, the University of Iowa, and STX Corporation.^[4] Geotail is an active mission as of 2021^[update].^[5] Geotail, WIND, Polar, SOHO, and Cluster were all part of the International Solar-Terrestrial Physics Science Initiative (ISTP) project.^[5]

In June 2022, the second and final of Geotail's two data recorders failed, jeopardizing science observation.^[6] It was decided to terminate the operation, and the spacecraft was deactivated on 28 November 2022.^[7]

Geotail data has been used to show that flux transfer events move faster than the ambient medium through the Magnetosphere.^[8] Those within the Magnetosheath were shown to move both faster and slower than the ambient medium.^[8]

During the lunar flybys Geotail identified oxygen, silicon, sodium and aluminium in the lunar atmosphere.^[2]

• International Solar-Terrestrial Physics Science Initiative
• Tom Krimigis

• JAXA | Magnetospheric Observation Satellite (GEOTAIL) Archived 30 April 2019 at the Wayback Machine
• GEOTAIL Magnetosphere Tail Observation Satellite | Spacecraft
• NASA Polar, Wind, and Geotail Projects