Artistic rendering of Arase in orbit.
|Mission type||Earth observation|
|Launch mass||~350 kg|
|Start of mission|
|Launch date||11:00:00, December 20, 2016 (UTC)|
|Perigee altitude||~460 km|
|Apogee altitude||~32110 km|
|Inclination||~31 degrees |
Arase, formerly known as Exploration of energization and Radiation in Geospace (ERG), is a scientific satellite to study the Van Allen belts. It was developed by the Institute of Space and Astronautical Science of JAXA. While there was a scientist working on a similar project with the surname Arase, the satellite's name has nothing to do with him but instead named after a river beside the launch point.
It was launched aboard Epsilon launch vehicle at 11:00:00, 20 December 2016 UTC into apogee height 32250 km, perigee 214 km orbit. Subsequent perigee-up operation moved its orbit to apogee 32110 km, perigee 460 km of 565 minutes period.
The Arase spacecraft is the second satellite based on SPRINT bus, after Hisaki (SPRINT-A). Arase weighs about 350 kg, measures about 1.5 m × 1.5 m × 2.7 m at launch. Once in orbit, it will extend four solar panels, two 5 m masts, and four 15 m wire antennas. The spacecraft is spin-stabilized at 7.5 rpm (8 seconds).
Planned mission duration was for one year of scientific observation,  but the mission remains active over 3 years later.
Arase carries following instruments:
MGF is located at the end of 5 m extended mast.
PWE consists of a search coil (PWE-MSC) located at the end of another 5 m extended mast, four 15 m wire antennae (PWE-WPT), and associated electronics unit (PWE-E).
S-WPIA will analyse the data obtained by other instruments.