|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:
- XEP-e (Extremely high-energy electron sensor)
- HEP-e (High-energy particle sensor – electron)
- MEP-e (Medium-energy particle sensor – electron)
- LEP-e (Low-energy particle sensor – electro)
- MEP-i (Medium-energy particle – ion)
- LEP-i (Low-energy particle – ion)
- MGF (Magnetic Field Experiment)
- PWE (Plasma Wave Experiment)
- S-WPIA (Software Wave-Particle Interaction Analyzer)
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.
- "Arase (ERG) Geospace Probe - JAXA". JAXA. Retrieved 2018-03-14.
- ジオスペース探査衛星「あらせ」（ERG）の軌道変更運用（近地点高度上昇）の完了について (in Japanese). JAXA. 13 January 2017. Retrieved 18 January 2017.
- "Archived copy" プレスキット/2016年11月18日（木） (PDF) (in Japanese). November 18, 2016. Archived from the original (PDF) on December 26, 2016. Retrieved November 27, 2016.CS1 maint: archived copy as title (link)
- Shogo Matsuda (16 January 2015). "Japan's Epsilon rocket shoved aside?". Nikkei Asian Review. Retrieved 6 February 2015.
- "Exploration of energization and Radiation in Geospace (ERG)". JAXA. 2012. Archived from the original on 2013-10-30. Retrieved 2013-09-08.
- Exploration of energization and Radiation in Geospace "ERG", JAXA
- Exploration of energization and Radiation in Geospace ERG, ISAS/JAXA
- on YouTube by JAXA
- ERG Science Center