Keywords:magnetosphere, aurora, imager, ultra violet, visible, ionosphere
We report science subject, design, development plan and identification of issues to be solved on the visible and ultraviolet imagers for a future satellite mission called FACTORS that aims to understand the coupling processes in the terrestrial magnetosphere/ionosphere/thermosphere and the acceleration and transportation of the space plasma and neutral atmospheric particles. FACTORS stands for Frontiers of Formation, Acceleration, Coupling, and Transport Mechanisms Observed by Outer Space Research System that is proposed as a multi-satellite formation flight mission. This will be a community exploration mission in Japanese apace research after the success of the ERG mission. The working group was approved by ISAS, JAXA this year, and we have started the discussion on detailed science targets, instrumental design, feasibility and so on. We mainly concern on visible and ultraviolet remote imaging of aurora and airglow for this mission. A visible imager (VISAI) on FACTORS will measure small-scale auroral structures at a wavelength of auroral prompt emission line, such as N2 1st PG, with high-time (~0.1s) and high-spatial (~1km) resolutions using a science CMOS or EMCCD. The FOV of 8 x 8 deg covers an area of 400 x 400 km viewed from 3000 km altitude. The high-spatial and high-time resolution imaging data is essential to understand small-scale variations of Alfven aurora, pulsating aurora, etc. Combined with particle and electric/magnetic field data by FACTORS, we will reveal the time and spatial variations of acceleration/scattering process in the complicated magnetosphere-ionosphere coupling system. A far-ultraviolet imager (FUVI) adopts a wide (~40 x 40 deg.) FOV objective mirror system which covers ~2500 x 2500 km area viewed from 3000 km altitude. We plan to adopt a filter wheal in FUV imager to change the wavelength between O 135.6 nm and the N2 LBH band at 140-160 nm. Wide-field multi-wavelength FUV images enable us to examine large-scale auroral dynamics like westward-travelling surge during substorm, omega-bands, and provide us to understand the global thermospheric activity from O/N2 airglow ratio. This year we plan to carry out specific studies for CMOS/EMCCD detectors suited for this mission, and perform radiation tests of detectors.
Related to the future FACTORS mission, we are now carrying out the developments of aural cameras for two sounding rocket projects, G-CHASER (Rocksat-XN) and LAMP. The G-CHASER (Rocksat-XN) rocket was successfully launched from Andøya, Norway on January 13, 2019. We installed an auroral camera (AIC) on this rocket to measure N2 1st PG emission with wide-angle FOV lens(96x75 deg), RG-665 filter, and CCD (WAT-910HX). In addition, we are developing two CMOS cameras AIC2 on the LAMP rocket that is scheduled to be launched at Poker Flat Research Range in winter of 2019. AIC2 will be installed on a despun platform to derotate rocket spin. One CMOS camera AIC2-S1 measures N2 1st PG emission with a narrow FOV lens (F-number=0.95, f=17mm, FOV=27x27deg.), and another CMOS camera AIC-S2 measures OI 844.6nm emission with a wide-angle lens (F-number=1.6, f=3.5mm, FOV=120x120deg.). Both cameras adopt the ZWO ASI 180 MM CMOS detector. AIC2-S1 will take fine structure of PsA in the region more than 100 x 100 km area around the magnetic footprint with a few kilo-meter resolution, while AIC2-S2 will obtain an altitude distribution of pulsating aurora in the F-region as well as distribution of PsA in wide-range. The precise imaging and altitude distribution of PsA are obtained with AIC2 at two wavelengths with 10Hz sampling. The imaging data combined with precipitating electron data in the wide energy range enable us to investigate the relativistic electron precipitation called microbursts that is probably caused by chorus waves in the magnetosphere.