Progress of Radiation Belt Exploration by a Constellation of Small Satellites TGCSS/SGRB,COSPAR

WU Ji YANG Xiaochao DAI Lei

(National Space Science Center, Chinese Academy of Sciences, Beijing 100190)

Abstract A COnstellation of Radiation BElt Survey (CORBES) program is proposed by the Sub-Group on Radiation Belt (SGRB) of TGCSS,COSPAR.The CORBES mission is expected to have a constellation of 10-plus small/CubeSats to take an ultra-fast survey of the Earth’s radiation belt.The general science goal for CORBES is to investigate two groups of physical processes related to the radiation belts:wave-particle interactions and radial transport.This mission is an international multilateral cooperation mission,an open and sharing data policy will be implemented.The data set of observations will be shared within the contributors of the constellation and the broad research community at large,then would be of great use for comprehensively understanding the dynamics of magnetospheric energetic populations and developing more standard models of the Earth’s radiation belts.Furthermore,from the application perspective,the ultra-fast survey of the radiation belt could serve as an important facility for monitoring space weather of the Earth as well.

Key words Radiation belts,Ultra-fast survey,Constellation

1 Introduction

In 2017,Committee On SPAce Research (COSPAR),which devote to bringing the nations of the world together to undertake creative space endeavors for a long time,assembled a group of researchers,managers,and policy makers to examine the question of how small satellites might be used to advance technology,science research,and space applications.The two-year COSPAR study[1]laid out a compelling scientific roadmap to give specific guidance concerning small spacecraft utilization.

To develop a performable plan for implementing the recommendations of the COSPAR Strategic Action Plan and the COSPAR Scientific Roadmap on Small Satellites for Space Science,the Task Group on establishing a Constellation of Small Satellites (TGCSS) was established by COSPAR in late 2019 and chaired by Daniel Baker.In pursuit of these objectives,the COSPAR leadership team also drew guidance from the organization’s Scientific Roadmap.

“COSPAR should facilitate a process whereby international teams can come together to define science goals and rules for a modular,international small satellite constellation.The role of COSPAR is one of an honest broker,coordinating not funding.The results of an international effort to build small satellite constellations would be valuable for all participants and would be more valuable than the individual parts.COSPAR is in a position to help foster this international collaboration,creating a precedent for setting up community science in a very open way.”

The TGCSS aims to encourage international cooperation and make a meaningful contribution to solutions of the problems that are important to humanity.The subsequent work of TGCSS has emphasized the need to address several program elements,e.g.ionosphere/thermosphere,radiation belt,solar energetic particle events,atmospheric remote sensing and also various other operational aspects such as ground station design,radio licensing,access to space,and data management and distribution.

For this purpose,a sub-group of TGCSS,Sub-Group on Radiation Belt (SGRB) was established to deal with radiation belt measurements.SGRB is chaired by Ji Wu,a member of TGCSS.SGRB members include Ji Wu from National Space Science Center (NSSC) of China,Lei Dai from NSSC of China,Maurizio Falanga from ISSI in Switzerland,Vladimir Kalegaev from Moscow State University of Russia,Wen Li from Boston University of USA,Yoshizumi Miyoshi from Nagoya University of Japan,Rumi Nakamura from Space Research Institute (IWF/OEAW) in Austria,Minna Palmroth from the University of Helsinki in Finland,Anatoli Petrukovich from Space Research Institute (IKI)of Russia,and Mohammad Ebrahimi Seyedabadi from APSCO.Besides,all TGCSS members are invited to join SGRB and participate in its meetings.

SGRB will focus on the implementation of a Small/CubeSats constellation mission for radiation belt exploration.In pursuit of this goal,a proposal of a program called COnstellation of Radiation BElt Survey(CORBES) from China has been presented at TGCSS in July 2021.

2 CORBES Mission

The idea for the CORBES mission is to carry out an ultra-fast survey of the Earth’s radiation belt by a constellation of 10-plus Small/CubeSats.Making use of the multi-satellite constellation,this mission is expected to significantly enhance both time and spatial resolutions to significantly improve the understanding of the Earth’s radiation belt dynamics.

The orbit of CORBES is designed to be near the equatorial plane and with an apogee altitude of about 7 Earth radii or similar to GTO (seeFig.1).The lifetime of each Small/CubeSat is expected to be at least one year to limit the cost of them.

Fig.1 A constellation of 10 (or more) CubeSats to probe energetic particles of the radiation belt

CORBES is an international multilateral cooperation mission,multiple institute/university/industry from Asia,Europe and America are potential participants in this mission.It is proposed that,each participating institute/university/industry should contribute one or several satellites to form the constellation.Each Small/CubeSat is equipped with baseline instruments to meet the primary science goal of CORBES,but not limited to these instruments.An open and sharing data policy will be implemented in CORBES mission,and the data set of observations will be shared within the contributors of the constellation and the broad research community at large.

3 CORBES Science Objectives and Instrument Requirements

The science goal of CORBES is to carry out a survey over outer radiation belt in both high temporal and spatial resolutions.It will provide high-time resolution measurements of energetic electron fluxes,the geomagnetic field and plasma waves,then investigate the physical processes responsible for the fast dynamics of the Earth’s outer radiation belt.Principal (and incomplete) targeted physical processes for investigation by CORBES are listed briefly as follows (schematically shown inFig.2)[2].

Fig.2 Schematic for low-frequency plasma waves and wave-particle interactions in the magnetosphere

(1) Local resonant interactions between electron and Very Low Frequency (VLF) waves such as the whistler-mode waves that are produced by unstable plasma distributions arising during storms (seeFig.3)[3,4].

Fig.3 Local resonant interactions between electron and VLF waves (L is the geocentric distance in Earth radii of the location where the corresponding magnetic field line crosses the geomagnetic equator)

(2) Acceleration and transport of radiation belt electrons by radial diffusion that is driven by Ultralow-Frequency (ULF) magnetospheric disturbances[3,5].

(3) Sudden,intense electron radial transport events such as shock-induced injection,substorm injection,storm convection caused by solar eruptions that hit the magnetosphere and subsequent large-scale reconfiguration of the electric and magnetic fields (seeFig.4)[6].

Fig.4 Radial transport processes of energetic electrons in the magnetosphere

(4) Losses of electrons by precipitation into the atmosphere attributed to the scattering by a variety of waves such as whistler hiss and Electromagnetic Ion Cyclotron (EMIC) waves,as well as the magnetopause shadowing that causes electrons to escape from the magnetosphere into the solar wind due to movement of the magnetopause.

Preliminary requirements on baseline instruments of CORBES can be deduced from the general science goal.Two types of instruments are considered primary for the program:the magnetometers including Magnetometer (MAG) and Search Coil Wave Detector(SCWD),which are required to measure the magnetic field,shock-induced pulse,substorm dipolarization,and magnetospheric plasma waves such as ULF waves,EMIC waves,whistler-mode chorus waves,plasmaspheric hiss,magnetosonic waves,as well as the High Energy Electron Detector (HEED),which is required to detect energetic electrons trapped by the geomagnetic field.

Proposed performance parameters for baseline instruments of CORBES have been presented by NSSC and agreed at the SGRB meeting.MAG:the measurement range is ±40000 nT;the dynamic range is＞80000 nT;the frequency response is Dc-10 Hz;the resolution is better than 0.1 nT;the accuracy is 1–2 nT at Apogee.SCWD:the noise is 30 fT/Hz1/2@1 kHz;the frequency response is 10 Hz–10 kHz.HEED:FOV is about 30°;the energy range is 0.1–4 MeV,which is logarithmically divided into 20 equal channels.

4 SGRB Science Activities on CORBES

Since the establishment of SGRB,there have been intensive discussions on the implementation of CORBES.More than twenty reports from potential participants have been invited to be presented in SGRB meetings.The profile,science objectives and instrument requirements of CORBES mission have been discussed in detail and preliminarily defined,and intensive discussions on science payloads,the CubeSat constellation,the ground support system,the launcher and CubeSat deployer for the CORBES project have been carried out.A possible AIT and launch approch to avoid the ITAR restrictions has been proposed as well.

A commercial company of launcher called CAS Space has shown their willingness to provide a free launch opportunity and CubeSat separations mechanism for CORBES.NSSC and Peking University (PKU) also showed their willingness to provide support for science operations.Several research institutes where the SGRB members come from,PKU,Beihang University (BU),Institute of Space and Astronautical Science (ISAS)Japan Aerospace Exploration Agency,Kanazawa University (KU) and Paul Scherrer Institute (PSI) have also presented their capabilities of one or all of baseline instruments (MAG,SCWD and HEED).Innovation Academy of Microsatellites of CAS (IAMC),Shanghai Jiao Tong University (SJTU),Harbin Institute of Technology (HIT),Kyushu Institute of Technology (KIT),and two commercial companies ZeroG and Cosats,are willing to participate in CORBES program and provide one or two CubeSats.National Institute for Space Research (INPE),Brazil expressed the willingness to participate in CORBES program and would provide Cube-Sats,ground support services for the mission.

CAS Space,the commercial company that will provide the free ride,has the ability to launch their rocket from a sea launch pad.In that case,the final integration of all CORBES satellites could be considered to carry out outside of China,for example in Singapore.While the sea launch pad sails to the launch location in the Pacific,it could stop at a harbor near the final integration site.In this way,the participants who had the ITAR or similar problems could ship their satellites to this location instead of China.

5 Summary

The Task Group on establishing a Constellation of Small Satellites (TGCSS) was established by COSPAR to develop an actionable plan for implementing the recommendations of the COSPAR Strategic Action Plan and the COSPAR Scientific Road map on Small Satellites for Space Science.To address the Earth’s radiation belt program,one of several programs addressed by the TGCSS,CORBES program from China was proposed in 2021 by the Sub-Group on Radiation Belt (SGRB) of TGCSS.

The CORBES mission is expected to have a constellation of 10-plus small/CubeSats to take an ultra-fast survey of the Earth’s radiation belt.The general science goal for CORBES is to investigate two groups of physical processes related to the radiation belts:wave-particle interactions and radial transport.It is proposed that each participating institute/university/industry can contribute one or several payloads/spacecraft to form the constellation.The data set from CORBES,which shall be shared by the contributors of the constellation and within the broad research community at large,would be of great use for comprehensively understanding the dynamics of magnetospheric energetic populations and developing a more standard model of the Earth’s radiation belts.Furthermore,from the application perspective,the ultra-fast survey of the radiation belt could be an important facility for monitoring the space weather of Earth as well.

The principle of this initiative is based on a nomoney exchange policy.However,COSPAR will act as the main role to coordinate the whole process whenever needed.COSPAR will act as a mutual negotiator between participating governments,universities and research institutions.