Progress of radiation belt exploration by a constellation of small satellites TGCSS/SGRB, COSPAR

Following the COSPAR Scientific Roadmap on Small Satellites for Space Science, SGRB of TGCSS proposed the CORBES mission to address the Earth’s radiation belt scientific survey program and has been propelling this mission over the past two years.

The CORBES mission aims to conduct an ultra-fast survey of the Earth’s radiation belt using a constellation of multi-Small/CubeSats. The orbit of CORBES is designed to closely align with the equatorial plane, with an apogee altitude of approximately 7 Earth radii, similar to that of Geostationary Transfer Orbits (GTO). By utilizing this multi-satellite constellation, the mission aims to differentiate between temporal and spatial variations in the radiation belts, thus significantly advancing our understanding of Earth’s radiation belt dynamics. Each Small/CubeSat is expected to have a minimum operational lifetime of one year to manage costs effectively.

The CORBES mission aims to elucidate the physical mechanisms governing Earth’s outer radiation belt dynamics, addressing key unresolved questions. Through a CubeSat constellation, CORBES will measure energetic electron flux, geomagnetic field variations, and plasma waves with unprecedented temporal and spatial resolution. This will enable a detailed investigation of the outer radiation belt, potentially uncovering fundamental physical processes underlying its rapid dynamics. Below are primary targeted physical processes for quantitative or quasi-quantitative investigation (not exhaustive).

1. Energy diffusion occurs due to local resonant interactions between electrons and Very Low Frequency (VLF) waves, including whistler-mode waves generated by unstable plasma distributions during storms.
2. Pitch angle scattering arises from local resonant interactions between electrons and magnetospheric plasma waves, including whistler hiss and electromagnetic ion cyclotron (EMIC) waves.
3. Radial transport driven by the drift resonance between electrons and Ultra-Low-Frequency (ULF) magnetospheric waves, alongside radial transport induced by sudden, intense electric fields resulting from large-scale magnetic field reconfiguration, including shock-induced injection, substorm depolarization injection, and storm convection.
4. Electron escape from the magnetosphere into the solar wind occurs via magnetopause shadowing and the combined effects of magnetopause shadowing and outward radial transport.

Analyzing these primary physical processes in detail will yield quantitative insights into electron transport, acceleration, and losses, elucidating their respective contributions to outer radiation belt dynamics. This comprehensive understanding will refine our knowledge of outer radiation behavior and improve prediction models for more accurate forecasts.

The CORBES program initiative contains satellites outfitted with three types of payloads: the Magnetometer (MAG), the Search Coil Wave Detector (SCWD), and the High Energy Electron Detector (HEED) .

In order to cover the outer radiation belts for the measurements, a highly eccentric and inclined orbit is suggested. The orbit apogee must permit adequate magnetic field exploration. An example of a standard science orbit is this: 280 km at the perigee, 7 Re at the apogee, and approximately 11 degrees of inclination. For such an orbit, the orbit period is then roughly 13.5 hours. The outer radiation band (3 Re to 7 Re) can be traveled through in around 10.5 hours. It is anticipated that every satellite will function in the same orbit, spinning at a speed of around eight revolutions per minute on a spin-stabilized axis that faces the sun. The mass of each satellite shouldn't be more than 30 kg. The program's lifespan cannot be shorter than a year.

For telecommand, either S-band or X-band will be utilized, while X-band is assigned for data downlink. The satellites are scheduled for launch by one or two rockets, with the fitted upper stage delivering them into the target orbit, and the connected dispenser releasing them individually according to the specified separation sequence.

Assembly Integration and Testing (AIT), radiation shielding, and cross-calibration are important components of the program. Cross-calibration of the payloads is optional before launch. To calibrate the technical standards, the payloads will undergo testing in an identical setting. Cross-calibration in orbit after launch is required to preserve data consistency and comparability. With regard to HEED specifically, this entails choosing electrons in the same energy range during the magnetospheric quiet phase (Kp<3) and contrasting the outcomes of various HEED observations made under identical L, B conditions. When MAG and SCWD compare observations made during a chosen calm period, a similar methodology is used.

There are currently three small satellite contributions: the HIT satellite at the Harbin Institute of Technology (HIT), the IMACAS satellites at the Innovation Academy of Microsatellites (IMAC), and the Foresail satellites at the Finnish Centre of Excellence in Research of Sustainable Space (FORESAIL). IMAC is going to provide two satellites.

FGM has three contributions: MAG at the National Space Science Center, FGM at Beihang University (BHU), and FGM at the Space Research Institute Graz (IWF). The NSSC will contribute two sets of FGM. SCWD has two contributions: SCWD at the National Space Science Center and SCWD at Beihang University. The NSSC will contribute two sets of SCWD. HEED has four contributions: HEED at the National Space Science Center, HEED at Beihang University (BHU), HEED at the University of Turku (UTU), and HEED at the Paul Scherrer Institute. The NSSC will contribute two sets of HEED.

CORBES is an international multilateral mission with potential participants from Asia, Europe, and America. Each entity is expected to contribute one or more satellites to form the constellation, equipped with baseline instruments to achieve CORBES’s primary science goals, or provide a related ground support system. A data-sharing policy will ensure open access to observations within the COSPAR mission, benefiting both contributors and the broader research community.

Over the past two years, SGRB has hosted more than forty online meetings to outline the CORBES mission profile, identify potential participants, establish the CORBES scientist team, and organize the mission's technical design. The CORBES scientist team discussed and defined the CORBES’s scientific objectives and demonstrated the scientific requirements of the payloads. 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. Two papers about the technical design and the scientific objectives of CORBES have been submitted to Advances in Space Research.

In propelling CORBES, COSPAR has played a key role in coordinating and managing the mission, as well as acting as a mediator between participating governments, universities, and research institutions.

The data set from CORBES will be shared among the contributors to the constellation and the broader research community. This data will be invaluable for comprehensively understanding the dynamics of magnetospheric energetic populations and developing a more standard model of the Earth’s radiation belts. Additionally, from an application perspective, the ultra-fast survey of the radiation belt will serve as a crucial tool for monitoring Earth's space weather.

See the article：

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

https://doi.org/10.11728/cjss2024.04.2024-yg25

https://www.cjss.ac.cn/cn/article/doi/10.11728/cjss2024.04.2024-yg25