Radiation conditions in medium circular orbit during the extreme magnetic storm in May 2024

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Introduction

The Experimental Dose Control Complex (EDCC) is designed to monitor the effects of radiation exposure on a spacecraft (SC) [1, 2]. The EDCC enables measurements of the absorbed dose levels of ionizing radiation present in outer space.

The EDCC is implemented as a monoblock unit that includes a matrix of modules for recording the integral accumulated dose (MIRAD matrix). Ionizing radiation is detected using identical sensitive elements within the MIRAD, arranged in a 3×3 grid. Under radiation exposure, the sensitive element experiences degradation of channel conductivity in the embedded field-effect transistor. By measuring the voltage drop across the sensitive element when a constant current is passed through it, the magnitude of the accumulated radiation dose can be determined.

The experimental concept is based on creating different conditions of mass shielding for each of the nine MIRAD elements. This is achieved through the use of a steel grid with cells of varying thicknesses. As a result, each sensitive element is exposed to unique irradiation conditions – mass shielding attenuates the flux of ionizing radiation and alters its energy spectrum (differently for each type of radiation).

This paper presents the results of dose load measurements from ionizing radiation behind various mass shielding configurations in orbit at an altitude of H = 8070 km during the period from October 23, 2022, to October 14, 2024 (722 days). This time frame corresponds to the first half of Solar Cycle 25 [3], which is characterized by increased heliophysical and geomagnetic activity. Notably, in May 2024, the strongest geomagnetic storm in the past 20 years was recorded [4]. The paper examines the effect of this storm on the radiation environment in the spacecraft's orbit. The analysis utilized geomagnetic indices Dst and Kp, along with data from satellites in circular orbits at H = 20,000 km and H = 36,000 km.

Results of measurement

 

Рис. 1. Данные ЭККД за 722 дня

Fig. 1. EDCC data collected over 722 days

 

Fig. 1 presents the EDCC data collected over 722 days and their comparison with theoretical estimates (the calculation methodology for the theoretical values is described in [5]). The 0.3 mm sensor was excluded due to reaching the upper limit of the measurable dose; the 1 mm sensor was also excluded. The reading from the 7.5 mm sensor is 1.38 times lower than the theoretical value. For the remaining sensors, the measured absorbed dose exceeds the theoretical estimate by approximately 1.5 times.

 

Рис. 2. Набор дозы ЭККД в зависимости от времени для различных защит (в мм алюминия)

Fig. 2. Dose set of EDCC depending on time for different protections (in mm of aluminum)

 

Fig. 2 shows dose accumulation curves over time for different shielding configurations of the EDCC. The graphs indicate a sharp increase in dose accumulation rate following the extreme geomagnetic storm on May 10, with elevated levels sustained between May 12, 2024, and June 30, 2024. This anomalously rapid dose accumulation during the specified period is the primary reason for the observed exceedance of theoretical values.

To investigate the mechanisms by which geomagnetic disturbances influence the radiation environment, we analyzed particle flux data of ionizing radiation from spacecraft in circular orbits at various altitudes.

 

Рис. 3. Уровни потоков протонов СКЛ по данным КА «GOES», Dst-индекс геомагнитной активности, уровни потоков высокоэнергичных электронов на геостационарной орбите и орбите 20000 км

Fig. 3. Levels of proton fluxes of the SCR according to the GOES spacecraft data, Dst index of geomagnetic activity, levels of high-energy electron fluxes in the geostationary orbit and the 20000 km orbit

 

Fig. 3 presents the proton flux levels of solar cosmic rays (SCR) based on data from the GOES spacecraft [6] (geostationary orbit), the values of the Dst geomagnetic activity index, and the flux levels of high-energy (E > 2 MeV) electrons at geostationary orbit and at an altitude of 20,000 km.

As shown in Fig. 3, on May 11, 2024, a significant increase in solar cosmic ray (SCR) proton flux was recorded (45 times above the background level for protons with E > 100 MeV), followed by an intense geomagnetic storm (Dst reached –412 nT). As a consequence of this geomagnetic storm, the flux of high-energy electrons in the Earth's outer radiation belt (ORB) increased. However, it can be seen that the electron flux at geostationary orbit decreases rapidly, whereas at an altitude of 20,000 km, it remains above 1500 cm⁻²·s⁻¹·sr⁻¹ up to May 30, 2024. This behavior may be explained by a shift of the ORB region with the highest electron concentration (the ORB maximum) closer to Earth. A similar scenario is described in [7–10]. In such a case, the geostationary orbit would no longer intersect the ORB. With a sufficiently strong inward shift, even the 8070 km orbit could enter the ORB, which may account for the anomalously high dose rate observed at that altitude.

Dynamics of radiation belts

According to the empirical relationship linking the position of the outer radiation belt maximum in L-coordinates (McIlwain L-parameter) with the Dst index of geomagnetic disturbance [7],

$\left|Ds{t}_{max}\right| =\raisebox{1ex}{$2,75·{10}^4$}\!\left/ \!\raisebox{-1ex}{$L_{\max }^4$}\right.$                                                (1)

For example, at Dst = –412, the maximum of the outer radiation belt is expected to shift downward to L_max = 2.85, whereas under quiet geomagnetic conditions, its typical position is L_max ≈ 4. The orbit at 8070 km near the equator corresponds to L = 2.25, which lies below the estimated position of the outer radiation belt maximum following the storm. The dynamics of the radiation belts during geomagnetic storms of similar intensity are described in [11], where the formation of a new outer belt peak in the L range of 2.3 to 3 is noted. For instance, during the geomagnetic storm of March 24, 1991 (Dst = –300 nT), a peak in the electron belt was observed at L = 2.3 for E > 8 MeV, and at L = 3.1 for E ≈ 2 MeV [12].

Additionally, during intense geomagnetic storms, proton injection into the inner radiation belt may occur, resulting in the formation of an additional proton maximum in the region 2 < L < 2.5 with energies ranging from 20 to 70 MeV [13, 14]. According to data from the CRRES spacecraft [15], following the March 1991 storm, a new proton belt was formed at L ≈ 2.8 with energies in the tens of MeV, comparable in intensity to the stable inner radiation belt, whose maximum typically lies at L ≈ 1.5.

 

Рис. 4. Набор дозы в зависимости от времени для различных орбит

Fig. 4. Dose accumulation depending on time for different orbits

 

Since the EDCC lacks instrumentation for measuring fluxes of ionizing radiation particles, in order to determine the dynamics of the radiation belt position shift, it is appropriate to compare the dose accumulation rates on spacecraft in orbits at 20.000 km and 8.070 km during the period from December 20, 2023, to August 26, 2024 (Fig. 4). For this comparison, the graphs were normalized so that the magnitude of the variation between May 12, 2024, and July 13, 2024, coincided.

As evident from the graphs, at 20.000 km the dose accumulation rate sharply increases immediately after the storm, whereas at 8.070 km the increase in rate begins approximately 11 days later. This behavior can be explained by a gradual displacement of the radiation belt followed by stabilization of the Earth's magnetic field intensity and restoration of the radiation belt position to its pre-storm level.

Conclusion

The radiation environment in a medium circular orbit at an altitude of 8.070 km remains poorly studied, making its investigation of considerable interest to developers of space technology operating in this orbit. This paper presents the results of the first long-term measurements of the absorbed dose of ionizing radiation for spacecraft in such an orbit conducted within domestic practice.

The measurements revealed that following an extreme geomagnetic storm, there is a significant increase in the dose accumulation rate. As a result, the dose recorded over 722 days exceeds the calculated value with an error margin of no more than 10 %: for 2 mm and 3 mm shielding, the excess is by factors of 1.18 and 1.24, respectively; for 2.5 mm and 4.8 mm shielding, approximately 1.54 times; for 4 mm shielding, 1.62 times; and for 6.3 mm shielding, 1.75 times. According to the authors, these effects may be attributed to changes in the intensity of the Earth’s magnetic field accompanied by a subsequent displacement of the radiation belt boundaries.

作者简介

Mark Shelepov

JSC “Information Satellite Systems” Academician M. F. Reshetnev Company”

编辑信件的主要联系方式.
Email: shelepovmd@iss-reshetnev.ru
ORCID iD: 0000-0003-3940-4937

Cand. Sc., Design engineer of the 2 category

俄罗斯联邦, 52, Lenin St., Zheleznogorsk, Krasnoyarsk region, 662972

Vladimir Ivanov

JSC “Information Satellite Systems” Academician M. F. Reshetnev Company”

Email: ivanov@iss-reshetnev.ru
ORCID iD: 0009-0009-0127-4162

Cand. Sc., Deputy Head of Department

俄罗斯联邦, 52, Lenin St., Zheleznogorsk, Krasnoyarsk region, 662972

Sergei Kochura

JSC “Information Satellite Systems” Academician M. F. Reshetnev Company”

Email: kochura@iss-reshetnev.ru
ORCID iD: 0009-0009-0844-8487

Cand. Sc., Deputy General Designer of electrical engineering and control systems of spacecraft

俄罗斯联邦, 52, Lenin St., Zheleznogorsk, Krasnoyarsk region, 662972

Igor Maksimov

JSC “Information Satellite Systems” Academician M. F. Reshetnev Company”

Email: mia@iss-reshetnev.ru
ORCID iD: 0009-0005-5953-4909

Dr. Sc., Head of Department

俄罗斯联邦, 52, Lenin St., Zheleznogorsk, Krasnoyarsk region, 662972

Konstantin Molchanov

Novosibirsk State University

Email: K.molchanov@nsu.ru
ORCID iD: 0009-0002-6560-3649

Engineer of the 2 category

俄罗斯联邦, 1, Pirogova St., Novosibirsk, 630090

Vitaly Prokopyev

Novosibirsk State University

Email: vprok@cosmos.nsu.ru
ORCID iD: 0000-0001-9314-5492

Head of Department

俄罗斯联邦, 1, Pirogova St., Novosibirsk, 630090

参考

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