Investigation of the Contribution of Charged Particles under the Radiation Belts to the Surface Dose of Spacecraft
O.R. Grigoryan, L.S. Novikov, V.V. Sinolits, A.N. Petrov, V.L. Petrov, V.N. Sheveleva
Skobeltsyn Institute of Nuclear Physics of Lomonosov Moscow State University
Russia, 119992, Moscow, Leninskie gory, SINP MSU
The study is devoted to investigation of charged particles (proton and electron fluxes) under the Radiation Belts and provides the estimation of an additional dose value due to existence of these formations at L<2. We processed satellite data obtained in several space experiments (COSMOS-484, OHZORA, MIR, ACTIVE, SAMPEX, CORONAS-I, NOAA POES-17, TATYANA and others). The analysis shows that the additional near equatorial and middle latitude formations are observed under the Radiation Belts in a wide altitude range from 200 km up to 1300 km. We obtained averaged flux spectra for three main types of particle formations at L<2: near equatorial proton zone (L<1.15), near equatorial electron zone (L<1.2), middle latitude electron zone (L=1.2-1.8).of these zones. Using the experimental spectra we calculated the dependence of surface dose value on depth for two thickness ranges (<10 m and >10 m) and compared our results with calculations based on AE8 and AP8 models for ISS orbit parameters. Present models of charged particles distribution do not take into account the existence of the particles at low and middle latitudes in the region L<2. Our investigation shows that observed particles formations under the Radiation Belts provide the additional contribution to the surface dose value. We present the results of surface dose calculations taking into account the existence of the observed “abnormal” formations at L<2. Although the contribution of such formations is not significant, it has to be taken into consideration in model calculations of LEO radiation dose for long-term operating spacecraft
This paper systematizes experimental data about the influence of proton and electron abnormal fluxes under the Radiation Belts on the surface dose of spacecraft. Charged particles’ formations are observed at near-equatorial, low and middle latitude regions at L-values < 2. These formations are marked schematically on figure 1. It is shown that besides Radiation Belts L>2 region (marked A on Fig.1) and South Atlantic Anomaly region (marked B on Fig.1) three following zones of particle formations are observed.
Fig. 1. A) South Atlantic Anomaly ; B) Radiation
Belts; I) proton zone L<1.15; II) electron zones L<1.2; III) electron zones 1.2
AP8 model take into account proton fluxes with energies from 100 keV and upper and doesn’t take into consideration particle fluxes with lower energies. In our study experimental data with energies beginning at 10 keV and up to several MeV are processed.
II) II) Near-equatorial electron zone, L- values < 1.2. At L-values < 1.2 in wide altitude range from 350 km up to 1100 km peaks of electron fluxes with energies of
observed sporadically. Longitudinal dependence is one of the main characteristics of this formation . AE8 model doesn’t take into account this electron formation as well, as the model is applicable at L-values >1.2.
III) Low and middle latitude zone, 1.2
Peaks of electron and proton fluxes were registered in the following experiments described in table 1. Using different satellite experimental datasets described we calculated charged particle spectra in above mentioned zones.
Figure 2 shows proton and electron spectra at I-III regions calculated for two altitude interval: 300-600 km and 800-1000 km. It is obvious that different experimental data for more than 30 years period obtained by various detecting devices can be approximated both for electrons and protons to a high accuracy (correspondent approximations are presented). Altitude intervals were selected conventionally due to parameters of satellite orbits. Using obtained charged particle experimental spectra the values of surface doses due to above mentioned formations are calculated and compared.
Experimental spectra for I-III zones at two altitude ranges are compared on Figure 3. It is shown that proton flux at L<1.15 practically doesn’t depend on altitude (this result is in accordance with theory of double recharge of ring current/radiation belts protons due to interaction with neutrals of exosphere). Contrary the intensity of electron flux does depend on altitude that is obvious from Figure 3.
Fig.2: A) Proton spectra at L< 1.15 due to ACTIVE, SPRUT-6 and OVI-17 experimental data; black dots – AP8 model spectra at altitude 300-600 km. B) Proton spectra at L< 1.15 due to ACTIVE, NOAA POES 18, experimental data; black dots – AP8 model spectra at altitude 800-1000 km. C) Electron spectra at L< 1.2 due to ACTIVE, SPRUT-6, SAMPEX, CORONAS-F, CORONAS-I, COSMOS-900 experimental data at altitude 300-600 km. D) Electron spectra at L< 1.2 due to ACTIVE, NOAA POES, TATYANA experimental data at altitude 800-1000 km; E) Electron spectra at 1.2
Grey marked areas show the energy ranges that are not included in AP8 and AE8 models
Fig 3. Proton spectra (A) and electron spectra (B) approximations for two selected altitude ranges
Using obtained experimental spectra the surface doses were calculated for two
altitude ranges for electrons and summarized spectra for protons. Dose curves are compared with dose data obtained using AP8 and AE8 model spectra at ISS orbits (350-500 km, inclination 51°)
Fig. 4 Surface dose due to proton spectra
The results of the absorbed radiation dose computations for proton fluxes with different spectra are presented on figure 4. The computations were made by SHIELDOSE-2 program for semi-infinite Al medium. Here is shown the dose accumulated during 1 day mission as the dependence on protection thickness. The spectra used for this calculation were obtained at L<1.15 by ACTIVE, SPRUT-VI, SAMPEX, OVI-17, NOAA TIROS, S81-1, AZUR missions. The computation of spectra at L>1.15 were made using AP-8 MAX and AP-8 MIN model for MIR/ISS stations orbit (altitude ~300-400 km). The main feature of these dose curves is the significant contribution of protons at L<1.15 into dose at small layers (d<50 m). Observed discrepancies could be caused by absence of low energy particle data (< 100 keV) in AP8 model as the energy deposition is higher at low thicknesses for low energy protons.
Fig.5 Surface dose due to electron spectra for two thickness ranges (<10 m and >10 m)
Figure 5 shows dependence of electron surface dose value on depth for two thickness ranges (<10 m and >10 m). Surface doses due to experimental spectra are compared with results of calculations based on AE8max/min model for ISS orbit parameters. It is obvious from figure 5 that at low thicknesses electron surface dose due to experimental spectra is higher than due to AE8 model. It is necessary to take into account electron fluxes at L<2. AP8 and AE8 models don’t take into account observed particles formations.
Obtained dose value can be a bit higher than real one as we compare experimental data for wide altitude range from 300 up to 600 km with AP8/AE8 models data due to ISS orbit parameters.
Present study continues our previous research about contribution of abnormal particles formation into surface dose value. 1) Using experimental data (AZUR OV1-17 OV1-19 COSMOS-378 COSMOS-484 ESRO-4 COSMOS 900 NOAA TIROS-N S81-1 OHZORA ACTIVE MIR station CORONAS-I SAMPEX CORONAS-F NOAA POES-17 TATYANA) we obtained averaged flux spectra for three main types of particle formations at L<2: near equatorial proton zone (L<1.15), near equatorial electron zone (L<1.2), middle latitude electron zone (L=1.2-1.8).of these zones.
2) For surface dose calculations we used electron and proton experimental spectra approximated by kappa and power functions.
3) At low thicknesses we confirmed the previous data obtained in paper [4, 5] about the role of abnormal protons at L<1.15 in the surface dose of spacecraft. Observed discrepancies could be caused by absence of low energy particle data (< 100 keV) in AP8 model as the energy deposition is higher at low thicknesses for low energy protons.
4) Obtained that at thicknesses <10 m electron surface dose can make a contribution to the surface dose calculated using AE8 model spectra. Value of surface dose at 1.2
5) At >10 m thicknesses the role of L<1.2 electron formation is not sufficient, but electron fluxes at 1.2
1. O.R. Grigoryan, M.I. Panasyuk, A.N. Petrov, K. Kudela, J. Stetiarov.
Low-Energy Near-Equatorial Protons: The Flux Dependence on Magnetic Coordinates // WDS'05 Proceedings of Contributed Papers. 2005. Part II 245–250.
2. L.S.Bratolyubova - Tsulukidze, E.A.Grachev, O.R.Grigoryan, O.Yu.Nechaev. Near-equatorial electrons according to MIR station. Kosmich. Issled., 39, 602, 2001.
3. E.A.Grachev, O.R.Grigorian, S.I.Klimov, K.Kudela, A.N.Petrov, K.Schingenschuh, V.N.Sheveleva, J.Stetiarova.
Altitude distribution analysis of electron fluxes at L=1.2-1.8 // Advances in Space Res., 2005. 36. 1992-1996.
4. E.A.Grachev, O.R.Grigoryan, L.S.Novikov, I.V.Tchurilo. The role of Proton and Electron «abnormal» formation in radiation influence on construction elements of spacecraft. Proceedings of the ICPMSE-6 International Conference on Protection of Materials from Space Environment May 1-3, 2002. Toronto, Canada, edited by Kleiman J.I., Iskanderoba Z., Kluwer academic publishers (Space Technology Proceedings), Dorrecht / Boston / London. 2003. p.123-130.
5. O.R.Grigoryan, L.S.Novikov, V.L.Petrov, V.N.Sheveleva. Electron fluxes with energy < 1 MeV in the surface dose of spacecrafts. Journal of spacecraft and rockets, 2006, V.43, No.3, p. 530-533.
|Radiosensitivity prognosis by radiation therapy of patients with hodgkin’s disease||Spacecraft 187 Roundtrip Interstellar Travel Using Laser-Pushed Lightsails|
1. /IPC-SM-782A.Surface mount design and land pattern standard.1993.pdf
1. /About modifiers.rtf
2. /Advantage at contact...