Advances in Space Research 34 (2004) 1424–1428

www.elsevier.com/locate/asr

The features of radiation dose variations onboard ISS and Mirspace station: comparative study

L.V. Tverskaya a,*, M.I. Panasyuk a, S.Ya. Reizman a, E.N. Sosnovets a, M.V. Teltsov a,V.V. Tsetlin b

a Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow 119992, Russiab Institute of Biomedical Problems, Moscow 123007, Russia

Received 22 November 2002; received in revised form 26 February 2004; accepted 26 February 2004

Abstract

The dynamics of the ISS-measured radiation dose variations since August 2000 is studied. Use is made of the data obtained with

the R-16 instrument, which consists of two ionization chambers behind different shielding thicknesses. The doses recorded during

solar energetic particle (SEP) events are compared with the data obtained also by R-16 on Mir space station. The SEP events in the

solar maximum of the current cycle make a much smaller contribution to the radiation dose compared with the October 1989 event

recorded on Mir space station. In the latter event, the proton intensity was peaking during a strong magnetic storm. The storm-time

effect of solar proton geomagnetic cutoff decreases on dose variations is estimated. The dose variations on Mir space stations due to

formation of a new radiation belt of high-energy protons and electrons during a sudden commencement of March 24, 1991 storm are

also studied. It was for the first time throughout the ISS and Mir dose measurement period that the counting rates recorded by both

R-16 channels on ISS in 2001–2002 were nearly the same during some time intervals. This effect may arise from the decreases of

relativistic electron fluxes in the outer radiation belt.

� 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

Keywords: Radiation dose; Space stations; Solar energetic particle events; Geosynchronous satellites

1. Introduction

As before, the radiation environment of manned

space stations is urgent to appraise and predict. The

main contribution to the radiation dose on Mir space

station and on ISS is from galactic cosmic rays and from

the high-energy radiation belt electrons and protons.The contribution from the solar flare protons to the

integral dose on Mir space station was about 3%

throughout the full space station flight time. However,

allowance should be made for the radiation hazard to

spacecraft crew during short-term solar energetic parti-

cle (SEP) events generated by large solar flares. For

example, the daily absorbed dose rate induced by the 19

October 1989 flare had increased more than a hun-dredfold by as early as 20 October (Tverskaya et al.,

* Corresponding author. Tel.: +7-95-939-2488; fax: +7-95-939-0896.

E-mail address: tverskaya@taspd.npi.msu.su (L.V. Tverskaya).

0273-1177/$30 � 2004 COSPAR. Published by Elsevier Ltd. All rights reser

doi:10.1016/j.asr.2004.02.010

1991), so appropriate measures were taken to enforce

conformity to protection standards for the movements

of spacecrew members inside the space station. The SEP

event-induced radiation dose on manned spacecraft is

determined by not only the intensity and spectrum of

particles, but also the time of spacecraft residence in the

polar plateau of solar protons. During geomagneticallyquiet periods, the invariant geomagnetic cutoff latitude

of the �40 MeV protons determined by the com-

mencement of the solar proton intensity decrease from

the polar plateau level is 64–66�, depending on local

time (Biryukov et al., 1983). It is during but one or two

passes of Mir space station and ISS within a day that the

spacecraft orbits reach the invariant latitudes P 66�.(Tverskaya et al., 1991). During geomagnetic distur-bances, however, the geomagnetic cutoff latitude can

lower even to �55� for >1 MeV protons (Sosnovets and

Tverskaya, 1986). Thus, the spacecraft residence time

on the polar plateau of solar protons may increase a

ved.

L.V. Tverskaya et al. / Advances in Space Research 34 (2004) 1424–1428 1425

few-fold. The minute correlations between the geomag-

netic cutoff latitude and the geomagnetic indices were

studied using the large >1 MeV proton dataset obtained

from the Cosmos satellites in 1972–1977. The position of

the geomagnetic cutoff latitude at different local times

proved to be determined best by the parameterAD ¼ ðD2

st þ 0:02AE2Þ1=2, where Dst and AE are standard

geomagnetic activity indices (Ivanova et al., 1985). The

dependence of cutoff on geomagnetic Kp index was

model-calculated (see Nymmik, 1999; and the references

therein). In the case of protons with energies of a few

tens of MeV, the detailed data on the storm-time geo-

magnetic cutoff variations were not published until re-

cently (Leske et al., 2001). The correlation coefficientsbetween the geomagnetic cutoff latitude and the stan-

dard Kp and Dst indices have been shown to be 0.76 and

)0.77, respectively.We shall discuss the radiation dose variations on Mir

space station and on ISS during some SEP events. The

long-term radiation dose variations induced partly by

radiation belt variations will also be discussed.

1.1. Equipment

The Mir space station radiation environment was on-

line monitored by the onboard R-16 dosimetry system,

which included two ionization chambers with electro-

static relay (Yuryatin et al., 1979). Either chamber was

of an almost isotropic sensitivity and measured the do-

ses to within a high accuracy (�5%). One of the cham-bers (D2) had its own wall of �0.5 g/cm2 acrylic plastic.

Another chamber (D1), which was identical with D2,

had an additional shielding, so that D1 was behind a �3

g/cm2 total shielding. Being placed inside the space

station, the R-16 system got shielded by the space sta-

tion matter. Therefore, chamber D2 was behind a �2 g/

cm2 shielding, while chamber D1 was behind a �4.5 g/

cm2 shielding. So, chambers D2 and D1 recorded pro-tons with energies above 40 and 70 MeV and electrons

above 4 and 8 MeV, respectively.

On ISS, the arrangement of chambers D2 and D1 is

different from the above, and the mass distribution is

known within an insufficient accuracy. An attempt was

made in (Kuznetsov et al., 2004) to use the method for

Table 1

Radiation doses (mGy) and proton fluences (cm�2 sr�1) measured during

Express-AS and GOES

Date Doses

Mir D1 Mir D2 ISS D1 ISS D

19–21 October 1989 – 27.2 – –

14–17 July 2000 0.5 7.0 – –

08–11 November 2000 0.5 2.85 0.3 1.4

24–27 September 2001 – – 0.25 1.4

04–07 November 2001 – – Back-ground 0.5

calculating radiation doses in different orbits during SEP

events (Nymmik, 1999) and calculate the empirical re-

lations between the shieldings of the chambers flown on

Mir and ISS basing on the data of simultaneous mea-

surements of a SEP event with all instruments. The 9

November 2000 SEP event was selected, which occurredduring a geomagnetically quiet period. Use was made of

the solar proton flux measurement data of geosynchro-

nous GOES-8 and 10 and the ionization chamber (D)

data of geosynchronous satellite Express-A3. The effec-

tive shielding was found to be 2.5–3 g/cm2 for Express-

A3 ionization chamber and �5 g/cm2 for ISS chamber

D2 and �10 g/cm2 for chamber D1.

1.2. SEP events

Table 1 presents the data on five large SEP events and

shows the event-integrated >30 and >50 MeV proton

fluxes recorded on GOES satellites and the event-inte-

grated radiation doses measured by the Mir and ISS

ionization chambers D2 and D1, and by the Express-A3

ionization chamber (D). During the October 1989 SEPevents, the measurements were taken with the chamber

D2 alone. The October 1989 event was unique in its size

and radiation dose increase rate (Tverskaya et al., 1991).

Fig. 1 shows the radiation dose variations inside Mir

space station during that event, the solar proton fluxes

recorded on GOES-7, the highest invariant latitudes of

the Mir station orbit in the northern and southern

hemispheres, as well as the Kp index and Dst variation.The additional proton intensity peak recorded at �1530

UT on 20 October coincided with development of a

strong magnetic storm (the Dst variation was 200 nT).

The Mir residence time in the polar zones filled with

solar protons increased a few-fold because of the geo-

magnetic cutoff suppression, probably down to �55�. By1700 UT on 20 October 1989, the dose had increased by

15 mGy within 3 h. The dose increased by �27 mGythroughout the 19–21 October 1989 SEP event period.

A few large SEP events were recorded during the

solar maximum years of 2000–2001. On Mir space sta-

tion, the �7 mGy dose induced by the 14 July 2000 SEP

was �4 times as low as the dose induced by the 19 Oc-

tober 1989 flare. The 14 July 2000 SEP event was also

some SEP events on Mir station, ISS, and geosynchronous satellites

Proton fluences

2 Express-A3 D GOSE Ep > 30 MeV GOSE Ep > 50 MeV

– 2 � 108 8:2 � 107

304 3:4 � 108 1:1 � 108

286 2:5 � 108 9 � 107

59 9:5 � 107 2:5 � 107

182 2:7 � 108 7:7 � 107

Fig. 1. The October 1989 SEP events. The curves are: (1) the radiation

dose on Mir station; (2) the >30 MeV proton fluxes (GOES); (3) the

highest invariant latitudes, K, of the Mir station orbits in the northern

(the dark circles) and southern (the light circles) hemispheres; (4) Kp;

(5) Dst.

Fig. 2. The 24 September 2001 (a) and the 4 November 2001 (b) SEP events. T

dose on Express-A3; (3) the highest invariant latitudes, K, of ISS orbits in the

(4) Kp; (5) Dst.

1426 L.V. Tverskaya et al. / Advances in Space Research 34 (2004) 1424–1428

accompanied by a large magnetic storm (Dst �)300 nT),but the solar proton fluxes decreased markedly during

that storm and failed to contribute much to the radia-

tion dose, unlike the 19 October 1989, SEP event.

Both Mir and ISS were operative during the 8 No-

vember 2000 SEP event. The doses induced by solarprotons in chambers D2 and D1 increased, respectively,

by 2.85 and 0.5 mGy on Mir and by 1.4 and 0.3 mGy on

ISS. The SEP event occurred during a geomagneti-

cally quiet period. The flare-integrated 30 MeV proton

flux was little different from the 19–20 October 1989

flare-integrated flux (see Table 1). However, the dose

recorded by chamber D2 on Mir space station in No-

vember 2000 was almost an order of magnitude lowerthan the dose induced by the 19 October 1989 SEP

event. The difference is mainly due to the strong mag-

netic disturbances that occurred during the SEP event

maximum of 20 October 1989.

The 24 September 2001 and 4 November 2001 SEP

events occurred when ISS alone was operative. The in-

tegrated proton fluence of 4 November 2001 SEP event

was much larger than the 24 September 2001 SEP event.The dose from the former event recorded by the ioni-

zation chamber on Express -A3 geosynchronous satellite

was �3 times as high as the dose from the latter event.

In contrast, the event-integrated dose on ISS was 3 times

as low.

he curves are: (1) the >50 MeV proton fluxes (GOES); (2) the radiation

northern (the dark circles) and southern (the light circles) hemispheres;

L.V. Tverskaya et al. / Advances in Space Research 34 (2004) 1424–1428 1427

Fig. 2 show some data on the above events, namely,

the >50 MeV proton fluxes recorded on GOES, the

radiation doses recorded on Express-A3, and the highest

invariant latitudes of each of the ISS orbits in the

northern and southern hemispheres. It is seen that, on 6

November 2001 SEP event, the solar proton fluxes werepeaking during the expansion phase of a strong mag-

netic storm (Dst ¼)277 nT). During that period, how-

ever, the ISS orbit latitudes were below 50�, so the orbit

was beyond reach for solar protons. Therefore, the do-

ses were received mainly in the high-latitude segment of

the orbit during quiet time (November 5) and at the

storm recovery phase (November 6). In the case of

the 24 September 2001 SEP event, when ISS traversedthe high latitudes, the Express-A3 chamber-recorded

doses were higher compared with the November 4 event.

From the above it follows that the prediction of the

ISS orbit radiation environment during SEP events re-

quires that the ISS residence time in the polar zones of

solar proton penetration should be calculated making

allowance for a possible geomagnetic cutoff suppression.

In this case, the Dst-variation is most expedient to usebecause it can be predicted to within a high accuracy

from the parameters of interplanetary medium (Burton

et al., 1975).

2. Radiation belt variations

Now, we shall examine the radiation dose variationson Mir space station due to formation of the new belt of

high-energy protons and electrons, which was formed on

L�2.5 within 1 min during the sudden commencement

of magnetic storm on 24 March 1991 (Blake, 1992). We

shall also discuss the features of the dose variations on

ISS, which are independent from SEP events.

Fig. 3 shows the 10 day averaged radiation doses

recorded by the Mir ionization chambers D2 and D1

Fig. 3. The 10 day averaged radiation doses on Mir station from

January 1991 to July 1992. The light and dark circles are the readings

of chambers D2 and D1, respectively.

from January 1991 to July 1992. A persistent ‘‘pedestal’’

is seen clearly in the time dependence of the doses in

both chambers. The pedestal was formed after the storm

in March 1991. The doses increased by �80% in

chamber D2 (Ep > 40 MeV) and by �30% in chamber

D1 (Ep >70 MeV), which corresponds approximately tothe ratio of dose increases in similar energy ranges re-

corded on CRRES (Gussenhoven et al., 1991). The later

history of the new belt is difficult to trace in the Mir

measurement data because its effect was ‘‘overlapped’’

from mid-1992 by the effect of dose increase due to the

solar cycle variations of the inner belt proton intensity

(Panasyuk et al., 1998). At the same time, the new belt is

known to be observable during a few years (Ginzburget al., 1993).

The formation mechanism of the new belt has been

studied quite properly (Pavlov et al., 1993; Li et al.,

1993). With the present-day level of knowledge, how-

ever, the amplitude and structure are impossible to

predict for the sudden pulse, during which the new ra-

diation belt was formed. The intensive cases of that type

are very rare and were probably observed 2–3 timesthroughout the space era.

Fig. 4 shows the daily radiation doses that were re-

corded with the ISS chambers D2 and D1 from the

operation start moment of the chambers to July 2002.

The periods attract attention, when the readings of

chambers D2 and D1 are alike, and even coincide ac-

tually sometimes. The similarity between the D2 and D1

readings may be explained probably by the hard spec-trum of the inner belt protons, given a negligible con-

tribution from the relativistic electrons of the belts.

According the measurement data of the Express-A2

geosynchronous satellite, the 4–6 MeV electron fluxes

decrease markedly during the said periods (Sosnovets

et al., 2002). However, any final conclusion can only be

drawn from a comparison with the low-orbiting satellite

data.

Fig. 4. The 10 day averaged radiation doses on ISS from August 2000

to July 2002. The light and dark circles are the readings of chambers

D2 and D1, respectively.

1428 L.V. Tverskaya et al. / Advances in Space Research 34 (2004) 1424–1428

3. Conclusions

• The radiation dose variations on Mir space stations

and on ISS have been studied. The dose is shown

to be defined by not only the intensity of a SEPevent, but also the features of the manned space-

craft orbits and geomagnetic disturbances. The

storm-time suppression of geomagnetic cutoff leads

to an increase of the spacecraft residence time in

the polar zones of solar proton penetration to the

magnetosphere, compared with geomagnetically

quiet periods.

• Throughout the period of manned spacecraftflights, the highest radiation hazard from SEP

events arose on 20 October 1989 due to coincidence

of the solar proton flux maximum with the abrupt

cutoff suppression (to �55�) during a strong mag-

netic storm.

• With the monitoring measurements of SEP events

outside the magnetosphere, the well-predictable pa-

rameter Dst is expedient to use for the purposes ofshort-term predicting the time within a current SEP

event for ISS residence in the polar zones of so-

lar proton penetration, depending on geomagnetic

activity.

• The shock-injected radiation belts similar to the belt

observed on 24 March 1991 constitute an additional

long-lived source of penetrating radiation. However,

although the formation mechanism of the shock-injected belt is clear and the belt structure can be

calculated from the sudden-pulse parameters, the am-

plitude and shape of the pulses are still unpredictable.

• The observed similarity between the readings of the

ISS ionization chambers D2 and D1 during separate

periods may be due to a decrease of the relativistic

electron fluxes in the outer radiation belt.

Acknowledgements

The authors thank all those who keep the Internet

sites with the interplanetary medium data, the GOES

relativistic electron data and ground-based geomagnetic

data. The work was supported by RFFI grant 0015–

96623 and ‘‘Universities of Russia’’ grant.

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