SKOBELTSYN INSTITUTE OF NUCLEAR PHYSICS,
LOMONOSOV MOSCOW STATE UNIVERSITY, RUSSIA
Radiation Conditions of a Mission to Jupiterʼs Moon
Ganymede
M. V. Podzolko, I. V. Getselev
In cooperation with scientists from IAM, IKI and Russian Ganymede Lander Team
– Strong charged particle fluxes and radiation doses in Jupiter’s magnetosphere
– Radiation dose in Ganymede’s orbit: risks considerably lower, than near Europa
– Radiation dose during gravity assists in Jupiter’s system: comparable, or several times
higher, than during 2 months in Ganymede’s orbit.
– Radiation doses during near-Earth and interplanetary flight: low, compared to doses in
Jupiter’s near-planetary space
– Conclusions, discussion
Magnetosphere and charged particles satellite measurements at Jupiter
mission
time
orbit
experiments
Pioneer 10
Dec. 1973
Fly-by at 130 ths. km
from Jupiter (2.8 RJ)
Pioneer 11
Dec. 1974
Fly-by at 43 ths. km
(1.6 RJ), high incl. orb.
Voyager 1
March 1979
Fly-by at 207 ths. km
(4 RJ)
Voyager 2
July 1979
Fly-by at 570 ths. km
(9 RJ)
Feb. 1992
Fly-by at 378 ths. km
(6.3 RJ), high incl. orb.
Galileo
1995–2003
35 highly elliptical orbital Magnetic field,
segments with rπ
electrons: 15 keV to >11 МeV,
typically 6–11 RJ
Ions: 10 keV to 200 MeV/nuc
Cassini
Nov. 2000
Fly-by at 10 mln. km
(140 RJ)
Magnetic field sync. w/Galileo,
high-energy electrons (radiation
spectrometer)
Fly-by at 2.3 mln. km
(32 RJ)
Local and remote (radiospectrometer) magnetic field
and charged particle
measurements
Ulysses
New
Horizons
Feb. 2007
Magnetic field,
electrons: 0.06 to >35 MeV,
protons: 0.6 to >80 MeV
Magnetic field,
low-energy particles,
electrons: 3–110 MeV,
ions: 1–500 MeV/nuc
Magnetic field,
electrons: 0.03 to >170 MeV
Ions: 0.05–75 MeV/nuc
doses
1.5·106 rad on the surface,
4.5·105 rad at 3 mm Al
4.3·105 rad on the surface,
1.2·105 rad at 3 mm Al
≈ 5·105 rad
estim. 6·104 rad (inside?)
Designed for 150 krad at
2.2 g/cm2, sustained >650
krad; “remarkably healthy”,
but damaged some
electronic systems
Models of Jupiter’s radiation belts
N. Divine, Jupiter radiation belt models, Techn. Mem. 33-715, 1974, 13 p. /1st model, used Pioneer
10 data/
R. W. Fillius, C. E. McIlwain, A. Mogro-Campero, Radiation belts of Jupiter: a second look, Science,
v. 188, 1975, p. 465–467. /An update of the model, using Pioneer 11 data/
N. Divine, H. B. Garrett, Charged particle distributions in Jupiter’s magnetosphere, J. Geophys. Res.,
v. 88, No 9, 1983, p. 6889–6903. /Model, based on the data from Pioneer 10, 11 and Voyager 1, 2/
M. H. Acuna, N. F. Ness, The main magnetic field of Jupiter, J. Geophys. Res., 81, 1976, p. 2917–
2922. /The “O4” Jupiter’s magnetic model, 15 Gauss coefficients/
I. V. Getselev, Yu. I. Gubar et al., Radiation conditions of the spacecraft flight in Jupiter’s nearplanetary space, MSU, VINITI No 4636-84, 1984. (in Russian).
I. V. Getselev, Yu. I. Gubar et al., Model of the radiation environment of Jupiter’s artificial satellites,
MSU, VINITI No 8970B, 1985. (in Russian).
H. B. Garrett, I. Jun, J. M. Ratliff, R. W. Evans, G. A. Clough, R. W. McEntire, Galileo interim
radiation electron model, Publication 03-006, Jet Prop. Lab., California Inst. Tech., Pasadena,
California, 85 p., 2003. /A revision of Divine-Garrett model for electrons at L = 8–16 using Galileo
data/
H. B. Garrett, S. M. Levin, S. J. Bolton, A revised model of Jupiter’s inner electron belts: updating the
Divine radiation model, Geophysical Research Letters, v. 32, L04104, 2005, 5 p. /A revision of
Divine-Garrett model for relativistic electrons at L < 4 from Cassini and VLA synchrotron
observations/
10
9
10
8
> 0.5 MeV
10
7
>2
> 10
106
10
5
10
4
108
f p, 1/(cm2s)
f e, 1/(cm2s)
Charged particle flux and radiation dose equatorial profiles at Jupiter
3
10
6
10
Dose, rad/day
10
2
4
6
8
10
12
14
16
2
10
1
10
0
24
26
5
[10 rad/day]
2
4
6
8
10
12
14
16
18
20
22
24
26
L, RJ
Amalthea
Io
Europa
10
6
10
5
> 2 MeV
> 10
> 30
104
103
2
2
4
6
8
10
12
L, RJ
[150 rad/day]
2.2, protons
7
10
2
2.2
10
22
1 g/cm
104
10
20
L, RJ]
[15 krad/day
5
3
18
10
Ganymede
Callisto
Equatorial profiles of integral
fluxes of >0.5, >2 and >10 MeV
electrons (upper left), >2, >10
and >30 MeV protons (upper
right) and doses behind 1, 2.2
and 5 g/cm2 (bottom) at Jupiter.
f e, 1/(cm2s)
10
8
10
7
Dose, rad/day
Calculated radiation doses in the orbits of Europa and Ganymede
10
6
10
5
10
4
10
3
102
106
10
101
0.01
5
10
4
10
3
0.1
1
Shielding, g/cm
10
2
Doses under various shielding in Europa’s (solid line)
and Ganymede’s (dash line) orbits.
10-1
100
101
102
Energy, MeV
Integral fluxes of electrons in Europa’s (solid
line) and Ganymede’s (dash line) orbits.
2-month doses in Europa’s and Ganymede’s
orbits, rad.
g/cm2
Europa
Ganymede
1.0
2.2·106
3.5·104
2.2
8.8·105
9.0·103
5.0
2.4·105
2.0·103
10.0
4.5·104
5.2·102
Computed electron fluxes on Europa’s surface and at 100 km altitude
90
90
5 MeV, 0 km
5 MeV, 100 km
60
Latitude, degrees
Latitude, degrees
60
30
0
-30
-60
90
180
270
-30
-90
90 0
360
50 MeV, 0 km
Longitude, degrees
90
30
0
-30
180
270
360
50 MeV, 100 km
Longitude, degrees
60
Latitude, degrees
60
Latitude, degrees
0
-60
-90
90 0
30
0
-30
-60
-60
-90
30
0
90
180
270
360
0.2
0.4
0.6
0
90
180
270
Longitude, degrees
Longitude, degrees
< 0.05
-90
0.8
Flux, relative to maximum
1
360
Radiation doses on Europa’s surface and at 100 km circular orbit
90
0.6
Dose, relative to maximum
2.2 g/cm2, 0 km
Latitude, degrees
60
30
0
-30
-60
-90
90 0
90
270
360
5 g/cm2, 0 km
Longitude, degrees
60
Latitude, degrees
180
0
-30
-60
0
90
180
270
360
Longitude, degrees
< 0.05
0.2
0.4
0.6
0.8
Dose, relative to maximum
0.4
0.3
0.2
0.1
0
30
60
Orbit inclination, degrees
30
-90
0.5
1
90
Ganymede: radiation risks considerably lower, compared to Europa
Mission to Europa
Radiation dose during 2 months behind 2.2 g/cm2: 1 Mrad
Modeling the “shading” by Europa; optimal orbit and landing site:
– 100 krad at the surface on the leading side relative to Europa’s orbital motion, and the
high-latitude regions;
– 250 krad in the 100 km orbit with inclination >60°
Mission to Ganymede
Radiation dose during 2 months behind 2.2 g/cm2: 10 krad
– Radiation risk can be considerably lower.
General scheme of gravity assist maneuvering in the system of Jupiter
1) First approach to Jupiter; firing the engines in the pericenter or using the gravity of one of
its moons for transferring to highly-elliptical orbit of Jupiters’s artificial satellite;
2) Several gravity assists near Jpuiter’s large moons for lowering the spacecraft’s speed
relative to Jupiter
Alexey Grushevskii et al., Keldysh Institute of Applied Mathematics, Moscow, Russia
Doses during the 1st fly-by and on the elliptical orbits around Jupiter
1.9
10
1.8
1.7
1.6
1.5
rp = 10 RJ
4
11
12
13
1.4
1.3
70
2 2, krad
g/cm
2.2г/cм
under
Dose
Дoзa
, крад
зa 2.2
i = 40, 30, 20, 0°
sin(i) = c·r–1/2
2
Dose, rad
+ dva(Гaнимeд), км/c
km/s
dvdv
p +
п dva(Ganymede),
2.1
10
2
3
4
5
6
rп, RJ
50
7
8
9
i = 0, 20, 30, 40°
sin(i) = c·r–1/2
14
20
30
50
70
100
140
ra, RJ
30
The dependency of the radiation doses under 2.2
g/cm2 during one full circuit of the orbit around
Jupiter from the orbit’s apocenter, for the values of
the pericenter rп = 10, 11, 12, 13 и 14 Jupiter radii
(RJ = 71490 km).
20
10
7
5
3
2
3
4
5
6
7
8
9
rп, RJ
Total impulse during the 1st circuit (upper plot) and radiation doze behind 2.2 g/cm2
during 1st Jupiter’s fly-by (lower plot) for the orbit’s inclination i = 0, 20, 30 и 40°. The
time of the 1st circuit was assumed equal to 90 days, the asymptotic speed – 6 km/s.
0
Low radiation risk strategy of gravity assists in the system of Jupiter
-20
Rising the pericenter of each circuit up to Ganymede’s orbit radius plus the asymptotic
distance by the impulse in apocenter.
-40
40
-60
40
20
-80
20
0
-200
-150
-100
00
-50
0
-20
-20
-40
-40
-60
-60
-80
-80
-200
-150
-100
-50
0
0
-200
Parameters of the considered series of gravity assists in Jupiter system
Total dose for the suggested sequence of gravity assists behind 2.2 g/cm2 amounts to 8 Krad.
No
Dist. from
Ganymede
km
rp, RJ
ra, RJ
Multiple of
Ganymede
circuits
Ʃ(dva),
km/s
0’ – straight entering of the orbit around Ganymede
dvG,100km,
km/s
4.000
Ʃ(dv),
km/s
Time,
days
4.000
0.10
1.150 km/s in orbit’s pericenter
0
12.50
1
12.50
225.11
Dose for
2.2 g/cm2,
Krad
1.00
0.0833
2.829
4.061
160.9
3.60
2
653
14.93
167.43
15
0.0884
2.696
3.934
268.5
3.86
3
942
14.93
133.38
11
0.0946
2.570
3.814
347.4
4.15
4
660
14.90
105.04
8
0.1041
2.410
3.663
404.9
4.46
5
723
14.88
84.25
6
0.1150
2.235
3.501
440.6
4.80
6
1768
14.93
72.78
5
0.1273
2.105
3.382
484.1
5.13
7
1250
14.87
60.72
4
0.1444
1.928
3.222
513.0
5.48
8
663
14.76
47.64
3
0.1766
1.665
2.990
534.9
5.87
9
2130
14.83
40.31
2 × 2.5
0.2043
1.471
2.824
571.0
6.62
10
2048
14.75
32.93
2
0.2477
1.229
2.626
585.8
7.05
11
1618
14.49
24.56
2 × 1.5
0.3402
0.900
2.390
608.0
8.00
Launch in 2020, approach to Jupiter in 6 years.
The 1st phase includes 1 gravity assist near
Venus and 2 – Earth and lasts 4 years, during
which the spacecraft flies at 0.7–2 AU from the
Sun. And then the final path to Jupiter.
Flux, 1/(cm2MeV)
Radiation on the interplanetary part of the trajectory
10
12
10
10
10
8
106
104
100
101
102
Energy, MeV
Total differential solar (solid line) and galactic
(dash line) proton spectra during the interplanetary
part of the mission, using models (R. Nymmik,
1993; Tulka et al., 1997; ISO 15390, 2004;).
Total dose behind 1–2 g/cm2 <1 krad.
Radiation during the flight in Earth’s radiation belts
y
y
10 12
F, cм
x
x
10
–2
10
10 8
10 6
0.1
z
z
x
1
10
100
Eнepгия, MэB
x
Trajectory of launching to the interplanetary space from
the low-altitude Earth’s orbit (left plot) and gravity assist
near Earth (right plot).
Upper estimation of the integral spectra of
protons (o) and electrons (□) during gravity
assists near Earth (solid lines) and in the
launch orbit (dashed lines). The radiation
dose is <100 rad.
Conclusions, discussion
– Main radiation hazard for the mission to Ganymede will come from Jupiter’s radiation belts.
The major radiation dose under shielding >1 g/cm2 will originate from relativistic electrons.
– The radiation dose under 2.2 g/cm2 during 2 months in the Ganymede’s orbit will amount to
≈10 krad. Thus the radiation risks for the mission to Ganymede can be considerably lower,
than for mission to Europa, during which the spacecraft will receive a dose of several
thousand krad behind the same shielding.
– Radiation dose on the trajectory of gravity assists in Jupiter system will be comparable or
several times higher, than during 2 months in vicinity of Ganymede
– The trajectory of the flight in Jupiter system should whenever possible pass not closer than
11–12 Jupiter radii from the planet to lower the radiation risks. Thus for the gravity assists it
is appropriate to use Ganymede and Callisto.
– Radiation dose during one orbital circuit in the “outer region” of Jupiter’s magnetosphere at
the dayside can amount to ≤150 rad. For the whole mission this value can reach up to 1–2
krad. This value is not negligible, but the main hazard still comes from the radiation belts.
– The dose during near-Earth and interplanetary parts of the mission will be low, compared to
that in Jupiter’s magnetosphere.
– Working on Ganymede Lander project we have to solve the complex optimization task,
simultaneously taking into account many factors: radiation, energy consumption, limits
on the size and weight of the scientific equipment, data transfer and so on.