Is the Terrestrial Magnetosphere a Natural Radiation Shield on Moon Space Missions ? R. Koleva, B. Tomov, T. Dachev, Yu. Matviichuk, Pl. Dimitrov, Space Research and Technologies Institute Bulgarian Academy of Sciences This work is partially supported by grant DID 02/8 from the Bulgarian National Science Fund

The conference Radiation and Dosimetry in various Fields of Research beginning: radiation effects at atomic level end: radiation in the interplanetary space Our team has carried out about 20 experiments in near-Earth space and has made 3 attempts to measure the radiation environment in extra-terrestrial space: - on 2 Russian missions to Mars - unsuccessful launches in 1996 and on Indian Moon Mission Chandrayaan-1 in

Sources of radiation in the Earth-Moon system complex radiation field Galactic cosmic Rays Solar Cosmic Rays Protons, neutrons electrons Gamma and Roentgen Protons, electrons and ions Jovianelectrons Anomalous cosmic rays Protons, electrons and ions

MOTIVATION  One potential method of radiation mitigation on extra-terrestrial missions is in the form of magnetic fields  For Moon missions the Earth magnetosphere is a source of magnetic field, as the Moon spends about 25% of its orbit inside it Moon orbit plots in GSE are provided by the Swedish Institute of Space Physics, Kiruna

Brief characteristics of the radiation environment around Moon as measured by RADOM on CHANDRAYAAN-1 in deep and prolonged solar minimum

Chandrayaan-1 spacecraft was launched from the Satish Dhawan Space Centre, SHAR, Sriharikota by PSLV-XL (PSLV-C11) on 22 October 2008 at 00:52 UT

Mission profile

Scientific Payload

RADOM Flight model external view 9 pin power and RS-232 data connector Place and size of the Si detector Size: 110x40x20 mm Weight: 98 g Consumption: 124 mW RADOM is a LIULIN type device The solid-state detector is shielded by several layers with equivalent shielding of about 0.45 g/cm 2. Thus, direct hits on the detector are possible for electrons with energies > 0.85 MeV and protons with energies > 17.5 MeV

Comparison of RADOM flux data (10 s. resolution) with Oulu neutron monitor count rate data (1 min. resolution) At the 100 km orbit (20/11/ /05/2009) overall particle flux was found to be 2.45 p.cm -2.s -1, and absorbed dose rate was 9.46  Gy.h -1 over 3545 hours of measurements. During the last three months of the mission (20/05/ /08/2009), Chandrayaan-1 was in 200 km orbit. The flux and dose rate increased slightly to 2.73 p.cm -2.s -1 and 10.7  Gy.h -1 respectively RADOM data present long-term increase in flux and dose as result of continued low solar activity and respectively increase of GCR.

Can the terrestrial magnetosphere mitigate radiation hazard on Moon missions? Model calculations are controversial On one hand Recent modelling [Winglee, R. M., and E. M. Harnett, GRL 2007], suggested that the terrestrial magnetotail magnetic field can provide a significant level of shielding, the latter depending on IMF orientation and position on lunar surface. On the other hand Modeling by Huang, Harlan and Kress, GRL 2009 concluded that Earth’s magnetosphere does not substantially modify GCR (with proton energies greater than 1 MeV) at the lunar environment during typical solar wind conditions.

Using RADOM data from Chandrayaan-1 satellite we try to check this hypothesis. More precisely: Does the magnetotail offer some protection in Moon orbit?

Magnetotail crossing in January 2009 Geomagnetic conditions: quiet. In the second half of 9 Jan IMF Bz ~ 5 nT No effect of the magnetotail on radiation in Moon orbiter! 50 per mov. avr RADOM average/day flux

In Solar cycle minimum conditions, when there are no SPE and GCR flux is enhanced, Earth magnetosphere does not seem to provide any shielding on Moon orbiter. The problem of Earth magnetosphere effect on Moon radiation environment needs more detailed investigation, because.... the magnetosphere can make things worse

There was one interesting event in RADOM records During the whole mission the particle flux was ~ 2.45 p/cm 2.s except on March

No SPE, no flares identified GOES satellites showed increase only in electrons >2Mev flux electrons >2 MeV GOES-10 GOES-11 On 13 March the magnetosphere was hit by an IS caused by fast solar wind. For several days MS was under continuous driving – conditions favorable for e - acceleration in the inner MS and generation of the ‘killer electrons’

Coronalhole March 13,2009 Fast solar wind flows originate from coronal holes in the Sun. In the interplanetary space, when the fast wind interacts with the regular slow solar wind an interplanetary shock is formed. Coronal holes live for several month; fast solar wind flows have a recurrent nature, they appear in several Sun rotations The appearance of ‘killer’ electrons in correlates well with the fast solar wind, usually ~2 days after the arrival of IS

GOES 10 X-rays GOES 10 el Similar event in February GOES-10 electrons >2 MeV GOES 10 el GOES 10 X-rays

CONCLUSION In Solar cycle minimum conditions, when there are no SPE and GCR flux is enhanced, we could not find any indication that Earth magnetosphere can provide additional shielding on Moon orbiter There are some evidence that magnetospheric disturbances could affect the radiation environment on Moon orbiter, but more detailed research should be done

Thank you for your attention!