ESA Document - Emits - ESA

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HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 228 of 422
3.3.9.3.3 Radiation shielding
According to the duration and type of mission, the radiation dose limits that an astronaut can
receive during the mission are different. These requirements are translated in terms of the ratio
mass per area, kg/m 2 of the protection material.
With the mass available on-board, it was analysed what was the protection provided, for the
THM and for the storm shelter, and the necessary amount of mass to be added to fulfil the
shielding requirements. The mass available on board that is able to provide shielding protection
is shown in Table 3-54:
Material Mass [kg]
THM Skin + Stiffening 4382.9
Internal Equipment 28754
THM Debris Shielding 964.9
MLI 525.68
Water 1200
Total mass 43 944
Table 3-54: Mass Budget for radiation protection
Shielding effectiveness depends largely upon the conductivity of the material. Materials with low
Z are considered to be effective. For preliminary calculations the density ratio to convert from
g/cm 2 to material shielding thickness was used, that is, 1 cm of H2O is generally equivalent to a 1
cm thick slab of water, or 4 mm of aluminium. The mass required for a certain shielding
requirement is therefore independent of the type of material, only the thickness will be different
from one material to the other.
With the mass available on-board, two configurations for the shielding protection were analysed.
The shielding effectiveness of each configuration, for nominal protection and for the storm-
shelter is described in Table 3-55.
Also on-board are the consumables, weighing 10 200 kg, which were not taken into account in
these calculations because it is not yet known what percentage will be able to be used as
shielding protection, after their usage. The mass necessary to add in the closures corresponds to
60.6% of the consumables. This value is assumed to be viable to be used as shielding material.
Shielding to this area may be provided by the consumables and by propulsion modules on one
side and on the other by the MEV.
The necessary mass to be added in the skirt is smaller in case 1. Due to all the facts presented,
case 1 was selected, and through this it's only necessary to add 2007kg of extra mass.
It was decided to add extra mass in the form of water. Then instead of having two separated
water tanks, the extra mass is located in the closures, and in the skirt the 2000 kg will be
consumables. Figure 3-71 shows the selected configuration.
Note that the shielding effectiveness of vehicle skin or equipment cases with metal walls of any
reasonable thickness is limited by the apertures, joints and others discontinuities, rather than the
metal itself.