RADIATION SHIELDING IN SPACE EXPLORATION–(C) RADIATION SHIELDING OF COMPOSITE SPACE ENCLOSURES


(BEING CONTINUED FROM 25/05/13)

Space electronic systems employ enclosures to shield sensitive components from space radiation. The purpose of
shielding is to attenuate the energy and the flux of ionizing radiation as they pass through the shield material, such
that the energy per unit mass (or dose) absorbed in silicon is sufficiently below the maximum dose ratings of
electronic components.
The received radiation amount varies significantly depending on several variables that include mission parameters
(orbit, altitude, inclination and duration), spacecraft design (spacecraft wall thickness and panel-enclosure location).
To achieve the optimum shielding with the minimum weight, all these variables have to be considered in the design.
Energetic particles, mainly electrons and protons, can destroy or cause malfunctions in spacecraft electronics. The
standard practice in space hardware is the use of aluminium as both a radiation shield and structural enclosure.
Composite structures show potential for significant mass savings. However, conventional graphite epoxy composites
are not as efficient shielding materials as aluminium because of their lower density, that is, for the same mass,
composites provide 30 to 40% less radiation attenuation than aluminium.
A solution is to embed high density (atomic weight) material into the laminate. This material, typically metallic
material, can be dispersed in the composite or used as layers in the laminate (foils).
The main objective of the “Radiation Shielding of Composite Space Enclosures” (SIDER) project is the
development of the technologies and tools required to obtain lightweight, safe, robust and reliable composite
structures. Two different strategies are being analysed as alternatives for radiation shielding: and he incorporation
of a high density material foil.
This paper will present and analyse the radiation shielding obtained by the incorporation of nanomaterials in
composite structures.

 

I. INTRODUCTION
The space radiation environment is a complex and  varying phenomenon that depends of many factors
including orbit, time of year and solar activity. Solar flares can dramatically alter the radiation exposure of
a satellite with no more than a few hours’ notice. A  proper understanding of the mission requirements and
the likely effects of radiation on satellite components  help ensure maximum operational reliability.
Energetic particles, mainly electrons and protons,can destroy or cause malfunctions in spacecraft
electronics. Therefore adequate protection for the  electronics has to be provided by the electronics
housing together with local shields.
Given the current trend toward Commercial Off-The-Shelf (COTS) components, the orbital lifetime of
space systems is substantially reduced since these  components are not designed for high radiation
tolerance. Therefore, systems with COTS electronics  require enclosures whose mass is determined by
substantial shielding requirements, rather than  structural requirements. Thus, significant weight
penalties can result when shielding space systems  that use COTS electronics and operate in high
radiation environments.
To reduce the structural weight, satellite designers  use composite materials which have higher strength
to weight ratios than aluminium. Composite materials are central in aerospace applications due to the
weight savings that could result from using low density polymer matrix composites made from high
modulus, high strength fibres. The attributes of composites include high specific strength (strength
per unit weight) and stiffness, corrosion and fatigue  resistance, tailorable conductivities, controlled
thermal expansion and the ability to be processed into complex shapes. They are lightweight, which is
critical for any aerospace platform and the physical,mechanical, electrical and thermal properties of
composites are highly tailorable, which can also  afford them multifunctionality. In Figure 1, the
prototype developed in the frame of the MULFUN  project (coordinated by TECNALIA) is presented.
Around 60 % of mass saving was obtained [1].
However, conventional graphite epoxy composites  are not as efficient radiation shielding materials as
aluminium (composites provide 30 to 40 % less  radiation attenuation, which is considered primary
design driver). Therefore, additional shielding is required [2].

 image
Figure 1: Composite electronic box (MULFUN  project).
From the classical theory of Bethe it can be shown  that to minimize mass of the shield, low atomic
number (low Z) elements are most effective on per  unit mass basis. If it is necessary to reduce the
thickness of the shield, then high atomic number  (high Z) elements are most effective on per unit
thickness basis. A “heavy” material (high Z i.e. high  atomic number) is better absorber of electrons and
bremsstrahlung than a low Z material even if the  production of bremsstrahlung is higher in materials of
high atomic number. However, a high Z material is  less effective in stopping protons. Therefore
structures where low Z and high Z layers are  combined to get effective radiation shielding are in
interest [2].
Preliminary transport computations showed that  shielding designs utilizing this concept can provide
weight savings in the excess of 25 % over aluminium  in electron dominated environments such as GPS and
Geosynchronous orbits. A multilayered shield of  1,016 mm composite / 0,127 mm tantalum / 1,016
mm composite with a combined areal weight of 0,61  g/cm2 has the same shielding effectiveness of 0,8
g/cm2 aluminium, resulting in about a 25 % weight  saving. Similar results were achieved when tungsten
was used as the high Z material. This is significant  because tungsten has almost three times the thermal
conductivity of tantalum [3].
In SIDER, composite materials will be developed  and modelling and test for space equipment
demonstrators will be performed. Countermeasures as  tungsten layers and nano-conductive materials will be
evaluated at simple samples to assess its shielding  capabilities for composites boxes. The activity will
also adapt / enhance analytical tools and the  capabilities, procedures and quality for the radiation
facilities directed to composite testing.
SIDER project aims to:

· improve and apply novel technologies for  the improvement of the radiation shielding  of composite materials.

image

 

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Because, their specials properties as high density  (19,25g/mL), low reactivity and toxicity, and the  possibility of blending into plastic for extrusion or  moulding and long-term storage possibilities,tungsten could be used for shielding applications at
nuclear facilities instead of other materials such as  lead and steel. Tungsten nanoparticles with  reference 9820XH were supplied by SkySpring nanomaterials, Inc.

 

G. Atxaga1TECNALIA, Spain, garbine.atxaga@tecnalia.com
J. Marcos2, M. Jurado3, A. Carapelle4, R. Orava5

1 TECNALIA. Transport Unit, Spain, garbine.atxaga@tecnalia.com
2 TECNALIA. Transport Unit, Spain, jesus.marcos@tecnalia.com
3 TECNALIA. Transport Unit, Spain, mariaje.jurado@tecnalia.com
4 CSL, Belgium, a.carapelle@ulg.ac.be
5 Sensor Center, Finland, risto.orava@sence.fi

(TO BE CONTINUED)

About sooteris kyritsis

Job title: (f)PHELLOW OF SOPHIA Profession: RESEARCHER Company: ANTHROOPISMOS Favorite quote: "ITS TIME FOR KOSMOPOLITANS(=HELLINES) TO FLY IN SPACE." Interested in: Activity Partners, Friends Fashion: Classic Humor: Friendly Places lived: EN THE HIGHLANDS OF KOSMOS THROUGH THE DARKNESS OF AMENTHE
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