CFRP ELECTRONICS HOUSING FOR A SATELLITE

摘要

The drive for continuous mass reductions in spacecraftstructures has promoted the use of carbon fibrereinforced plastics. CFRP has excellent specificstiffness and strength, which makes it possible toconstruct lightweight structures. CFRP is typically usedin applications where electrical, thermal and radiationprotection properties are not decisive.Spacecraft has several housings for electronics andequipment. These are typically made of aluminium.Electronics housing multifunctional performancerequirements can also be met using composite materials.In the course of an ESA/ESTEC technology study'Advanced Equipment Design (AED)' a novel conceptfor a CFRP electronics housing was developed. Thermalconductivity of the structure was managed with highconductivity pitch based carbon fibres. The selectedK1100 fibre provides as a ply about four times higherthermal conductivity in the direction of fibres thantypical aluminium alloys. PAN based carbon fibre M40Jwas used as structural fibre.Electrical properties and particle radiation protectionwere managed with a metal foil inside the CFRPlaminate. The primary material selection for the foil waswolfram due to its high radiation attenuation capability,mechanical characteristics, and its good thermalconductivity.A breadboard model was designed and constructed forthe ADPMS unit of PROBA 2 satellite. Design driverswere a considerable mass saving compared toequivalent aluminium housing, parts integration,minimising the number of aluminium parts andmanufacturability of the parts. All essentialrequirements set for the aluminium housing wereapplied to the CFRP housing with no majormodifications.In the breadboard model the wolfram foil was replacedwith a steel foil. However, sample tests were conductedto applicable wolfram embedded laminate structures to evaluate the radiation attenuation properties. The resultsindicated viability of the concept.The external dimensions as well as the location of PCBsand connectors were determined by the requirements setfor the aluminium housing. This restricted the freedomof design and resulted in some non-preferred designdetails. Limited space and strict tolerances gavechallenge to the design, manufacture and assembly.The finite element structural and thermal analyses wereperformed. Also, some radiation attenuationcalculations and simulations were performed. Thecorrelation between the modelled and measuredperformance was analysed.The breadboard model was subjected to EMI/EMC,thermal and mechanical qualification tests. The testperformance was promising but indicated need forcertain design changes. The major problem was relatedto the original materials selection where K1100 fibrewith polycyanate ester resin was selected. This turnedout to be a poor selection due to very low adhesionstrength of the K1100 fibre to the matrix material. Thiscaused a strong tendency to a delamination type failurein the laminate.It can be concluded that there is a considerable potentialof mass saving over the aluminium housing whenutilizing multiple properties of composite materials.However, the cost of the CFRP housing should bedecreased, especially material and manufacturing costs.