Introduction

The driving design factor for space structures is the stiffness-to-weight ratio of the system. Hosting a payload straight up to escape Earth's gravity requires a phenomenal expenditure of energy, and every gram saved in either launch vehicle or payload weight translates to lower overall costs. Lunching an object on the LEO (Low Earth Orbit) is estimated to be 20 000$/kg [1]. For this reason the weight is a critical parameter to be controlled carefully in the design phase of the systems and structures (i.e. for satellites). Within the three classes of the lightweight materials, composites, the PMCs-polymeric onces are the lighter. Polymeric composite materials have been widely used to take advantage of their large specific strength and stiffness, and their unique and highly tailorable properties. Likewise, compared to metals they can be moulded in very complex shapes. However, there are space applications where high temperatures (above 300°C) or very low temperature compatibility issues related to polymeric composites still remain to be answered. In addition, their thermal conductivity, far lower than that of metallic alloys, can have negative affects in some space applications (i.e. space packaging). Simultaneous exposure to AO atomic oxygen exposure and UV radiation can dramatically increase the rate of degradation of polymeric materials. Lack of abrasion and impact resistance for certain polymers or CFRP composites can be also a critical point with respect to space debris exposure in space environment. Solutions for all these incovinients must be provided too. Developing space structures and components answering to space requirements related to better dimensional stability, thermal cycling, UV and ionization radiation, impact and abrasion (space debris, micro-meteoroid particles) along with active structural control systems integrated, lower weight and higher stiffness it is clearly necessary today, but not an easy task. The characteristics of polymeric composites clearly made them attractive for use in aerospace in applications including structures, housings, storage vassels. Nevertheless, to realize the full advantages of PMCs in space vehicles and overcome these dezadvanteges, new composite material systems or solutions must be developed. Developing innovative advanced composite structural designs coated systems could be the answer. Appropriate coatings can solve a diverse array of space requirements related problems and provide protection against erosion, wear damage, electromagnetic and radiation or temperature cycling. Still, polymer substrates are more challenging than metallic substrates for the coating deposition process. The adhesion refers to two bodies (in this case polymer matrix of the composite-metallic or oxide layer), made of different materials holding together by a range of different forces acting across their contact area on a molecular level. So, the (energetic) state of the two surfaces brought into contact will determine the magnitude of adhesion. The energetic state of a surface is quantified by surface energy. While the surfaces of inorganic solids such as metals exhibit a high surface energy, polymer surfaces show a much lower surface energy. Moreover, coatings are restricted by the temperature and conductivity limitations of polymer substrates.

Project summary

New developments in the space industry indicate a much higher usage of composite materials in spacecraft structures. Hoisting a payload straight up to escape Earth's gravity requires a phenomenal expenditure of energy, and every ounce saved in either launch vehicle or payload weight translates to lower project costs. Lightweight and strong composite materials are already deployed in many applications, such as launch vehicle bodies, fairings and payload components. The goal of the ADCOTMAT's project is to develop a lightweight, high strength and stiffness, advanced metallic coated composite packaging space structure integrating solutions (special reinforcement, dopping and coating system materials) providing also proper thermal conductivity (tailorable properties designs) radiation atomic oxygen, abrasion, impact protection and EMI/RFI shielding. The project activities are carried out in a consortium (between a research institute and an economic agent) and will focus on the functionality of the proposed composite structure and not on the packaging structure design aspects. The project result, after accomplishment of the proposed project objectives, consist in a CFRP lightweight demonstrator space structure which answers to critical space functioning requirements in (LEO- Low Earth Orbit, altitudine < 2 000 km) space environenment.

General objectives

The goal of the ADCOTMAT's project is to develop a lightweight, high strength, enhanced thermal management, impact, radiation, AO (atomic oxygen) eposure and abrasion resistance, integrating health monitoring and active control advanced coated composite structures, for different spacecraft components/applications where these issues are critical. The project activities will focus on the study and developemnet of different designs, configurations of materials structures along with different coating systems for space structures/components. Within the innovative coated composite system proposed, using advanced composite substrates, lightweight, large specific strength and stiffness, dimentional stability, appropriate thermal conductivity and the possibility of tailoring all these properties can achived, whereas the coatings will assure substarte thermal barrier Coating, EMI/RFI shielding, abrasion, impact , AO exposure protection. The composite coated structures will prove their functionality during experimental testing champaign (adhesion, structural, thermal cycling, mechanical, radiation resistance). The project end products and results will be at least three composite structure experimental models evaluated trough tests prooving it meet the structural and environmental requirements for space, as well as its functionality.

The measurable objectives of the project are in accordance with the STAR programme objectives regarding RDI projects. The project's specific objectives are in accordance with the programme objectives and priorities, in that:

• the project allows identification of national technological research niches, with application in both space and aeronautical domains, by achieving a complete fabrication cycle for the composite material space structures integrating metallic surface coating systems;
• the ADCOSSPA project activities are aligned to the optional ESA programme' objectives, mainly to the constant demand of weight reduction and increase functional performances (by using special surface coating systems) for spacecraft structure (including microsatellites);
• complex research and technological development activities include fundamental and applied research, and they are conducted inside a national representative consortium for designing, developing and testing composite materials structures. In that respect, the objectives of the project are being undertaken by a consortium including one research institution and one economic agent, with knowledge and expertise in both composite materials and surface coatings fields, ensuring technical and scientific competence in the targeted domains.

• Define and assess the suitable composite materials precursors, coating systems, health monitoring system elements and the integration solutions;
• Provide innovative designed advanced composite coated space structures;
• Provide high stiffness, strength, lower weight, tailorable thermal/electrical conductivities, thermal cycling resistance, good fatigue, vibration and impact resistance along with space environemet reliability, leading to better space structures performances;
• Provide performant coated composite space structures protected against corrosion, wear damage or high temperature and with increased realibility related to the substrate performances;