268 B.Defoort,V.Peypoudat,M.C.Bernasconi,K.Chuda and X.Coqueret structure's rigidity and shape.This concept is very attractive,and was used in flight on the Echo-2 satellites in the sixties [33],as well as on the Optical Calibration Sphere in 2000.The main advantages of this rigidization process are its reversibility,simplicity,predictability and rapidity.Furthermore it does not require additional power,has good space durability and no specific stor- age constraints.However,the anisotropy of the stresses and the need for an accurate control of the pressurization levels are issues that affect this tech- nique for its application to cylindrical or toroidal objects.L'Garde proposes a solution to that problem which is based on fibers winding around a tubular structure [34.Two main issues remain with regard to this technology:the first one is the different thermally induced dilatation of the constituting ma- terials (polymer and aluminum)and the second is the compatibility of this technology with rolled-up storage. Physically induced rigidization:cold rigidization,shape memory and solvent evaporation The cold rigidization process relies on the exposure of originally flexible plastic layers-typically elastomers [35-to the deep space thermal sink to cool them below their glass-transition temperature,rigidizing the structure essentially by freezing the matrix.This concept appears particularly indicated for shield- ing applications outside Earth's orbit,and was studied for shadowing shields of cryogenic stages for Mars flights.More recently,ILC Dover and L'Garde presented structures rigidized using this technique,respectively a hexapod structure [36 and the Space Solar Power Truss [37.This technique is attrac- tive mostly because of its reversibility,simplicity and low energy requirements compare to thermal curing.However,the need for temperature control and the coefficient of thermal expansion of the resins are serious drawbacks. Recently,a number of studies have been conducted on shape memory composites,materials that mimic the behaviour of metallic shape-memory alloys 38,39,40.The structure is completed on ground and consolidated at an elevated temperature,to set the material's geometric shape.The material will return to its original shape when heated above its glass transition temperature. For packaging,the structure is softened by heating it above Tg,taking care to keep it below its set temperature.After cooling,it is kept stowed.Prior to deployment,the stowed structure is again heated above Tg to make it flexible enough to be deployed by inflation.This is quite a complex process that limits the overall size of an object.The deployment in space requires a fair amount of power and control functions,as the heating must be rather uniform overall; also,presumably,the temperature should not drop below Tg. Rigidization of a structure can also be obtained using evaporation of a solvent or a plasticizer in the material.The major issue of this solution is the large amount of solvent or plasticizer involved (e.g.between 13-50%for the Ciba polyimide tested during the Contraves ISRS program [41]).During the 1960s,a fairly large effort was dedicated to the study of rigidizable structures268 B. Defoort, V. Peypoudat, M.C. Bernasconi, K. Chuda and X. Coqueret structure’s rigidity and shape. This concept is very attractive, and was used in flight on the Echo-2 satellites in the sixties [33], as well as on the Optical Calibration Sphere in 2000. The main advantages of this rigidization process are its reversibility, simplicity, predictability and rapidity. Furthermore it does not require additional power, has good space durability and no specific stor￾age constraints. However, the anisotropy of the stresses and the need for an accurate control of the pressurization levels are issues that affect this tech￾nique for its application to cylindrical or toroidal objects. L’Garde proposes a solution to that problem which is based on fibers winding around a tubular structure [34]. Two main issues remain with regard to this technology: the first one is the different thermally induced dilatation of the constituting ma￾terials (polymer and aluminum) and the second is the compatibility of this technology with rolled-up storage. Physically induced rigidization: cold rigidization, shape memory and solvent evaporation The cold rigidization process relies on the exposure of originally flexible plastic layers – typically elastomers [35] – to the deep space thermal sink to cool them below their glass-transition temperature, rigidizing the structure essentially by freezing the matrix. This concept appears particularly indicated for shield￾ing applications outside Earth’s orbit, and was studied for shadowing shields of cryogenic stages for Mars flights. More recently, ILC Dover and L’Garde presented structures rigidized using this technique, respectively a hexapod structure [36] and the Space Solar Power Truss [37]. This technique is attrac￾tive mostly because of its reversibility, simplicity and low energy requirements compare to thermal curing. However, the need for temperature control and the coefficient of thermal expansion of the resins are serious drawbacks. Recently, a number of studies have been conducted on shape memory composites, materials that mimic the behaviour of metallic shape-memory alloys [38,39,40]. The structure is completed on ground and consolidated at an elevated temperature, to set the material’s geometric shape. The material will return to its original shape when heated above its glass transition temperature. For packaging, the structure is softened by heating it above Tg , taking care to keep it below its set temperature. After cooling, it is kept stowed. Prior to deployment, the stowed structure is again heated above Tg to make it flexible enough to be deployed by inflation. This is quite a complex process that limits the overall size of an object. The deployment in space requires a fair amount of power and control functions, as the heating must be rather uniform overall; also, presumably, the temperature should not drop below Tg. Rigidization of a structure can also be obtained using evaporation of a solvent or a plasticizer in the material. The major issue of this solution is the large amount of solvent or plasticizer involved (e.g. between 13-50% for the Ciba polyimide tested during the Contraves ISRS program [41]). During the 1960s, a fairly large effort was dedicated to the study of rigidizable structures