264 B.Defoort,V.Peypoudat,M.C.Bernasconi,K.Chuda and X.Coqueret Fig.2.The LOAD-10 offset reflector While the ESA initiative originally had but vague relations to previous US work,it contributed to the renewed interest there,when ESTEC person- nel introduced the work done at Contraves to several JPL science projects teams.On the other hand,in 1980,L'Garde had proposed new approaches to continuously inflated antenna reflectors [14]and,after a number of develop- ment activities,in 1996 they finally achieved a test flight for a 15-m object, deployed from the Shuttle Orbiter 15.Work on those inflatable reflectors continues [16]. Finally,under the USAF leadership,the inflatable solar concentrator was born again,this time to support the development of solar-thermal propul- sion 17,a concept originally introduced by Ehricke [18.While most designs foresee two offset parabolic reflectors,alternative configurations have investi- gated the use of flexible Fresnel lenses,also supported by gossamer elements. ESA has also sponsored studies for applying solar-thermal propulsion to upper stages for geocentric transportation [19](Fig.3). Backbones Concepts,type of applications,and study and development activities have been too numerous to attempt even a brief summary as done for the preci- sion structures above.Many backbone structures (but not all by any means) involve skeletons,assembled from tubular components.Indeed,such a "one- dimensional"element forms the simplest backbone morphology.Following evolutionary considerations,one may discuss morphology and applications of backbones in the following order:264 B. Defoort, V. Peypoudat, M.C. Bernasconi, K. Chuda and X. Coqueret Fig. 2. The LOAD-10 offset reflector While the ESA initiative originally had but vague relations to previous US work, it contributed to the renewed interest there, when ESTEC person￾nel introduced the work done at Contraves to several JPL science projects teams. On the other hand, in 1980, L’Garde had proposed new approaches to continuously inflated antenna reflectors [14] and, after a number of develop￾ment activities, in 1996 they finally achieved a test flight for a 15-m object, deployed from the Shuttle Orbiter [15]. Work on those inflatable reflectors continues [16]. Finally, under the USAF leadership, the inflatable solar concentrator was born again, this time to support the development of solar-thermal propul￾sion [17], a concept originally introduced by Ehricke [18]. While most designs foresee two offset parabolic reflectors, alternative configurations have investi￾gated the use of flexible Fresnel lenses, also supported by gossamer elements. ESA has also sponsored studies for applying solar-thermal propulsion to upper stages for geocentric transportation [19] (Fig. 3). Backbones Concepts, type of applications, and study and development activities have been too numerous to attempt even a brief summary as done for the preci￾sion structures above. Many backbone structures (but not all by any means) involve skeletons, assembled from tubular components. Indeed, such a ”one￾dimensional” element forms the simplest backbone morphology. Following evolutionary considerations, one may discuss morphology and applications of backbones in the following order: