This paper gives an outline of conceptual design works for prospective development of mechanically/capillary pumped two-phase fluid loops with space radiators. Considered first are two types of capillary pump evaporators configured as a cold plate. They basically consist of porously separated vapor/liquid channels, taking a double pipe array or a tube-included rectangular duct in shape. A newly devised sizing procedure for the two is mathematically described in the table together with empirically-determined practical design formulas. Four types of deployable/retractable rigid/flexible radiators are then considered as variable capacitance heat rejection systems feasible in the existing state of technology. A unified design/performance analysis procedure for the four is also given in the table, arranged in a convenient way for comparison. Axial. linear expansion/contraction of flexible radiators under possible maximum/minimum sink temperatures are mainly discussed from an angle of thermomechanical design. Reconsiderations made in this study are rather mechanically-assisted than simply-capillary-pumped loops, owing to steadiness of loop start-up and technical ease of active control. A computational method for line diameter sizing and pump capacity scaling is presented for the system design of such hybridized fluid loops. All the procedures coupled with mass/power estimate models have evolved into a computer program, graphically displaying numerical results of design/performance calculations. System trade-off studies, practiced over a wide range of parameter values, have arrived at a conclusion that most available would be a hybrid capillary pumped loop with a retractable flexible radiator. Significant results of thermal/hydraulic/mechanical analyses have finally turned into preliminary design specifications for an engineering model of that system.