achieve precise accuracies. For example, space antennas and mirrors can be activated to precise orientation. As space technology advances, some sensitive equipment (namely interferometric optical and infrared astronomical instruments) are required to be accurate in position as delicate as a few nanometres, while the supporting active structure is tens of metres in dimensions. Design Human-made actuators existing in the market, even the most sophisticated ones, are nearly all one-dimensional. This means they are only capable of extending and contracting along, or rotating about 1 axis. Actuators capable of movement in both forward and reverse directions are known as two-way actuators, as opposed to one-way actuators which can only move in one direction. The limiting capability of actuators has restricted active structures to two main types: active truss structures, based on linear actuators, and manipulator arms, based on rotary actuators. A good active structure has a number of requirements. First, it needs to be easily actuated. The actuation should be energy-saving. A structure which is very stiff and strongly resists morphing is therefore not desirable. Second, the resulting structure must have structural integrity to carry the design loads. Therefore, the process of actuation should not jeopardize the structure's strength. More precisely, we can say: We seek an active structure where actuation of some members will lead to a geometry change without substantially altering its stress state. In other words, a structure that has both statical determinacy and kinematic determinacy is optimal for actuation. Applications Active-control technology is applied in civil engineering, mechanical engineering and aerospace engineering. Although most civil engineering structures are static, active control is utilized in some civil structures for deployment against seismic loading, wind loading and environmental vibration. Also, active control is proposed to be used for damage tolerance purposes where human intervention is restricted. Korkmaz et al. demonstrated configuration of active control system for a damage tolerance and deployment of a bridge. See also James E. Hubbard, Jr. Tuned mass damper References External links Swiss Federal Institute of Technology (EPFL), Applied Computing and Mechanics Laboratory (IMAC) Cambridge University Deployable Structures Lab Hoberman Associates - Transformable Design CRG Technology: Morphing Processes A free-standing space elevator structure: A practical alternative to the space tether Engineering concepts Structure